Dermatopathology

THE DIAGNOSIS:

Cutaneous Metastatic Mesothelioma

Biopsies of the larger erythematous papules revealed an infiltrate of atypical tumor cells with mitoses (Figure 1) that were immunoreactive for calretinin (Figure 2) and lacked nuclear BRCA1 associated protein-1, BAP1, expression (not shown). The patient’s prior mesothelioma was re-reviewed, and the cutaneous tumor cells were similar to the primary mesothelioma. A diagnosis of cutaneous metastatic mesothelioma (CMM) was made.

Mesothelioma is a rare neoplasm arising from the pleura, pericardium, peritoneum, and tunica vaginalis,¹ with an estimated annual incidence of 2500 cases.² The predominant risk factor for the development of pleural mesothelioma is asbestos exposure, which has been identified in up to 90% of cases. Mesothelioma can give rise to local and less frequently distant hematogenous metastases. Cutaneous involvement of mesothelioma is rare.³ More than 80% of CMM cases are attributed to seeding the skin at procedure sites or by direct infiltration of scars. Distant CMM is rare and typically presents as subcutaneous nodules.⁴ Few cases of inflammatory CMM have been published,^1,4,5 with even fewer mimicking herpes zoster infection (HZI), as seen in our patient.

The most specific stain for mesothelioma is calretinin, which strongly and diffusely stains both the nucleus and cytoplasm. Other markers include Wilms tumor 1, cytokeratin 5/6, thrombomodulin, and HBME-1. Immunohistochemistry to detect the loss of BAP1 staining in the nucleus is important for differentiating between mesothelioma and mesothelial hyperplasia.³

Cutaneous metastases occur in 0.7% to 9% of patients with internal malignant disease. Most commonly, cutaneous metastases present as cutaneous nodules, though other reported inflammatory presentations include erysipeloides, generalized erythematous patches, telangiectasia, and zosteriform distributions.⁶ Zosteriform distributions are particularly rare and most commonly are due to breast carcinomas or lymphomas. The mechanism of zosteriform metastasis is unknown, but theories include tumoral spread along vessels, invasion of the thoracic perineural sheaths, localized spread of tumor cells from a surgical site, or a Koebner-like reaction at the site of an existing HZI. Regardless of primary tumor type or presentation, cutaneous metastasis is a poor prognostic sign, with survival rates varying based on primary tumor type.⁷

Other differential diagnoses include herpes zoster granulomatous dermatitis, radiation recall dermatitis, cutaneous Rosai-Dorfman disease, and zosteriform lichen planus, all of which have been reported after HZI.^8-10 Herpes zoster granulomatous dermatitis typically presents weeks to years after acute HZI with erythematous to violaceous papules and plaques at the site of the prior HZI. A biopsy reveals interstitial granulomatous dermatitis and multinucleated giant cells.⁸ Radiation recall dermatitis is a cutaneous inflammatory reaction limited to regions of prior radiation exposure after the administration of a triggering medication. Radiation recall dermatitis can present days to many years after the completion of treatment.⁹ Although the eruption in our patient was at the site of prior radiation, the pathologic and clinical presentation was not consistent with radiation recall dermatitis. Cutaneous Rosai-Dorfman disease is a non-Langerhans cell histiocytosis that may present as either solitary or numerous papules, plaques, or nodules and has been reported to occur after HZI. Biopsy reveals a diffuse dermal histiocytic infiltration with plasma cells and lymphocytes. In contrast to metastatic disease, mitoses and nuclear atypia are rare in cutaneous RosaiDorfman disease.¹¹ Lichen planus is an inflammatory disease of unknown etiology presenting as flat-topped, violaceous, pruritic papules¹² that may present in a zosteriform pattern.¹³

Although it is uncommon, metastatic spread should be considered in patients with known malignancy presenting with zosteriform eruptions.² Our patient remained on treatment with immunotherapy, as he was unable to undergo additional radiation and had failed multiple other lines of therapy. He died 3 months after presentation.

THE DIAGNOSIS:

Cutaneous Metastatic Mesothelioma

Biopsies of the larger erythematous papules revealed an infiltrate of atypical tumor cells with mitoses (Figure 1) that were immunoreactive for calretinin (Figure 2) and lacked nuclear BRCA1 associated protein-1, BAP1, expression (not shown). The patient’s prior mesothelioma was re-reviewed, and the cutaneous tumor cells were similar to the primary mesothelioma. A diagnosis of cutaneous metastatic mesothelioma (CMM) was made.

Mesothelioma is a rare neoplasm arising from the pleura, pericardium, peritoneum, and tunica vaginalis,¹ with an estimated annual incidence of 2500 cases.² The predominant risk factor for the development of pleural mesothelioma is asbestos exposure, which has been identified in up to 90% of cases. Mesothelioma can give rise to local and less frequently distant hematogenous metastases. Cutaneous involvement of mesothelioma is rare.³ More than 80% of CMM cases are attributed to seeding the skin at procedure sites or by direct infiltration of scars. Distant CMM is rare and typically presents as subcutaneous nodules.⁴ Few cases of inflammatory CMM have been published,^1,4,5 with even fewer mimicking herpes zoster infection (HZI), as seen in our patient.

The most specific stain for mesothelioma is calretinin, which strongly and diffusely stains both the nucleus and cytoplasm. Other markers include Wilms tumor 1, cytokeratin 5/6, thrombomodulin, and HBME-1. Immunohistochemistry to detect the loss of BAP1 staining in the nucleus is important for differentiating between mesothelioma and mesothelial hyperplasia.³

Cutaneous metastases occur in 0.7% to 9% of patients with internal malignant disease. Most commonly, cutaneous metastases present as cutaneous nodules, though other reported inflammatory presentations include erysipeloides, generalized erythematous patches, telangiectasia, and zosteriform distributions.⁶ Zosteriform distributions are particularly rare and most commonly are due to breast carcinomas or lymphomas. The mechanism of zosteriform metastasis is unknown, but theories include tumoral spread along vessels, invasion of the thoracic perineural sheaths, localized spread of tumor cells from a surgical site, or a Koebner-like reaction at the site of an existing HZI. Regardless of primary tumor type or presentation, cutaneous metastasis is a poor prognostic sign, with survival rates varying based on primary tumor type.⁷

Other differential diagnoses include herpes zoster granulomatous dermatitis, radiation recall dermatitis, cutaneous Rosai-Dorfman disease, and zosteriform lichen planus, all of which have been reported after HZI.^8-10 Herpes zoster granulomatous dermatitis typically presents weeks to years after acute HZI with erythematous to violaceous papules and plaques at the site of the prior HZI. A biopsy reveals interstitial granulomatous dermatitis and multinucleated giant cells.⁸ Radiation recall dermatitis is a cutaneous inflammatory reaction limited to regions of prior radiation exposure after the administration of a triggering medication. Radiation recall dermatitis can present days to many years after the completion of treatment.⁹ Although the eruption in our patient was at the site of prior radiation, the pathologic and clinical presentation was not consistent with radiation recall dermatitis. Cutaneous Rosai-Dorfman disease is a non-Langerhans cell histiocytosis that may present as either solitary or numerous papules, plaques, or nodules and has been reported to occur after HZI. Biopsy reveals a diffuse dermal histiocytic infiltration with plasma cells and lymphocytes. In contrast to metastatic disease, mitoses and nuclear atypia are rare in cutaneous RosaiDorfman disease.¹¹ Lichen planus is an inflammatory disease of unknown etiology presenting as flat-topped, violaceous, pruritic papules¹² that may present in a zosteriform pattern.¹³

Although it is uncommon, metastatic spread should be considered in patients with known malignancy presenting with zosteriform eruptions.² Our patient remained on treatment with immunotherapy, as he was unable to undergo additional radiation and had failed multiple other lines of therapy. He died 3 months after presentation.

THE DIAGNOSIS:

Cutaneous Metastatic Mesothelioma

Biopsies of the larger erythematous papules revealed an infiltrate of atypical tumor cells with mitoses (Figure 1) that were immunoreactive for calretinin (Figure 2) and lacked nuclear BRCA1 associated protein-1, BAP1, expression (not shown). The patient’s prior mesothelioma was re-reviewed, and the cutaneous tumor cells were similar to the primary mesothelioma. A diagnosis of cutaneous metastatic mesothelioma (CMM) was made.

Mesothelioma is a rare neoplasm arising from the pleura, pericardium, peritoneum, and tunica vaginalis,¹ with an estimated annual incidence of 2500 cases.² The predominant risk factor for the development of pleural mesothelioma is asbestos exposure, which has been identified in up to 90% of cases. Mesothelioma can give rise to local and less frequently distant hematogenous metastases. Cutaneous involvement of mesothelioma is rare.³ More than 80% of CMM cases are attributed to seeding the skin at procedure sites or by direct infiltration of scars. Distant CMM is rare and typically presents as subcutaneous nodules.⁴ Few cases of inflammatory CMM have been published,^1,4,5 with even fewer mimicking herpes zoster infection (HZI), as seen in our patient.

The most specific stain for mesothelioma is calretinin, which strongly and diffusely stains both the nucleus and cytoplasm. Other markers include Wilms tumor 1, cytokeratin 5/6, thrombomodulin, and HBME-1. Immunohistochemistry to detect the loss of BAP1 staining in the nucleus is important for differentiating between mesothelioma and mesothelial hyperplasia.³

Cutaneous metastases occur in 0.7% to 9% of patients with internal malignant disease. Most commonly, cutaneous metastases present as cutaneous nodules, though other reported inflammatory presentations include erysipeloides, generalized erythematous patches, telangiectasia, and zosteriform distributions.⁶ Zosteriform distributions are particularly rare and most commonly are due to breast carcinomas or lymphomas. The mechanism of zosteriform metastasis is unknown, but theories include tumoral spread along vessels, invasion of the thoracic perineural sheaths, localized spread of tumor cells from a surgical site, or a Koebner-like reaction at the site of an existing HZI. Regardless of primary tumor type or presentation, cutaneous metastasis is a poor prognostic sign, with survival rates varying based on primary tumor type.⁷

Other differential diagnoses include herpes zoster granulomatous dermatitis, radiation recall dermatitis, cutaneous Rosai-Dorfman disease, and zosteriform lichen planus, all of which have been reported after HZI.^8-10 Herpes zoster granulomatous dermatitis typically presents weeks to years after acute HZI with erythematous to violaceous papules and plaques at the site of the prior HZI. A biopsy reveals interstitial granulomatous dermatitis and multinucleated giant cells.⁸ Radiation recall dermatitis is a cutaneous inflammatory reaction limited to regions of prior radiation exposure after the administration of a triggering medication. Radiation recall dermatitis can present days to many years after the completion of treatment.⁹ Although the eruption in our patient was at the site of prior radiation, the pathologic and clinical presentation was not consistent with radiation recall dermatitis. Cutaneous Rosai-Dorfman disease is a non-Langerhans cell histiocytosis that may present as either solitary or numerous papules, plaques, or nodules and has been reported to occur after HZI. Biopsy reveals a diffuse dermal histiocytic infiltration with plasma cells and lymphocytes. In contrast to metastatic disease, mitoses and nuclear atypia are rare in cutaneous RosaiDorfman disease.¹¹ Lichen planus is an inflammatory disease of unknown etiology presenting as flat-topped, violaceous, pruritic papules¹² that may present in a zosteriform pattern.¹³

Although it is uncommon, metastatic spread should be considered in patients with known malignancy presenting with zosteriform eruptions.² Our patient remained on treatment with immunotherapy, as he was unable to undergo additional radiation and had failed multiple other lines of therapy. He died 3 months after presentation.

THE DIAGNOSIS: Vegetative Majocchi Granuloma

A biopsy and tissue culture showed acute dermal inflammation with granulomatous features and numerous fungal hyphae within the stratum corneum (Figure 1A), which were confirmed on GrocottGomori methenamine-silver staining (Figure 1B). Gram and Fite stains were negative for bacteria. A tissue culture speciated Trichophyton rubrum, which led to a diagnosis of deep dermatophyte infection (Majocchi granuloma) with a highly unusual clinical presentation of vegetative plaques. Predisposing factors included treatment with topical corticosteroids and possibly poor health and nutritional status at baseline. Our patient was treated with fluconazole 200 mg daily for 6 weeks, with near resolution of lesions at 3-week follow-up (Figure 2).

Dermatophytes are a common cause of superficial skin infections. The classic morphology consists of an annular scaly plaque; however, a wide variety of presentations have been observed (eg, verrucous, vesicular, pustular, granulomatous). Therefore, dermatophyte infections often mimic other dermatologic conditions, including atopic dermatitis, rosacea, psoriasis, bacterial abscess, erythema gyratum repens, lupus, granuloma annulare, cutaneous lymphoma, Hailey-Hailey disease, scarring alopecia, and syphilis.¹

Notably, when dermatophytes grow downward along hair follicles causing deeper infection, disruption of the follicular wall can lead to an excessive inflammatory response with granulomatous features.² Risk factors include cutaneous trauma, long-standing infection, immunocompromise, and treatment with topical corticosteroids.³ This disease evolution clinically appears as a nodule or infiltrated plaque, often without scale. The most well-known example is a kerion on the scalp. Elsewhere on the body, lesions often are termed Majocchi granulomas.²

Vegetative plaques, as seen in our patient, are a highly unusual morphology for deep tinea infection. Guanziroli et al⁴ reported a case of vegetative lesions on the forearm of a 67-year-old immunocompromised man that were successfully treated with a 3-month course of oral terbinafine after Trichophyton verrucosum was isolated. Skorepova et al⁵ reported a case of pyoderma vegetans triggered by recurrent Trichophyton mentagrophytes on the dorsal hands of a 64-year-old man with immunoglobulin deficiency of unknown etiology. The lesions were successfully treated with a prolonged course of doxycycline, topical triamcinolone, and intravenous immunoglobulin following 2 initial courses of terbinafine.

The differential diagnosis for vegetative lesions includes pemphigus vegetans, a vegetative variant of pyoderma gangrenosum; halogenoderma; and a variety of infections, including dimorphic fungi (histoplasmosis, blastomycosis), blastomycosislike pyoderma (bacterial), and candidiasis.⁶ These conditions usually can be distinguished based on histopathology. Clinically, pemphigus vegetans presents with pustules and vegetative lesions, as in our patient, but usually is more diffuse and favors the intertriginous areas. Histology likely would reveal foci of acantholysis and eosinophils. Vegetative pyoderma gangrenosum favors the trunk, particularly in sites of surgical trauma. In our patient, no lesions were present near the abdominal surgical sites, and there was no antecedent cribriform ulceration. Halogenoderma was a strong initial consideration given the localization, presence of large pustules, and history of numerous contrast computed tomography studies; however, our patient’s iodine levels were normal. Infectious etiologies including dimorphic fungi and blastomycosislike pyoderma generally are not restricted to the head and neck, and tissue culture helps exclude them. Vegetative lesions may occur in the setting of other infections, and tissue culture may be necessary to differentiate them if histopathology is not suggestive.

Deep dermatophyte infections require treatment with oral antifungals, as topicals do not penetrate adequately into the hair follicles. Exact regimens vary, but generally oral terbinafine or an oral azole (except ketoconazole) is administered for 2 to 6 weeks, with immunocompromise necessitating longer courses.

We present a rare case of vegetative Majocchi granuloma secondary to T rubrum infection. A dermatophyte infection should be included in the differential for vegetative lesions, especially in dense hair-bearing areas such as the beard. Treatment generally is straightforward with oral antifungals.

THE DIAGNOSIS: Vegetative Majocchi Granuloma

A biopsy and tissue culture showed acute dermal inflammation with granulomatous features and numerous fungal hyphae within the stratum corneum (Figure 1A), which were confirmed on GrocottGomori methenamine-silver staining (Figure 1B). Gram and Fite stains were negative for bacteria. A tissue culture speciated Trichophyton rubrum, which led to a diagnosis of deep dermatophyte infection (Majocchi granuloma) with a highly unusual clinical presentation of vegetative plaques. Predisposing factors included treatment with topical corticosteroids and possibly poor health and nutritional status at baseline. Our patient was treated with fluconazole 200 mg daily for 6 weeks, with near resolution of lesions at 3-week follow-up (Figure 2).

Dermatophytes are a common cause of superficial skin infections. The classic morphology consists of an annular scaly plaque; however, a wide variety of presentations have been observed (eg, verrucous, vesicular, pustular, granulomatous). Therefore, dermatophyte infections often mimic other dermatologic conditions, including atopic dermatitis, rosacea, psoriasis, bacterial abscess, erythema gyratum repens, lupus, granuloma annulare, cutaneous lymphoma, Hailey-Hailey disease, scarring alopecia, and syphilis.¹

Notably, when dermatophytes grow downward along hair follicles causing deeper infection, disruption of the follicular wall can lead to an excessive inflammatory response with granulomatous features.² Risk factors include cutaneous trauma, long-standing infection, immunocompromise, and treatment with topical corticosteroids.³ This disease evolution clinically appears as a nodule or infiltrated plaque, often without scale. The most well-known example is a kerion on the scalp. Elsewhere on the body, lesions often are termed Majocchi granulomas.²

Vegetative plaques, as seen in our patient, are a highly unusual morphology for deep tinea infection. Guanziroli et al⁴ reported a case of vegetative lesions on the forearm of a 67-year-old immunocompromised man that were successfully treated with a 3-month course of oral terbinafine after Trichophyton verrucosum was isolated. Skorepova et al⁵ reported a case of pyoderma vegetans triggered by recurrent Trichophyton mentagrophytes on the dorsal hands of a 64-year-old man with immunoglobulin deficiency of unknown etiology. The lesions were successfully treated with a prolonged course of doxycycline, topical triamcinolone, and intravenous immunoglobulin following 2 initial courses of terbinafine.

The differential diagnosis for vegetative lesions includes pemphigus vegetans, a vegetative variant of pyoderma gangrenosum; halogenoderma; and a variety of infections, including dimorphic fungi (histoplasmosis, blastomycosis), blastomycosislike pyoderma (bacterial), and candidiasis.⁶ These conditions usually can be distinguished based on histopathology. Clinically, pemphigus vegetans presents with pustules and vegetative lesions, as in our patient, but usually is more diffuse and favors the intertriginous areas. Histology likely would reveal foci of acantholysis and eosinophils. Vegetative pyoderma gangrenosum favors the trunk, particularly in sites of surgical trauma. In our patient, no lesions were present near the abdominal surgical sites, and there was no antecedent cribriform ulceration. Halogenoderma was a strong initial consideration given the localization, presence of large pustules, and history of numerous contrast computed tomography studies; however, our patient’s iodine levels were normal. Infectious etiologies including dimorphic fungi and blastomycosislike pyoderma generally are not restricted to the head and neck, and tissue culture helps exclude them. Vegetative lesions may occur in the setting of other infections, and tissue culture may be necessary to differentiate them if histopathology is not suggestive.

Deep dermatophyte infections require treatment with oral antifungals, as topicals do not penetrate adequately into the hair follicles. Exact regimens vary, but generally oral terbinafine or an oral azole (except ketoconazole) is administered for 2 to 6 weeks, with immunocompromise necessitating longer courses.

We present a rare case of vegetative Majocchi granuloma secondary to T rubrum infection. A dermatophyte infection should be included in the differential for vegetative lesions, especially in dense hair-bearing areas such as the beard. Treatment generally is straightforward with oral antifungals.

THE DIAGNOSIS: Vegetative Majocchi Granuloma

A biopsy and tissue culture showed acute dermal inflammation with granulomatous features and numerous fungal hyphae within the stratum corneum (Figure 1A), which were confirmed on GrocottGomori methenamine-silver staining (Figure 1B). Gram and Fite stains were negative for bacteria. A tissue culture speciated Trichophyton rubrum, which led to a diagnosis of deep dermatophyte infection (Majocchi granuloma) with a highly unusual clinical presentation of vegetative plaques. Predisposing factors included treatment with topical corticosteroids and possibly poor health and nutritional status at baseline. Our patient was treated with fluconazole 200 mg daily for 6 weeks, with near resolution of lesions at 3-week follow-up (Figure 2).

Dermatophytes are a common cause of superficial skin infections. The classic morphology consists of an annular scaly plaque; however, a wide variety of presentations have been observed (eg, verrucous, vesicular, pustular, granulomatous). Therefore, dermatophyte infections often mimic other dermatologic conditions, including atopic dermatitis, rosacea, psoriasis, bacterial abscess, erythema gyratum repens, lupus, granuloma annulare, cutaneous lymphoma, Hailey-Hailey disease, scarring alopecia, and syphilis.¹

Notably, when dermatophytes grow downward along hair follicles causing deeper infection, disruption of the follicular wall can lead to an excessive inflammatory response with granulomatous features.² Risk factors include cutaneous trauma, long-standing infection, immunocompromise, and treatment with topical corticosteroids.³ This disease evolution clinically appears as a nodule or infiltrated plaque, often without scale. The most well-known example is a kerion on the scalp. Elsewhere on the body, lesions often are termed Majocchi granulomas.²

Vegetative plaques, as seen in our patient, are a highly unusual morphology for deep tinea infection. Guanziroli et al⁴ reported a case of vegetative lesions on the forearm of a 67-year-old immunocompromised man that were successfully treated with a 3-month course of oral terbinafine after Trichophyton verrucosum was isolated. Skorepova et al⁵ reported a case of pyoderma vegetans triggered by recurrent Trichophyton mentagrophytes on the dorsal hands of a 64-year-old man with immunoglobulin deficiency of unknown etiology. The lesions were successfully treated with a prolonged course of doxycycline, topical triamcinolone, and intravenous immunoglobulin following 2 initial courses of terbinafine.

The differential diagnosis for vegetative lesions includes pemphigus vegetans, a vegetative variant of pyoderma gangrenosum; halogenoderma; and a variety of infections, including dimorphic fungi (histoplasmosis, blastomycosis), blastomycosislike pyoderma (bacterial), and candidiasis.⁶ These conditions usually can be distinguished based on histopathology. Clinically, pemphigus vegetans presents with pustules and vegetative lesions, as in our patient, but usually is more diffuse and favors the intertriginous areas. Histology likely would reveal foci of acantholysis and eosinophils. Vegetative pyoderma gangrenosum favors the trunk, particularly in sites of surgical trauma. In our patient, no lesions were present near the abdominal surgical sites, and there was no antecedent cribriform ulceration. Halogenoderma was a strong initial consideration given the localization, presence of large pustules, and history of numerous contrast computed tomography studies; however, our patient’s iodine levels were normal. Infectious etiologies including dimorphic fungi and blastomycosislike pyoderma generally are not restricted to the head and neck, and tissue culture helps exclude them. Vegetative lesions may occur in the setting of other infections, and tissue culture may be necessary to differentiate them if histopathology is not suggestive.

Deep dermatophyte infections require treatment with oral antifungals, as topicals do not penetrate adequately into the hair follicles. Exact regimens vary, but generally oral terbinafine or an oral azole (except ketoconazole) is administered for 2 to 6 weeks, with immunocompromise necessitating longer courses.

We present a rare case of vegetative Majocchi granuloma secondary to T rubrum infection. A dermatophyte infection should be included in the differential for vegetative lesions, especially in dense hair-bearing areas such as the beard. Treatment generally is straightforward with oral antifungals.

The Diagnosis: Dermatomyofibroma

Dermatomyofibroma is an uncommon, benign, cutaneous mesenchymal neoplasm composed of fibroblasts and myofibroblasts.^1-3 This skin tumor was first described in 1991 by Hugel⁴ in the German literature as plaquelike fibromatosis. Pediatric dermatomyofibromas are exceedingly rare, with pediatric patients ranging in age from infants to teenagers.¹

Clinically, dermatomyofibromas appear as long-standing, isolated, ill-demarcated, flesh-colored, slightly hyperpigmented or erythematous nodules or plaques that may be raised or indurated.¹ Dermatomyofibromas may present with constant mild pain or pruritus, though in most cases the lesions are asymptomatic.^1,3 The clinical presentation of dermatomyofibroma has a few distinct differences in children compared to adults. In adulthood, dermatomyofibroma has a strong female predominance and most commonly is located on the shoulder and adjacent upper body regions, including the axilla, neck, upper arm, and upper trunk.^1-3 In childhood, the majority of dermatomyofibromas occur in young boys and usually are located on the neck with other upper body regions occurring less frequently.^1,2 A shared characteristic includes the tendency for dermatomyofibromas to have an initial period of enlargement followed by stabilization or slow growth.¹ Reported pediatric lesions have ranged in size from 4 to 60 mm with an average size of 14.9 mm (median, 12 mm).²

The diagnosis of dermatomyofibroma is based on histopathologic features in addition to clinical presentation. Histology from punch biopsy usually reveals a noninvasive dermal proliferation of bland, uniform, slender spindle cells oriented parallel to the overlying epidermis with increased and fragmented elastic fibers.^1,3 Infiltration into the mid or deep dermis is common. The adnexal structures usually are spared; the stroma contains collagen and increased small blood vessels; and there typically is no inflammatory infiltrate, except for occasional scattered mast cells.² Cytologically, the monomorphic spindleshaped tumor cells have an ill-defined, pale, eosinophilic cytoplasm and nuclei that are elongated with tapered edges.³ Dermatomyofibroma has a variable immunohistochemical profile, as it may stain focally positive for CD34 or smooth muscle actin, with occasional staining of factor XIIIa, desmin, calponin, or vimentin.^1-3 Normal to increased levels of often fragmented elastic fibers is a helpful clue in distinguishing dermatomyofibroma from dermatofibroma, hypertrophic scar, dermatofibrosarcoma protuberans, and pilar leiomyoma, in which elastic fibers typically are reduced.³ Differential diagnoses of mesenchymal tumors in children include desmoid fibromatosis, connective tissue nevus, myofibromatosis, and smooth muscle hamartoma.¹

A punch biopsy with clinical observation and followup is recommended for the management of lesions in cosmetically sensitive areas or in very young children who may not tolerate surgery. In symptomatic or cosmetically unappealing cases of dermatomyofibroma, simple surgical excision remains a viable treatment option. Recurrence is uncommon, even if only partially excised, and no instances of metastasis have been reported.^1-5

Dermatomyofibromas may be mistaken for several other entities both benign and malignant. For example, the benign dermatofibroma is the second most common fibrohistiocytic tumor of the skin and presents as a firm, nontender, minimally elevated to dome-shaped papule that usually measures less than or equal to 1 cm in diameter with or without overlying skin changes.^5,6 It primarily is seen in adults with a slight female predominance and favors the lower extremities.⁵ Patients usually are asymptomatic but often report a history of local trauma at the lesion site.⁶ Histologically, dermatofibroma is characterized by a nodular dermal proliferation of spindleshaped fibrous cells and histiocytes in a storiform pattern (Figure 1).⁶ Epidermal induction with acanthosis overlying the tumor often is found with occasional basilar hyperpigmentation.⁵ Dermatofibroma also characteristically has trapped collagen (“collagen balls”) seen at the periphery.^5,6

Piloleiomyomas are benign smooth muscle tumors arising from arrector pili muscles that may be solitary or multiple.⁵ Clinically, they typically present as firm, reddish-brown to flesh-colored papules or nodules that develop more commonly in adulthood.^5,7 Piloleiomyomas favor the extremities and trunk, particularly the shoulder, and can be associated with spontaneous or induced pain. Histologically, piloleiomyomas are well circumscribed and centered within the reticular dermis situated closely to hair follicles (Figure 2).⁵ They are composed of numerous interlacing fascicles or whorls of smooth muscle cells with abundant eosinophilic cytoplasm and blunt-ended, cigar-shaped nuclei.^5,7

Solitary cutaneous myofibroma is a benign fibrous tumor found in adolescents and adults and is the counterpart to infantile myofibromatosis.⁸ Clinically, myofibromas typically present as painless, slow-growing, firm nodules with an occasional bluish hue. Histologically, solitary cutaneous myofibromas appear in a biphasic pattern, with hemangiopericytomatous components as well as spindle cells arranged in short bundles and fascicles resembling leiomyoma (Figure 3). The spindle cells also have abundant eosinophilic cytoplasm with short plump nuclei; the random, irregularly intersecting angles can be used to help differentiate myofibromas from smooth muscle lesions.⁸ Solitary cutaneous myofibroma is in the differential diagnosis for dermatomyofibroma because of their shared myofibroblastic nature.⁹

Dermatofibrosarcoma protuberans (DFSP) is an uncommon, locally invasive sarcoma with a high recurrence rate that favors young to middle-aged adults, with rare childhood onset reported.^5,10,11 Clinically, DFSP typically presents as an asymptomatic, slow-growing, firm, flesh-colored, indurated plaque that develops into a violaceous to reddish-brown nodule.⁵ The atrophic variant of DFSP is characterized by a nonprotuberant lesion and can be especially difficult to distinguish from other entities such as dermatomyofibroma.¹¹ The majority of DFSP lesions occur on the trunk, particularly in the shoulder or pelvic region.⁵ Histologically, early plaque lesions are comprised of monomorphic spindle cells arranged in long fascicles (parallel to the skin surface), infiltrating adnexal structures, and subcutaneous adipocytes in a multilayered honeycomb pattern; the spindle cells of late nodular lesions are arranged in short fascicles in a matted or storiform pattern (Figure 4).^5,10 Early stages of DFSP as well as variations in childhood-onset DFSP can easily be misdiagnosed and incompletely excised.⁵

The Diagnosis: Dermatomyofibroma

Dermatomyofibroma is an uncommon, benign, cutaneous mesenchymal neoplasm composed of fibroblasts and myofibroblasts.^1-3 This skin tumor was first described in 1991 by Hugel⁴ in the German literature as plaquelike fibromatosis. Pediatric dermatomyofibromas are exceedingly rare, with pediatric patients ranging in age from infants to teenagers.¹

Clinically, dermatomyofibromas appear as long-standing, isolated, ill-demarcated, flesh-colored, slightly hyperpigmented or erythematous nodules or plaques that may be raised or indurated.¹ Dermatomyofibromas may present with constant mild pain or pruritus, though in most cases the lesions are asymptomatic.^1,3 The clinical presentation of dermatomyofibroma has a few distinct differences in children compared to adults. In adulthood, dermatomyofibroma has a strong female predominance and most commonly is located on the shoulder and adjacent upper body regions, including the axilla, neck, upper arm, and upper trunk.^1-3 In childhood, the majority of dermatomyofibromas occur in young boys and usually are located on the neck with other upper body regions occurring less frequently.^1,2 A shared characteristic includes the tendency for dermatomyofibromas to have an initial period of enlargement followed by stabilization or slow growth.¹ Reported pediatric lesions have ranged in size from 4 to 60 mm with an average size of 14.9 mm (median, 12 mm).²

The diagnosis of dermatomyofibroma is based on histopathologic features in addition to clinical presentation. Histology from punch biopsy usually reveals a noninvasive dermal proliferation of bland, uniform, slender spindle cells oriented parallel to the overlying epidermis with increased and fragmented elastic fibers.^1,3 Infiltration into the mid or deep dermis is common. The adnexal structures usually are spared; the stroma contains collagen and increased small blood vessels; and there typically is no inflammatory infiltrate, except for occasional scattered mast cells.² Cytologically, the monomorphic spindleshaped tumor cells have an ill-defined, pale, eosinophilic cytoplasm and nuclei that are elongated with tapered edges.³ Dermatomyofibroma has a variable immunohistochemical profile, as it may stain focally positive for CD34 or smooth muscle actin, with occasional staining of factor XIIIa, desmin, calponin, or vimentin.^1-3 Normal to increased levels of often fragmented elastic fibers is a helpful clue in distinguishing dermatomyofibroma from dermatofibroma, hypertrophic scar, dermatofibrosarcoma protuberans, and pilar leiomyoma, in which elastic fibers typically are reduced.³ Differential diagnoses of mesenchymal tumors in children include desmoid fibromatosis, connective tissue nevus, myofibromatosis, and smooth muscle hamartoma.¹

A punch biopsy with clinical observation and followup is recommended for the management of lesions in cosmetically sensitive areas or in very young children who may not tolerate surgery. In symptomatic or cosmetically unappealing cases of dermatomyofibroma, simple surgical excision remains a viable treatment option. Recurrence is uncommon, even if only partially excised, and no instances of metastasis have been reported.^1-5

Dermatomyofibromas may be mistaken for several other entities both benign and malignant. For example, the benign dermatofibroma is the second most common fibrohistiocytic tumor of the skin and presents as a firm, nontender, minimally elevated to dome-shaped papule that usually measures less than or equal to 1 cm in diameter with or without overlying skin changes.^5,6 It primarily is seen in adults with a slight female predominance and favors the lower extremities.⁵ Patients usually are asymptomatic but often report a history of local trauma at the lesion site.⁶ Histologically, dermatofibroma is characterized by a nodular dermal proliferation of spindleshaped fibrous cells and histiocytes in a storiform pattern (Figure 1).⁶ Epidermal induction with acanthosis overlying the tumor often is found with occasional basilar hyperpigmentation.⁵ Dermatofibroma also characteristically has trapped collagen (“collagen balls”) seen at the periphery.^5,6

Piloleiomyomas are benign smooth muscle tumors arising from arrector pili muscles that may be solitary or multiple.⁵ Clinically, they typically present as firm, reddish-brown to flesh-colored papules or nodules that develop more commonly in adulthood.^5,7 Piloleiomyomas favor the extremities and trunk, particularly the shoulder, and can be associated with spontaneous or induced pain. Histologically, piloleiomyomas are well circumscribed and centered within the reticular dermis situated closely to hair follicles (Figure 2).⁵ They are composed of numerous interlacing fascicles or whorls of smooth muscle cells with abundant eosinophilic cytoplasm and blunt-ended, cigar-shaped nuclei.^5,7

Solitary cutaneous myofibroma is a benign fibrous tumor found in adolescents and adults and is the counterpart to infantile myofibromatosis.⁸ Clinically, myofibromas typically present as painless, slow-growing, firm nodules with an occasional bluish hue. Histologically, solitary cutaneous myofibromas appear in a biphasic pattern, with hemangiopericytomatous components as well as spindle cells arranged in short bundles and fascicles resembling leiomyoma (Figure 3). The spindle cells also have abundant eosinophilic cytoplasm with short plump nuclei; the random, irregularly intersecting angles can be used to help differentiate myofibromas from smooth muscle lesions.⁸ Solitary cutaneous myofibroma is in the differential diagnosis for dermatomyofibroma because of their shared myofibroblastic nature.⁹

Dermatofibrosarcoma protuberans (DFSP) is an uncommon, locally invasive sarcoma with a high recurrence rate that favors young to middle-aged adults, with rare childhood onset reported.^5,10,11 Clinically, DFSP typically presents as an asymptomatic, slow-growing, firm, flesh-colored, indurated plaque that develops into a violaceous to reddish-brown nodule.⁵ The atrophic variant of DFSP is characterized by a nonprotuberant lesion and can be especially difficult to distinguish from other entities such as dermatomyofibroma.¹¹ The majority of DFSP lesions occur on the trunk, particularly in the shoulder or pelvic region.⁵ Histologically, early plaque lesions are comprised of monomorphic spindle cells arranged in long fascicles (parallel to the skin surface), infiltrating adnexal structures, and subcutaneous adipocytes in a multilayered honeycomb pattern; the spindle cells of late nodular lesions are arranged in short fascicles in a matted or storiform pattern (Figure 4).^5,10 Early stages of DFSP as well as variations in childhood-onset DFSP can easily be misdiagnosed and incompletely excised.⁵

The Diagnosis: Dermatomyofibroma

Dermatomyofibroma is an uncommon, benign, cutaneous mesenchymal neoplasm composed of fibroblasts and myofibroblasts.^1-3 This skin tumor was first described in 1991 by Hugel⁴ in the German literature as plaquelike fibromatosis. Pediatric dermatomyofibromas are exceedingly rare, with pediatric patients ranging in age from infants to teenagers.¹

Clinically, dermatomyofibromas appear as long-standing, isolated, ill-demarcated, flesh-colored, slightly hyperpigmented or erythematous nodules or plaques that may be raised or indurated.¹ Dermatomyofibromas may present with constant mild pain or pruritus, though in most cases the lesions are asymptomatic.^1,3 The clinical presentation of dermatomyofibroma has a few distinct differences in children compared to adults. In adulthood, dermatomyofibroma has a strong female predominance and most commonly is located on the shoulder and adjacent upper body regions, including the axilla, neck, upper arm, and upper trunk.^1-3 In childhood, the majority of dermatomyofibromas occur in young boys and usually are located on the neck with other upper body regions occurring less frequently.^1,2 A shared characteristic includes the tendency for dermatomyofibromas to have an initial period of enlargement followed by stabilization or slow growth.¹ Reported pediatric lesions have ranged in size from 4 to 60 mm with an average size of 14.9 mm (median, 12 mm).²

The diagnosis of dermatomyofibroma is based on histopathologic features in addition to clinical presentation. Histology from punch biopsy usually reveals a noninvasive dermal proliferation of bland, uniform, slender spindle cells oriented parallel to the overlying epidermis with increased and fragmented elastic fibers.^1,3 Infiltration into the mid or deep dermis is common. The adnexal structures usually are spared; the stroma contains collagen and increased small blood vessels; and there typically is no inflammatory infiltrate, except for occasional scattered mast cells.² Cytologically, the monomorphic spindleshaped tumor cells have an ill-defined, pale, eosinophilic cytoplasm and nuclei that are elongated with tapered edges.³ Dermatomyofibroma has a variable immunohistochemical profile, as it may stain focally positive for CD34 or smooth muscle actin, with occasional staining of factor XIIIa, desmin, calponin, or vimentin.^1-3 Normal to increased levels of often fragmented elastic fibers is a helpful clue in distinguishing dermatomyofibroma from dermatofibroma, hypertrophic scar, dermatofibrosarcoma protuberans, and pilar leiomyoma, in which elastic fibers typically are reduced.³ Differential diagnoses of mesenchymal tumors in children include desmoid fibromatosis, connective tissue nevus, myofibromatosis, and smooth muscle hamartoma.¹

A punch biopsy with clinical observation and followup is recommended for the management of lesions in cosmetically sensitive areas or in very young children who may not tolerate surgery. In symptomatic or cosmetically unappealing cases of dermatomyofibroma, simple surgical excision remains a viable treatment option. Recurrence is uncommon, even if only partially excised, and no instances of metastasis have been reported.^1-5

Dermatomyofibromas may be mistaken for several other entities both benign and malignant. For example, the benign dermatofibroma is the second most common fibrohistiocytic tumor of the skin and presents as a firm, nontender, minimally elevated to dome-shaped papule that usually measures less than or equal to 1 cm in diameter with or without overlying skin changes.^5,6 It primarily is seen in adults with a slight female predominance and favors the lower extremities.⁵ Patients usually are asymptomatic but often report a history of local trauma at the lesion site.⁶ Histologically, dermatofibroma is characterized by a nodular dermal proliferation of spindleshaped fibrous cells and histiocytes in a storiform pattern (Figure 1).⁶ Epidermal induction with acanthosis overlying the tumor often is found with occasional basilar hyperpigmentation.⁵ Dermatofibroma also characteristically has trapped collagen (“collagen balls”) seen at the periphery.^5,6

Piloleiomyomas are benign smooth muscle tumors arising from arrector pili muscles that may be solitary or multiple.⁵ Clinically, they typically present as firm, reddish-brown to flesh-colored papules or nodules that develop more commonly in adulthood.^5,7 Piloleiomyomas favor the extremities and trunk, particularly the shoulder, and can be associated with spontaneous or induced pain. Histologically, piloleiomyomas are well circumscribed and centered within the reticular dermis situated closely to hair follicles (Figure 2).⁵ They are composed of numerous interlacing fascicles or whorls of smooth muscle cells with abundant eosinophilic cytoplasm and blunt-ended, cigar-shaped nuclei.^5,7

Solitary cutaneous myofibroma is a benign fibrous tumor found in adolescents and adults and is the counterpart to infantile myofibromatosis.⁸ Clinically, myofibromas typically present as painless, slow-growing, firm nodules with an occasional bluish hue. Histologically, solitary cutaneous myofibromas appear in a biphasic pattern, with hemangiopericytomatous components as well as spindle cells arranged in short bundles and fascicles resembling leiomyoma (Figure 3). The spindle cells also have abundant eosinophilic cytoplasm with short plump nuclei; the random, irregularly intersecting angles can be used to help differentiate myofibromas from smooth muscle lesions.⁸ Solitary cutaneous myofibroma is in the differential diagnosis for dermatomyofibroma because of their shared myofibroblastic nature.⁹

Dermatofibrosarcoma protuberans (DFSP) is an uncommon, locally invasive sarcoma with a high recurrence rate that favors young to middle-aged adults, with rare childhood onset reported.^5,10,11 Clinically, DFSP typically presents as an asymptomatic, slow-growing, firm, flesh-colored, indurated plaque that develops into a violaceous to reddish-brown nodule.⁵ The atrophic variant of DFSP is characterized by a nonprotuberant lesion and can be especially difficult to distinguish from other entities such as dermatomyofibroma.¹¹ The majority of DFSP lesions occur on the trunk, particularly in the shoulder or pelvic region.⁵ Histologically, early plaque lesions are comprised of monomorphic spindle cells arranged in long fascicles (parallel to the skin surface), infiltrating adnexal structures, and subcutaneous adipocytes in a multilayered honeycomb pattern; the spindle cells of late nodular lesions are arranged in short fascicles in a matted or storiform pattern (Figure 4).^5,10 Early stages of DFSP as well as variations in childhood-onset DFSP can easily be misdiagnosed and incompletely excised.⁵

The Diagnosis: Multicentric Reticulohistiocytosis

Te patient presented with pink papules coalescing into plaques on the upper chest and lower back (Figure 1) as well as a characteristic finding of periungual papules with a coral bead appearance. Histopathologic examination revealed a dense infiltrate of epithelioid histiocytes with amphophilic ground-glass cytoplasm in a nodular configuration (Figure 2). This pattern in conjunction with the clinical features seen in our patient was consistent with a diagnosis of multicentric reticulohistiocytosis (MRH).^1-3 The cutaneous symptoms were managed with triamcinolone ointment 0.1% twice daily and oral hydroxyzine 10 mg 3 times daily as needed for itching with moderate improvement. She was referred to rheumatology for arthritis management, and the initial cancer screening was negative.

Multicentric reticulohistiocytosis is a rare granulomatous disease characterized by papulonodular cutaneous lesions and severe erosive arthritis. It has an insidious onset and most commonly affects middle-aged women.¹ Multicentric reticulohistiocytosis typically presents as rounded pruritic papules or nodules that may be pink, red, or brown primarily affecting the face and distal upper extremities.^1,3 Mucosal involvement occurs in more than half of patients and is characterized by multiple erythematous papules and nodules on the oral and nasopharyngeal mucosae that rarely can produce leonine facies.² A hallmark feature of MRH is the presence of multiple shiny erythematous papules along the proximal and lateral nail folds that take on a coral bead appearance.^1,3,4 Furthermore, nail changes such as atrophy, longitudinal ridging, brittleness, and hyperpigmentation can occur secondary to a synovial reaction that disturbs the nail matrix.^4,5

Joint involvement precedes cutaneous involvement in most cases of MRH.^1,5 Multicentric reticulohistiocytosis is associated with a symmetric destructive arthritis affecting the hands, knees, shoulders, and hips that often is associated with pain, stiffness, and swelling.^1,3 The arthritis rapidly progresses in the early stages of the disease but then becomes less active over the subsequent 8 to 10 years.¹ It has the potential to develop into arthritis mutilans, an end-stage form of arthritis also seen in psoriatic and rheumatoid arthritis that leads to severe joint deformity and debilitation.^1,2

The etiology of MRH still is unknown, but it has an association with underlying malignancy in up to 25% of patients.⁶ Multicentric reticulohistiocytosis has been reported in the context of a wide variety of malignancies including melanoma; sarcoma; lymphoma; leukemia; and carcinomas of the breast, colon, and lung. In some cases, the diagnosis of MRH may even precede the diagnosis of cancer.³ Multicentric reticulohistiocytosis also may be associated with autoimmune conditions,³ as seen in our patient who had a history of both hypothyroidism and vitiligo.

Histopathologic examination is essential in distinguishing MRH from other autoimmune disorders associated with hand lesions, rash, and arthralgia. Erythema elevatum diutinum is associated with symmetric, violaceous, red or brown papules and plaques located on the extensor surfaces of the extremities and hands; however, histology reveals a leukocytoclastic vasculitis with a mixture of polymorphonuclear leukocytes and lymphocytes.⁷ Dermatomyositis may present with arthralgia, flattopped, erythematous (Gottron) papules localized over the proximal interphalangeal and distal interphalangeal joints, as well as proximal nail findings. The latter generally presents with periungual erythema associated with dilated capillary loops rather than the discrete orderly papules seen in MRH. Histologic examination of dermatomyositis shows mild epidermal atrophy, vacuolar changes in the basal keratinocyte layer, and a dermal perivascular lymphocytic infiltrate.⁸ Because MRH initially can present with joint symptoms and hand nodules, it may be confused with rheumatoid arthritis. However, rheumatoid arthritis typically is associated with severe osteopenia and tends to affect the metacarpophalangeal and proximal interphalangeal joints rather than the distal interphalangeal joints that most often are affected in MRH.¹ Histologic examination of rheumatoid nodules reveals palisading granulomas surrounding a central area of fibrinoid necrosis.⁹ Sarcoidosis is a multisystem disease that can present with cutaneous involvement including erythema nodosum, skin plaques, subcutaneous nodules, and papular eruptions in addition to joint lesions.¹⁰ Sarcoidosis most frequently involves the lungs, manifesting as diffuse interstitial lung disease with bilateral hilar lymphadenopathy. Furthermore, histologic examination of lesions demonstrates classic noncaseating granulomas containing epithelioid cells, multinucleated giant cells with inclusion bodies, and lymphocytes.¹¹

A skin biopsy is required to establish the diagnosis of MRH. In general, patients with MRH and no underlying malignancy have a good prognosis and respond to anti-inflammatory therapies such as nonsteroidal antiinflammatory drugs and corticosteroids. Other agents including methotrexate, cyclophosphamide, and tumor necrosis factor α inhibitors also have been effective in more severe cases.^1,3,12 Finally, in addition to treating the cutaneous manifestations of MRH, it is important to screen patients for underlying malignancies and other autoimmune conditions.

The Diagnosis: Multicentric Reticulohistiocytosis

Te patient presented with pink papules coalescing into plaques on the upper chest and lower back (Figure 1) as well as a characteristic finding of periungual papules with a coral bead appearance. Histopathologic examination revealed a dense infiltrate of epithelioid histiocytes with amphophilic ground-glass cytoplasm in a nodular configuration (Figure 2). This pattern in conjunction with the clinical features seen in our patient was consistent with a diagnosis of multicentric reticulohistiocytosis (MRH).^1-3 The cutaneous symptoms were managed with triamcinolone ointment 0.1% twice daily and oral hydroxyzine 10 mg 3 times daily as needed for itching with moderate improvement. She was referred to rheumatology for arthritis management, and the initial cancer screening was negative.

Multicentric reticulohistiocytosis is a rare granulomatous disease characterized by papulonodular cutaneous lesions and severe erosive arthritis. It has an insidious onset and most commonly affects middle-aged women.¹ Multicentric reticulohistiocytosis typically presents as rounded pruritic papules or nodules that may be pink, red, or brown primarily affecting the face and distal upper extremities.^1,3 Mucosal involvement occurs in more than half of patients and is characterized by multiple erythematous papules and nodules on the oral and nasopharyngeal mucosae that rarely can produce leonine facies.² A hallmark feature of MRH is the presence of multiple shiny erythematous papules along the proximal and lateral nail folds that take on a coral bead appearance.^1,3,4 Furthermore, nail changes such as atrophy, longitudinal ridging, brittleness, and hyperpigmentation can occur secondary to a synovial reaction that disturbs the nail matrix.^4,5

Joint involvement precedes cutaneous involvement in most cases of MRH.^1,5 Multicentric reticulohistiocytosis is associated with a symmetric destructive arthritis affecting the hands, knees, shoulders, and hips that often is associated with pain, stiffness, and swelling.^1,3 The arthritis rapidly progresses in the early stages of the disease but then becomes less active over the subsequent 8 to 10 years.¹ It has the potential to develop into arthritis mutilans, an end-stage form of arthritis also seen in psoriatic and rheumatoid arthritis that leads to severe joint deformity and debilitation.^1,2

The etiology of MRH still is unknown, but it has an association with underlying malignancy in up to 25% of patients.⁶ Multicentric reticulohistiocytosis has been reported in the context of a wide variety of malignancies including melanoma; sarcoma; lymphoma; leukemia; and carcinomas of the breast, colon, and lung. In some cases, the diagnosis of MRH may even precede the diagnosis of cancer.³ Multicentric reticulohistiocytosis also may be associated with autoimmune conditions,³ as seen in our patient who had a history of both hypothyroidism and vitiligo.

Histopathologic examination is essential in distinguishing MRH from other autoimmune disorders associated with hand lesions, rash, and arthralgia. Erythema elevatum diutinum is associated with symmetric, violaceous, red or brown papules and plaques located on the extensor surfaces of the extremities and hands; however, histology reveals a leukocytoclastic vasculitis with a mixture of polymorphonuclear leukocytes and lymphocytes.⁷ Dermatomyositis may present with arthralgia, flattopped, erythematous (Gottron) papules localized over the proximal interphalangeal and distal interphalangeal joints, as well as proximal nail findings. The latter generally presents with periungual erythema associated with dilated capillary loops rather than the discrete orderly papules seen in MRH. Histologic examination of dermatomyositis shows mild epidermal atrophy, vacuolar changes in the basal keratinocyte layer, and a dermal perivascular lymphocytic infiltrate.⁸ Because MRH initially can present with joint symptoms and hand nodules, it may be confused with rheumatoid arthritis. However, rheumatoid arthritis typically is associated with severe osteopenia and tends to affect the metacarpophalangeal and proximal interphalangeal joints rather than the distal interphalangeal joints that most often are affected in MRH.¹ Histologic examination of rheumatoid nodules reveals palisading granulomas surrounding a central area of fibrinoid necrosis.⁹ Sarcoidosis is a multisystem disease that can present with cutaneous involvement including erythema nodosum, skin plaques, subcutaneous nodules, and papular eruptions in addition to joint lesions.¹⁰ Sarcoidosis most frequently involves the lungs, manifesting as diffuse interstitial lung disease with bilateral hilar lymphadenopathy. Furthermore, histologic examination of lesions demonstrates classic noncaseating granulomas containing epithelioid cells, multinucleated giant cells with inclusion bodies, and lymphocytes.¹¹

A skin biopsy is required to establish the diagnosis of MRH. In general, patients with MRH and no underlying malignancy have a good prognosis and respond to anti-inflammatory therapies such as nonsteroidal antiinflammatory drugs and corticosteroids. Other agents including methotrexate, cyclophosphamide, and tumor necrosis factor α inhibitors also have been effective in more severe cases.^1,3,12 Finally, in addition to treating the cutaneous manifestations of MRH, it is important to screen patients for underlying malignancies and other autoimmune conditions.

The Diagnosis: Multicentric Reticulohistiocytosis

Te patient presented with pink papules coalescing into plaques on the upper chest and lower back (Figure 1) as well as a characteristic finding of periungual papules with a coral bead appearance. Histopathologic examination revealed a dense infiltrate of epithelioid histiocytes with amphophilic ground-glass cytoplasm in a nodular configuration (Figure 2). This pattern in conjunction with the clinical features seen in our patient was consistent with a diagnosis of multicentric reticulohistiocytosis (MRH).^1-3 The cutaneous symptoms were managed with triamcinolone ointment 0.1% twice daily and oral hydroxyzine 10 mg 3 times daily as needed for itching with moderate improvement. She was referred to rheumatology for arthritis management, and the initial cancer screening was negative.

Multicentric reticulohistiocytosis is a rare granulomatous disease characterized by papulonodular cutaneous lesions and severe erosive arthritis. It has an insidious onset and most commonly affects middle-aged women.¹ Multicentric reticulohistiocytosis typically presents as rounded pruritic papules or nodules that may be pink, red, or brown primarily affecting the face and distal upper extremities.^1,3 Mucosal involvement occurs in more than half of patients and is characterized by multiple erythematous papules and nodules on the oral and nasopharyngeal mucosae that rarely can produce leonine facies.² A hallmark feature of MRH is the presence of multiple shiny erythematous papules along the proximal and lateral nail folds that take on a coral bead appearance.^1,3,4 Furthermore, nail changes such as atrophy, longitudinal ridging, brittleness, and hyperpigmentation can occur secondary to a synovial reaction that disturbs the nail matrix.^4,5

Joint involvement precedes cutaneous involvement in most cases of MRH.^1,5 Multicentric reticulohistiocytosis is associated with a symmetric destructive arthritis affecting the hands, knees, shoulders, and hips that often is associated with pain, stiffness, and swelling.^1,3 The arthritis rapidly progresses in the early stages of the disease but then becomes less active over the subsequent 8 to 10 years.¹ It has the potential to develop into arthritis mutilans, an end-stage form of arthritis also seen in psoriatic and rheumatoid arthritis that leads to severe joint deformity and debilitation.^1,2

The etiology of MRH still is unknown, but it has an association with underlying malignancy in up to 25% of patients.⁶ Multicentric reticulohistiocytosis has been reported in the context of a wide variety of malignancies including melanoma; sarcoma; lymphoma; leukemia; and carcinomas of the breast, colon, and lung. In some cases, the diagnosis of MRH may even precede the diagnosis of cancer.³ Multicentric reticulohistiocytosis also may be associated with autoimmune conditions,³ as seen in our patient who had a history of both hypothyroidism and vitiligo.

Histopathologic examination is essential in distinguishing MRH from other autoimmune disorders associated with hand lesions, rash, and arthralgia. Erythema elevatum diutinum is associated with symmetric, violaceous, red or brown papules and plaques located on the extensor surfaces of the extremities and hands; however, histology reveals a leukocytoclastic vasculitis with a mixture of polymorphonuclear leukocytes and lymphocytes.⁷ Dermatomyositis may present with arthralgia, flattopped, erythematous (Gottron) papules localized over the proximal interphalangeal and distal interphalangeal joints, as well as proximal nail findings. The latter generally presents with periungual erythema associated with dilated capillary loops rather than the discrete orderly papules seen in MRH. Histologic examination of dermatomyositis shows mild epidermal atrophy, vacuolar changes in the basal keratinocyte layer, and a dermal perivascular lymphocytic infiltrate.⁸ Because MRH initially can present with joint symptoms and hand nodules, it may be confused with rheumatoid arthritis. However, rheumatoid arthritis typically is associated with severe osteopenia and tends to affect the metacarpophalangeal and proximal interphalangeal joints rather than the distal interphalangeal joints that most often are affected in MRH.¹ Histologic examination of rheumatoid nodules reveals palisading granulomas surrounding a central area of fibrinoid necrosis.⁹ Sarcoidosis is a multisystem disease that can present with cutaneous involvement including erythema nodosum, skin plaques, subcutaneous nodules, and papular eruptions in addition to joint lesions.¹⁰ Sarcoidosis most frequently involves the lungs, manifesting as diffuse interstitial lung disease with bilateral hilar lymphadenopathy. Furthermore, histologic examination of lesions demonstrates classic noncaseating granulomas containing epithelioid cells, multinucleated giant cells with inclusion bodies, and lymphocytes.¹¹

A skin biopsy is required to establish the diagnosis of MRH. In general, patients with MRH and no underlying malignancy have a good prognosis and respond to anti-inflammatory therapies such as nonsteroidal antiinflammatory drugs and corticosteroids. Other agents including methotrexate, cyclophosphamide, and tumor necrosis factor α inhibitors also have been effective in more severe cases.^1,3,12 Finally, in addition to treating the cutaneous manifestations of MRH, it is important to screen patients for underlying malignancies and other autoimmune conditions.

Direct immunofluorescence (DIF) is the go-to diagnostic test when evaluating vesiculobullous eruptions, connective tissue disease, and vasculitis. This specialized test allows visualization of autoantibodies and their reaction products in the epidermis and dermis (skin) and epithelium and subepithelium (mucosa). Indirect immunofluorescence (IIF) and enzyme-linked immunosorbent assay (ELISA) are additional tests that can help in the diagnosis of autoimmune blistering disease. In the blistering autoimmune diseases, the autoantibodies target components in skin and mucous membranes that are essential for cell-cell and cell-matrix adhesion causing separation within or beneath the epidermis, depending on where the target components are located. This article is intended to serve as a helpful primer for immunofluorescence testing in dermatology, with an overview of the tests available as well as pragmatic tips for optimal biopsy sites and specimen transport.

Direct Immunofluorescence

Immunofluorescence techniques date back to 1941 when Albert Coons, an American physician, pathologist, and immunologist, fluorescently labelled antibodies to visualize pneumococcal antigens in infected tissues.^1-3 In dermatology, similar methodology was used to visualize the deposition of immunoglobulins and complement in the skin of patients with systemic lupus erythematosus in 1963.⁴ Basement membrane zone antibodies were first visualized via DIF in bullous pemphigoid in 1967.⁵ This elegant test utilizes specific antibodies labeled with fluorophores that are then incubated with the patient’s tissue, ultimately forming antibody-antigen conjugates that can be visualized with a fluorescent microscope. Antibodies usually include IgG, IgM, IgA, fibrinogen, and C3. Some institutions also evaluate for IgG4.

Transport medium is critical for proper evaluation of tissues using DIF. Inappropriate storage of tissue can degrade the antigen and confuse the interpretation of specimens. An acceptable medium for DIF includes Michel transport medium, which allows tissue to be stored for days while being transported at ambient temperature without loss of signal.^6,7 Zeus medium also can be used and is more readily available. Alternatively, biopsy tissue can be snap frozen using liquid nitrogen. Specimens also may be stored on saline gauze but should be analyzed within 24 to 48 hours.⁸ Most importantly, do not place the specimen in formalin; even a brief soak in formalin can greatly alter results, especially when trying to diagnose pemphigus.⁹ Proper transport conditions are critical to prevent autolysis, mitigate putrefaction, and preserve morphology while maintaining antigenicity.¹⁰

Indirect Immunofluorescence

Indirect immunofluorescence can be helpful for detecting antibodies circulating in patient serum. Indirect immunofluorescence can be used to help diagnose pemphigoid, pemphigus, epidermolysis bullosa acquisita, bullous lupus erythematosus, and dermatitis herpetiformis. Serum testing also can be a helpful alternative when obtaining tissue is difficult, such as in children.

Indirect immunofluorescence is a 2-part technique that takes a bit longer to assay than DIF.¹¹ The first step involves incubating prepared tissue substrates with patient serum. Unlabeled antibodies in the patient serum are allowed to bind to antigens in the substrate tissue for about 30 minutes. Doubling dilutions of patient serum can be performed to titer antibody levels. The second step uses fluorescein-labeled antihuman antibodies to recognize the antigen-antibody conjugates. Normal whole tissues (eg, monkey esophagus for pemphigus vulgaris, rat bladder for paraneoplastic pemphigus, salt-split normal human skin substrate for pemphigoid and epidermolysis bullosa) are the usual substrates for testing.^11,12 Again, this test requires serum and should be collected in a red-top tube or serum-separator tube. Usually, a minimum of 0.5 mL is required for testing, but check with your preferred immunodermatology send-out laboratory before collecting.¹³

Indirect immunofluorescence usually involves an initial screening panel using 1 or 2 tissue substrates followed by individual antigen-specific assays that correspond to the clinical suspicion and IIF screening results.¹¹ Salt-split skin is used to localize basement membrane zone autoantibodies to either the epidermal (roof) or dermal (floor) side. Although many dermatopathology laboratories offer DIF testing, IIF is more specialized and may be a send-out test at your institution.

Enzyme-linked Immunosorbent Assays

Another tool in the immunodermatology armamentarium is ELISA. Commercial ELISA systems are available for the detection of autoantibodies against bullous pemphigoid (BP) antigen 180, BP230, type VII collagen, desmoglein (Dsg) 1, Dsg3, and envoplakin.¹¹ This test allows semiquantitative measurement of antibody levels and thus can be used to monitor response to treatment or identify relapse and treatment failure.¹¹ For example, in BP, significantly increased baseline anti-BP180 IgG levels correlate with 1-year mortality rates (P=.001) and relapse rates (P=.041).^14,15 Numerous additional studies support the observation that monitoring anti-BP180 as a potential marker of disease relapse can be helpful.^16,17 In pemphigus, the presence or increase of autoantibodies at remission, either anti-Dsg3 or anti-Dsg1, may be a useful tool in predicting disease relapse.¹⁸ It is important for physicians to be aware of this to be able to offer guidance on prognosis.

 

 

Where Should I Biopsy?

Knowing where to biopsy can be confusing when beginning residency. But the short answer is, it depends. Let your clinical suspicion guide your specimen site. The Figure provides a quick reference for which location will give you the highest yield for a specific diagnosis.

A few cardinal rules should guide which site is biopsied. Avoid obtaining specimens from the lower extremities as much as possible, as this site has been linked with false-negative results, especially in bullous pemphigoid.^19,20 As a dependent area prone to stasis, this site gets a lot of abuse and inflammatory changes secondary to everyday insults that can theoretically alter DIF findings, especially fibrinogen deposition.

Although tissue sent for hematoxylin and eosin staining should be lesional, biopsy for DIF ideally should not contain a new or active blister, ulcer, erosion, or bulla. Immunoreactants are more likely to be degraded in these areas, and DIF may be falsely negative.²¹

It is worthwhile to briefly discuss the definitions of the terms perilesional and nonlesional. Perilesional skin most frequently refers to skin adjacent to a bulla or vesicle. This skin can be erythematous/inflamed or appear normal. When obtaining tissue for a diagnosis of blistering disease, the general recommendation is to obtain the biopsy from lesional nonbullous skin or perilesional uninvolved skin within 1 cm of the bulla.^22-24 The only exception to this is dermatitis herpetiformis, which is best diagnosed on tissue obtained from normal-appearing perilesional skin within 1 cm of an active lesion.²⁵ Additionally, if your patient has oral disease, the recommendation is to obtain the biopsy from nonlesional buccal mucosa, especially if there is desquamative gingivitis.^26,27

The ideal biopsy size is 4 or 5 mm. If considering both DIF and histopathology, it is best to procure 2 separate specimens. One larger biopsy can be carefully bisected in 2 but often is subject to more handling artifacts, which can affect findings. In the case of 1 biopsy bisected into 2 specimens, the punch should be at least 6 mm. Shave biopsies also can be performed as long as they extend into the reticular dermis.²³

For vasculitis, biopsies for DIF should be taken from lesions that are less than 24 hours old for highest yield, as the level of tissue immunoreactants tends to decline over time.²⁸ This guideline does differ from hematoxylin and eosin specimens sent for evaluation of vasculitis, which ideally should be lesional tissue over 72 hours old. When evaluating for lupus (including subacute cutaneous lupus, discoid lupus, and systemic lupus), DIF is more likely to be positive in well-established, active lesions.

Which Test Should I Order?

The answer to this question depends, but the use of all 3 tests has a specificity close to 100% when evaluating for autoantibody-associated diseases.²³ For autoimmune blistering disease, DIF is considered the diagnostic standard. The sensitivity of DIF for diagnosing BP is in the range of 82% to 90.5%, while specificity is 98%.^29-31 Other autoimmune blistering diseases, such as pemphigus or dermatitis herpetiformis, have even higher sensitivities and specificities. Direct immunofluorescence often is used as a screening test, but false negatives do occur.^32,33 Although rare, false positives also can occur, especially in cases of infection, and should be suspected when there is a lack of clinicopathologic correlation.³⁴ If DIF is negative but clinical suspicion remains high, IIF should be ordered to directly evaluate a patient’s serum for autoantibodies.

In acute cutaneous lupus, subacute cutaneous lupus, and discoid lupus, DIF of active lesions may be helpful if histopathologic examination of a cutaneous lupus erythematosus lesion is nondiagnostic. However, histopathologic examination of formalin-fixed tissue remains the standard for these diagnoses. In vasculitis, while DIF is not used for diagnosis, it is useful to evaluate for IgA deposition. This is important in adults, as IgA deposition has been associated with a greater risk for developing end-stage renal disease.³⁵

Final Thoughts

This is an overview of the tests available for diagnosing autoimmune blistering diseases. Residents should keep in mind that these tests are just one part of the puzzle when it comes to diagnosing these diseases. Results of DIF, IIF, and ELISA testing should be considered in conjunction with patient history and physical examination as well as histopathologic examination of lesional tissue when evaluating for dermatologic diseases with autoantibodies.

Direct immunofluorescence (DIF) is the go-to diagnostic test when evaluating vesiculobullous eruptions, connective tissue disease, and vasculitis. This specialized test allows visualization of autoantibodies and their reaction products in the epidermis and dermis (skin) and epithelium and subepithelium (mucosa). Indirect immunofluorescence (IIF) and enzyme-linked immunosorbent assay (ELISA) are additional tests that can help in the diagnosis of autoimmune blistering disease. In the blistering autoimmune diseases, the autoantibodies target components in skin and mucous membranes that are essential for cell-cell and cell-matrix adhesion causing separation within or beneath the epidermis, depending on where the target components are located. This article is intended to serve as a helpful primer for immunofluorescence testing in dermatology, with an overview of the tests available as well as pragmatic tips for optimal biopsy sites and specimen transport.

Direct Immunofluorescence

Immunofluorescence techniques date back to 1941 when Albert Coons, an American physician, pathologist, and immunologist, fluorescently labelled antibodies to visualize pneumococcal antigens in infected tissues.^1-3 In dermatology, similar methodology was used to visualize the deposition of immunoglobulins and complement in the skin of patients with systemic lupus erythematosus in 1963.⁴ Basement membrane zone antibodies were first visualized via DIF in bullous pemphigoid in 1967.⁵ This elegant test utilizes specific antibodies labeled with fluorophores that are then incubated with the patient’s tissue, ultimately forming antibody-antigen conjugates that can be visualized with a fluorescent microscope. Antibodies usually include IgG, IgM, IgA, fibrinogen, and C3. Some institutions also evaluate for IgG4.

Transport medium is critical for proper evaluation of tissues using DIF. Inappropriate storage of tissue can degrade the antigen and confuse the interpretation of specimens. An acceptable medium for DIF includes Michel transport medium, which allows tissue to be stored for days while being transported at ambient temperature without loss of signal.^6,7 Zeus medium also can be used and is more readily available. Alternatively, biopsy tissue can be snap frozen using liquid nitrogen. Specimens also may be stored on saline gauze but should be analyzed within 24 to 48 hours.⁸ Most importantly, do not place the specimen in formalin; even a brief soak in formalin can greatly alter results, especially when trying to diagnose pemphigus.⁹ Proper transport conditions are critical to prevent autolysis, mitigate putrefaction, and preserve morphology while maintaining antigenicity.¹⁰

Indirect Immunofluorescence

Indirect immunofluorescence can be helpful for detecting antibodies circulating in patient serum. Indirect immunofluorescence can be used to help diagnose pemphigoid, pemphigus, epidermolysis bullosa acquisita, bullous lupus erythematosus, and dermatitis herpetiformis. Serum testing also can be a helpful alternative when obtaining tissue is difficult, such as in children.

Indirect immunofluorescence is a 2-part technique that takes a bit longer to assay than DIF.¹¹ The first step involves incubating prepared tissue substrates with patient serum. Unlabeled antibodies in the patient serum are allowed to bind to antigens in the substrate tissue for about 30 minutes. Doubling dilutions of patient serum can be performed to titer antibody levels. The second step uses fluorescein-labeled antihuman antibodies to recognize the antigen-antibody conjugates. Normal whole tissues (eg, monkey esophagus for pemphigus vulgaris, rat bladder for paraneoplastic pemphigus, salt-split normal human skin substrate for pemphigoid and epidermolysis bullosa) are the usual substrates for testing.^11,12 Again, this test requires serum and should be collected in a red-top tube or serum-separator tube. Usually, a minimum of 0.5 mL is required for testing, but check with your preferred immunodermatology send-out laboratory before collecting.¹³

Indirect immunofluorescence usually involves an initial screening panel using 1 or 2 tissue substrates followed by individual antigen-specific assays that correspond to the clinical suspicion and IIF screening results.¹¹ Salt-split skin is used to localize basement membrane zone autoantibodies to either the epidermal (roof) or dermal (floor) side. Although many dermatopathology laboratories offer DIF testing, IIF is more specialized and may be a send-out test at your institution.

Enzyme-linked Immunosorbent Assays

Another tool in the immunodermatology armamentarium is ELISA. Commercial ELISA systems are available for the detection of autoantibodies against bullous pemphigoid (BP) antigen 180, BP230, type VII collagen, desmoglein (Dsg) 1, Dsg3, and envoplakin.¹¹ This test allows semiquantitative measurement of antibody levels and thus can be used to monitor response to treatment or identify relapse and treatment failure.¹¹ For example, in BP, significantly increased baseline anti-BP180 IgG levels correlate with 1-year mortality rates (P=.001) and relapse rates (P=.041).^14,15 Numerous additional studies support the observation that monitoring anti-BP180 as a potential marker of disease relapse can be helpful.^16,17 In pemphigus, the presence or increase of autoantibodies at remission, either anti-Dsg3 or anti-Dsg1, may be a useful tool in predicting disease relapse.¹⁸ It is important for physicians to be aware of this to be able to offer guidance on prognosis.

 

 

Where Should I Biopsy?

Knowing where to biopsy can be confusing when beginning residency. But the short answer is, it depends. Let your clinical suspicion guide your specimen site. The Figure provides a quick reference for which location will give you the highest yield for a specific diagnosis.

A few cardinal rules should guide which site is biopsied. Avoid obtaining specimens from the lower extremities as much as possible, as this site has been linked with false-negative results, especially in bullous pemphigoid.^19,20 As a dependent area prone to stasis, this site gets a lot of abuse and inflammatory changes secondary to everyday insults that can theoretically alter DIF findings, especially fibrinogen deposition.

Although tissue sent for hematoxylin and eosin staining should be lesional, biopsy for DIF ideally should not contain a new or active blister, ulcer, erosion, or bulla. Immunoreactants are more likely to be degraded in these areas, and DIF may be falsely negative.²¹

It is worthwhile to briefly discuss the definitions of the terms perilesional and nonlesional. Perilesional skin most frequently refers to skin adjacent to a bulla or vesicle. This skin can be erythematous/inflamed or appear normal. When obtaining tissue for a diagnosis of blistering disease, the general recommendation is to obtain the biopsy from lesional nonbullous skin or perilesional uninvolved skin within 1 cm of the bulla.^22-24 The only exception to this is dermatitis herpetiformis, which is best diagnosed on tissue obtained from normal-appearing perilesional skin within 1 cm of an active lesion.²⁵ Additionally, if your patient has oral disease, the recommendation is to obtain the biopsy from nonlesional buccal mucosa, especially if there is desquamative gingivitis.^26,27

The ideal biopsy size is 4 or 5 mm. If considering both DIF and histopathology, it is best to procure 2 separate specimens. One larger biopsy can be carefully bisected in 2 but often is subject to more handling artifacts, which can affect findings. In the case of 1 biopsy bisected into 2 specimens, the punch should be at least 6 mm. Shave biopsies also can be performed as long as they extend into the reticular dermis.²³

For vasculitis, biopsies for DIF should be taken from lesions that are less than 24 hours old for highest yield, as the level of tissue immunoreactants tends to decline over time.²⁸ This guideline does differ from hematoxylin and eosin specimens sent for evaluation of vasculitis, which ideally should be lesional tissue over 72 hours old. When evaluating for lupus (including subacute cutaneous lupus, discoid lupus, and systemic lupus), DIF is more likely to be positive in well-established, active lesions.

Which Test Should I Order?

The answer to this question depends, but the use of all 3 tests has a specificity close to 100% when evaluating for autoantibody-associated diseases.²³ For autoimmune blistering disease, DIF is considered the diagnostic standard. The sensitivity of DIF for diagnosing BP is in the range of 82% to 90.5%, while specificity is 98%.^29-31 Other autoimmune blistering diseases, such as pemphigus or dermatitis herpetiformis, have even higher sensitivities and specificities. Direct immunofluorescence often is used as a screening test, but false negatives do occur.^32,33 Although rare, false positives also can occur, especially in cases of infection, and should be suspected when there is a lack of clinicopathologic correlation.³⁴ If DIF is negative but clinical suspicion remains high, IIF should be ordered to directly evaluate a patient’s serum for autoantibodies.

In acute cutaneous lupus, subacute cutaneous lupus, and discoid lupus, DIF of active lesions may be helpful if histopathologic examination of a cutaneous lupus erythematosus lesion is nondiagnostic. However, histopathologic examination of formalin-fixed tissue remains the standard for these diagnoses. In vasculitis, while DIF is not used for diagnosis, it is useful to evaluate for IgA deposition. This is important in adults, as IgA deposition has been associated with a greater risk for developing end-stage renal disease.³⁵

Final Thoughts

This is an overview of the tests available for diagnosing autoimmune blistering diseases. Residents should keep in mind that these tests are just one part of the puzzle when it comes to diagnosing these diseases. Results of DIF, IIF, and ELISA testing should be considered in conjunction with patient history and physical examination as well as histopathologic examination of lesional tissue when evaluating for dermatologic diseases with autoantibodies.

Direct immunofluorescence (DIF) is the go-to diagnostic test when evaluating vesiculobullous eruptions, connective tissue disease, and vasculitis. This specialized test allows visualization of autoantibodies and their reaction products in the epidermis and dermis (skin) and epithelium and subepithelium (mucosa). Indirect immunofluorescence (IIF) and enzyme-linked immunosorbent assay (ELISA) are additional tests that can help in the diagnosis of autoimmune blistering disease. In the blistering autoimmune diseases, the autoantibodies target components in skin and mucous membranes that are essential for cell-cell and cell-matrix adhesion causing separation within or beneath the epidermis, depending on where the target components are located. This article is intended to serve as a helpful primer for immunofluorescence testing in dermatology, with an overview of the tests available as well as pragmatic tips for optimal biopsy sites and specimen transport.

Direct Immunofluorescence

Immunofluorescence techniques date back to 1941 when Albert Coons, an American physician, pathologist, and immunologist, fluorescently labelled antibodies to visualize pneumococcal antigens in infected tissues.^1-3 In dermatology, similar methodology was used to visualize the deposition of immunoglobulins and complement in the skin of patients with systemic lupus erythematosus in 1963.⁴ Basement membrane zone antibodies were first visualized via DIF in bullous pemphigoid in 1967.⁵ This elegant test utilizes specific antibodies labeled with fluorophores that are then incubated with the patient’s tissue, ultimately forming antibody-antigen conjugates that can be visualized with a fluorescent microscope. Antibodies usually include IgG, IgM, IgA, fibrinogen, and C3. Some institutions also evaluate for IgG4.

Transport medium is critical for proper evaluation of tissues using DIF. Inappropriate storage of tissue can degrade the antigen and confuse the interpretation of specimens. An acceptable medium for DIF includes Michel transport medium, which allows tissue to be stored for days while being transported at ambient temperature without loss of signal.^6,7 Zeus medium also can be used and is more readily available. Alternatively, biopsy tissue can be snap frozen using liquid nitrogen. Specimens also may be stored on saline gauze but should be analyzed within 24 to 48 hours.⁸ Most importantly, do not place the specimen in formalin; even a brief soak in formalin can greatly alter results, especially when trying to diagnose pemphigus.⁹ Proper transport conditions are critical to prevent autolysis, mitigate putrefaction, and preserve morphology while maintaining antigenicity.¹⁰

Indirect Immunofluorescence

Indirect immunofluorescence can be helpful for detecting antibodies circulating in patient serum. Indirect immunofluorescence can be used to help diagnose pemphigoid, pemphigus, epidermolysis bullosa acquisita, bullous lupus erythematosus, and dermatitis herpetiformis. Serum testing also can be a helpful alternative when obtaining tissue is difficult, such as in children.

Indirect immunofluorescence is a 2-part technique that takes a bit longer to assay than DIF.¹¹ The first step involves incubating prepared tissue substrates with patient serum. Unlabeled antibodies in the patient serum are allowed to bind to antigens in the substrate tissue for about 30 minutes. Doubling dilutions of patient serum can be performed to titer antibody levels. The second step uses fluorescein-labeled antihuman antibodies to recognize the antigen-antibody conjugates. Normal whole tissues (eg, monkey esophagus for pemphigus vulgaris, rat bladder for paraneoplastic pemphigus, salt-split normal human skin substrate for pemphigoid and epidermolysis bullosa) are the usual substrates for testing.^11,12 Again, this test requires serum and should be collected in a red-top tube or serum-separator tube. Usually, a minimum of 0.5 mL is required for testing, but check with your preferred immunodermatology send-out laboratory before collecting.¹³

Indirect immunofluorescence usually involves an initial screening panel using 1 or 2 tissue substrates followed by individual antigen-specific assays that correspond to the clinical suspicion and IIF screening results.¹¹ Salt-split skin is used to localize basement membrane zone autoantibodies to either the epidermal (roof) or dermal (floor) side. Although many dermatopathology laboratories offer DIF testing, IIF is more specialized and may be a send-out test at your institution.

Enzyme-linked Immunosorbent Assays

Another tool in the immunodermatology armamentarium is ELISA. Commercial ELISA systems are available for the detection of autoantibodies against bullous pemphigoid (BP) antigen 180, BP230, type VII collagen, desmoglein (Dsg) 1, Dsg3, and envoplakin.¹¹ This test allows semiquantitative measurement of antibody levels and thus can be used to monitor response to treatment or identify relapse and treatment failure.¹¹ For example, in BP, significantly increased baseline anti-BP180 IgG levels correlate with 1-year mortality rates (P=.001) and relapse rates (P=.041).^14,15 Numerous additional studies support the observation that monitoring anti-BP180 as a potential marker of disease relapse can be helpful.^16,17 In pemphigus, the presence or increase of autoantibodies at remission, either anti-Dsg3 or anti-Dsg1, may be a useful tool in predicting disease relapse.¹⁸ It is important for physicians to be aware of this to be able to offer guidance on prognosis.

 

 

Where Should I Biopsy?

Knowing where to biopsy can be confusing when beginning residency. But the short answer is, it depends. Let your clinical suspicion guide your specimen site. The Figure provides a quick reference for which location will give you the highest yield for a specific diagnosis.

A few cardinal rules should guide which site is biopsied. Avoid obtaining specimens from the lower extremities as much as possible, as this site has been linked with false-negative results, especially in bullous pemphigoid.^19,20 As a dependent area prone to stasis, this site gets a lot of abuse and inflammatory changes secondary to everyday insults that can theoretically alter DIF findings, especially fibrinogen deposition.

Although tissue sent for hematoxylin and eosin staining should be lesional, biopsy for DIF ideally should not contain a new or active blister, ulcer, erosion, or bulla. Immunoreactants are more likely to be degraded in these areas, and DIF may be falsely negative.²¹

It is worthwhile to briefly discuss the definitions of the terms perilesional and nonlesional. Perilesional skin most frequently refers to skin adjacent to a bulla or vesicle. This skin can be erythematous/inflamed or appear normal. When obtaining tissue for a diagnosis of blistering disease, the general recommendation is to obtain the biopsy from lesional nonbullous skin or perilesional uninvolved skin within 1 cm of the bulla.^22-24 The only exception to this is dermatitis herpetiformis, which is best diagnosed on tissue obtained from normal-appearing perilesional skin within 1 cm of an active lesion.²⁵ Additionally, if your patient has oral disease, the recommendation is to obtain the biopsy from nonlesional buccal mucosa, especially if there is desquamative gingivitis.^26,27

The ideal biopsy size is 4 or 5 mm. If considering both DIF and histopathology, it is best to procure 2 separate specimens. One larger biopsy can be carefully bisected in 2 but often is subject to more handling artifacts, which can affect findings. In the case of 1 biopsy bisected into 2 specimens, the punch should be at least 6 mm. Shave biopsies also can be performed as long as they extend into the reticular dermis.²³

For vasculitis, biopsies for DIF should be taken from lesions that are less than 24 hours old for highest yield, as the level of tissue immunoreactants tends to decline over time.²⁸ This guideline does differ from hematoxylin and eosin specimens sent for evaluation of vasculitis, which ideally should be lesional tissue over 72 hours old. When evaluating for lupus (including subacute cutaneous lupus, discoid lupus, and systemic lupus), DIF is more likely to be positive in well-established, active lesions.

Which Test Should I Order?

The answer to this question depends, but the use of all 3 tests has a specificity close to 100% when evaluating for autoantibody-associated diseases.²³ For autoimmune blistering disease, DIF is considered the diagnostic standard. The sensitivity of DIF for diagnosing BP is in the range of 82% to 90.5%, while specificity is 98%.^29-31 Other autoimmune blistering diseases, such as pemphigus or dermatitis herpetiformis, have even higher sensitivities and specificities. Direct immunofluorescence often is used as a screening test, but false negatives do occur.^32,33 Although rare, false positives also can occur, especially in cases of infection, and should be suspected when there is a lack of clinicopathologic correlation.³⁴ If DIF is negative but clinical suspicion remains high, IIF should be ordered to directly evaluate a patient’s serum for autoantibodies.

In acute cutaneous lupus, subacute cutaneous lupus, and discoid lupus, DIF of active lesions may be helpful if histopathologic examination of a cutaneous lupus erythematosus lesion is nondiagnostic. However, histopathologic examination of formalin-fixed tissue remains the standard for these diagnoses. In vasculitis, while DIF is not used for diagnosis, it is useful to evaluate for IgA deposition. This is important in adults, as IgA deposition has been associated with a greater risk for developing end-stage renal disease.³⁵

Final Thoughts

This is an overview of the tests available for diagnosing autoimmune blistering diseases. Residents should keep in mind that these tests are just one part of the puzzle when it comes to diagnosing these diseases. Results of DIF, IIF, and ELISA testing should be considered in conjunction with patient history and physical examination as well as histopathologic examination of lesional tissue when evaluating for dermatologic diseases with autoantibodies.

The Diagnosis: Osteoma Cutis

Osteoma cutis is the heterotopic development of cutaneous ossifications in the dermis or subcutaneous fat and presents as plaquelike, stony, hard nodules. It can manifest as either a primary or secondary condition based on the presence or absence of a prior skin insult at the lesion site. Primary osteoma cutis occurs in 15% of patients and arises either de novo or in association with any of several inflammatory, neoplastic, and metabolic diseases that provide a favorable environment for abnormal mesenchymal stem cell commitment to osteoid,¹ including Albright hereditary osteodystrophy, myositis ossificans progressiva, and progressive osseous heteroplasia, which are all associated with mutations in the heterotrimeric G-protein alpha subunit encoding gene, GNAS. ^1,2 It is suggested that an insufficiency of Gsα leads to uncontrolled negative regulation of nonosseous connective tissue differentiation, forming osteoid.³ Additionally, diseases involving gain-of-function mutations in the activin A receptor type 1 encoding gene, ACVR1, such as fibrodysplasia ossificans progressiva, have been associated with osteoma cutis.⁴ These mutations lead to decreased receptor affinity to molecular safeguards of bone morphogenetic protein signaling, ultimately contributing to progressive ectopic bone formation.⁵ Secondary osteoma cutis occurs in 85% of patients and develops at the site of prior skin damage due to inflammation, neoplasm, or trauma.⁶ It is believed that tissue damage and degeneration lead to mesenchymal stem cell proliferation and skeletogenicinducing factor recruitment forming cartilaginous tissue, later replaced by bone through endochondral ossification.⁷

Although osteoma cutis previously was believed to be rare, more recent radiologic studies suggest otherwise, detecting cutaneous osteomas in up to 42.1% of patients.⁸ Consequently, it is likely that osteoma cutis is underdiagnosed due to its subclinical nature. Our patient, however, presented with a solitary osteoma cutis with perforation of the epidermis, a rare phenomenon.^9-12

A shave biopsy in our patient revealed moderate to focally marked, irregular epidermal hyperplasia with a large focus of moderate, compact, parakeratotic crust overlying the epidermis in the center of the specimen. The papillary dermis in the center of the specimen revealed large foci of dark pink to purple bone fragments surrounded by moderate lymphocytic infiltrate with few foci perforating through the overlying epidermis (Figure, A). These findings were characteristic of osteoma cutis with perforation through the overlying epidermis.

The diagnosis of osteoma cutis at the age of 62 years suggested that the lesion was not primary in association with previously described diseases. Furthermore, the lack of phenotypic features of these diseases including obesity, developmental disability, and high parathyroid hormone levels essentially excluded this possibility. The presence of the lesion on the lower extremities initially may have suggested osteoma cutis secondary to chronic venous insufficiency¹³; however, the absence of visible varicose veins or obvious signs of stasis disease made this unlikely. No further cutaneous disorders at or around the lesion site clinically and histologically suggested that our patient’s lesion was primary and of idiopathic nature. Dermatofibroma can present similarly in appearance but would characteristically dimple centrally when pinched. Keratoacanthoma presents with central ulceration and keratin plugging. Pilomatricoma more commonly presents on the head and neck and less frequently as a firm nodule. Lastly, prurigo nodularis more commonly presents as a symmetrically diffuse rash compared to an isolated nodule.

Osteoma cutis is a cutaneous ossification that may be primary or secondary in nature and less rare than originally thought. Workup for potentially associated inflammatory, neoplastic, and metabolic diseases should be considered in patients with this condition. Perforating osteoma cutis is a rare variant that presents as solitary or multiple nodules with central erosion and crust. The mechanism of transepidermal elimination leading to skin perforation is hypothesized to involve epidermal hyperproliferation leading to upward movement.¹⁴ Shave biopsy establishes a definitive histopathologic diagnosis and often is curative. Given that lesions of osteoma cutis themselves are benign, removal may not be necessary.

The Diagnosis: Osteoma Cutis

Osteoma cutis is the heterotopic development of cutaneous ossifications in the dermis or subcutaneous fat and presents as plaquelike, stony, hard nodules. It can manifest as either a primary or secondary condition based on the presence or absence of a prior skin insult at the lesion site. Primary osteoma cutis occurs in 15% of patients and arises either de novo or in association with any of several inflammatory, neoplastic, and metabolic diseases that provide a favorable environment for abnormal mesenchymal stem cell commitment to osteoid,¹ including Albright hereditary osteodystrophy, myositis ossificans progressiva, and progressive osseous heteroplasia, which are all associated with mutations in the heterotrimeric G-protein alpha subunit encoding gene, GNAS. ^1,2 It is suggested that an insufficiency of Gsα leads to uncontrolled negative regulation of nonosseous connective tissue differentiation, forming osteoid.³ Additionally, diseases involving gain-of-function mutations in the activin A receptor type 1 encoding gene, ACVR1, such as fibrodysplasia ossificans progressiva, have been associated with osteoma cutis.⁴ These mutations lead to decreased receptor affinity to molecular safeguards of bone morphogenetic protein signaling, ultimately contributing to progressive ectopic bone formation.⁵ Secondary osteoma cutis occurs in 85% of patients and develops at the site of prior skin damage due to inflammation, neoplasm, or trauma.⁶ It is believed that tissue damage and degeneration lead to mesenchymal stem cell proliferation and skeletogenicinducing factor recruitment forming cartilaginous tissue, later replaced by bone through endochondral ossification.⁷

Although osteoma cutis previously was believed to be rare, more recent radiologic studies suggest otherwise, detecting cutaneous osteomas in up to 42.1% of patients.⁸ Consequently, it is likely that osteoma cutis is underdiagnosed due to its subclinical nature. Our patient, however, presented with a solitary osteoma cutis with perforation of the epidermis, a rare phenomenon.^9-12

A shave biopsy in our patient revealed moderate to focally marked, irregular epidermal hyperplasia with a large focus of moderate, compact, parakeratotic crust overlying the epidermis in the center of the specimen. The papillary dermis in the center of the specimen revealed large foci of dark pink to purple bone fragments surrounded by moderate lymphocytic infiltrate with few foci perforating through the overlying epidermis (Figure, A). These findings were characteristic of osteoma cutis with perforation through the overlying epidermis.

The diagnosis of osteoma cutis at the age of 62 years suggested that the lesion was not primary in association with previously described diseases. Furthermore, the lack of phenotypic features of these diseases including obesity, developmental disability, and high parathyroid hormone levels essentially excluded this possibility. The presence of the lesion on the lower extremities initially may have suggested osteoma cutis secondary to chronic venous insufficiency¹³; however, the absence of visible varicose veins or obvious signs of stasis disease made this unlikely. No further cutaneous disorders at or around the lesion site clinically and histologically suggested that our patient’s lesion was primary and of idiopathic nature. Dermatofibroma can present similarly in appearance but would characteristically dimple centrally when pinched. Keratoacanthoma presents with central ulceration and keratin plugging. Pilomatricoma more commonly presents on the head and neck and less frequently as a firm nodule. Lastly, prurigo nodularis more commonly presents as a symmetrically diffuse rash compared to an isolated nodule.

Osteoma cutis is a cutaneous ossification that may be primary or secondary in nature and less rare than originally thought. Workup for potentially associated inflammatory, neoplastic, and metabolic diseases should be considered in patients with this condition. Perforating osteoma cutis is a rare variant that presents as solitary or multiple nodules with central erosion and crust. The mechanism of transepidermal elimination leading to skin perforation is hypothesized to involve epidermal hyperproliferation leading to upward movement.¹⁴ Shave biopsy establishes a definitive histopathologic diagnosis and often is curative. Given that lesions of osteoma cutis themselves are benign, removal may not be necessary.

The Diagnosis: Osteoma Cutis

Osteoma cutis is the heterotopic development of cutaneous ossifications in the dermis or subcutaneous fat and presents as plaquelike, stony, hard nodules. It can manifest as either a primary or secondary condition based on the presence or absence of a prior skin insult at the lesion site. Primary osteoma cutis occurs in 15% of patients and arises either de novo or in association with any of several inflammatory, neoplastic, and metabolic diseases that provide a favorable environment for abnormal mesenchymal stem cell commitment to osteoid,¹ including Albright hereditary osteodystrophy, myositis ossificans progressiva, and progressive osseous heteroplasia, which are all associated with mutations in the heterotrimeric G-protein alpha subunit encoding gene, GNAS. ^1,2 It is suggested that an insufficiency of Gsα leads to uncontrolled negative regulation of nonosseous connective tissue differentiation, forming osteoid.³ Additionally, diseases involving gain-of-function mutations in the activin A receptor type 1 encoding gene, ACVR1, such as fibrodysplasia ossificans progressiva, have been associated with osteoma cutis.⁴ These mutations lead to decreased receptor affinity to molecular safeguards of bone morphogenetic protein signaling, ultimately contributing to progressive ectopic bone formation.⁵ Secondary osteoma cutis occurs in 85% of patients and develops at the site of prior skin damage due to inflammation, neoplasm, or trauma.⁶ It is believed that tissue damage and degeneration lead to mesenchymal stem cell proliferation and skeletogenicinducing factor recruitment forming cartilaginous tissue, later replaced by bone through endochondral ossification.⁷

Although osteoma cutis previously was believed to be rare, more recent radiologic studies suggest otherwise, detecting cutaneous osteomas in up to 42.1% of patients.⁸ Consequently, it is likely that osteoma cutis is underdiagnosed due to its subclinical nature. Our patient, however, presented with a solitary osteoma cutis with perforation of the epidermis, a rare phenomenon.^9-12

A shave biopsy in our patient revealed moderate to focally marked, irregular epidermal hyperplasia with a large focus of moderate, compact, parakeratotic crust overlying the epidermis in the center of the specimen. The papillary dermis in the center of the specimen revealed large foci of dark pink to purple bone fragments surrounded by moderate lymphocytic infiltrate with few foci perforating through the overlying epidermis (Figure, A). These findings were characteristic of osteoma cutis with perforation through the overlying epidermis.

The diagnosis of osteoma cutis at the age of 62 years suggested that the lesion was not primary in association with previously described diseases. Furthermore, the lack of phenotypic features of these diseases including obesity, developmental disability, and high parathyroid hormone levels essentially excluded this possibility. The presence of the lesion on the lower extremities initially may have suggested osteoma cutis secondary to chronic venous insufficiency¹³; however, the absence of visible varicose veins or obvious signs of stasis disease made this unlikely. No further cutaneous disorders at or around the lesion site clinically and histologically suggested that our patient’s lesion was primary and of idiopathic nature. Dermatofibroma can present similarly in appearance but would characteristically dimple centrally when pinched. Keratoacanthoma presents with central ulceration and keratin plugging. Pilomatricoma more commonly presents on the head and neck and less frequently as a firm nodule. Lastly, prurigo nodularis more commonly presents as a symmetrically diffuse rash compared to an isolated nodule.

Osteoma cutis is a cutaneous ossification that may be primary or secondary in nature and less rare than originally thought. Workup for potentially associated inflammatory, neoplastic, and metabolic diseases should be considered in patients with this condition. Perforating osteoma cutis is a rare variant that presents as solitary or multiple nodules with central erosion and crust. The mechanism of transepidermal elimination leading to skin perforation is hypothesized to involve epidermal hyperproliferation leading to upward movement.¹⁴ Shave biopsy establishes a definitive histopathologic diagnosis and often is curative. Given that lesions of osteoma cutis themselves are benign, removal may not be necessary.

The Diagnosis: Infantile Digital Fibromatosis

Infantile digital fibromatosis (IDF) is a rare benign neoplasm of infancy prone to recurrence after resection but not to metastasis. It usually is limited to the fingers and toes.¹ One-third of cases occur at birth. Most patients develop clinical symptoms within the first year of life, but presentation can occur in adolescents and adults. The exact etiology and pathogenesis of IDF remain unclear, but trauma is thought to be a trigger.

Physical examination reveals single or multiple smooth, round, pink papules or nodules confined to the sides and backs of the fingers, sparing the thumb and first toe.^2,3 The nodules typically are firm, less than 2 cm in diameter, and often painless. Infantile digital fibromatosis exhibits an indolent progression followed by a rapid growth phase during several months, which may lead to functional impairment and joint deformities.^4,5 Histopathology displays spindle cells with eosinophilic cytoplasmic inclusions that range from round to oval with uneven distribution, lack of refraction, and a large size difference (3–15 μm).6 The inclusions are deep red with Masson trichrome staining and can express smooth muscle actin and calponin. Tumor cells usually express vimentin, smooth muscle actin, calponin, and desmin but fail to express S-100 protein. The Ki67 proliferation index is 2% to 15%.^6,7

Nonsurgical treatments for IDF include topical imiquimod, topical or intradermal injection of glucocorticoids, and intradermal injection of 5-fluorouracil. Complete resection should be reserved for cases with invasive growth that may lead to joint deformities, tendon or ligament involvement, digit or contracture deformity, and complications such as decreased joint mobility. Although there is a recurrence rate of up to 50% after excision, most lesions eventually will spontaneously regress and will leave no scar.^8-10

The clinical and histopathologic differential diagnoses of IDF include other cutaneous diseases that occur in the digits. A dermatofibroma is a round, firm, fibrohistiocytic nodule that mainly occurs on the extensor limbs. Histopathology includes both fibrous and cellular types.¹¹ Histologic analysis shows an ill-defined dermal proliferation of spindled fibroblasts with pale eosinophilic cytoplasm and bland fusiform nuclei growing in bands or fascicles that trap collagen fibers at the periphery (Figure 1). Generally, dermatofibromas have marked epidermal hyperplasia, which differs from IDF.

A digital myxoid cyst is characterized by a fleshcolored, hemispherical, and translucent cystic nodule that arises from the dorsum of the distal interphalangeal joint.¹² It commonly is associated with injury and chronic pressure. Translucent viscous liquid may flow out when the cyst is punctured, a hallmark feature of this entity. Clinical variants of myxoid cyst include myxomatous and ganglion types. Histopathology reveals excessive mucin deposited in the dermis, and the surrounding collagen is compressed to form the pseudocyst (Figure 2).

A giant cell tumor of the tendon sheath presents with asymptomatic nodules or lumps. Lesions frequently are localized to the tendon sheath, especially on the fingers and wrists, with no malignant tendency or propensity for spontaneous regression.¹³ The local recurrence rate is as high as 45%, which is related to surgical resection insufficiency.¹⁴ Histopathologic examination shows lobulated tumor tissue surrounded by dense fibrosis. The tumor cells are histiocytic with scattered giant cells (Figure 3). The characteristic osteoclastlike giant cells have eosinophilic cytoplasm and irregularly arranged nuclei in varying numbers.

Keloids are connective tissue hyperplasias caused by skin injury. Histopathologically, keloids are characterized by nodules of thick hyalinized collagen bundles and whorled fibroblasts (Figure 4). No inclusions in the fibroblasts and a history of trauma can differentiate keloids from IDF.

The Diagnosis: Infantile Digital Fibromatosis

Infantile digital fibromatosis (IDF) is a rare benign neoplasm of infancy prone to recurrence after resection but not to metastasis. It usually is limited to the fingers and toes.¹ One-third of cases occur at birth. Most patients develop clinical symptoms within the first year of life, but presentation can occur in adolescents and adults. The exact etiology and pathogenesis of IDF remain unclear, but trauma is thought to be a trigger.

Physical examination reveals single or multiple smooth, round, pink papules or nodules confined to the sides and backs of the fingers, sparing the thumb and first toe.^2,3 The nodules typically are firm, less than 2 cm in diameter, and often painless. Infantile digital fibromatosis exhibits an indolent progression followed by a rapid growth phase during several months, which may lead to functional impairment and joint deformities.^4,5 Histopathology displays spindle cells with eosinophilic cytoplasmic inclusions that range from round to oval with uneven distribution, lack of refraction, and a large size difference (3–15 μm).6 The inclusions are deep red with Masson trichrome staining and can express smooth muscle actin and calponin. Tumor cells usually express vimentin, smooth muscle actin, calponin, and desmin but fail to express S-100 protein. The Ki67 proliferation index is 2% to 15%.^6,7

Nonsurgical treatments for IDF include topical imiquimod, topical or intradermal injection of glucocorticoids, and intradermal injection of 5-fluorouracil. Complete resection should be reserved for cases with invasive growth that may lead to joint deformities, tendon or ligament involvement, digit or contracture deformity, and complications such as decreased joint mobility. Although there is a recurrence rate of up to 50% after excision, most lesions eventually will spontaneously regress and will leave no scar.^8-10

The clinical and histopathologic differential diagnoses of IDF include other cutaneous diseases that occur in the digits. A dermatofibroma is a round, firm, fibrohistiocytic nodule that mainly occurs on the extensor limbs. Histopathology includes both fibrous and cellular types.¹¹ Histologic analysis shows an ill-defined dermal proliferation of spindled fibroblasts with pale eosinophilic cytoplasm and bland fusiform nuclei growing in bands or fascicles that trap collagen fibers at the periphery (Figure 1). Generally, dermatofibromas have marked epidermal hyperplasia, which differs from IDF.

A digital myxoid cyst is characterized by a fleshcolored, hemispherical, and translucent cystic nodule that arises from the dorsum of the distal interphalangeal joint.¹² It commonly is associated with injury and chronic pressure. Translucent viscous liquid may flow out when the cyst is punctured, a hallmark feature of this entity. Clinical variants of myxoid cyst include myxomatous and ganglion types. Histopathology reveals excessive mucin deposited in the dermis, and the surrounding collagen is compressed to form the pseudocyst (Figure 2).

A giant cell tumor of the tendon sheath presents with asymptomatic nodules or lumps. Lesions frequently are localized to the tendon sheath, especially on the fingers and wrists, with no malignant tendency or propensity for spontaneous regression.¹³ The local recurrence rate is as high as 45%, which is related to surgical resection insufficiency.¹⁴ Histopathologic examination shows lobulated tumor tissue surrounded by dense fibrosis. The tumor cells are histiocytic with scattered giant cells (Figure 3). The characteristic osteoclastlike giant cells have eosinophilic cytoplasm and irregularly arranged nuclei in varying numbers.

Keloids are connective tissue hyperplasias caused by skin injury. Histopathologically, keloids are characterized by nodules of thick hyalinized collagen bundles and whorled fibroblasts (Figure 4). No inclusions in the fibroblasts and a history of trauma can differentiate keloids from IDF.

The Diagnosis: Infantile Digital Fibromatosis

Infantile digital fibromatosis (IDF) is a rare benign neoplasm of infancy prone to recurrence after resection but not to metastasis. It usually is limited to the fingers and toes.¹ One-third of cases occur at birth. Most patients develop clinical symptoms within the first year of life, but presentation can occur in adolescents and adults. The exact etiology and pathogenesis of IDF remain unclear, but trauma is thought to be a trigger.

Physical examination reveals single or multiple smooth, round, pink papules or nodules confined to the sides and backs of the fingers, sparing the thumb and first toe.^2,3 The nodules typically are firm, less than 2 cm in diameter, and often painless. Infantile digital fibromatosis exhibits an indolent progression followed by a rapid growth phase during several months, which may lead to functional impairment and joint deformities.^4,5 Histopathology displays spindle cells with eosinophilic cytoplasmic inclusions that range from round to oval with uneven distribution, lack of refraction, and a large size difference (3–15 μm).6 The inclusions are deep red with Masson trichrome staining and can express smooth muscle actin and calponin. Tumor cells usually express vimentin, smooth muscle actin, calponin, and desmin but fail to express S-100 protein. The Ki67 proliferation index is 2% to 15%.^6,7

Nonsurgical treatments for IDF include topical imiquimod, topical or intradermal injection of glucocorticoids, and intradermal injection of 5-fluorouracil. Complete resection should be reserved for cases with invasive growth that may lead to joint deformities, tendon or ligament involvement, digit or contracture deformity, and complications such as decreased joint mobility. Although there is a recurrence rate of up to 50% after excision, most lesions eventually will spontaneously regress and will leave no scar.^8-10

The clinical and histopathologic differential diagnoses of IDF include other cutaneous diseases that occur in the digits. A dermatofibroma is a round, firm, fibrohistiocytic nodule that mainly occurs on the extensor limbs. Histopathology includes both fibrous and cellular types.¹¹ Histologic analysis shows an ill-defined dermal proliferation of spindled fibroblasts with pale eosinophilic cytoplasm and bland fusiform nuclei growing in bands or fascicles that trap collagen fibers at the periphery (Figure 1). Generally, dermatofibromas have marked epidermal hyperplasia, which differs from IDF.

A digital myxoid cyst is characterized by a fleshcolored, hemispherical, and translucent cystic nodule that arises from the dorsum of the distal interphalangeal joint.¹² It commonly is associated with injury and chronic pressure. Translucent viscous liquid may flow out when the cyst is punctured, a hallmark feature of this entity. Clinical variants of myxoid cyst include myxomatous and ganglion types. Histopathology reveals excessive mucin deposited in the dermis, and the surrounding collagen is compressed to form the pseudocyst (Figure 2).

A giant cell tumor of the tendon sheath presents with asymptomatic nodules or lumps. Lesions frequently are localized to the tendon sheath, especially on the fingers and wrists, with no malignant tendency or propensity for spontaneous regression.¹³ The local recurrence rate is as high as 45%, which is related to surgical resection insufficiency.¹⁴ Histopathologic examination shows lobulated tumor tissue surrounded by dense fibrosis. The tumor cells are histiocytic with scattered giant cells (Figure 3). The characteristic osteoclastlike giant cells have eosinophilic cytoplasm and irregularly arranged nuclei in varying numbers.

Keloids are connective tissue hyperplasias caused by skin injury. Histopathologically, keloids are characterized by nodules of thick hyalinized collagen bundles and whorled fibroblasts (Figure 4). No inclusions in the fibroblasts and a history of trauma can differentiate keloids from IDF.

The proposed 2022 Medicare physician fee schedule and quality payment program (QPP) regulations were released on July 13, 2021.¹ Final regulations are expected to be released on or around November 1, 2021, but they may be delayed. Multiple national medical organizations, including the College of American Pathologists (CAP), the American Society of Dermatopathology, the American Academy of Dermatology Association (AADA), and the American Medical Association (AMA) Physicians’ Grassroots Network all work together to engage with the Centers for Medicare & Medicaid Services (CMS) to influence these regulations. Stated advocacy priorities include protecting the value of dermatopathology services, mobilizing dermatopathologists for political action, ensuring dermatopathologists can participate in new payment models, strengthening the profession with advocacy on a state level, and conducting socioeconomic research. Is your practice aware and prepared to handle the changes coming in 2022?

2021 Medicare Cuts

The recent revisions and revaluations of the outpatient evaluation and management (E/M) codes² resulted in a considerable redistribution of Medicare dollars in 2021, negatively impacting dermatopathologists and other specialties and services due to budget neutrality required by law (Figure). Important steps were taken to mitigate the 2021 Medicare cuts for all non–office-based dermatopathology services (eg, pathology, surgical services, emergency department).^1,3 Direct engagement by the CAP, American Society of Dermatopathology, and AADA, along with the AMA Physicians’ Grassroots Network resulted in legislative action on December 27, 2020, which directed Medicare to make a 3.75% positive adjustment to the 2021 physician payments. Additionally, the CMS updated the 2021 physician conversion factor to $34.8931, a 3.3% reduction from the 2020 conversion factor rather than $32.41, or a 10.20% decrease. The 2% payment adjustment (sequestration) through December 21, 2021, also was suspended, and Congress and the Biden administration mandated delayed implementation of the inherent complexity add-on code for E/M services (G2211) until 2024.^1,3

Threat of Medicare Cuts in 2022

Based on dermatopathology utilization data, the overall impact on reimbursement for 2022 represents an approximately 5% decrease from 2021 dermatopathology payments (Table 1).^1,4 This represents a 3.75% cut from revaluation of E/M services, and a 1% cut due to changes in practice expense pricing. The estimated change in reimbursement for independent laboratories is a 6% decrease. Advocacy groups have been working to mitigate the 2022 cuts by engaging with Congress and urging them to act before these changes go into effect next year. Keep in mind that approximately half of all pathology Current Procedural Terminology (CPT) codes have been targeted for evaluation by the CMS since 2006.^1,4

Coding for Clinical Pathology Consultation Services

The current clinical pathology consultation services (CPT codes 80500 and 80502) previously were identified as potentially misvalued for review by the AMA Relative Value Scale Update Committee’s (RUC’s) relativity assessment workgroup.⁴ Consequently, the CAP worked with the AMA’s CPT Editorial Panel to delete codes 80500 and 80502, as well as to modernize and create the 4 new clinical pathology consultation codes: 80XX0, 80XX1, 80XX2, and 80XX3. Then the CAP worked with the RUC to develop physician work and practice expense values for the new clinical pathology consultation codes. Once the fee schedule is finalized, pathologists can begin using the new codes to bill these services in 2022 (Table 2).⁴

According to CPT, clinical pathology consultation services may be reported when the following criteria have been met: (1) the pathologist renders a clinical pathology consultation at the request of a physician or qualified health care professional at the same or another institution; (2) the pathology clinical consultation request relating to pathology and laboratory findings or other relevant clinical or diagnostic information requiring additional medical interpretative judgment is made; and (3) these codes are not reported in conjunction with codes 88321, 88323, and 88325.⁴

Proposed 2022 Medicare QPP Requirements

On July 13, 2021, the CMS also published its proposed 2022 QPP proposals that will take effect next year.⁴ According to the proposed regulation, nearly all dermatopathologists will be required to participate in Medicare’s QPP, either through advanced alternative payment models (APMs) or the Merit-based Incentive Payment System (MIPS). The CAP has long advocated for reducing MIPS reporting burdens for dermatopathologists. In this regulation, the CMS is proposing key program changes that move the program forward but also introduce additional complexities; for example, the CMS will move forward with a new participation pathway called MIPS Value Pathways (MVPs). The CMS proposed 7 specific MVPs that align with certain clinical topics; however, it will not implement these MVPs until the 2023 MIPS performance period.

In 2022, dermatopathologists who are eligible for MIPS will have to take action to avoid penalties that reduce future Medicare Part B payments for their services. Performance in MIPS in 2022 affects Medicare Part B payments in 2024 by an increase of 9% to a decrease of 9%.

In its proposed 2022 QPP regulations, the CMS proposed an increase of the performance threshold from 60 MIPS points to 75 MIPS points. It also proposed an increase of the exceptional Performance Threshold from 85 MIPS points to 89 MIPS points.

The CMS also proposed notable scoring changes for quality measures, including removing the 3-point floor for measures that can be scored against a benchmark. These measures would receive 1 to 10 points. Measures without a benchmark or that do not meet case requirements would earn 0 points, with an exception for small practices. The CMS also proposed removing bonus points for reporting additional outcomes and high-priority measures beyond the 1 that is required, as well as establishing a 5-point floor for the first 2 performance periods for new measures, which is in line with the CAP’s advocacy.

The Pathology Specialty Measure Set will remain the same as the 2021 set containing 6 quality measures, including the AADA-stewarded quality measure #440 (skin cancer: biopsy reporting time—pathologist to clinician). Although the CAP recognizes the importance of prompt turnaround of biopsy reports, it also is working with the CMS and the AADA to mitigate the operational challenges dermatopathologists encounter when using this measure. 

Due to advocacy from the CAP, the CMS included a CAP-proposed improvement activity on implementation of a laboratory preparedness plan to support continued or expanded patient care during the COVID-19 pandemic or another public health emergency. This plan should address how the laboratory would maintain or expand access to improve beneficiary health outcomes and reduce health care disparities.

The CAP has actively worked with the CMS to demonstrate the need for more appropriate and alternative measures and improvement activities so that pathologists can more fully participate in MIPS. 

Alternative Payment Models—For those dermatopathologists who practice in an APM, the proposed 2022 QPP makes minimal changes to the advanced APM track while adding transition time for accountable care organizations in the Medicare Shared Savings Program to report on certain quality measures and increasing flexibility related to the program’s quality performance standard.

Cures Act 2021: To Do No Harm

The 21st Century Cures Act (Cures Act) was signed into federal law in 2016. The Office of the National Coordinator for Health Information Technology (ONC) laid the groundwork for patients to have easier access to and control of their health information.⁵ The ONC’s final rule, which went into effect on April 5, 2021, requires that all providers make their office notes, laboratory results, and other diagnostic reports (including dermatopathology reports) available to patients as soon as the physician’s office receives an electronic copy. Penalty for noncompliance has not been determined.

There are information-blocking exceptions, but delaying access to a patient’s report so that a provider can review the result before the patient receives it is not considered an exception.⁶ The exceptions are situational and must be evaluated by the referring clinician or their employer. Documentation of the exception is critical. The specific facts and circumstances associated with your decision to use an exception will be important to include in your documentation. Information blocking necessary to prevent “harm” to a patient or another person requires a reasonable belief that the practice will substantially reduce the risk of harm.⁶

The AMA passed a resolution in June 2021 calling for changes to this rule to allow for a delay of pathology results, advocating to the Office for Civil Rights to revise the harm exception to include psychological distress.⁶ In August 2021, the AADA met with senior officials at the ONC also asking to revise its definition of harm, sharing examples of emotional strain that resulted from receiving results without clinical context.⁷ California enacted a law requiring a delay before a patient receives the result of a malignant diagnosis, giving the clinician time to contact the patient before they see their report.⁸

The Cures Act requirements are about patients accessing their health care information. Always consider what is best for the patient and ensure that your policies and procedures reflect this.⁵

Final Thoughts

It is important to learn and support advocacy priorities and efforts and to join forces to protect your practice. Physician advocacy is no longer an elective pursuit. We need to be involved and engaged through our medical societies to help patients, communities, and ourselves.

The proposed 2022 Medicare physician fee schedule and quality payment program (QPP) regulations were released on July 13, 2021.¹ Final regulations are expected to be released on or around November 1, 2021, but they may be delayed. Multiple national medical organizations, including the College of American Pathologists (CAP), the American Society of Dermatopathology, the American Academy of Dermatology Association (AADA), and the American Medical Association (AMA) Physicians’ Grassroots Network all work together to engage with the Centers for Medicare & Medicaid Services (CMS) to influence these regulations. Stated advocacy priorities include protecting the value of dermatopathology services, mobilizing dermatopathologists for political action, ensuring dermatopathologists can participate in new payment models, strengthening the profession with advocacy on a state level, and conducting socioeconomic research. Is your practice aware and prepared to handle the changes coming in 2022?

2021 Medicare Cuts

The recent revisions and revaluations of the outpatient evaluation and management (E/M) codes² resulted in a considerable redistribution of Medicare dollars in 2021, negatively impacting dermatopathologists and other specialties and services due to budget neutrality required by law (Figure). Important steps were taken to mitigate the 2021 Medicare cuts for all non–office-based dermatopathology services (eg, pathology, surgical services, emergency department).^1,3 Direct engagement by the CAP, American Society of Dermatopathology, and AADA, along with the AMA Physicians’ Grassroots Network resulted in legislative action on December 27, 2020, which directed Medicare to make a 3.75% positive adjustment to the 2021 physician payments. Additionally, the CMS updated the 2021 physician conversion factor to $34.8931, a 3.3% reduction from the 2020 conversion factor rather than $32.41, or a 10.20% decrease. The 2% payment adjustment (sequestration) through December 21, 2021, also was suspended, and Congress and the Biden administration mandated delayed implementation of the inherent complexity add-on code for E/M services (G2211) until 2024.^1,3

Threat of Medicare Cuts in 2022

Based on dermatopathology utilization data, the overall impact on reimbursement for 2022 represents an approximately 5% decrease from 2021 dermatopathology payments (Table 1).^1,4 This represents a 3.75% cut from revaluation of E/M services, and a 1% cut due to changes in practice expense pricing. The estimated change in reimbursement for independent laboratories is a 6% decrease. Advocacy groups have been working to mitigate the 2022 cuts by engaging with Congress and urging them to act before these changes go into effect next year. Keep in mind that approximately half of all pathology Current Procedural Terminology (CPT) codes have been targeted for evaluation by the CMS since 2006.^1,4

Coding for Clinical Pathology Consultation Services

The current clinical pathology consultation services (CPT codes 80500 and 80502) previously were identified as potentially misvalued for review by the AMA Relative Value Scale Update Committee’s (RUC’s) relativity assessment workgroup.⁴ Consequently, the CAP worked with the AMA’s CPT Editorial Panel to delete codes 80500 and 80502, as well as to modernize and create the 4 new clinical pathology consultation codes: 80XX0, 80XX1, 80XX2, and 80XX3. Then the CAP worked with the RUC to develop physician work and practice expense values for the new clinical pathology consultation codes. Once the fee schedule is finalized, pathologists can begin using the new codes to bill these services in 2022 (Table 2).⁴

According to CPT, clinical pathology consultation services may be reported when the following criteria have been met: (1) the pathologist renders a clinical pathology consultation at the request of a physician or qualified health care professional at the same or another institution; (2) the pathology clinical consultation request relating to pathology and laboratory findings or other relevant clinical or diagnostic information requiring additional medical interpretative judgment is made; and (3) these codes are not reported in conjunction with codes 88321, 88323, and 88325.⁴

Proposed 2022 Medicare QPP Requirements

On July 13, 2021, the CMS also published its proposed 2022 QPP proposals that will take effect next year.⁴ According to the proposed regulation, nearly all dermatopathologists will be required to participate in Medicare’s QPP, either through advanced alternative payment models (APMs) or the Merit-based Incentive Payment System (MIPS). The CAP has long advocated for reducing MIPS reporting burdens for dermatopathologists. In this regulation, the CMS is proposing key program changes that move the program forward but also introduce additional complexities; for example, the CMS will move forward with a new participation pathway called MIPS Value Pathways (MVPs). The CMS proposed 7 specific MVPs that align with certain clinical topics; however, it will not implement these MVPs until the 2023 MIPS performance period.

In 2022, dermatopathologists who are eligible for MIPS will have to take action to avoid penalties that reduce future Medicare Part B payments for their services. Performance in MIPS in 2022 affects Medicare Part B payments in 2024 by an increase of 9% to a decrease of 9%.

In its proposed 2022 QPP regulations, the CMS proposed an increase of the performance threshold from 60 MIPS points to 75 MIPS points. It also proposed an increase of the exceptional Performance Threshold from 85 MIPS points to 89 MIPS points.

The CMS also proposed notable scoring changes for quality measures, including removing the 3-point floor for measures that can be scored against a benchmark. These measures would receive 1 to 10 points. Measures without a benchmark or that do not meet case requirements would earn 0 points, with an exception for small practices. The CMS also proposed removing bonus points for reporting additional outcomes and high-priority measures beyond the 1 that is required, as well as establishing a 5-point floor for the first 2 performance periods for new measures, which is in line with the CAP’s advocacy.

The Pathology Specialty Measure Set will remain the same as the 2021 set containing 6 quality measures, including the AADA-stewarded quality measure #440 (skin cancer: biopsy reporting time—pathologist to clinician). Although the CAP recognizes the importance of prompt turnaround of biopsy reports, it also is working with the CMS and the AADA to mitigate the operational challenges dermatopathologists encounter when using this measure. 

Due to advocacy from the CAP, the CMS included a CAP-proposed improvement activity on implementation of a laboratory preparedness plan to support continued or expanded patient care during the COVID-19 pandemic or another public health emergency. This plan should address how the laboratory would maintain or expand access to improve beneficiary health outcomes and reduce health care disparities.

The CAP has actively worked with the CMS to demonstrate the need for more appropriate and alternative measures and improvement activities so that pathologists can more fully participate in MIPS. 

Alternative Payment Models—For those dermatopathologists who practice in an APM, the proposed 2022 QPP makes minimal changes to the advanced APM track while adding transition time for accountable care organizations in the Medicare Shared Savings Program to report on certain quality measures and increasing flexibility related to the program’s quality performance standard.

Cures Act 2021: To Do No Harm

The 21st Century Cures Act (Cures Act) was signed into federal law in 2016. The Office of the National Coordinator for Health Information Technology (ONC) laid the groundwork for patients to have easier access to and control of their health information.⁵ The ONC’s final rule, which went into effect on April 5, 2021, requires that all providers make their office notes, laboratory results, and other diagnostic reports (including dermatopathology reports) available to patients as soon as the physician’s office receives an electronic copy. Penalty for noncompliance has not been determined.

There are information-blocking exceptions, but delaying access to a patient’s report so that a provider can review the result before the patient receives it is not considered an exception.⁶ The exceptions are situational and must be evaluated by the referring clinician or their employer. Documentation of the exception is critical. The specific facts and circumstances associated with your decision to use an exception will be important to include in your documentation. Information blocking necessary to prevent “harm” to a patient or another person requires a reasonable belief that the practice will substantially reduce the risk of harm.⁶

The AMA passed a resolution in June 2021 calling for changes to this rule to allow for a delay of pathology results, advocating to the Office for Civil Rights to revise the harm exception to include psychological distress.⁶ In August 2021, the AADA met with senior officials at the ONC also asking to revise its definition of harm, sharing examples of emotional strain that resulted from receiving results without clinical context.⁷ California enacted a law requiring a delay before a patient receives the result of a malignant diagnosis, giving the clinician time to contact the patient before they see their report.⁸

The Cures Act requirements are about patients accessing their health care information. Always consider what is best for the patient and ensure that your policies and procedures reflect this.⁵

Final Thoughts

It is important to learn and support advocacy priorities and efforts and to join forces to protect your practice. Physician advocacy is no longer an elective pursuit. We need to be involved and engaged through our medical societies to help patients, communities, and ourselves.

The proposed 2022 Medicare physician fee schedule and quality payment program (QPP) regulations were released on July 13, 2021.¹ Final regulations are expected to be released on or around November 1, 2021, but they may be delayed. Multiple national medical organizations, including the College of American Pathologists (CAP), the American Society of Dermatopathology, the American Academy of Dermatology Association (AADA), and the American Medical Association (AMA) Physicians’ Grassroots Network all work together to engage with the Centers for Medicare & Medicaid Services (CMS) to influence these regulations. Stated advocacy priorities include protecting the value of dermatopathology services, mobilizing dermatopathologists for political action, ensuring dermatopathologists can participate in new payment models, strengthening the profession with advocacy on a state level, and conducting socioeconomic research. Is your practice aware and prepared to handle the changes coming in 2022?

2021 Medicare Cuts

The recent revisions and revaluations of the outpatient evaluation and management (E/M) codes² resulted in a considerable redistribution of Medicare dollars in 2021, negatively impacting dermatopathologists and other specialties and services due to budget neutrality required by law (Figure). Important steps were taken to mitigate the 2021 Medicare cuts for all non–office-based dermatopathology services (eg, pathology, surgical services, emergency department).^1,3 Direct engagement by the CAP, American Society of Dermatopathology, and AADA, along with the AMA Physicians’ Grassroots Network resulted in legislative action on December 27, 2020, which directed Medicare to make a 3.75% positive adjustment to the 2021 physician payments. Additionally, the CMS updated the 2021 physician conversion factor to $34.8931, a 3.3% reduction from the 2020 conversion factor rather than $32.41, or a 10.20% decrease. The 2% payment adjustment (sequestration) through December 21, 2021, also was suspended, and Congress and the Biden administration mandated delayed implementation of the inherent complexity add-on code for E/M services (G2211) until 2024.^1,3

Threat of Medicare Cuts in 2022

Based on dermatopathology utilization data, the overall impact on reimbursement for 2022 represents an approximately 5% decrease from 2021 dermatopathology payments (Table 1).^1,4 This represents a 3.75% cut from revaluation of E/M services, and a 1% cut due to changes in practice expense pricing. The estimated change in reimbursement for independent laboratories is a 6% decrease. Advocacy groups have been working to mitigate the 2022 cuts by engaging with Congress and urging them to act before these changes go into effect next year. Keep in mind that approximately half of all pathology Current Procedural Terminology (CPT) codes have been targeted for evaluation by the CMS since 2006.^1,4

Coding for Clinical Pathology Consultation Services

The current clinical pathology consultation services (CPT codes 80500 and 80502) previously were identified as potentially misvalued for review by the AMA Relative Value Scale Update Committee’s (RUC’s) relativity assessment workgroup.⁴ Consequently, the CAP worked with the AMA’s CPT Editorial Panel to delete codes 80500 and 80502, as well as to modernize and create the 4 new clinical pathology consultation codes: 80XX0, 80XX1, 80XX2, and 80XX3. Then the CAP worked with the RUC to develop physician work and practice expense values for the new clinical pathology consultation codes. Once the fee schedule is finalized, pathologists can begin using the new codes to bill these services in 2022 (Table 2).⁴

According to CPT, clinical pathology consultation services may be reported when the following criteria have been met: (1) the pathologist renders a clinical pathology consultation at the request of a physician or qualified health care professional at the same or another institution; (2) the pathology clinical consultation request relating to pathology and laboratory findings or other relevant clinical or diagnostic information requiring additional medical interpretative judgment is made; and (3) these codes are not reported in conjunction with codes 88321, 88323, and 88325.⁴

Proposed 2022 Medicare QPP Requirements

On July 13, 2021, the CMS also published its proposed 2022 QPP proposals that will take effect next year.⁴ According to the proposed regulation, nearly all dermatopathologists will be required to participate in Medicare’s QPP, either through advanced alternative payment models (APMs) or the Merit-based Incentive Payment System (MIPS). The CAP has long advocated for reducing MIPS reporting burdens for dermatopathologists. In this regulation, the CMS is proposing key program changes that move the program forward but also introduce additional complexities; for example, the CMS will move forward with a new participation pathway called MIPS Value Pathways (MVPs). The CMS proposed 7 specific MVPs that align with certain clinical topics; however, it will not implement these MVPs until the 2023 MIPS performance period.

In 2022, dermatopathologists who are eligible for MIPS will have to take action to avoid penalties that reduce future Medicare Part B payments for their services. Performance in MIPS in 2022 affects Medicare Part B payments in 2024 by an increase of 9% to a decrease of 9%.

In its proposed 2022 QPP regulations, the CMS proposed an increase of the performance threshold from 60 MIPS points to 75 MIPS points. It also proposed an increase of the exceptional Performance Threshold from 85 MIPS points to 89 MIPS points.

The CMS also proposed notable scoring changes for quality measures, including removing the 3-point floor for measures that can be scored against a benchmark. These measures would receive 1 to 10 points. Measures without a benchmark or that do not meet case requirements would earn 0 points, with an exception for small practices. The CMS also proposed removing bonus points for reporting additional outcomes and high-priority measures beyond the 1 that is required, as well as establishing a 5-point floor for the first 2 performance periods for new measures, which is in line with the CAP’s advocacy.

The Pathology Specialty Measure Set will remain the same as the 2021 set containing 6 quality measures, including the AADA-stewarded quality measure #440 (skin cancer: biopsy reporting time—pathologist to clinician). Although the CAP recognizes the importance of prompt turnaround of biopsy reports, it also is working with the CMS and the AADA to mitigate the operational challenges dermatopathologists encounter when using this measure. 

Due to advocacy from the CAP, the CMS included a CAP-proposed improvement activity on implementation of a laboratory preparedness plan to support continued or expanded patient care during the COVID-19 pandemic or another public health emergency. This plan should address how the laboratory would maintain or expand access to improve beneficiary health outcomes and reduce health care disparities.

The CAP has actively worked with the CMS to demonstrate the need for more appropriate and alternative measures and improvement activities so that pathologists can more fully participate in MIPS. 

Alternative Payment Models—For those dermatopathologists who practice in an APM, the proposed 2022 QPP makes minimal changes to the advanced APM track while adding transition time for accountable care organizations in the Medicare Shared Savings Program to report on certain quality measures and increasing flexibility related to the program’s quality performance standard.

Cures Act 2021: To Do No Harm

The 21st Century Cures Act (Cures Act) was signed into federal law in 2016. The Office of the National Coordinator for Health Information Technology (ONC) laid the groundwork for patients to have easier access to and control of their health information.⁵ The ONC’s final rule, which went into effect on April 5, 2021, requires that all providers make their office notes, laboratory results, and other diagnostic reports (including dermatopathology reports) available to patients as soon as the physician’s office receives an electronic copy. Penalty for noncompliance has not been determined.

There are information-blocking exceptions, but delaying access to a patient’s report so that a provider can review the result before the patient receives it is not considered an exception.⁶ The exceptions are situational and must be evaluated by the referring clinician or their employer. Documentation of the exception is critical. The specific facts and circumstances associated with your decision to use an exception will be important to include in your documentation. Information blocking necessary to prevent “harm” to a patient or another person requires a reasonable belief that the practice will substantially reduce the risk of harm.⁶

The AMA passed a resolution in June 2021 calling for changes to this rule to allow for a delay of pathology results, advocating to the Office for Civil Rights to revise the harm exception to include psychological distress.⁶ In August 2021, the AADA met with senior officials at the ONC also asking to revise its definition of harm, sharing examples of emotional strain that resulted from receiving results without clinical context.⁷ California enacted a law requiring a delay before a patient receives the result of a malignant diagnosis, giving the clinician time to contact the patient before they see their report.⁸

The Cures Act requirements are about patients accessing their health care information. Always consider what is best for the patient and ensure that your policies and procedures reflect this.⁵

Final Thoughts

It is important to learn and support advocacy priorities and efforts and to join forces to protect your practice. Physician advocacy is no longer an elective pursuit. We need to be involved and engaged through our medical societies to help patients, communities, and ourselves.

Pilomatrix carcinoma is a rare adnexal tumor with origin from the germinative matrical cells of the hair follicle. Clinically, it presents as a solitary lesion commonly found in the head and neck region as well as the upper back. The tumors cannot be distinguished by their clinical appearance only and frequently are mistaken for cysts. Histopathologic examination provides the definitive diagnosis in most cases. These carcinomas are aggressive neoplasms with a high probability of local recurrence and distant metastasis. Assessment of the Wnt signaling pathway components such as β-catenin, lymphoid enhancer-binding factor 1 (LEF-1), and caudal-related homeobox transcription factor 2 (CDX-2) potentially can be used for diagnostic purposes and targeted therapy.

We report a rare and unique case of early pilomatrix carcinoma with intralesional melanocytes. We review the molecular pathology and pathogenesis of these carcinomas as well as the significance of early diagnosis.

Case Report

A 73-year-old man with a history of extensive sun exposure presented with a 1-cm, raised, rapidly growing, slightly irregular, purple lesion on the right forearm of 3 months’ duration with tendency to bleed. He did not have a history of skin cancers and was otherwise healthy. Excision was recommended due to the progressive and rapid growth of the lesion.

Histopathologic Findings—Gross examination revealed a 0.9×0.7-cm, raised, slightly irregular lesion located 1 mm away from the closest peripheral margin. Histologically, the lesion was a relatively circumscribed, dermal-based basaloid neoplasm with slightly ill-defined edges involving the superficial and deep dermis (Figure 1A). The neoplasm was formed predominantly of sheets of basaloid cells and small nests of ghost cells, in addition to some squamoid and transitional cells (Figure 1B). The basaloid cells exhibited severe nuclear atypia, pleomorphism, increased nuclear to cytoplasmic ratio (Figure 1C), minimal to moderate amounts of eosinophilic cytoplasm, enlarged nuclei, prominent nucleoli, and coarse chromatin pattern. Abundant mitotic activity and apoptotic bodies were present as well as focal area of central necrosis (Figure 1C). Also, melanophages and a multinucleated giant cell reaction was noted. Elastic trichrome special stain highlighted focal infiltration of the neoplastic cells into the adjacent desmoplastic stroma. Melanin stain was negative for melanin pigment within the neoplasm. Given the presence of severely atypical basaloid cells along with ghost cells indicating matrical differentiation, a diagnosis of pilomatrix carcinoma was rendered.

Immunohistochemistry—The neoplastic cells were diffusely positive for p63, CDX-2 (Figure 2A), β-catenin (Figure 2B), and CD10 (Figure 2C), and focally and weakly positive for cytokeratin (CK) 5, BerEP4 (staining the tumor periphery), androgen receptor, and CK18 (a low-molecular-weight keratin). They were negative for monoclonal carcinoembryonic antigen, epithelial membrane antigen, CK7, CK20, CD34, SOX-10, CD56, synaptophysin, and chromogranin. Cytokeratin 14 was positive in the squamoid cells but negative in the basaloid cells. SOX-10 and melanoma cocktail immunostains demonstrated few intralesional dendritic melanocytes.

Comment

Pilomatrix carcinoma is a rare malignant cutaneous adnexal neoplasm with origin from the germinative matrix of the hair bulb region of hair follicles. Pilomatrix carcinoma was first reported in 1980.^1,2 These tumors are characterized by rapid growth and aggressive behavior. Their benign counterpart, pilomatrixoma, is a slow-growing, dermal or subcutaneous tumor that rarely recurs after complete excision.

As with pilomatrixoma, pilomatrix carcinomas are asymptomatic and present as solitary dermal or subcutaneous masses^3,4 that most commonly are found in the posterior neck, upper back, and preauricular regions of middle-aged or elderly adults with male predominance.⁵ They range in size from 0.5 to 20 cm with a mean of 4 cm that is slightly larger than pilomatrixoma. Pilomatrix carcinomas predominantly are firm tumors with or without cystic components, and they exhibit a high probability of recurrence and have risk for distant metastasis.^6-15

The differential diagnosis includes epidermal cysts, pilomatrixoma, basal cell carcinoma with matrical differentiation, trichoblastoma/trichoblastic carcinoma, and trichilemmal carcinoma. Pilomatrix carcinomas frequently are mistaken for epidermal cysts on clinical examination. Such a distinction can be easily resolved by histopathologic evaluation. The more challenging differential diagnosis is with pilomatrixoma. Histologically, pilomatrixomas consist of a distinct population of cells including basaloid, squamoid, transitional, and shadow cells in variable proportions. The basaloid cells transition to shadow cells in an organized zonal fashion.¹⁶ Compared to pilomatrixomas, pilomatrix carcinomas often show predominance of the basaloid cells; marked cytologic atypia and pleomorphism; numerous mitotic figures; deep infiltrative pattern into subcutaneous fat, fascia, and skeletal muscle; stromal desmoplasia; necrosis; and neurovascular invasion (Tables 1 and 2). Furthermore, the shadow cells tend to form a small nested pattern in pilomatrix carcinoma instead of the flat sheetlike pattern usually observed in pilomatrixoma.¹⁶ Basal cell carcinoma with matrical differentiation can pose a diagnostic challenge in the differential diagnosis; basal cell carcinoma usually exhibits a peripheral palisade of the basaloid cells accompanied by retraction spaces separating the tumor from the stroma. Trichoblastoma/trichoblastic carcinoma with matrical differentiation can be distinguished by its exuberant stroma, prominent primitive hair follicles, and papillary mesenchymal bodies. Trichilemmal carcinomas are recognized by their connection to the overlying epidermis, peripheral palisading, and presence of clear cells, while pilomatrix carcinoma lacks connection to the surface epithelium.

Immunohistochemical stains have little to no role in the differential diagnosis, and morphology is the mainstay in making the diagnosis. Rarely, pilomatrix carcinoma can be confused with poorly differentiated sebaceous carcinoma and poorly differentiated squamous cell carcinoma. Although careful scrutiny of the histologic features may help identify mature sebocytes in sebaceous carcinoma, evidence of keratinization in squamous cell carcinoma and ghost cells in pilomatrix carcinoma, using a panel of immunohistochemical stains can be helpful in reaching the final diagnosis (Table 3).

The development of hair matrix tumors have been known to harbor mutations in exon 3 of the catenin beta-1 gene, CTNNB1, that encodes for β-catenin, a downstream effector in the Wnt signaling pathway responsible for differentiation, proliferation, and adhesion of epithelial stem cells.^17-21 In a study conducted by Kazakov et al,²² DNA was extracted from 86 lesions: 4 were pilomatrixomas and 1 was a pilomatrix carcinoma. A polymerase chain reaction assay revealed 8 pathogenic variants of the β-catenin gene. D32Y (CTNNB1):c.94G>T (p.Asp32Tyr) and G34R (CTNNB1):c.100G>C (p.Gly34Arg) were the mutations present in pilomatrixoma and pilomatrix carcinoma, respectively.²² In addition, there are several proteins that are part of the Wnt pathway in addition to β-catenin—LEF-1 and CDX-2.

Tumminello and Hosler²³ found that pilomatrixomas and pilomatrix carcinomas were positive for CDX-2, β-catenin, and LEF-1 by immunohistochemistry. These downstream molecules in the Wnt signaling pathway could have the potential to be used as diagnostic and prognostic markers.^2,13,15,23

Although the pathogenesis is unclear, there are 2 possible mechanisms by which pilomatrix carcinomas develop. They can either arise as de novo tumors, or it is possible that initial mutations in β-catenin result in the formation of pilomatrixomas at an early age that may undergo malignant transformation in elderly patients over time with additional mutations.²

Our case was strongly and diffusely positive for β-catenin in a nuclear and cytoplasmic pattern and CDX-2 in a nuclear pattern, supporting the role of the Wnt signaling pathway in such tumors. Furthermore, our case demonstrated the presence of few intralesional normal dendritic melanocytes, a rare finding^1,24,25 but not unexpected, as melanocytes normally are present within the hair follicle matrix.

Pilomatrix carcinomas are aggressive tumors with a high risk for local recurrence and tendency for metastasis. In a study of 13 cases of pilomatrix carcinomas, Herrmann et al¹³ found that metastasis was significantly associated with local tumor recurrence (P<.0413). They concluded that the combination of overall high local recurrence and metastatic rates of pilomatrix carcinoma as well as documented tumor-related deaths would warrant continued patient follow-up, especially for recurrent tumors.¹³ Rapid growth of a tumor, either de novo or following several months of stable size, should alert physicians to perform a diagnostic biopsy.

Management options of pilomatrix carcinoma include surgery or radiation with close follow-up. The most widely reported treatment of pilomatrix carcinoma is wide local excision with histologically confirmed clear margins. Mohs micrographic surgery is an excellent treatment option.^2,13-15 Adjuvant radiation therapy may be necessary following excision. Currently there is no consensus on surgical management, and standard excisional margins have not been defined.²⁶ Jones et al² concluded that complete excision with wide margins likely is curative, with decreased rates of recurrence, and better awareness of this carcinoma would lead to appropriate treatment while avoiding unnecessary diagnostic tests.²

Conclusion

We report an exceptionally unique case of early pilomatrix carcinoma with a discussion on the pathogenesis and molecular pathology of hair matrix tumors. A large cohort of patients with longer follow-up periods and better molecular characterization is essential in drawing accurate information about their prognosis, identifying molecular markers that can be used as therapeutic targets, and determining ideal management strategy.

Pilomatrix carcinoma is a rare adnexal tumor with origin from the germinative matrical cells of the hair follicle. Clinically, it presents as a solitary lesion commonly found in the head and neck region as well as the upper back. The tumors cannot be distinguished by their clinical appearance only and frequently are mistaken for cysts. Histopathologic examination provides the definitive diagnosis in most cases. These carcinomas are aggressive neoplasms with a high probability of local recurrence and distant metastasis. Assessment of the Wnt signaling pathway components such as β-catenin, lymphoid enhancer-binding factor 1 (LEF-1), and caudal-related homeobox transcription factor 2 (CDX-2) potentially can be used for diagnostic purposes and targeted therapy.

We report a rare and unique case of early pilomatrix carcinoma with intralesional melanocytes. We review the molecular pathology and pathogenesis of these carcinomas as well as the significance of early diagnosis.

Case Report

A 73-year-old man with a history of extensive sun exposure presented with a 1-cm, raised, rapidly growing, slightly irregular, purple lesion on the right forearm of 3 months’ duration with tendency to bleed. He did not have a history of skin cancers and was otherwise healthy. Excision was recommended due to the progressive and rapid growth of the lesion.

Histopathologic Findings—Gross examination revealed a 0.9×0.7-cm, raised, slightly irregular lesion located 1 mm away from the closest peripheral margin. Histologically, the lesion was a relatively circumscribed, dermal-based basaloid neoplasm with slightly ill-defined edges involving the superficial and deep dermis (Figure 1A). The neoplasm was formed predominantly of sheets of basaloid cells and small nests of ghost cells, in addition to some squamoid and transitional cells (Figure 1B). The basaloid cells exhibited severe nuclear atypia, pleomorphism, increased nuclear to cytoplasmic ratio (Figure 1C), minimal to moderate amounts of eosinophilic cytoplasm, enlarged nuclei, prominent nucleoli, and coarse chromatin pattern. Abundant mitotic activity and apoptotic bodies were present as well as focal area of central necrosis (Figure 1C). Also, melanophages and a multinucleated giant cell reaction was noted. Elastic trichrome special stain highlighted focal infiltration of the neoplastic cells into the adjacent desmoplastic stroma. Melanin stain was negative for melanin pigment within the neoplasm. Given the presence of severely atypical basaloid cells along with ghost cells indicating matrical differentiation, a diagnosis of pilomatrix carcinoma was rendered.

Immunohistochemistry—The neoplastic cells were diffusely positive for p63, CDX-2 (Figure 2A), β-catenin (Figure 2B), and CD10 (Figure 2C), and focally and weakly positive for cytokeratin (CK) 5, BerEP4 (staining the tumor periphery), androgen receptor, and CK18 (a low-molecular-weight keratin). They were negative for monoclonal carcinoembryonic antigen, epithelial membrane antigen, CK7, CK20, CD34, SOX-10, CD56, synaptophysin, and chromogranin. Cytokeratin 14 was positive in the squamoid cells but negative in the basaloid cells. SOX-10 and melanoma cocktail immunostains demonstrated few intralesional dendritic melanocytes.

Comment

Pilomatrix carcinoma is a rare malignant cutaneous adnexal neoplasm with origin from the germinative matrix of the hair bulb region of hair follicles. Pilomatrix carcinoma was first reported in 1980.^1,2 These tumors are characterized by rapid growth and aggressive behavior. Their benign counterpart, pilomatrixoma, is a slow-growing, dermal or subcutaneous tumor that rarely recurs after complete excision.

As with pilomatrixoma, pilomatrix carcinomas are asymptomatic and present as solitary dermal or subcutaneous masses^3,4 that most commonly are found in the posterior neck, upper back, and preauricular regions of middle-aged or elderly adults with male predominance.⁵ They range in size from 0.5 to 20 cm with a mean of 4 cm that is slightly larger than pilomatrixoma. Pilomatrix carcinomas predominantly are firm tumors with or without cystic components, and they exhibit a high probability of recurrence and have risk for distant metastasis.^6-15

The differential diagnosis includes epidermal cysts, pilomatrixoma, basal cell carcinoma with matrical differentiation, trichoblastoma/trichoblastic carcinoma, and trichilemmal carcinoma. Pilomatrix carcinomas frequently are mistaken for epidermal cysts on clinical examination. Such a distinction can be easily resolved by histopathologic evaluation. The more challenging differential diagnosis is with pilomatrixoma. Histologically, pilomatrixomas consist of a distinct population of cells including basaloid, squamoid, transitional, and shadow cells in variable proportions. The basaloid cells transition to shadow cells in an organized zonal fashion.¹⁶ Compared to pilomatrixomas, pilomatrix carcinomas often show predominance of the basaloid cells; marked cytologic atypia and pleomorphism; numerous mitotic figures; deep infiltrative pattern into subcutaneous fat, fascia, and skeletal muscle; stromal desmoplasia; necrosis; and neurovascular invasion (Tables 1 and 2). Furthermore, the shadow cells tend to form a small nested pattern in pilomatrix carcinoma instead of the flat sheetlike pattern usually observed in pilomatrixoma.¹⁶ Basal cell carcinoma with matrical differentiation can pose a diagnostic challenge in the differential diagnosis; basal cell carcinoma usually exhibits a peripheral palisade of the basaloid cells accompanied by retraction spaces separating the tumor from the stroma. Trichoblastoma/trichoblastic carcinoma with matrical differentiation can be distinguished by its exuberant stroma, prominent primitive hair follicles, and papillary mesenchymal bodies. Trichilemmal carcinomas are recognized by their connection to the overlying epidermis, peripheral palisading, and presence of clear cells, while pilomatrix carcinoma lacks connection to the surface epithelium.

Immunohistochemical stains have little to no role in the differential diagnosis, and morphology is the mainstay in making the diagnosis. Rarely, pilomatrix carcinoma can be confused with poorly differentiated sebaceous carcinoma and poorly differentiated squamous cell carcinoma. Although careful scrutiny of the histologic features may help identify mature sebocytes in sebaceous carcinoma, evidence of keratinization in squamous cell carcinoma and ghost cells in pilomatrix carcinoma, using a panel of immunohistochemical stains can be helpful in reaching the final diagnosis (Table 3).

The development of hair matrix tumors have been known to harbor mutations in exon 3 of the catenin beta-1 gene, CTNNB1, that encodes for β-catenin, a downstream effector in the Wnt signaling pathway responsible for differentiation, proliferation, and adhesion of epithelial stem cells.^17-21 In a study conducted by Kazakov et al,²² DNA was extracted from 86 lesions: 4 were pilomatrixomas and 1 was a pilomatrix carcinoma. A polymerase chain reaction assay revealed 8 pathogenic variants of the β-catenin gene. D32Y (CTNNB1):c.94G>T (p.Asp32Tyr) and G34R (CTNNB1):c.100G>C (p.Gly34Arg) were the mutations present in pilomatrixoma and pilomatrix carcinoma, respectively.²² In addition, there are several proteins that are part of the Wnt pathway in addition to β-catenin—LEF-1 and CDX-2.

Tumminello and Hosler²³ found that pilomatrixomas and pilomatrix carcinomas were positive for CDX-2, β-catenin, and LEF-1 by immunohistochemistry. These downstream molecules in the Wnt signaling pathway could have the potential to be used as diagnostic and prognostic markers.^2,13,15,23

Although the pathogenesis is unclear, there are 2 possible mechanisms by which pilomatrix carcinomas develop. They can either arise as de novo tumors, or it is possible that initial mutations in β-catenin result in the formation of pilomatrixomas at an early age that may undergo malignant transformation in elderly patients over time with additional mutations.²

Our case was strongly and diffusely positive for β-catenin in a nuclear and cytoplasmic pattern and CDX-2 in a nuclear pattern, supporting the role of the Wnt signaling pathway in such tumors. Furthermore, our case demonstrated the presence of few intralesional normal dendritic melanocytes, a rare finding^1,24,25 but not unexpected, as melanocytes normally are present within the hair follicle matrix.

Pilomatrix carcinomas are aggressive tumors with a high risk for local recurrence and tendency for metastasis. In a study of 13 cases of pilomatrix carcinomas, Herrmann et al¹³ found that metastasis was significantly associated with local tumor recurrence (P<.0413). They concluded that the combination of overall high local recurrence and metastatic rates of pilomatrix carcinoma as well as documented tumor-related deaths would warrant continued patient follow-up, especially for recurrent tumors.¹³ Rapid growth of a tumor, either de novo or following several months of stable size, should alert physicians to perform a diagnostic biopsy.

Management options of pilomatrix carcinoma include surgery or radiation with close follow-up. The most widely reported treatment of pilomatrix carcinoma is wide local excision with histologically confirmed clear margins. Mohs micrographic surgery is an excellent treatment option.^2,13-15 Adjuvant radiation therapy may be necessary following excision. Currently there is no consensus on surgical management, and standard excisional margins have not been defined.²⁶ Jones et al² concluded that complete excision with wide margins likely is curative, with decreased rates of recurrence, and better awareness of this carcinoma would lead to appropriate treatment while avoiding unnecessary diagnostic tests.²

Conclusion

We report an exceptionally unique case of early pilomatrix carcinoma with a discussion on the pathogenesis and molecular pathology of hair matrix tumors. A large cohort of patients with longer follow-up periods and better molecular characterization is essential in drawing accurate information about their prognosis, identifying molecular markers that can be used as therapeutic targets, and determining ideal management strategy.

Pilomatrix carcinoma is a rare adnexal tumor with origin from the germinative matrical cells of the hair follicle. Clinically, it presents as a solitary lesion commonly found in the head and neck region as well as the upper back. The tumors cannot be distinguished by their clinical appearance only and frequently are mistaken for cysts. Histopathologic examination provides the definitive diagnosis in most cases. These carcinomas are aggressive neoplasms with a high probability of local recurrence and distant metastasis. Assessment of the Wnt signaling pathway components such as β-catenin, lymphoid enhancer-binding factor 1 (LEF-1), and caudal-related homeobox transcription factor 2 (CDX-2) potentially can be used for diagnostic purposes and targeted therapy.

We report a rare and unique case of early pilomatrix carcinoma with intralesional melanocytes. We review the molecular pathology and pathogenesis of these carcinomas as well as the significance of early diagnosis.

Case Report

A 73-year-old man with a history of extensive sun exposure presented with a 1-cm, raised, rapidly growing, slightly irregular, purple lesion on the right forearm of 3 months’ duration with tendency to bleed. He did not have a history of skin cancers and was otherwise healthy. Excision was recommended due to the progressive and rapid growth of the lesion.

Histopathologic Findings—Gross examination revealed a 0.9×0.7-cm, raised, slightly irregular lesion located 1 mm away from the closest peripheral margin. Histologically, the lesion was a relatively circumscribed, dermal-based basaloid neoplasm with slightly ill-defined edges involving the superficial and deep dermis (Figure 1A). The neoplasm was formed predominantly of sheets of basaloid cells and small nests of ghost cells, in addition to some squamoid and transitional cells (Figure 1B). The basaloid cells exhibited severe nuclear atypia, pleomorphism, increased nuclear to cytoplasmic ratio (Figure 1C), minimal to moderate amounts of eosinophilic cytoplasm, enlarged nuclei, prominent nucleoli, and coarse chromatin pattern. Abundant mitotic activity and apoptotic bodies were present as well as focal area of central necrosis (Figure 1C). Also, melanophages and a multinucleated giant cell reaction was noted. Elastic trichrome special stain highlighted focal infiltration of the neoplastic cells into the adjacent desmoplastic stroma. Melanin stain was negative for melanin pigment within the neoplasm. Given the presence of severely atypical basaloid cells along with ghost cells indicating matrical differentiation, a diagnosis of pilomatrix carcinoma was rendered.

Immunohistochemistry—The neoplastic cells were diffusely positive for p63, CDX-2 (Figure 2A), β-catenin (Figure 2B), and CD10 (Figure 2C), and focally and weakly positive for cytokeratin (CK) 5, BerEP4 (staining the tumor periphery), androgen receptor, and CK18 (a low-molecular-weight keratin). They were negative for monoclonal carcinoembryonic antigen, epithelial membrane antigen, CK7, CK20, CD34, SOX-10, CD56, synaptophysin, and chromogranin. Cytokeratin 14 was positive in the squamoid cells but negative in the basaloid cells. SOX-10 and melanoma cocktail immunostains demonstrated few intralesional dendritic melanocytes.

Comment

Pilomatrix carcinoma is a rare malignant cutaneous adnexal neoplasm with origin from the germinative matrix of the hair bulb region of hair follicles. Pilomatrix carcinoma was first reported in 1980.^1,2 These tumors are characterized by rapid growth and aggressive behavior. Their benign counterpart, pilomatrixoma, is a slow-growing, dermal or subcutaneous tumor that rarely recurs after complete excision.

As with pilomatrixoma, pilomatrix carcinomas are asymptomatic and present as solitary dermal or subcutaneous masses^3,4 that most commonly are found in the posterior neck, upper back, and preauricular regions of middle-aged or elderly adults with male predominance.⁵ They range in size from 0.5 to 20 cm with a mean of 4 cm that is slightly larger than pilomatrixoma. Pilomatrix carcinomas predominantly are firm tumors with or without cystic components, and they exhibit a high probability of recurrence and have risk for distant metastasis.^6-15

The differential diagnosis includes epidermal cysts, pilomatrixoma, basal cell carcinoma with matrical differentiation, trichoblastoma/trichoblastic carcinoma, and trichilemmal carcinoma. Pilomatrix carcinomas frequently are mistaken for epidermal cysts on clinical examination. Such a distinction can be easily resolved by histopathologic evaluation. The more challenging differential diagnosis is with pilomatrixoma. Histologically, pilomatrixomas consist of a distinct population of cells including basaloid, squamoid, transitional, and shadow cells in variable proportions. The basaloid cells transition to shadow cells in an organized zonal fashion.¹⁶ Compared to pilomatrixomas, pilomatrix carcinomas often show predominance of the basaloid cells; marked cytologic atypia and pleomorphism; numerous mitotic figures; deep infiltrative pattern into subcutaneous fat, fascia, and skeletal muscle; stromal desmoplasia; necrosis; and neurovascular invasion (Tables 1 and 2). Furthermore, the shadow cells tend to form a small nested pattern in pilomatrix carcinoma instead of the flat sheetlike pattern usually observed in pilomatrixoma.¹⁶ Basal cell carcinoma with matrical differentiation can pose a diagnostic challenge in the differential diagnosis; basal cell carcinoma usually exhibits a peripheral palisade of the basaloid cells accompanied by retraction spaces separating the tumor from the stroma. Trichoblastoma/trichoblastic carcinoma with matrical differentiation can be distinguished by its exuberant stroma, prominent primitive hair follicles, and papillary mesenchymal bodies. Trichilemmal carcinomas are recognized by their connection to the overlying epidermis, peripheral palisading, and presence of clear cells, while pilomatrix carcinoma lacks connection to the surface epithelium.

Immunohistochemical stains have little to no role in the differential diagnosis, and morphology is the mainstay in making the diagnosis. Rarely, pilomatrix carcinoma can be confused with poorly differentiated sebaceous carcinoma and poorly differentiated squamous cell carcinoma. Although careful scrutiny of the histologic features may help identify mature sebocytes in sebaceous carcinoma, evidence of keratinization in squamous cell carcinoma and ghost cells in pilomatrix carcinoma, using a panel of immunohistochemical stains can be helpful in reaching the final diagnosis (Table 3).

The development of hair matrix tumors have been known to harbor mutations in exon 3 of the catenin beta-1 gene, CTNNB1, that encodes for β-catenin, a downstream effector in the Wnt signaling pathway responsible for differentiation, proliferation, and adhesion of epithelial stem cells.^17-21 In a study conducted by Kazakov et al,²² DNA was extracted from 86 lesions: 4 were pilomatrixomas and 1 was a pilomatrix carcinoma. A polymerase chain reaction assay revealed 8 pathogenic variants of the β-catenin gene. D32Y (CTNNB1):c.94G>T (p.Asp32Tyr) and G34R (CTNNB1):c.100G>C (p.Gly34Arg) were the mutations present in pilomatrixoma and pilomatrix carcinoma, respectively.²² In addition, there are several proteins that are part of the Wnt pathway in addition to β-catenin—LEF-1 and CDX-2.

Tumminello and Hosler²³ found that pilomatrixomas and pilomatrix carcinomas were positive for CDX-2, β-catenin, and LEF-1 by immunohistochemistry. These downstream molecules in the Wnt signaling pathway could have the potential to be used as diagnostic and prognostic markers.^2,13,15,23

Although the pathogenesis is unclear, there are 2 possible mechanisms by which pilomatrix carcinomas develop. They can either arise as de novo tumors, or it is possible that initial mutations in β-catenin result in the formation of pilomatrixomas at an early age that may undergo malignant transformation in elderly patients over time with additional mutations.²

Our case was strongly and diffusely positive for β-catenin in a nuclear and cytoplasmic pattern and CDX-2 in a nuclear pattern, supporting the role of the Wnt signaling pathway in such tumors. Furthermore, our case demonstrated the presence of few intralesional normal dendritic melanocytes, a rare finding^1,24,25 but not unexpected, as melanocytes normally are present within the hair follicle matrix.

Pilomatrix carcinomas are aggressive tumors with a high risk for local recurrence and tendency for metastasis. In a study of 13 cases of pilomatrix carcinomas, Herrmann et al¹³ found that metastasis was significantly associated with local tumor recurrence (P<.0413). They concluded that the combination of overall high local recurrence and metastatic rates of pilomatrix carcinoma as well as documented tumor-related deaths would warrant continued patient follow-up, especially for recurrent tumors.¹³ Rapid growth of a tumor, either de novo or following several months of stable size, should alert physicians to perform a diagnostic biopsy.

Management options of pilomatrix carcinoma include surgery or radiation with close follow-up. The most widely reported treatment of pilomatrix carcinoma is wide local excision with histologically confirmed clear margins. Mohs micrographic surgery is an excellent treatment option.^2,13-15 Adjuvant radiation therapy may be necessary following excision. Currently there is no consensus on surgical management, and standard excisional margins have not been defined.²⁶ Jones et al² concluded that complete excision with wide margins likely is curative, with decreased rates of recurrence, and better awareness of this carcinoma would lead to appropriate treatment while avoiding unnecessary diagnostic tests.²

Conclusion

We report an exceptionally unique case of early pilomatrix carcinoma with a discussion on the pathogenesis and molecular pathology of hair matrix tumors. A large cohort of patients with longer follow-up periods and better molecular characterization is essential in drawing accurate information about their prognosis, identifying molecular markers that can be used as therapeutic targets, and determining ideal management strategy.

The Diagnosis: Ecthyma Gangrenosum

Histopathology revealed basophilic bacterial rods around necrotic vessels with thrombosis and edema (Figure). Blood and tissue cultures grew Pseudomonas aeruginosa. Based on the histopathology and clinical presentation, a diagnosis of P aeruginosa–associated ecthyma gangrenosum (EG) was made. The patient’s symptoms resolved with intravenous cefepime, and he later was transitioned to oral levofloxacin for outpatient treatment.

Ecthyma gangrenosum is an uncommon cutaneous manifestation of bacteremia that most commonly occurs secondary to P aeruginosa in immunocompromised patients, particularly patients with severe neutropenia in the setting of recent chemotherapy.^1,2 Ecthyma gangrenosum can occur anywhere on the body, predominantly in moist areas such as the axillae and groin; the arms and legs, such as in our patient, as well as the trunk and face also may be involved.³ Other causes of EG skin lesions include methicillin-resistant Staphylococcus aureus, Citrobacter freundii, Escherichia coli, fungi such as Candida, and viruses such as herpes simplex virus.^2,4-6 Common predisposing conditions associated with EG include neutropenia, leukemia, HIV, diabetes mellitus, extensive burn wounds, and a history of immunosuppressive medications. It also has been known to occur in otherwise healthy, immunocompetent individuals with no difference in clinical manifestation.²

The diagnosis is clinicopathologic, with initial evaluation including blood and wound cultures as well as a complete blood cell count once EG is suspected. An excisional or punch biopsy is performed for confirmation, showing many gram-negative, rod-shaped bacteria in cases of pseudomonal EG.⁷ Histopathology is characterized by bacterial perivascular invasion that then leads to secondary arteriole thrombosis, tissue edema, and separation of the epidermis.^7,8 Resultant ischemic necrosis results in the classic macroscopic appearance of an erythematous macule that rapidly progresses into a central necrotic lesion surrounded by an erythematous or violaceous halo after undergoing a hemorrhagic bullous stage.1,9 A Wood lamp can be used to expedite the diagnosis, as Pseudomonas bacteria excretes a pigment (pyoverdine) that fluoresces yellowish green.¹⁰

Ecthyma gangrenosum can be classified as a primary skin lesion that may or may not be followed by bacteremia or as a lesion secondary to pseudomonal bacteremia.¹¹ Bacteremia has been reported in half of cases, with hematogenous metastasis of the infection, likely in manifestations with multiple bilateral lesions.² Our patient’s presentation of a single lesion revealed a positive blood culture result. Lesions also can develop by direct inoculation of the epidermis causing local destruction of the surrounding tissue. The nonbacteremic form of EG has been associated with a lower mortality rate of around 15% compared to patients with bacteremia ranging from 38% to 96%.¹² The presence of neutropenia is the most important prognostic factor for mortality at the time of diagnosis.¹³

Prompt empiric therapy should be initiated after obtaining wound and blood cultures in those with infection until the causative organism and its susceptibility are identified. Pseudomonal infections account for 4% of all cases of hospital-acquired bacteremia and are the third leading cause of gram-negative bloodstream infection.⁷ Initial broad-spectrum antibiotics include antipseudomonal β-lactams (piperacillin-tazobactam), cephalosporins (cefepime), fluoroquinolones (levofloxacin), and carbapenems (imipenem).^1,7 Medical therapy alone may be sufficient without requiring extensive surgical debridement to remove necrotic tissue in some patients. Surgical debridement usually is warranted for lesions larger than 10 cm in diameter.³ Our patient was treated with intravenous cefepime with resolution and was followed with outpatient oral levofloxacin as appropriate. A high index of suspicion should be maintained for relapsing pseudomonal EG infection among patients with AIDS, as the reported recurrence rate is 57%.¹⁴

Clinically, the differential diagnosis of EG presenting in immunocompromised patients or individuals with underlying malignancy includes pyoderma gangrenosum, papulonecrotic tuberculid, and leukemia cutis. An erythematous rash with central necrosis presenting in a patient with systemic symptoms is pathognomonic for erythema migrans and should be considered as a diagnostic possibility in areas endemic for Lyme disease in the United States, including the northeastern, mid-Atlantic, and north-central regions.¹⁵ A thorough history, physical examination, basic laboratory studies, and histopathology are critical to differentiate between these entities with similar macroscopic features. Pyoderma gangrenosum histologically manifests as a noninfectious, deep, suppurative folliculitis with leukocytoclastic vasculitis in 40% of cases.¹⁶ Although papulonecrotic tuberculid can present with dermal necrosis resulting from a hypersensitivity reaction to antigenic components of mycobacteria, there typically are granulomatous infiltrates present and a lack of observed organisms on histopathology.¹⁷ Although leukemia cutis infrequently occurs in patients diagnosed with leukemia, its salient features on pathology are nodular or diffuse infiltrates of leukemic cells in the dermis and subcutis with a high nuclear-to-cytoplasmic ratio, often with prominent nucleoli.¹⁸ Lyme disease can present in various ways; however, cutaneous involvement in the primary lesion is histologically characterized by a perivascular lymphohistiocytic infiltrate containing plasma cells at the periphery of the expanding annular lesion and eosinophils present at the center.¹⁹

The Diagnosis: Ecthyma Gangrenosum

Histopathology revealed basophilic bacterial rods around necrotic vessels with thrombosis and edema (Figure). Blood and tissue cultures grew Pseudomonas aeruginosa. Based on the histopathology and clinical presentation, a diagnosis of P aeruginosa–associated ecthyma gangrenosum (EG) was made. The patient’s symptoms resolved with intravenous cefepime, and he later was transitioned to oral levofloxacin for outpatient treatment.

Ecthyma gangrenosum is an uncommon cutaneous manifestation of bacteremia that most commonly occurs secondary to P aeruginosa in immunocompromised patients, particularly patients with severe neutropenia in the setting of recent chemotherapy.^1,2 Ecthyma gangrenosum can occur anywhere on the body, predominantly in moist areas such as the axillae and groin; the arms and legs, such as in our patient, as well as the trunk and face also may be involved.³ Other causes of EG skin lesions include methicillin-resistant Staphylococcus aureus, Citrobacter freundii, Escherichia coli, fungi such as Candida, and viruses such as herpes simplex virus.^2,4-6 Common predisposing conditions associated with EG include neutropenia, leukemia, HIV, diabetes mellitus, extensive burn wounds, and a history of immunosuppressive medications. It also has been known to occur in otherwise healthy, immunocompetent individuals with no difference in clinical manifestation.²

The diagnosis is clinicopathologic, with initial evaluation including blood and wound cultures as well as a complete blood cell count once EG is suspected. An excisional or punch biopsy is performed for confirmation, showing many gram-negative, rod-shaped bacteria in cases of pseudomonal EG.⁷ Histopathology is characterized by bacterial perivascular invasion that then leads to secondary arteriole thrombosis, tissue edema, and separation of the epidermis.^7,8 Resultant ischemic necrosis results in the classic macroscopic appearance of an erythematous macule that rapidly progresses into a central necrotic lesion surrounded by an erythematous or violaceous halo after undergoing a hemorrhagic bullous stage.1,9 A Wood lamp can be used to expedite the diagnosis, as Pseudomonas bacteria excretes a pigment (pyoverdine) that fluoresces yellowish green.¹⁰

Ecthyma gangrenosum can be classified as a primary skin lesion that may or may not be followed by bacteremia or as a lesion secondary to pseudomonal bacteremia.¹¹ Bacteremia has been reported in half of cases, with hematogenous metastasis of the infection, likely in manifestations with multiple bilateral lesions.² Our patient’s presentation of a single lesion revealed a positive blood culture result. Lesions also can develop by direct inoculation of the epidermis causing local destruction of the surrounding tissue. The nonbacteremic form of EG has been associated with a lower mortality rate of around 15% compared to patients with bacteremia ranging from 38% to 96%.¹² The presence of neutropenia is the most important prognostic factor for mortality at the time of diagnosis.¹³

Prompt empiric therapy should be initiated after obtaining wound and blood cultures in those with infection until the causative organism and its susceptibility are identified. Pseudomonal infections account for 4% of all cases of hospital-acquired bacteremia and are the third leading cause of gram-negative bloodstream infection.⁷ Initial broad-spectrum antibiotics include antipseudomonal β-lactams (piperacillin-tazobactam), cephalosporins (cefepime), fluoroquinolones (levofloxacin), and carbapenems (imipenem).^1,7 Medical therapy alone may be sufficient without requiring extensive surgical debridement to remove necrotic tissue in some patients. Surgical debridement usually is warranted for lesions larger than 10 cm in diameter.³ Our patient was treated with intravenous cefepime with resolution and was followed with outpatient oral levofloxacin as appropriate. A high index of suspicion should be maintained for relapsing pseudomonal EG infection among patients with AIDS, as the reported recurrence rate is 57%.¹⁴

Clinically, the differential diagnosis of EG presenting in immunocompromised patients or individuals with underlying malignancy includes pyoderma gangrenosum, papulonecrotic tuberculid, and leukemia cutis. An erythematous rash with central necrosis presenting in a patient with systemic symptoms is pathognomonic for erythema migrans and should be considered as a diagnostic possibility in areas endemic for Lyme disease in the United States, including the northeastern, mid-Atlantic, and north-central regions.¹⁵ A thorough history, physical examination, basic laboratory studies, and histopathology are critical to differentiate between these entities with similar macroscopic features. Pyoderma gangrenosum histologically manifests as a noninfectious, deep, suppurative folliculitis with leukocytoclastic vasculitis in 40% of cases.¹⁶ Although papulonecrotic tuberculid can present with dermal necrosis resulting from a hypersensitivity reaction to antigenic components of mycobacteria, there typically are granulomatous infiltrates present and a lack of observed organisms on histopathology.¹⁷ Although leukemia cutis infrequently occurs in patients diagnosed with leukemia, its salient features on pathology are nodular or diffuse infiltrates of leukemic cells in the dermis and subcutis with a high nuclear-to-cytoplasmic ratio, often with prominent nucleoli.¹⁸ Lyme disease can present in various ways; however, cutaneous involvement in the primary lesion is histologically characterized by a perivascular lymphohistiocytic infiltrate containing plasma cells at the periphery of the expanding annular lesion and eosinophils present at the center.¹⁹

The Diagnosis: Ecthyma Gangrenosum

Histopathology revealed basophilic bacterial rods around necrotic vessels with thrombosis and edema (Figure). Blood and tissue cultures grew Pseudomonas aeruginosa. Based on the histopathology and clinical presentation, a diagnosis of P aeruginosa–associated ecthyma gangrenosum (EG) was made. The patient’s symptoms resolved with intravenous cefepime, and he later was transitioned to oral levofloxacin for outpatient treatment.

Ecthyma gangrenosum is an uncommon cutaneous manifestation of bacteremia that most commonly occurs secondary to P aeruginosa in immunocompromised patients, particularly patients with severe neutropenia in the setting of recent chemotherapy.^1,2 Ecthyma gangrenosum can occur anywhere on the body, predominantly in moist areas such as the axillae and groin; the arms and legs, such as in our patient, as well as the trunk and face also may be involved.³ Other causes of EG skin lesions include methicillin-resistant Staphylococcus aureus, Citrobacter freundii, Escherichia coli, fungi such as Candida, and viruses such as herpes simplex virus.^2,4-6 Common predisposing conditions associated with EG include neutropenia, leukemia, HIV, diabetes mellitus, extensive burn wounds, and a history of immunosuppressive medications. It also has been known to occur in otherwise healthy, immunocompetent individuals with no difference in clinical manifestation.²

The diagnosis is clinicopathologic, with initial evaluation including blood and wound cultures as well as a complete blood cell count once EG is suspected. An excisional or punch biopsy is performed for confirmation, showing many gram-negative, rod-shaped bacteria in cases of pseudomonal EG.⁷ Histopathology is characterized by bacterial perivascular invasion that then leads to secondary arteriole thrombosis, tissue edema, and separation of the epidermis.^7,8 Resultant ischemic necrosis results in the classic macroscopic appearance of an erythematous macule that rapidly progresses into a central necrotic lesion surrounded by an erythematous or violaceous halo after undergoing a hemorrhagic bullous stage.1,9 A Wood lamp can be used to expedite the diagnosis, as Pseudomonas bacteria excretes a pigment (pyoverdine) that fluoresces yellowish green.¹⁰

Ecthyma gangrenosum can be classified as a primary skin lesion that may or may not be followed by bacteremia or as a lesion secondary to pseudomonal bacteremia.¹¹ Bacteremia has been reported in half of cases, with hematogenous metastasis of the infection, likely in manifestations with multiple bilateral lesions.² Our patient’s presentation of a single lesion revealed a positive blood culture result. Lesions also can develop by direct inoculation of the epidermis causing local destruction of the surrounding tissue. The nonbacteremic form of EG has been associated with a lower mortality rate of around 15% compared to patients with bacteremia ranging from 38% to 96%.¹² The presence of neutropenia is the most important prognostic factor for mortality at the time of diagnosis.¹³

Prompt empiric therapy should be initiated after obtaining wound and blood cultures in those with infection until the causative organism and its susceptibility are identified. Pseudomonal infections account for 4% of all cases of hospital-acquired bacteremia and are the third leading cause of gram-negative bloodstream infection.⁷ Initial broad-spectrum antibiotics include antipseudomonal β-lactams (piperacillin-tazobactam), cephalosporins (cefepime), fluoroquinolones (levofloxacin), and carbapenems (imipenem).^1,7 Medical therapy alone may be sufficient without requiring extensive surgical debridement to remove necrotic tissue in some patients. Surgical debridement usually is warranted for lesions larger than 10 cm in diameter.³ Our patient was treated with intravenous cefepime with resolution and was followed with outpatient oral levofloxacin as appropriate. A high index of suspicion should be maintained for relapsing pseudomonal EG infection among patients with AIDS, as the reported recurrence rate is 57%.¹⁴

Clinically, the differential diagnosis of EG presenting in immunocompromised patients or individuals with underlying malignancy includes pyoderma gangrenosum, papulonecrotic tuberculid, and leukemia cutis. An erythematous rash with central necrosis presenting in a patient with systemic symptoms is pathognomonic for erythema migrans and should be considered as a diagnostic possibility in areas endemic for Lyme disease in the United States, including the northeastern, mid-Atlantic, and north-central regions.¹⁵ A thorough history, physical examination, basic laboratory studies, and histopathology are critical to differentiate between these entities with similar macroscopic features. Pyoderma gangrenosum histologically manifests as a noninfectious, deep, suppurative folliculitis with leukocytoclastic vasculitis in 40% of cases.¹⁶ Although papulonecrotic tuberculid can present with dermal necrosis resulting from a hypersensitivity reaction to antigenic components of mycobacteria, there typically are granulomatous infiltrates present and a lack of observed organisms on histopathology.¹⁷ Although leukemia cutis infrequently occurs in patients diagnosed with leukemia, its salient features on pathology are nodular or diffuse infiltrates of leukemic cells in the dermis and subcutis with a high nuclear-to-cytoplasmic ratio, often with prominent nucleoli.¹⁸ Lyme disease can present in various ways; however, cutaneous involvement in the primary lesion is histologically characterized by a perivascular lymphohistiocytic infiltrate containing plasma cells at the periphery of the expanding annular lesion and eosinophils present at the center.¹⁹