David Esguerra, DO

The Diagnosis: Drug-Induced Hyperpigmentation

Additional history provided by the patient’s caretaker elucidated an extensive list of medications including chlorpromazine and minocycline, among several others. The caretaker revealed that the patient began treatment for acne vulgaris 2 years prior; despite the acne resolving, therapy was not discontinued. The blue-gray and brown pigmentation on our patient’s shins likely was attributed to a medication he was taking.

Both chlorpromazine and minocycline, among many other medications, are known to cause abnormal pigmentation of the skin.¹ Minocycline is a tetracycline antibiotic prescribed for acne and other inflammatory cutaneous conditions. It is highly lipophilic, allowing it to reach high drug concentrations in the skin and nail unit.² Patients taking minocycline long term and at high doses are at greatest risk for pigment deposition.^3,4

Minocycline-induced hyperpigmentation is classified into 3 types. Type I describes blue-black deposition of pigment in acne scars and areas of inflammation, typically on facial skin.^1,5 Histologically, type I stains positive for Perls Prussian blue, indicating an increased deposition of iron as hemosiderin,¹ which likely occurs because minocycline is thought to play a role in defective clearance of hemosiderin from the dermis of injured tissue.⁵ Type II hyperpigmentation presents as bluegray pigment on the lower legs and occasionally the arms.^6,7 Type II stains positive for both Perls Prussian blue and Fontana-Masson, demonstrating hemosiderin and melanin, respectively.⁶ The third form of hyperpigmentation results in diffuse, dark brown to gray pigmentation with a predilection for sun-exposed areas.⁸ Histology of type III shows increased pigment in the basal portion of the epidermis and brown-black pigment in macrophages of the dermis. Type III stains positive for Fontana-Masson and negative for Perls Prussian blue. The etiology of hyperpigmentation has been suspected to be caused by minocycline stimulating melanin production and/or deposition of minocycline-melanin complexes in dermal macrophages after a certain drug level; this largely is seen in patients receiving 100 to 200 mg daily as early as 1 year into treatment.⁸

Chlorpromazine is a typical antipsychotic that causes abnormal skin pigmentation in sun-exposed areas due to increased melanogenesis.⁹ Similar to type III minocyclineinduced hyperpigmentation, a histologic specimen may stain positive for Fontana-Masson yet negative for Perls Prussian blue. Lal et al10 demonstrated complete resolution of abnormal skin pigmentation within 5 years after stopping chlorpromazine. In contrast, minocyclineinduced hyperpigmentation may be permanent in some cases. There is substantial clinical and histologic overlap for drug-induced hyperpigmentation etiologies; it would behoove the clinician to focus on the most common locations affected and the generalized coloration.

Treatment of minocycline-induced hyperpigmentation includes the use of Q-switched lasers, specifically Q-switched ruby and Q-switched alexandrite.¹¹ The use of the Q-switched Nd:YAG laser appears to be ineffective at clearing minocycline-induced pigmentation.^7,11 In our patient, minocycline was discontinued immediately. Due to the patient’s critical condition, he deferred all other therapy. Erythema dyschromicum perstans, also referred to as ashy dermatosis, is an idiopathic form of hyperpigmentation.¹² Lesions start as blue-gray to ashy gray macules, occasionally surrounded by a slightly erythematous, raised border.

Erythema dyschromicum perstans typically presents on the trunk, face, and arms of patients with Fitzpatrick skin types III and IV; it is considered a variant of lichen planus actinicus.¹² Histologically, erythema dyschromicum perstans may mimic lichen planus pigmentosus (LPP); however, subtle differences exist to distinguish the 2 conditions. Erythema dyschromicum perstans demonstrates a mild lichenoid infiltrate, focal basal vacuolization at the dermoepidermal junction, and melanophage deposition.¹³ In contrast, LPP demonstrates pigmentary incontinence and a more severe inflammatory infiltrate. A perifollicular infiltrate and fibrosis also can be seen in LPP, which may explain the frontal fibrosing alopecia that often precedes LPP.¹³

Addison disease, also known as primary adrenal insufficiency, can cause diffuse hyperpigmentation in the skin, mucosae, and nail beds. The pigmentation is prominent in regions of naturally increased pigmentation, such as the flexural surfaces and intertriginous areas.¹⁴ Patients with adrenal insufficiency will have accompanying weight loss, hypotension, and fatigue, among other symptoms related to deficiency of cortisol and aldosterone. Skin biopsy shows acanthosis, hyperkeratosis, focal parakeratosis, spongiosis, superficial perivascular lymphocytic infiltrate, basal melanin deposition, and superficial dermal macrophages.¹⁵

Confluent and reticulated papillomatosis is an uncommon dermatosis that presents with multiple hyperpigmented macules and papules that coalesce to form patches and plaques centrally with reticulation in the periphery.¹⁶ Confluent and reticulated papillomatosis commonly presents on the upper trunk, axillae, and neck, though involvement can include flexural surfaces as well as the lower trunk and legs.^16,17 Biopsy demonstrates undulating hyperkeratosis, papillomatosis, acanthosis, and negative fungal staining.¹⁶

Pretibial myxedema most commonly is associated with Graves disease and presents as well-defined thickening and induration with overlying pink or purple-brown papules in the pretibial region.¹⁸ An acral surface and mucin deposition within the entire dermis may be appreciated on histology with staining for colloidal iron or Alcian blue.

The Diagnosis: Drug-Induced Hyperpigmentation

Additional history provided by the patient’s caretaker elucidated an extensive list of medications including chlorpromazine and minocycline, among several others. The caretaker revealed that the patient began treatment for acne vulgaris 2 years prior; despite the acne resolving, therapy was not discontinued. The blue-gray and brown pigmentation on our patient’s shins likely was attributed to a medication he was taking.

Both chlorpromazine and minocycline, among many other medications, are known to cause abnormal pigmentation of the skin.¹ Minocycline is a tetracycline antibiotic prescribed for acne and other inflammatory cutaneous conditions. It is highly lipophilic, allowing it to reach high drug concentrations in the skin and nail unit.² Patients taking minocycline long term and at high doses are at greatest risk for pigment deposition.^3,4

Minocycline-induced hyperpigmentation is classified into 3 types. Type I describes blue-black deposition of pigment in acne scars and areas of inflammation, typically on facial skin.^1,5 Histologically, type I stains positive for Perls Prussian blue, indicating an increased deposition of iron as hemosiderin,¹ which likely occurs because minocycline is thought to play a role in defective clearance of hemosiderin from the dermis of injured tissue.⁵ Type II hyperpigmentation presents as bluegray pigment on the lower legs and occasionally the arms.^6,7 Type II stains positive for both Perls Prussian blue and Fontana-Masson, demonstrating hemosiderin and melanin, respectively.⁶ The third form of hyperpigmentation results in diffuse, dark brown to gray pigmentation with a predilection for sun-exposed areas.⁸ Histology of type III shows increased pigment in the basal portion of the epidermis and brown-black pigment in macrophages of the dermis. Type III stains positive for Fontana-Masson and negative for Perls Prussian blue. The etiology of hyperpigmentation has been suspected to be caused by minocycline stimulating melanin production and/or deposition of minocycline-melanin complexes in dermal macrophages after a certain drug level; this largely is seen in patients receiving 100 to 200 mg daily as early as 1 year into treatment.⁸

Chlorpromazine is a typical antipsychotic that causes abnormal skin pigmentation in sun-exposed areas due to increased melanogenesis.⁹ Similar to type III minocyclineinduced hyperpigmentation, a histologic specimen may stain positive for Fontana-Masson yet negative for Perls Prussian blue. Lal et al10 demonstrated complete resolution of abnormal skin pigmentation within 5 years after stopping chlorpromazine. In contrast, minocyclineinduced hyperpigmentation may be permanent in some cases. There is substantial clinical and histologic overlap for drug-induced hyperpigmentation etiologies; it would behoove the clinician to focus on the most common locations affected and the generalized coloration.

Treatment of minocycline-induced hyperpigmentation includes the use of Q-switched lasers, specifically Q-switched ruby and Q-switched alexandrite.¹¹ The use of the Q-switched Nd:YAG laser appears to be ineffective at clearing minocycline-induced pigmentation.^7,11 In our patient, minocycline was discontinued immediately. Due to the patient’s critical condition, he deferred all other therapy. Erythema dyschromicum perstans, also referred to as ashy dermatosis, is an idiopathic form of hyperpigmentation.¹² Lesions start as blue-gray to ashy gray macules, occasionally surrounded by a slightly erythematous, raised border.

Erythema dyschromicum perstans typically presents on the trunk, face, and arms of patients with Fitzpatrick skin types III and IV; it is considered a variant of lichen planus actinicus.¹² Histologically, erythema dyschromicum perstans may mimic lichen planus pigmentosus (LPP); however, subtle differences exist to distinguish the 2 conditions. Erythema dyschromicum perstans demonstrates a mild lichenoid infiltrate, focal basal vacuolization at the dermoepidermal junction, and melanophage deposition.¹³ In contrast, LPP demonstrates pigmentary incontinence and a more severe inflammatory infiltrate. A perifollicular infiltrate and fibrosis also can be seen in LPP, which may explain the frontal fibrosing alopecia that often precedes LPP.¹³

Addison disease, also known as primary adrenal insufficiency, can cause diffuse hyperpigmentation in the skin, mucosae, and nail beds. The pigmentation is prominent in regions of naturally increased pigmentation, such as the flexural surfaces and intertriginous areas.¹⁴ Patients with adrenal insufficiency will have accompanying weight loss, hypotension, and fatigue, among other symptoms related to deficiency of cortisol and aldosterone. Skin biopsy shows acanthosis, hyperkeratosis, focal parakeratosis, spongiosis, superficial perivascular lymphocytic infiltrate, basal melanin deposition, and superficial dermal macrophages.¹⁵

Confluent and reticulated papillomatosis is an uncommon dermatosis that presents with multiple hyperpigmented macules and papules that coalesce to form patches and plaques centrally with reticulation in the periphery.¹⁶ Confluent and reticulated papillomatosis commonly presents on the upper trunk, axillae, and neck, though involvement can include flexural surfaces as well as the lower trunk and legs.^16,17 Biopsy demonstrates undulating hyperkeratosis, papillomatosis, acanthosis, and negative fungal staining.¹⁶

Pretibial myxedema most commonly is associated with Graves disease and presents as well-defined thickening and induration with overlying pink or purple-brown papules in the pretibial region.¹⁸ An acral surface and mucin deposition within the entire dermis may be appreciated on histology with staining for colloidal iron or Alcian blue.

The Diagnosis: Drug-Induced Hyperpigmentation

Additional history provided by the patient’s caretaker elucidated an extensive list of medications including chlorpromazine and minocycline, among several others. The caretaker revealed that the patient began treatment for acne vulgaris 2 years prior; despite the acne resolving, therapy was not discontinued. The blue-gray and brown pigmentation on our patient’s shins likely was attributed to a medication he was taking.

Both chlorpromazine and minocycline, among many other medications, are known to cause abnormal pigmentation of the skin.¹ Minocycline is a tetracycline antibiotic prescribed for acne and other inflammatory cutaneous conditions. It is highly lipophilic, allowing it to reach high drug concentrations in the skin and nail unit.² Patients taking minocycline long term and at high doses are at greatest risk for pigment deposition.^3,4

Minocycline-induced hyperpigmentation is classified into 3 types. Type I describes blue-black deposition of pigment in acne scars and areas of inflammation, typically on facial skin.^1,5 Histologically, type I stains positive for Perls Prussian blue, indicating an increased deposition of iron as hemosiderin,¹ which likely occurs because minocycline is thought to play a role in defective clearance of hemosiderin from the dermis of injured tissue.⁵ Type II hyperpigmentation presents as bluegray pigment on the lower legs and occasionally the arms.^6,7 Type II stains positive for both Perls Prussian blue and Fontana-Masson, demonstrating hemosiderin and melanin, respectively.⁶ The third form of hyperpigmentation results in diffuse, dark brown to gray pigmentation with a predilection for sun-exposed areas.⁸ Histology of type III shows increased pigment in the basal portion of the epidermis and brown-black pigment in macrophages of the dermis. Type III stains positive for Fontana-Masson and negative for Perls Prussian blue. The etiology of hyperpigmentation has been suspected to be caused by minocycline stimulating melanin production and/or deposition of minocycline-melanin complexes in dermal macrophages after a certain drug level; this largely is seen in patients receiving 100 to 200 mg daily as early as 1 year into treatment.⁸

Chlorpromazine is a typical antipsychotic that causes abnormal skin pigmentation in sun-exposed areas due to increased melanogenesis.⁹ Similar to type III minocyclineinduced hyperpigmentation, a histologic specimen may stain positive for Fontana-Masson yet negative for Perls Prussian blue. Lal et al10 demonstrated complete resolution of abnormal skin pigmentation within 5 years after stopping chlorpromazine. In contrast, minocyclineinduced hyperpigmentation may be permanent in some cases. There is substantial clinical and histologic overlap for drug-induced hyperpigmentation etiologies; it would behoove the clinician to focus on the most common locations affected and the generalized coloration.

Treatment of minocycline-induced hyperpigmentation includes the use of Q-switched lasers, specifically Q-switched ruby and Q-switched alexandrite.¹¹ The use of the Q-switched Nd:YAG laser appears to be ineffective at clearing minocycline-induced pigmentation.^7,11 In our patient, minocycline was discontinued immediately. Due to the patient’s critical condition, he deferred all other therapy. Erythema dyschromicum perstans, also referred to as ashy dermatosis, is an idiopathic form of hyperpigmentation.¹² Lesions start as blue-gray to ashy gray macules, occasionally surrounded by a slightly erythematous, raised border.

Erythema dyschromicum perstans typically presents on the trunk, face, and arms of patients with Fitzpatrick skin types III and IV; it is considered a variant of lichen planus actinicus.¹² Histologically, erythema dyschromicum perstans may mimic lichen planus pigmentosus (LPP); however, subtle differences exist to distinguish the 2 conditions. Erythema dyschromicum perstans demonstrates a mild lichenoid infiltrate, focal basal vacuolization at the dermoepidermal junction, and melanophage deposition.¹³ In contrast, LPP demonstrates pigmentary incontinence and a more severe inflammatory infiltrate. A perifollicular infiltrate and fibrosis also can be seen in LPP, which may explain the frontal fibrosing alopecia that often precedes LPP.¹³

Addison disease, also known as primary adrenal insufficiency, can cause diffuse hyperpigmentation in the skin, mucosae, and nail beds. The pigmentation is prominent in regions of naturally increased pigmentation, such as the flexural surfaces and intertriginous areas.¹⁴ Patients with adrenal insufficiency will have accompanying weight loss, hypotension, and fatigue, among other symptoms related to deficiency of cortisol and aldosterone. Skin biopsy shows acanthosis, hyperkeratosis, focal parakeratosis, spongiosis, superficial perivascular lymphocytic infiltrate, basal melanin deposition, and superficial dermal macrophages.¹⁵

Confluent and reticulated papillomatosis is an uncommon dermatosis that presents with multiple hyperpigmented macules and papules that coalesce to form patches and plaques centrally with reticulation in the periphery.¹⁶ Confluent and reticulated papillomatosis commonly presents on the upper trunk, axillae, and neck, though involvement can include flexural surfaces as well as the lower trunk and legs.^16,17 Biopsy demonstrates undulating hyperkeratosis, papillomatosis, acanthosis, and negative fungal staining.¹⁶

Pretibial myxedema most commonly is associated with Graves disease and presents as well-defined thickening and induration with overlying pink or purple-brown papules in the pretibial region.¹⁸ An acral surface and mucin deposition within the entire dermis may be appreciated on histology with staining for colloidal iron or Alcian blue.

Nevus sebaceus (NS) is a benign hair follicle neoplasm present in approximately 1.3% of the population, typically involving the scalp, neck, or face.¹ These lesions usually are present at birth or identified soon after, during the first year. They present as a yellowish hairless patch or plaque but can develop a more papillomatous appearance, especially after puberty. Historically, the concern with NS was its tendency to transform into basal cell carcinoma (BCC), which prompted surgical excision of the lesion during childhood. This theory has been discounted more recently, as further research has suggested that what was once thought to be BCC may have been confused with the similarly appearing trichoblastoma; however, malignant transformation of NS does still occur, with BCC still being the most common.² We present the case of a long-standing NS with rare transformation to apocrine carcinoma.

Case Report

A 76-year-old woman presented with several new lesions within a previously diagnosed NS. She reported having the large plaque for as long as she could recall but reported that several new growths developed within the plaque over the last 2 months, slowly increasing in size. She reported a prior biopsy within the growth several years prior, which she described as an irritated seborrheic keratosis.

Physical examination demonstrated 4 distinct lesions within the flesh-colored, verrucous plaque located on the left side of the temporal scalp (Figure 1). The first lesion was a 2.5-cm pearly, pink, exophytic tumor (labeled as A in Figure 1). The next 2 lesions were brown, pedunculated, verrucous papules (labeled as B and C in Figure 1). The last lesion was a purple papule (labeled as D in Figure 1). Four shave biopsies were performed for histologic analysis of the lesions. Lesions B, C, and D were consistent with trichoblastomas, as pathology showed basaloid epithelial tumors that displayed primitive follicular structures, areas of stromal induction, and some pigmentation. Lesion A, originally thought to be suspicious for a BCC, was determined to be a primary cutaneous apocrine adenocarcinoma upon pathologic review. The pathology showed a dermal tumor displaying solid and tubular areas with decapitation secretion. Nuclear pleomorphism and mitoses were present (Figure 2), and staining for carcinoembryonic antigen was positive (Figure 3). Immunoreactivity with epithelial membrane antigen and cytokeratin 7 was noted as well as focal positivity for mammaglobin. Primary apocrine carcinoma was favored over metastatic carcinoma due to the location of the lesion within an NS along with a negative history of internal malignancy. Dermatopathology recommended complete removal of all lesions within the NS.

Comment

Presentation
Nevus sebaceus is the most common adnexal tumor and is classified as a benign congenital hair follicle tumor that is located most commonly on the scalp but also occurs on the face and neck.¹ The lesions usually are present at birth but also can develop during the first year of life.² Diagnosis may be later, during adolescence, when patients seek medical attention during the lesion’s rapid growth phase.¹ Nevus sebaceus also is known as an organoid nevus because it may contain all components of the skin. It was originally identified by Jadassohn in 1895.³ It presents as a yellowish, smooth, hairless patch or plaque in prepubertal patients. During adolescence, the lesion typically becomes more yellowish, as well as papillomatous, scaly, or warty. The reported incidence of NS is 0.05% to 1% in dermatology patients.²

Differential
Nevus sebaceus also is a component of several syndromes that should be kept in mind, including Schimmelpenning-Feuerstein-Mims syndrome, which presents with neurologic, skeletal, genitourinary, cardiovascular, and ophthalmic disorders, in addition to cutaneous features. Others include phacomatosis pigmentokeratotica, didmyosis aplasticosebacea, SCALP syndrome (sebaceus nevus, central nervous system malformations, aplasia cutis congenita, limbal dermoid, and pigmented nevus), and more.^4,5

Etiology
The etiology of NS has not been completely determined. One study that evaluated 44 NS tissue samples suggested the presence of human papillomavirus (HPV) in NS formation, finding that 82% of NS lesions studied contained HPV DNA. From these results, Carlson et al⁶ suggested a possible maternal transmission of HPV and infection of ectodermal cells as a potential cause of NS; however, this hypothesis was soon challenged by a study that showed a complete absence of HPV in 16 samples via histological evaluation and polymerase chain reaction for a broad range of HPV types.⁷ There were investigations into a patched (PTCH) deletion as the cause of NS and thus explained the historically high rate of secondary BCC.⁸ Further studies showed no mutations at the PTCH locus in trichoblastomas or other tumors arising from NS.^9,10

More recent studies have recognized HRAS and KRAS mutations as a causative factor in NS.¹¹ Nevus sebaceus belongs to a group of syndromes resulting from lethal mutations that survive via mosaicism. Nevus sebaceus is caused by postzygotic HRAS or KRAS mutations and is known as a mosaic RASopathy.¹² In fact, there is growing evidence to suggest that other nevoid proliferations including keratinocytic epidermal nevi and melanocytic nevi also fall into the spectrum of mosaic RASopathies.¹³

Staging
There are 3 clinical stages of NS, originally described by Mehregan and Pinkus.¹⁴ In stage I (historically known as the infantile stage), the lesion presents as a yellow to pink, smooth, hairless patch. Histologic features include immature hair follicles and hypoplastic sebaceous glands. In stage II (also known as the puberty stage), the lesion becomes more pronounced. Firmer plaques can develop with hyperkeratosis. Hormonal changes cause sebaceous glands to develop, accompanied by epidermal hyperplasia and maturation of apocrine glands. Stage III (the tumoral stage) is a period that various neoplasms have the highest likelihood of occurring. Nevus sebaceus in an adolescent or adult demonstrates mature adnexal structures and greater epidermal hyperplasia.^2,4,15

Malignancy
By virtue of these stages of NS development, malignant transformation is expected most often during stage III. However, cases have been reported of malignant tumor development in NS in children before puberty. Two case reports described a 7-year-old boy and a 10-year-old boy diagnosed with a BCC arising from an NS.^16,17 However, secondary BCC formation before 16 years of age is rare. Basal cell carcinoma arising from an NS has been commonly reported and is the most common malignant neoplasm in NS (1.1%).^2,3 However, the most common neoplasm overall is trichoblastoma (7.4%). The second most common tumor was syringocystadenoma papilliferum, occurring in approximately 5.2% of NS cases. The neoplasm rate in NS was found to be proportional to the patient age.^2,18 Multiple studies have shown the overall rate of secondary neoplasms in NS to be 13% to 21.4%, with malignant tumors composing 0.8% to 2.5%.^2,15,19 Other neoplasms that have been reported include keratoacanthoma, trichilemmoma, sebaceoma, nevocellular nevus, squamous cell carcinoma, adnexal carcinoma, apocrine adenocarcinoma, and malignant melanoma.^19-21

It is argued that the reported rate of BCC formation is overestimated, as prior studies incorrectly labeled trichoblastomas as BCCs. In fact, the largest studies of NS from the 1990s revealed lower rates of malignant secondary tumors than previously determined.⁴

The identification of apocrine adenocarcinoma tumors arising from NS is exceedingly rare. A study performed by Cribier et al¹⁹ in 2000 retrospectively analyzed 596 cases of excised NS from 1932 to 1998. No apocrine carcinomas were reported in this study.¹⁹ Approximately 12 cases have been previously reported throughout the literature.^20-26 Apocrine carcinomas occur most frequently in apocrine-rich areas such as the axillae, external ears, eyelids, and anogenital area. However, in the cases with apocrine carcinomas that developed from NS, the carcinomas have been located almost exclusively on the scalp.²³

Histopathology
Histopathologic examination reveals considerable variation in morphology, and an underlying pattern has been difficult to recognize. Unfortunately, some authors have concluded that the diagnosis of apocrine carcinoma is relatively subjective.²⁶ Robson et al²⁶ identified 3 general architectural patterns: tubular, tubulopapillary, and solid. Tubular structures consisted of glands and ducts lined by a single or multilayered epithelium. Tubulopapillary architecture was characterized by epithelium forming papillary folds without a fibrovascular core. The solid morphology showed sheets of cells with limited ductal or tubular formation.²⁶ The most specific criteria of these apocrine carcinomas are identification of decapitation secretion, periodic acid–Schiff–positive diastase-resistant material present in the cells or lumen, and positive immunostaining for gross cystic disease fluid protein-15.²⁷

Robson et al²⁶ reported estrogen receptor positivity and androgen receptor positivity in 62% and 64% of 24 primary apocrine carcinoma cases, respectively. However, whether these markers are as common in NS-related apocrine carcinomas has yet to be noted in the literature. One study reports a case of apocrine carcinoma from NS with positive staining for human epidermal growth factor-2, a cell membrane receptor tyrosine kinase commonly investigated in breast cancers and extramammary Paget disease.²²

These apocrine carcinomas do have the potential for lymphatic metastasis, as seen with multiple studies. Domingo and Helwig²¹ identified regional lymph node metastasis in 2 of its 4 apocrine carcinoma patients. Robson et al²⁶ reported lymphovascular invasion in 4 cases and perineural invasion in 2 of 24 patients studied. However, even in the context of recurrence and regional metastasis, the prognosis was good and seldom fatal.²⁶

Treatment
The most effective treatment of NS is excision of dermal and epidermal components. Excision should be completed with a minimum of 2- to 3-mm margins and full thickness down to the underlying supporting fat.²⁸ Historically, the practice of prophylactic excision of NS was supported by the potential for malignant transformation; however, early excision of NS may be less reasonable in light of these more recent studies showing lower incidence of BCC (0.8%), replaced by benign trichoblastomas.¹⁹ In the case of apocrine carcinoma development, excision is undoubtedly recommended, with unclear recommendations regarding further evaluation for metastasis.

Excision also may be favored for cosmetic purposes, given the visible regions where NS tends to develop. Chepla and Gosain²⁹ argued that surgical intervention should be based on other factors such as location on the scalp, alopecia, and other issues affecting appearance and monitoring rather than incidence of malignant transformation. Close monitoring and biopsy of suspicious areas is a more conservative option.

Other therapies include CO₂ laser, as demonstrated by Kiedrowicz et al,³⁰ on linear NS in a patient with Schimmelpenning-Feuerstein-Mims syndrome.³¹ However, this approach is palliative and not effective in removing the entire lesion. Electrodesiccation and curettage and dermabrasion also are not good options for the same reason.⁴

Occurrence in Children
Nevus sebaceus in children, accompanied by other findings suggestive of epidermal nevus syndromes, should prompt further investigation. Schimmelpenning-Feuerstein-Mims syndrome includes major neurological abnormalities including hemimegalencephaly and seizures.³²

Conclusion

Apocrine carcinomas are malignant neoplasms that may rarely arise within an NS. Their clinical identification is difficult and requires histopathologic evaluation. Upon recognition, prompt excision with tumor-free margins is recommended. As a rare entity, little data is available regarding its metastatic potential or overall survival rates. Further investigation is clearly necessary as new cases arise.

Nevus sebaceus (NS) is a benign hair follicle neoplasm present in approximately 1.3% of the population, typically involving the scalp, neck, or face.¹ These lesions usually are present at birth or identified soon after, during the first year. They present as a yellowish hairless patch or plaque but can develop a more papillomatous appearance, especially after puberty. Historically, the concern with NS was its tendency to transform into basal cell carcinoma (BCC), which prompted surgical excision of the lesion during childhood. This theory has been discounted more recently, as further research has suggested that what was once thought to be BCC may have been confused with the similarly appearing trichoblastoma; however, malignant transformation of NS does still occur, with BCC still being the most common.² We present the case of a long-standing NS with rare transformation to apocrine carcinoma.

Case Report

A 76-year-old woman presented with several new lesions within a previously diagnosed NS. She reported having the large plaque for as long as she could recall but reported that several new growths developed within the plaque over the last 2 months, slowly increasing in size. She reported a prior biopsy within the growth several years prior, which she described as an irritated seborrheic keratosis.

Physical examination demonstrated 4 distinct lesions within the flesh-colored, verrucous plaque located on the left side of the temporal scalp (Figure 1). The first lesion was a 2.5-cm pearly, pink, exophytic tumor (labeled as A in Figure 1). The next 2 lesions were brown, pedunculated, verrucous papules (labeled as B and C in Figure 1). The last lesion was a purple papule (labeled as D in Figure 1). Four shave biopsies were performed for histologic analysis of the lesions. Lesions B, C, and D were consistent with trichoblastomas, as pathology showed basaloid epithelial tumors that displayed primitive follicular structures, areas of stromal induction, and some pigmentation. Lesion A, originally thought to be suspicious for a BCC, was determined to be a primary cutaneous apocrine adenocarcinoma upon pathologic review. The pathology showed a dermal tumor displaying solid and tubular areas with decapitation secretion. Nuclear pleomorphism and mitoses were present (Figure 2), and staining for carcinoembryonic antigen was positive (Figure 3). Immunoreactivity with epithelial membrane antigen and cytokeratin 7 was noted as well as focal positivity for mammaglobin. Primary apocrine carcinoma was favored over metastatic carcinoma due to the location of the lesion within an NS along with a negative history of internal malignancy. Dermatopathology recommended complete removal of all lesions within the NS.

Comment

Presentation
Nevus sebaceus is the most common adnexal tumor and is classified as a benign congenital hair follicle tumor that is located most commonly on the scalp but also occurs on the face and neck.¹ The lesions usually are present at birth but also can develop during the first year of life.² Diagnosis may be later, during adolescence, when patients seek medical attention during the lesion’s rapid growth phase.¹ Nevus sebaceus also is known as an organoid nevus because it may contain all components of the skin. It was originally identified by Jadassohn in 1895.³ It presents as a yellowish, smooth, hairless patch or plaque in prepubertal patients. During adolescence, the lesion typically becomes more yellowish, as well as papillomatous, scaly, or warty. The reported incidence of NS is 0.05% to 1% in dermatology patients.²

Differential
Nevus sebaceus also is a component of several syndromes that should be kept in mind, including Schimmelpenning-Feuerstein-Mims syndrome, which presents with neurologic, skeletal, genitourinary, cardiovascular, and ophthalmic disorders, in addition to cutaneous features. Others include phacomatosis pigmentokeratotica, didmyosis aplasticosebacea, SCALP syndrome (sebaceus nevus, central nervous system malformations, aplasia cutis congenita, limbal dermoid, and pigmented nevus), and more.^4,5

Etiology
The etiology of NS has not been completely determined. One study that evaluated 44 NS tissue samples suggested the presence of human papillomavirus (HPV) in NS formation, finding that 82% of NS lesions studied contained HPV DNA. From these results, Carlson et al⁶ suggested a possible maternal transmission of HPV and infection of ectodermal cells as a potential cause of NS; however, this hypothesis was soon challenged by a study that showed a complete absence of HPV in 16 samples via histological evaluation and polymerase chain reaction for a broad range of HPV types.⁷ There were investigations into a patched (PTCH) deletion as the cause of NS and thus explained the historically high rate of secondary BCC.⁸ Further studies showed no mutations at the PTCH locus in trichoblastomas or other tumors arising from NS.^9,10

More recent studies have recognized HRAS and KRAS mutations as a causative factor in NS.¹¹ Nevus sebaceus belongs to a group of syndromes resulting from lethal mutations that survive via mosaicism. Nevus sebaceus is caused by postzygotic HRAS or KRAS mutations and is known as a mosaic RASopathy.¹² In fact, there is growing evidence to suggest that other nevoid proliferations including keratinocytic epidermal nevi and melanocytic nevi also fall into the spectrum of mosaic RASopathies.¹³

Staging
There are 3 clinical stages of NS, originally described by Mehregan and Pinkus.¹⁴ In stage I (historically known as the infantile stage), the lesion presents as a yellow to pink, smooth, hairless patch. Histologic features include immature hair follicles and hypoplastic sebaceous glands. In stage II (also known as the puberty stage), the lesion becomes more pronounced. Firmer plaques can develop with hyperkeratosis. Hormonal changes cause sebaceous glands to develop, accompanied by epidermal hyperplasia and maturation of apocrine glands. Stage III (the tumoral stage) is a period that various neoplasms have the highest likelihood of occurring. Nevus sebaceus in an adolescent or adult demonstrates mature adnexal structures and greater epidermal hyperplasia.^2,4,15

Malignancy
By virtue of these stages of NS development, malignant transformation is expected most often during stage III. However, cases have been reported of malignant tumor development in NS in children before puberty. Two case reports described a 7-year-old boy and a 10-year-old boy diagnosed with a BCC arising from an NS.^16,17 However, secondary BCC formation before 16 years of age is rare. Basal cell carcinoma arising from an NS has been commonly reported and is the most common malignant neoplasm in NS (1.1%).^2,3 However, the most common neoplasm overall is trichoblastoma (7.4%). The second most common tumor was syringocystadenoma papilliferum, occurring in approximately 5.2% of NS cases. The neoplasm rate in NS was found to be proportional to the patient age.^2,18 Multiple studies have shown the overall rate of secondary neoplasms in NS to be 13% to 21.4%, with malignant tumors composing 0.8% to 2.5%.^2,15,19 Other neoplasms that have been reported include keratoacanthoma, trichilemmoma, sebaceoma, nevocellular nevus, squamous cell carcinoma, adnexal carcinoma, apocrine adenocarcinoma, and malignant melanoma.^19-21

It is argued that the reported rate of BCC formation is overestimated, as prior studies incorrectly labeled trichoblastomas as BCCs. In fact, the largest studies of NS from the 1990s revealed lower rates of malignant secondary tumors than previously determined.⁴

The identification of apocrine adenocarcinoma tumors arising from NS is exceedingly rare. A study performed by Cribier et al¹⁹ in 2000 retrospectively analyzed 596 cases of excised NS from 1932 to 1998. No apocrine carcinomas were reported in this study.¹⁹ Approximately 12 cases have been previously reported throughout the literature.^20-26 Apocrine carcinomas occur most frequently in apocrine-rich areas such as the axillae, external ears, eyelids, and anogenital area. However, in the cases with apocrine carcinomas that developed from NS, the carcinomas have been located almost exclusively on the scalp.²³

Histopathology
Histopathologic examination reveals considerable variation in morphology, and an underlying pattern has been difficult to recognize. Unfortunately, some authors have concluded that the diagnosis of apocrine carcinoma is relatively subjective.²⁶ Robson et al²⁶ identified 3 general architectural patterns: tubular, tubulopapillary, and solid. Tubular structures consisted of glands and ducts lined by a single or multilayered epithelium. Tubulopapillary architecture was characterized by epithelium forming papillary folds without a fibrovascular core. The solid morphology showed sheets of cells with limited ductal or tubular formation.²⁶ The most specific criteria of these apocrine carcinomas are identification of decapitation secretion, periodic acid–Schiff–positive diastase-resistant material present in the cells or lumen, and positive immunostaining for gross cystic disease fluid protein-15.²⁷

Robson et al²⁶ reported estrogen receptor positivity and androgen receptor positivity in 62% and 64% of 24 primary apocrine carcinoma cases, respectively. However, whether these markers are as common in NS-related apocrine carcinomas has yet to be noted in the literature. One study reports a case of apocrine carcinoma from NS with positive staining for human epidermal growth factor-2, a cell membrane receptor tyrosine kinase commonly investigated in breast cancers and extramammary Paget disease.²²

These apocrine carcinomas do have the potential for lymphatic metastasis, as seen with multiple studies. Domingo and Helwig²¹ identified regional lymph node metastasis in 2 of its 4 apocrine carcinoma patients. Robson et al²⁶ reported lymphovascular invasion in 4 cases and perineural invasion in 2 of 24 patients studied. However, even in the context of recurrence and regional metastasis, the prognosis was good and seldom fatal.²⁶

Treatment
The most effective treatment of NS is excision of dermal and epidermal components. Excision should be completed with a minimum of 2- to 3-mm margins and full thickness down to the underlying supporting fat.²⁸ Historically, the practice of prophylactic excision of NS was supported by the potential for malignant transformation; however, early excision of NS may be less reasonable in light of these more recent studies showing lower incidence of BCC (0.8%), replaced by benign trichoblastomas.¹⁹ In the case of apocrine carcinoma development, excision is undoubtedly recommended, with unclear recommendations regarding further evaluation for metastasis.

Excision also may be favored for cosmetic purposes, given the visible regions where NS tends to develop. Chepla and Gosain²⁹ argued that surgical intervention should be based on other factors such as location on the scalp, alopecia, and other issues affecting appearance and monitoring rather than incidence of malignant transformation. Close monitoring and biopsy of suspicious areas is a more conservative option.

Other therapies include CO₂ laser, as demonstrated by Kiedrowicz et al,³⁰ on linear NS in a patient with Schimmelpenning-Feuerstein-Mims syndrome.³¹ However, this approach is palliative and not effective in removing the entire lesion. Electrodesiccation and curettage and dermabrasion also are not good options for the same reason.⁴

Occurrence in Children
Nevus sebaceus in children, accompanied by other findings suggestive of epidermal nevus syndromes, should prompt further investigation. Schimmelpenning-Feuerstein-Mims syndrome includes major neurological abnormalities including hemimegalencephaly and seizures.³²

Conclusion

Apocrine carcinomas are malignant neoplasms that may rarely arise within an NS. Their clinical identification is difficult and requires histopathologic evaluation. Upon recognition, prompt excision with tumor-free margins is recommended. As a rare entity, little data is available regarding its metastatic potential or overall survival rates. Further investigation is clearly necessary as new cases arise.

Nevus sebaceus (NS) is a benign hair follicle neoplasm present in approximately 1.3% of the population, typically involving the scalp, neck, or face.¹ These lesions usually are present at birth or identified soon after, during the first year. They present as a yellowish hairless patch or plaque but can develop a more papillomatous appearance, especially after puberty. Historically, the concern with NS was its tendency to transform into basal cell carcinoma (BCC), which prompted surgical excision of the lesion during childhood. This theory has been discounted more recently, as further research has suggested that what was once thought to be BCC may have been confused with the similarly appearing trichoblastoma; however, malignant transformation of NS does still occur, with BCC still being the most common.² We present the case of a long-standing NS with rare transformation to apocrine carcinoma.

Case Report

A 76-year-old woman presented with several new lesions within a previously diagnosed NS. She reported having the large plaque for as long as she could recall but reported that several new growths developed within the plaque over the last 2 months, slowly increasing in size. She reported a prior biopsy within the growth several years prior, which she described as an irritated seborrheic keratosis.

Physical examination demonstrated 4 distinct lesions within the flesh-colored, verrucous plaque located on the left side of the temporal scalp (Figure 1). The first lesion was a 2.5-cm pearly, pink, exophytic tumor (labeled as A in Figure 1). The next 2 lesions were brown, pedunculated, verrucous papules (labeled as B and C in Figure 1). The last lesion was a purple papule (labeled as D in Figure 1). Four shave biopsies were performed for histologic analysis of the lesions. Lesions B, C, and D were consistent with trichoblastomas, as pathology showed basaloid epithelial tumors that displayed primitive follicular structures, areas of stromal induction, and some pigmentation. Lesion A, originally thought to be suspicious for a BCC, was determined to be a primary cutaneous apocrine adenocarcinoma upon pathologic review. The pathology showed a dermal tumor displaying solid and tubular areas with decapitation secretion. Nuclear pleomorphism and mitoses were present (Figure 2), and staining for carcinoembryonic antigen was positive (Figure 3). Immunoreactivity with epithelial membrane antigen and cytokeratin 7 was noted as well as focal positivity for mammaglobin. Primary apocrine carcinoma was favored over metastatic carcinoma due to the location of the lesion within an NS along with a negative history of internal malignancy. Dermatopathology recommended complete removal of all lesions within the NS.

Comment

Presentation
Nevus sebaceus is the most common adnexal tumor and is classified as a benign congenital hair follicle tumor that is located most commonly on the scalp but also occurs on the face and neck.¹ The lesions usually are present at birth but also can develop during the first year of life.² Diagnosis may be later, during adolescence, when patients seek medical attention during the lesion’s rapid growth phase.¹ Nevus sebaceus also is known as an organoid nevus because it may contain all components of the skin. It was originally identified by Jadassohn in 1895.³ It presents as a yellowish, smooth, hairless patch or plaque in prepubertal patients. During adolescence, the lesion typically becomes more yellowish, as well as papillomatous, scaly, or warty. The reported incidence of NS is 0.05% to 1% in dermatology patients.²

Differential
Nevus sebaceus also is a component of several syndromes that should be kept in mind, including Schimmelpenning-Feuerstein-Mims syndrome, which presents with neurologic, skeletal, genitourinary, cardiovascular, and ophthalmic disorders, in addition to cutaneous features. Others include phacomatosis pigmentokeratotica, didmyosis aplasticosebacea, SCALP syndrome (sebaceus nevus, central nervous system malformations, aplasia cutis congenita, limbal dermoid, and pigmented nevus), and more.^4,5

Etiology
The etiology of NS has not been completely determined. One study that evaluated 44 NS tissue samples suggested the presence of human papillomavirus (HPV) in NS formation, finding that 82% of NS lesions studied contained HPV DNA. From these results, Carlson et al⁶ suggested a possible maternal transmission of HPV and infection of ectodermal cells as a potential cause of NS; however, this hypothesis was soon challenged by a study that showed a complete absence of HPV in 16 samples via histological evaluation and polymerase chain reaction for a broad range of HPV types.⁷ There were investigations into a patched (PTCH) deletion as the cause of NS and thus explained the historically high rate of secondary BCC.⁸ Further studies showed no mutations at the PTCH locus in trichoblastomas or other tumors arising from NS.^9,10

More recent studies have recognized HRAS and KRAS mutations as a causative factor in NS.¹¹ Nevus sebaceus belongs to a group of syndromes resulting from lethal mutations that survive via mosaicism. Nevus sebaceus is caused by postzygotic HRAS or KRAS mutations and is known as a mosaic RASopathy.¹² In fact, there is growing evidence to suggest that other nevoid proliferations including keratinocytic epidermal nevi and melanocytic nevi also fall into the spectrum of mosaic RASopathies.¹³

Staging
There are 3 clinical stages of NS, originally described by Mehregan and Pinkus.¹⁴ In stage I (historically known as the infantile stage), the lesion presents as a yellow to pink, smooth, hairless patch. Histologic features include immature hair follicles and hypoplastic sebaceous glands. In stage II (also known as the puberty stage), the lesion becomes more pronounced. Firmer plaques can develop with hyperkeratosis. Hormonal changes cause sebaceous glands to develop, accompanied by epidermal hyperplasia and maturation of apocrine glands. Stage III (the tumoral stage) is a period that various neoplasms have the highest likelihood of occurring. Nevus sebaceus in an adolescent or adult demonstrates mature adnexal structures and greater epidermal hyperplasia.^2,4,15

Malignancy
By virtue of these stages of NS development, malignant transformation is expected most often during stage III. However, cases have been reported of malignant tumor development in NS in children before puberty. Two case reports described a 7-year-old boy and a 10-year-old boy diagnosed with a BCC arising from an NS.^16,17 However, secondary BCC formation before 16 years of age is rare. Basal cell carcinoma arising from an NS has been commonly reported and is the most common malignant neoplasm in NS (1.1%).^2,3 However, the most common neoplasm overall is trichoblastoma (7.4%). The second most common tumor was syringocystadenoma papilliferum, occurring in approximately 5.2% of NS cases. The neoplasm rate in NS was found to be proportional to the patient age.^2,18 Multiple studies have shown the overall rate of secondary neoplasms in NS to be 13% to 21.4%, with malignant tumors composing 0.8% to 2.5%.^2,15,19 Other neoplasms that have been reported include keratoacanthoma, trichilemmoma, sebaceoma, nevocellular nevus, squamous cell carcinoma, adnexal carcinoma, apocrine adenocarcinoma, and malignant melanoma.^19-21

It is argued that the reported rate of BCC formation is overestimated, as prior studies incorrectly labeled trichoblastomas as BCCs. In fact, the largest studies of NS from the 1990s revealed lower rates of malignant secondary tumors than previously determined.⁴

The identification of apocrine adenocarcinoma tumors arising from NS is exceedingly rare. A study performed by Cribier et al¹⁹ in 2000 retrospectively analyzed 596 cases of excised NS from 1932 to 1998. No apocrine carcinomas were reported in this study.¹⁹ Approximately 12 cases have been previously reported throughout the literature.^20-26 Apocrine carcinomas occur most frequently in apocrine-rich areas such as the axillae, external ears, eyelids, and anogenital area. However, in the cases with apocrine carcinomas that developed from NS, the carcinomas have been located almost exclusively on the scalp.²³

Histopathology
Histopathologic examination reveals considerable variation in morphology, and an underlying pattern has been difficult to recognize. Unfortunately, some authors have concluded that the diagnosis of apocrine carcinoma is relatively subjective.²⁶ Robson et al²⁶ identified 3 general architectural patterns: tubular, tubulopapillary, and solid. Tubular structures consisted of glands and ducts lined by a single or multilayered epithelium. Tubulopapillary architecture was characterized by epithelium forming papillary folds without a fibrovascular core. The solid morphology showed sheets of cells with limited ductal or tubular formation.²⁶ The most specific criteria of these apocrine carcinomas are identification of decapitation secretion, periodic acid–Schiff–positive diastase-resistant material present in the cells or lumen, and positive immunostaining for gross cystic disease fluid protein-15.²⁷

Robson et al²⁶ reported estrogen receptor positivity and androgen receptor positivity in 62% and 64% of 24 primary apocrine carcinoma cases, respectively. However, whether these markers are as common in NS-related apocrine carcinomas has yet to be noted in the literature. One study reports a case of apocrine carcinoma from NS with positive staining for human epidermal growth factor-2, a cell membrane receptor tyrosine kinase commonly investigated in breast cancers and extramammary Paget disease.²²

These apocrine carcinomas do have the potential for lymphatic metastasis, as seen with multiple studies. Domingo and Helwig²¹ identified regional lymph node metastasis in 2 of its 4 apocrine carcinoma patients. Robson et al²⁶ reported lymphovascular invasion in 4 cases and perineural invasion in 2 of 24 patients studied. However, even in the context of recurrence and regional metastasis, the prognosis was good and seldom fatal.²⁶

Treatment
The most effective treatment of NS is excision of dermal and epidermal components. Excision should be completed with a minimum of 2- to 3-mm margins and full thickness down to the underlying supporting fat.²⁸ Historically, the practice of prophylactic excision of NS was supported by the potential for malignant transformation; however, early excision of NS may be less reasonable in light of these more recent studies showing lower incidence of BCC (0.8%), replaced by benign trichoblastomas.¹⁹ In the case of apocrine carcinoma development, excision is undoubtedly recommended, with unclear recommendations regarding further evaluation for metastasis.

Excision also may be favored for cosmetic purposes, given the visible regions where NS tends to develop. Chepla and Gosain²⁹ argued that surgical intervention should be based on other factors such as location on the scalp, alopecia, and other issues affecting appearance and monitoring rather than incidence of malignant transformation. Close monitoring and biopsy of suspicious areas is a more conservative option.

Other therapies include CO₂ laser, as demonstrated by Kiedrowicz et al,³⁰ on linear NS in a patient with Schimmelpenning-Feuerstein-Mims syndrome.³¹ However, this approach is palliative and not effective in removing the entire lesion. Electrodesiccation and curettage and dermabrasion also are not good options for the same reason.⁴

Occurrence in Children
Nevus sebaceus in children, accompanied by other findings suggestive of epidermal nevus syndromes, should prompt further investigation. Schimmelpenning-Feuerstein-Mims syndrome includes major neurological abnormalities including hemimegalencephaly and seizures.³²

Conclusion

Apocrine carcinomas are malignant neoplasms that may rarely arise within an NS. Their clinical identification is difficult and requires histopathologic evaluation. Upon recognition, prompt excision with tumor-free margins is recommended. As a rare entity, little data is available regarding its metastatic potential or overall survival rates. Further investigation is clearly necessary as new cases arise.