Adam I. Rubin, MD

The Diagnosis: Blaschkoid Graft-vs-host Disease

The patient had a history of myelodysplastic syndrome and underwent a bone marrow transplant 1 year prior to presentation. She had acute graft-vs-host disease (GVHD) 6 weeks following the transplant, which resolved with high-dose prednisone followed by UVB phototherapy. Skin biopsy demonstrated lichenoid dermatitis with vacuolar degeneration, dyskeratosis, and prominent pigment incontinence (Figure). Based on these findings and her clinical presentation, a diagnosis of blaschkoid GVHD was made.

Although acute GVHD is the result of immunocompetent donor T cells recognizing host tissues as foreign and initiating an immune response, the pathophysiology of chronic GVHD is not well understood.^1,2 Theories for disease pathogenesis in chronic GVHD suggest an underlying autoimmune and/or alloreactive process.^2-5 The skin often is the first organ affected in acute GVHD, and patients generally present with a pruritic morbilliform eruption that begins on the trunk and spreads to the rest of the body.^1,2 Cutaneous manifestations of chronic GVHD may be protean. Lesions can resemble systemic sclerosis or morphea, lichen planus, psoriasis, ichthyosis, and many other conditions.²

The differential diagnosis of linear dermatoses includes herpes zoster, contact dermatitis, lichen striatus (blaschkitis), nevus unius lateris, inflammatory linear verrucous epidermal nevus, and incontinentia pigmenti.^6,7 Lichen planus-like chronic GVHD occurring in a linear distribution has been described.^6-14 Distinction between dermatomal and blaschkoid processes is diagnostically important. In the case of GVHD, dermatomal distribution may suggest an association between GVHD and prior herpes simplex virus or varicella-zoster virus infection.^6,8 Herpesvirus may alter surface antigens of keratinocytes, rendering them targets of donor lymphocytes, and antibodies to viral particles may cross-react with host keratinocyte HLA antigens. It also is possible that dermatomal GVHD may simply be a type of isomorphic response (Köbner phenomenon).⁸

When cutaneous GVHD follows Blaschko lines, other mechanisms appear to be at play.^9-14 It is plausible that these patients have an underlying genetic mosaicism, perhaps the result of a postzygotic mutation, that results in a daughter cell population that expresses surface antigens different from those of the primary cell population found elsewhere in the skin. Donor lymphocytes may selectively react to this mosaic population, leading to the clinical picture of chronic GVHD oriented along Blaschko lines.^10,11,13,14 

In conclusion, lichenoid linear GVHD following Blaschko lines is an uncommon presentation of chronic GVHD that highlights the heterogeneity of this disease and should be considered in the appropriate clinical setting.

The Diagnosis: Blaschkoid Graft-vs-host Disease

The patient had a history of myelodysplastic syndrome and underwent a bone marrow transplant 1 year prior to presentation. She had acute graft-vs-host disease (GVHD) 6 weeks following the transplant, which resolved with high-dose prednisone followed by UVB phototherapy. Skin biopsy demonstrated lichenoid dermatitis with vacuolar degeneration, dyskeratosis, and prominent pigment incontinence (Figure). Based on these findings and her clinical presentation, a diagnosis of blaschkoid GVHD was made.

Although acute GVHD is the result of immunocompetent donor T cells recognizing host tissues as foreign and initiating an immune response, the pathophysiology of chronic GVHD is not well understood.^1,2 Theories for disease pathogenesis in chronic GVHD suggest an underlying autoimmune and/or alloreactive process.^2-5 The skin often is the first organ affected in acute GVHD, and patients generally present with a pruritic morbilliform eruption that begins on the trunk and spreads to the rest of the body.^1,2 Cutaneous manifestations of chronic GVHD may be protean. Lesions can resemble systemic sclerosis or morphea, lichen planus, psoriasis, ichthyosis, and many other conditions.²

The differential diagnosis of linear dermatoses includes herpes zoster, contact dermatitis, lichen striatus (blaschkitis), nevus unius lateris, inflammatory linear verrucous epidermal nevus, and incontinentia pigmenti.^6,7 Lichen planus-like chronic GVHD occurring in a linear distribution has been described.^6-14 Distinction between dermatomal and blaschkoid processes is diagnostically important. In the case of GVHD, dermatomal distribution may suggest an association between GVHD and prior herpes simplex virus or varicella-zoster virus infection.^6,8 Herpesvirus may alter surface antigens of keratinocytes, rendering them targets of donor lymphocytes, and antibodies to viral particles may cross-react with host keratinocyte HLA antigens. It also is possible that dermatomal GVHD may simply be a type of isomorphic response (Köbner phenomenon).⁸

When cutaneous GVHD follows Blaschko lines, other mechanisms appear to be at play.^9-14 It is plausible that these patients have an underlying genetic mosaicism, perhaps the result of a postzygotic mutation, that results in a daughter cell population that expresses surface antigens different from those of the primary cell population found elsewhere in the skin. Donor lymphocytes may selectively react to this mosaic population, leading to the clinical picture of chronic GVHD oriented along Blaschko lines.^10,11,13,14 

In conclusion, lichenoid linear GVHD following Blaschko lines is an uncommon presentation of chronic GVHD that highlights the heterogeneity of this disease and should be considered in the appropriate clinical setting.

The Diagnosis: Blaschkoid Graft-vs-host Disease

The patient had a history of myelodysplastic syndrome and underwent a bone marrow transplant 1 year prior to presentation. She had acute graft-vs-host disease (GVHD) 6 weeks following the transplant, which resolved with high-dose prednisone followed by UVB phototherapy. Skin biopsy demonstrated lichenoid dermatitis with vacuolar degeneration, dyskeratosis, and prominent pigment incontinence (Figure). Based on these findings and her clinical presentation, a diagnosis of blaschkoid GVHD was made.

Although acute GVHD is the result of immunocompetent donor T cells recognizing host tissues as foreign and initiating an immune response, the pathophysiology of chronic GVHD is not well understood.^1,2 Theories for disease pathogenesis in chronic GVHD suggest an underlying autoimmune and/or alloreactive process.^2-5 The skin often is the first organ affected in acute GVHD, and patients generally present with a pruritic morbilliform eruption that begins on the trunk and spreads to the rest of the body.^1,2 Cutaneous manifestations of chronic GVHD may be protean. Lesions can resemble systemic sclerosis or morphea, lichen planus, psoriasis, ichthyosis, and many other conditions.²

The differential diagnosis of linear dermatoses includes herpes zoster, contact dermatitis, lichen striatus (blaschkitis), nevus unius lateris, inflammatory linear verrucous epidermal nevus, and incontinentia pigmenti.^6,7 Lichen planus-like chronic GVHD occurring in a linear distribution has been described.^6-14 Distinction between dermatomal and blaschkoid processes is diagnostically important. In the case of GVHD, dermatomal distribution may suggest an association between GVHD and prior herpes simplex virus or varicella-zoster virus infection.^6,8 Herpesvirus may alter surface antigens of keratinocytes, rendering them targets of donor lymphocytes, and antibodies to viral particles may cross-react with host keratinocyte HLA antigens. It also is possible that dermatomal GVHD may simply be a type of isomorphic response (Köbner phenomenon).⁸

When cutaneous GVHD follows Blaschko lines, other mechanisms appear to be at play.^9-14 It is plausible that these patients have an underlying genetic mosaicism, perhaps the result of a postzygotic mutation, that results in a daughter cell population that expresses surface antigens different from those of the primary cell population found elsewhere in the skin. Donor lymphocytes may selectively react to this mosaic population, leading to the clinical picture of chronic GVHD oriented along Blaschko lines.^10,11,13,14 

In conclusion, lichenoid linear GVHD following Blaschko lines is an uncommon presentation of chronic GVHD that highlights the heterogeneity of this disease and should be considered in the appropriate clinical setting.

Granular Cell Basal Cell Carcinoma

Basal cell carcinoma (BCC) is the most common human epithelial malignancy. There are several histologic variants, the rarest being granular cell BCC (GBCC).¹ Granular cell BCC is reported most commonly in men with a mean age of 63 years. Sixty-four percent of cases develop on the face, with the remainder arising on the chest or trunk. Granular cell BCC has distinct histologic features but has no specific epidemiologic or clinical features that differentiate it from more common forms of BCC. Treatment of GBCC is identical to BCC and demonstrates similar outcomes. The presence of granular cells can make GBCC difficult to differentiate from other benign and malignant lesions that display similar granular histologic changes.^1,2 Rarely, tumors that are histologically similar to human GBCC have been reported in animals.¹

Histologically, GBCC commonly demonstrates the architecture of a nodular BCC or may extend from an existing nodular BCC (quiz images A and B). Granular cell BCC is comprised of large islands of basaloid cells extending from the epidermis with rare mitotic activity. Certain variants showing no epidermal attachments have been described,^1,3 as in the current case. Classically, BCC and GBCC both demonstrate a peripheral palisade of blue basal cells; however, GBCC may lack this palisading feature in some cases. Therefore, GBCC may be comprised of granular cells only, which may be more easily confused with other tumors with granular cell differentiation. Even when GBCC retains the traditional peripheral palisade of blue basal cells, the central cells are filled with eosinophilic granules.^1,2

Electron microscopy of GBCC usually reveals bundles of cytoplasmic tonofilaments and desmosomes in both granular cells and the peripherally palisaded cells. Electron microscopy imaging also demonstrates 0.1- to 0.5-µm membrane-bound lysosomelike structures. In certain reports, these structures show focal positivity for lysozymes.^1,2 The etiology of the granules is unclear; however, they are thought to represent degenerative changes related to metabolic alteration and accumulation of lysosomelike structures. These lysosomelike structures have been highlighted with CD68 staining, which was negative in our case.^1,2 The lesional cells in GBCC stain positively for cytokeratins, p63, and Ber-EP4, and negatively for S-100 protein, epithelial membrane antigen, and carcinoembryonic antigen. The granules in GBCC generally are positive on periodic acid–Schiff staining.^1-4

The histologic differential diagnosis for GBCC includes granular cell tumor as well as other tumors that can present with granular cell changes such as ameloblastoma, leiomyoma, leiomyosarcoma, angiosarcoma, malignant peripheral nerve sheath tumor, and granular cell trichoblastoma. Granular cell ameloblastomas have histologic features and staining patterns that are identical to GBCC; however, ameloblastomas are distinguished by their location within the oral cavity. Granular cell tumors and malignant peripheral nerve sheath tumors stain positive for S-100 protein, and angiosarcomas stain positive for D2-40 and CD31. Leiomyomas and leiomyosarcomas can be differentiated by staining with smooth muscle actin or desmin.¹ Granular cell trichoblastomas can be differentiated by the follicular stem cell marker protein PHLDA1 positivity.⁵

Desmoplastic trichilemmoma is difficult to distinguish from BCC. These tumors are comprised of superficial lobules of basaloid cells with a perilobular hyaline mantel surrounding a central desmoplastic stroma (Figure 1). The basaloid cells in desmoplastic trichoepithelioma demonstrate clear cell change; however, granular features are not seen. The cells within the desmoplastic areas are arranged haphazardly in cords and nests and can mimic an invasive carcinoma; however, nuclear atypia and mitotic activity generally are absent in desmoplastic trichilemmoma.⁶

Granular cell tumors generally are poorly circumscribed dermal nodules comprised of large polygonal cells with an eosinophilic granular cytoplasm (Figure 2). The nuclei are generally small and round, and cytological atypia, necrosis, and mitotic activity are uncommon. The cells are positive for S-100 protein and neuron-specific enolase but negative for CD68. The granules are positive for periodic acid–Schiff stain and are diastase resistant. Rarely, these tumors can be malignant.⁷

Sebaceous adenoma is a well-circumscribed tumor comprised of lobules of characteristic mature sebocytes with bubbly or multivacuolated cytoplasm and crenated nuclei (Figure 3). There is an expansion and increased prominence of the peripherally located basaloid cells; however, in contrast to sebaceous epithelioma, less than 50% of the tumor usually is comprised of these basaloid cells.⁸

Xanthogranuloma demonstrates a dense collection of histiocytes in the dermis, commonly with Touton giant cell formation (Figure 4). The cells often have a foamy cytoplasm and cytoplasmic vacuoles are observed. The histiocytes are positive for factor XIIIa and CD68, and generally negative for S-100 protein and CD1a, which allows for differentiation from Langerhans cells.⁹

Granular Cell Basal Cell Carcinoma

Basal cell carcinoma (BCC) is the most common human epithelial malignancy. There are several histologic variants, the rarest being granular cell BCC (GBCC).¹ Granular cell BCC is reported most commonly in men with a mean age of 63 years. Sixty-four percent of cases develop on the face, with the remainder arising on the chest or trunk. Granular cell BCC has distinct histologic features but has no specific epidemiologic or clinical features that differentiate it from more common forms of BCC. Treatment of GBCC is identical to BCC and demonstrates similar outcomes. The presence of granular cells can make GBCC difficult to differentiate from other benign and malignant lesions that display similar granular histologic changes.^1,2 Rarely, tumors that are histologically similar to human GBCC have been reported in animals.¹

Histologically, GBCC commonly demonstrates the architecture of a nodular BCC or may extend from an existing nodular BCC (quiz images A and B). Granular cell BCC is comprised of large islands of basaloid cells extending from the epidermis with rare mitotic activity. Certain variants showing no epidermal attachments have been described,^1,3 as in the current case. Classically, BCC and GBCC both demonstrate a peripheral palisade of blue basal cells; however, GBCC may lack this palisading feature in some cases. Therefore, GBCC may be comprised of granular cells only, which may be more easily confused with other tumors with granular cell differentiation. Even when GBCC retains the traditional peripheral palisade of blue basal cells, the central cells are filled with eosinophilic granules.^1,2

Electron microscopy of GBCC usually reveals bundles of cytoplasmic tonofilaments and desmosomes in both granular cells and the peripherally palisaded cells. Electron microscopy imaging also demonstrates 0.1- to 0.5-µm membrane-bound lysosomelike structures. In certain reports, these structures show focal positivity for lysozymes.^1,2 The etiology of the granules is unclear; however, they are thought to represent degenerative changes related to metabolic alteration and accumulation of lysosomelike structures. These lysosomelike structures have been highlighted with CD68 staining, which was negative in our case.^1,2 The lesional cells in GBCC stain positively for cytokeratins, p63, and Ber-EP4, and negatively for S-100 protein, epithelial membrane antigen, and carcinoembryonic antigen. The granules in GBCC generally are positive on periodic acid–Schiff staining.^1-4

The histologic differential diagnosis for GBCC includes granular cell tumor as well as other tumors that can present with granular cell changes such as ameloblastoma, leiomyoma, leiomyosarcoma, angiosarcoma, malignant peripheral nerve sheath tumor, and granular cell trichoblastoma. Granular cell ameloblastomas have histologic features and staining patterns that are identical to GBCC; however, ameloblastomas are distinguished by their location within the oral cavity. Granular cell tumors and malignant peripheral nerve sheath tumors stain positive for S-100 protein, and angiosarcomas stain positive for D2-40 and CD31. Leiomyomas and leiomyosarcomas can be differentiated by staining with smooth muscle actin or desmin.¹ Granular cell trichoblastomas can be differentiated by the follicular stem cell marker protein PHLDA1 positivity.⁵

Desmoplastic trichilemmoma is difficult to distinguish from BCC. These tumors are comprised of superficial lobules of basaloid cells with a perilobular hyaline mantel surrounding a central desmoplastic stroma (Figure 1). The basaloid cells in desmoplastic trichoepithelioma demonstrate clear cell change; however, granular features are not seen. The cells within the desmoplastic areas are arranged haphazardly in cords and nests and can mimic an invasive carcinoma; however, nuclear atypia and mitotic activity generally are absent in desmoplastic trichilemmoma.⁶

Granular cell tumors generally are poorly circumscribed dermal nodules comprised of large polygonal cells with an eosinophilic granular cytoplasm (Figure 2). The nuclei are generally small and round, and cytological atypia, necrosis, and mitotic activity are uncommon. The cells are positive for S-100 protein and neuron-specific enolase but negative for CD68. The granules are positive for periodic acid–Schiff stain and are diastase resistant. Rarely, these tumors can be malignant.⁷

Sebaceous adenoma is a well-circumscribed tumor comprised of lobules of characteristic mature sebocytes with bubbly or multivacuolated cytoplasm and crenated nuclei (Figure 3). There is an expansion and increased prominence of the peripherally located basaloid cells; however, in contrast to sebaceous epithelioma, less than 50% of the tumor usually is comprised of these basaloid cells.⁸

Xanthogranuloma demonstrates a dense collection of histiocytes in the dermis, commonly with Touton giant cell formation (Figure 4). The cells often have a foamy cytoplasm and cytoplasmic vacuoles are observed. The histiocytes are positive for factor XIIIa and CD68, and generally negative for S-100 protein and CD1a, which allows for differentiation from Langerhans cells.⁹

Granular Cell Basal Cell Carcinoma

Basal cell carcinoma (BCC) is the most common human epithelial malignancy. There are several histologic variants, the rarest being granular cell BCC (GBCC).¹ Granular cell BCC is reported most commonly in men with a mean age of 63 years. Sixty-four percent of cases develop on the face, with the remainder arising on the chest or trunk. Granular cell BCC has distinct histologic features but has no specific epidemiologic or clinical features that differentiate it from more common forms of BCC. Treatment of GBCC is identical to BCC and demonstrates similar outcomes. The presence of granular cells can make GBCC difficult to differentiate from other benign and malignant lesions that display similar granular histologic changes.^1,2 Rarely, tumors that are histologically similar to human GBCC have been reported in animals.¹

Histologically, GBCC commonly demonstrates the architecture of a nodular BCC or may extend from an existing nodular BCC (quiz images A and B). Granular cell BCC is comprised of large islands of basaloid cells extending from the epidermis with rare mitotic activity. Certain variants showing no epidermal attachments have been described,^1,3 as in the current case. Classically, BCC and GBCC both demonstrate a peripheral palisade of blue basal cells; however, GBCC may lack this palisading feature in some cases. Therefore, GBCC may be comprised of granular cells only, which may be more easily confused with other tumors with granular cell differentiation. Even when GBCC retains the traditional peripheral palisade of blue basal cells, the central cells are filled with eosinophilic granules.^1,2

Electron microscopy of GBCC usually reveals bundles of cytoplasmic tonofilaments and desmosomes in both granular cells and the peripherally palisaded cells. Electron microscopy imaging also demonstrates 0.1- to 0.5-µm membrane-bound lysosomelike structures. In certain reports, these structures show focal positivity for lysozymes.^1,2 The etiology of the granules is unclear; however, they are thought to represent degenerative changes related to metabolic alteration and accumulation of lysosomelike structures. These lysosomelike structures have been highlighted with CD68 staining, which was negative in our case.^1,2 The lesional cells in GBCC stain positively for cytokeratins, p63, and Ber-EP4, and negatively for S-100 protein, epithelial membrane antigen, and carcinoembryonic antigen. The granules in GBCC generally are positive on periodic acid–Schiff staining.^1-4

The histologic differential diagnosis for GBCC includes granular cell tumor as well as other tumors that can present with granular cell changes such as ameloblastoma, leiomyoma, leiomyosarcoma, angiosarcoma, malignant peripheral nerve sheath tumor, and granular cell trichoblastoma. Granular cell ameloblastomas have histologic features and staining patterns that are identical to GBCC; however, ameloblastomas are distinguished by their location within the oral cavity. Granular cell tumors and malignant peripheral nerve sheath tumors stain positive for S-100 protein, and angiosarcomas stain positive for D2-40 and CD31. Leiomyomas and leiomyosarcomas can be differentiated by staining with smooth muscle actin or desmin.¹ Granular cell trichoblastomas can be differentiated by the follicular stem cell marker protein PHLDA1 positivity.⁵

Desmoplastic trichilemmoma is difficult to distinguish from BCC. These tumors are comprised of superficial lobules of basaloid cells with a perilobular hyaline mantel surrounding a central desmoplastic stroma (Figure 1). The basaloid cells in desmoplastic trichoepithelioma demonstrate clear cell change; however, granular features are not seen. The cells within the desmoplastic areas are arranged haphazardly in cords and nests and can mimic an invasive carcinoma; however, nuclear atypia and mitotic activity generally are absent in desmoplastic trichilemmoma.⁶

Granular cell tumors generally are poorly circumscribed dermal nodules comprised of large polygonal cells with an eosinophilic granular cytoplasm (Figure 2). The nuclei are generally small and round, and cytological atypia, necrosis, and mitotic activity are uncommon. The cells are positive for S-100 protein and neuron-specific enolase but negative for CD68. The granules are positive for periodic acid–Schiff stain and are diastase resistant. Rarely, these tumors can be malignant.⁷

Sebaceous adenoma is a well-circumscribed tumor comprised of lobules of characteristic mature sebocytes with bubbly or multivacuolated cytoplasm and crenated nuclei (Figure 3). There is an expansion and increased prominence of the peripherally located basaloid cells; however, in contrast to sebaceous epithelioma, less than 50% of the tumor usually is comprised of these basaloid cells.⁸

Xanthogranuloma demonstrates a dense collection of histiocytes in the dermis, commonly with Touton giant cell formation (Figure 4). The cells often have a foamy cytoplasm and cytoplasmic vacuoles are observed. The histiocytes are positive for factor XIIIa and CD68, and generally negative for S-100 protein and CD1a, which allows for differentiation from Langerhans cells.⁹