A Case of Syringotropic Melanoma Presenting as a Dark Brown Patch around the Toenail

Dear Editor: The superficial acrosyringium may sometimes be involved in melanomas. However, very rarely, melanomas spread in situ within the eccrine apparatus and invade the deep dermis1,2. Syringotropic melanoma is defined as melanoma that spreads within the eccrine apparatus into the reticular dermis and/or subcutaneous tissue, deeper than any (if present) associated invasive melanoma2. Here, we report a case of syringotropic melanoma presenting as a dark brown patch. A 79-year-old man presented with a pigmented lesion on the toe, which persisted for 5 years. Skin examination showed a dark brown patch around the right 1st toenail (Fig. 1A). Under suspicion of melanoma in situ, an incisional biopsy was performed after a nail extraction. Histopathology from the incision showed proliferation of atypical melanocytes along the basal layer (Fig. 1B). Additionally, atypical cells containing melanin pigments were observed within the eccrine ducts. Immunohistochemical staining for human melanoma black 45 (HMB-45) was positive in the atypical melanocytes along the basal layer and in the eccrine ducts (data not shown). Therefore, a diagnosis of acral lentiginous melanoma in situ, spreading to the eccrine ducts, without dermal invasion was made. Total excision was performed and histopathology showed melanoma cells along the basal layer. In addition to melanoma cells within the eccrine ducts, dermal invasion of melanoma cells from the eccrine ducts was noted (Fig. 1C). Immunohistochemical staining for HMB-45 was positive in cells of eccrine ducts and around the eccrine ducts (Fig. 1D). Finally, the condition was diagnosed as melanoma in situ with microinvasion from coiled eccrine ducts. Fig. 1 (A) Skin examination shows a dark brown patch on the right 1st toe. (B) Histopathology from the incision shows proliferation of atypical melanocytes along the basal layer. Further, atypical cells containing melanin pigments are seen within the eccrine ... Thus far, 8 cases of syringotropic melanoma have been reported in the English literature1,2. Seven of them showed dermal invasion of melanoma cells from the epidermis, suggesting that syringotropic melanoma is associated with invasive melanoma rather than melanoma in situ. Syringocentric invasion was noted in 4 cases. Two patients had acral lentiginous melanoma; one patient with acral lentiginous melanoma showed dermal invasion from the epidermis without dermal invasion from the eccrine ducts; and the other patient showed dermal invasion of melanoma cells from the epidermis and eccrine ducts. Our current patient showed acral lentiginous melanoma in situ and dermal invasion of melanoma cells from the eccrine ducts. It is difficult to distinguish between syringotropic melanoma in situ localized to the eccrine ducts and syringotropic invasion to the surrounding tissue. Previously, a patient presented with a macule despite the presence of dermal syringocentric invasion, which was identified later on biopsy2. Similarly, our patient presented with a patch around the toenail, suggesting melanoma in situ, despite the presence of dermal syringocentric invasion, which was identified later on excisional biopsy. These 2 cases suggest that although clinically, melanoma lesions look superficial, they may have a deep syringotropic component. In our case, the incisional biopsy showed acral lentiginous melanoma in situ spreading to the eccrine ducts without dermal invasion, but the excision showed dermal invasion of melanoma cells from the eccrine ducts. Our case suggests that serial sections in cases of syringotropic melanoma may show syringocentric invasion. Barnhill et al.3 reported a case of melanoma invading from within skin adnexa. They concluded that Breslow thickness (depth of invasion) should not be measured from the granular layer of the epidermis because this value would overestimates tumor depth. Instead, tumor thickness should be measured from the granular layer equivalent of the skin adnexa. Although measurement from the innermost layer of the eccrine duct may be ideal, it may not be possible because eccrine ducts are coiled. In conclusion, our findings suggest that in cases of syringotropic melanoma in situ, the eccrine apparatus may be involved. Further studies on eccrine involvement in melanoma and the significance of the presence of melanoma cells in and outside the eccrine apparatus are required.

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