Abstract

A 78-year-old male presented with a mass involving the nail plate of the left thumb. Biopsy showed a neoplasm situated in the onychodermis with no connection to the overlying nail matrix/bed arranged in cords and dyscohesive nests. The cells were monomorphic with scant cytoplasm, small round nuclei and prominent nucleoli embedded in a myxoid stroma. The cells were positive for SOX-10, S-100 (focally) and negative for HMB-45 and MART-1. Ki-67 was increased (20%). Work-up for enlarged axillary lymph node revealed cytologically similar cells. Based on the overall findings, a diagnosis of nevoid SM with left axillary involvement was rendered. Subungal melanoma is an uncommon tumor with higher mortality rate compared with melanoma at other sites. It can be amelanotic and present with nail dystrophy, leading to delayed diagnosis and greater depth of invasion on initial biopsy. The most common subtype of SM is acral lentiginous; however, nevoid melanoma has rarely been reported. This case was challenging because of the uncommon histologic subtype, the fragmented biopsy and the lack of overlying connection. We present this case to increase awareness of nevoid melanoma occurring in this anatomic location, and address pitfalls which could delay diagnosis and initiation of treatment.

Financial Disclosure:
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