Longitudinal deep fissure and distal onycholysis of the right thumb. Amelanotic subungual melanoma

A 74-year-old white woman presented with an approximately 1-year history of median longitudinal ridging of the right thumb that had evolved in a deep fissure along with distal onycholysis. She had previously been diagnosed as having onychomycosis and had been treated with topical and systemic antimycotic drugs, with no improvement. The medial part of the nail plate had progressively become thin and brittle, causing median longitudinal fissuring of the whole nail and isolating 2 lateral parts of normal nail plate. The nail bed, which was exposed by onychodystrophy, was yellowish red and had a few scales. The nail fold was not involved, and the hyponychium was not ulcerated and looked only slightly hyperkeratotic. The digital pulp was normal and painless. A punch biopsy specimen of the lesion was obtained, and a total excision of the nail apparatus was subsequently performed. The specimens were stained with hematoxylin-eosin and HMB-45.