Abstract

A 67-year-old female with a history of basal cell carcinoma presented with a 4-month history of a painful, growing, and bleeding lesion within the right second fingernail unit. The patient had no recent trauma, no new medications, and review of systems was negative. Examination of the right second fingernail unit showed 8mm x 5mm distal longitudinal erythronychia and leukonychia with pterygium-inversus-ungis–like adherent crust and oozing. The clinical appearance was concerning for nail unit squamous cell carcinoma and nail unit amelanotic melanoma. The lesion was excised. Histopathology demonstrated distinct collections of prominent keratin-derived amyloid in the dermis and many onycholemmal cysts. The amyloid was highlighted by crystal violet, congo red, cytokeratin AE1/AE3, and cytokeratin 5/6 stains. Cam 5.2, Luna, and GMS stains were negative. We herein present this case as a novel clinicopathologic entity. Amyloid deposition in the nail is exceptional and when present, has been reported in a polydactylous manner in primary systemic amyloidosis or multiple myeloma. These cases usually present with polydactylous trachonychia and clinically can be indistinguishable from nail unit lichen planus. Onycholemmal cysts are generally thought to be a reactive phenomenon, but the related calcified subungual epidermoid inclusions are similar and have been reported as a distinct clinicopathologic entity. The combination of many onycholemmal cysts and keratin-derived amyloid with a unique clinical appearance is a novel nail unit clinicopathologic entity.

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