Extensive Perineural Spread of Subungual Melanoma.

Abstract

Subungual melanoma (SUM) is a rare form of melanoma confined to the nailbed and is rarely of the desmoplastic subtype. The often subtle nature of SUM, initially starting as a small dark spot or line in the nailbed, means deeper invasion can occur before a patient seeks clinical evaluation for a large, ulcerated lesion. We report the only known case of perineural spread of SUM of the lower extremity and describe its extensive path of perineural spread from the toe. A 72-year-old man with a distant history of SUM status post second ray amputation, presented for evaluation of ipsilateral foot drop. Imaging revealed nodular involvement of tibial, peroneal, and sciatic nerves. Biopsies revealed desmoplastic melanoma and he was treated with nivolumab. We report the only known case of perineural spread of SUM of the lower extremity and describe the pathoanatomy of perineural spread. A high index of suspicion for recurrent disease should be maintained even many years after completion of treatment.