Background: Longitudinal melanonychia (LM) is characterized by the appearance of a longitudinal pigmented band in the nail plate. Melanonychia can occur from many causes, including racial predisposition, trauma, drugs, pregnancy, Addison disease, Peutz-Jeghers syndrome, Laugier-Hunziker syndrome, Bowen disease, onychomycosis, benign nail matrix nevi, and melanoma.
Objective: We present a case of diffuse melanonychia developing several months following Mohs surgery for a human papillomavirus-induced recurrent squamous cell carcinoma in situ of the nail bed.
Conclusions: This case illustrates the diagnostic dilemma in determining the etiology of the melanonychia and considers the differential diagnosis.