A case of adult-onset longitudinal melanonychia due to nail matrix compound nevus.

A case of adult-onset longitudinal melanonychia caused by a compound nevus is described. Longitudinal melanonychias are mainly caused by melanocytic activation (hypermelanosis), lentigo (benign melanocytic hyperplasia), nevus, and melanoma. Nevi are more commonly seen in children than adults; however, melanocytic activation, atypical melanocytic proliferation, and melanoma are more frequent in adults. The majority of nail matrix nevi causing longitudinal melanonychia first appear in childhood and are junctional. Rarely, compound nevi are reported to cause longitudinal melanonychia in childhood.