Acquired dermal melanocytosis of the hand at the site of treated psoriasis.

Dermal melanocytosis is a benign phenomenon most commonly noted in people with darkly pigmented skin. Multiple entities with dermal melanocytosis are described, including Mongolian spot, nevus of Ota, nevus of Ito, nevus of Hori, and acquired dermal melanocytosis. We report a case of acquired dermal melanocytosis occurring in a 42-year-old Hispanic man with psoriasis treated with infliximab for 9 months. The patient presented with an isolated pigmented patch on his left dorsal hand. Histopathologic examination of the skin revealed numerous dendritic, heavily pigmented melanocytes in the papillary and upper reticular dermis. We review the literature and discuss the pathogenesis of acquired dermal melanocytosis.