Functional melanonychia due to involvement of the nail matrix in systemic lupus erythematosus.

Longitudinal melanonychia is an unusual finding in systemic lupus erythematosus. We report the case of a patient of Arabic extraction with cutaneous lesions of lupus erythematosus on the cheek and chest and longitudinal melanonychia affecting several fingers. Results of histologic examination of the skin and direct immunofluorescence analysis confirmed the diagnosis of systemic lupus erythematosus. The distal matrix revealed changes suggestive of systemic lupus erythematosus accompanied by increased activity of melanocytes but without melanocytic hyperplasia. In this case, longitudinal melanonychia associated with systemic lupus erythematosus was of functional origin.