Transverse melanonychia secondary to total skin electron beam therapy: a report of 3 cases.

Longitudinal melanonychia is a common phenomenon, known to be the result of numerous etiologies. Transverse melanonychia, on the other hand, is uncommon. It has been reported in association with conventional x-ray therapy, psoralen plus ultraviolet A, infliximab, zidovudine, antimalarials, and several chemotherapeutic agents.