Extensive unilateral speckled lentiginous nevus.

We report a case of speckled lentiginous nevus with extensive unilateral distribution in a 53-year-old man. The lesions involved the left back, extending from the midline anteriorly to the thorax, arm, and forearm. The background pigmentary patch covered only the back and upper arm. Histologic examination revealed a lentiginous pattern as well as a congenital nevocytic pattern, even in the areas where the background was nontanned skin. This combined clinical pattern in the same patient fits the descriptions for both the usual and unusual speckled lentiginous nevus. Cases with variants of extensive unilateral distribution are infrequent and pathologists should pay particular attention to them because of the possibility of their malignant transformation.