Segmental arrangement of multiple, partly congenital and partly acquired melanocytic nevi.

A 15 year-old girl presented with numerous congenital melanocytic nevi, occasionally hairy, with a segmental distribution at the left pre-auricular region. On the left side of the back of the neck there were multiple melanocytic nevi with a warty appearance, which had started to appear when she was 5 and which had remained stable from the time she was 10. These lesions had a distribution reminiscent of an epidermal nevus with a pattern similar to Blaschko's lines. On general physical examination there was a moderate degree of idiopathic scoliosis, with a left lumbar curvature. Biopsies were taken from both types of nevus which were diagnosed as congenital compound melanocytic nevus and acquired compound melanocytic nevus respectively. We consider that the segmental distribution of the melanocytic nevi of this patient supports the theory that a genetic defect determined the appearance of both these congenital and acquired lesions.