Smooth muscle hamartoma associated with a congenital pattern melanocytic nevus, a case report and review of the literature.

Smooth muscle hamartoma (SMH) is a rare benign congenital or acquired lesion sometimes associated with Becker's nevus (Becker's melanosis). We report an unusual lesion with combined features of SMH and melanocytic nevus. The patient is a 49-year-old male with a history of a changing 'mole' on the left upper back. Clinical examination showed a solitary 1.2-cm nodule with central gray pigmentation. Histological examination showed a relatively well-circumscribed intradermal lesion. The superficial portion of the lesion consisted of melanocytes with nevoid morphology. The melanocytes had congenital pattern of distribution. Lesional melanocytes acquired a spindled morphology in the deeper dermis. The base of the lesion consisted of intersecting smooth muscle fascicles focally admixed with spindled melanocytes. The melanocytic component strongly expressed melanoma antigen recognized by T-cells-1 (MART-1) and HMB-45. The smooth muscle component was strongly positive for smooth muscle actin and h-caldesmon. Neither components showed significant cytological atypia or mitotic activity. Unlike a recently reported case of SMH combined with a melanocytic nevus and basal cell carcinoma, the current lesion did not occur in association with a Becker's nevus. Copyright Blackwell Munksgaard 2008.