Becker's nevus syndrome.

Becker's nevus (BN) is a unilateral hyperpigmented, often hairy, cutaneous hamartoma, with geographic borders. It is usually localized on the shoulder, anterior chest, scapula, or upper arm, but there have been reports of BN in other areas (eg, lower extremities, face). In most cases, the lesion appears in late childhood or adolescence, and both congenital and familial cases have been described.