Neurocutaneous melanosis (NCM) is a neurodevelopmental disorder of melanotic cell development and migration (Rokitansky, 1861). The disorder has been described by a confusing array of names (giant melanocytic nevus, melanose neurocutanee, dark hairy nevus syndrome, congenital melanocytic hairy nevi, giant hairy nevus, garment hairy pigmented nevus, nevus pigmentosus et pillosus, nevomelanocytic nevus, melanotic nevus, Becker hairy nevus, and heredofamilial melanosis or Van Bogaert syndrome). The term NCM is used when there is abnormal melanocytic proliferation in the central nervous system, especially along the leptomeninges, in association with cutaneous dark nevi. Congenital melanocytic nevi may occur without central nervous system (CNS) involvement and conversely, melanin is found normally in the central nervous system in the absence of congenital nevi.
Neurocutaneous melanosis apparently occurs sporadically and affects males and females with equal frequency (DeDavid et al., 1996). The incidence of NCM is unknown but it is uncommon. Ascertainment of NCM is probably fairly complete because the characteristic and often dramatic skin lesions rarely escape notice.
The characteristic lesions are very dark to light brown hairy nevi (Fig. 8.1) that are present at birth. Multiple small nevi (‘satellite nevi’) usually occur around one giant nevus that most commonly appears on the lower trunk and perineal area (‘swimming trunk nevus’) or over the shoulders, upper arms and lower neck (‘cape nevus’). About a third of patients have a cape nevus. A giant nevus is absent in a substantial number of patients with NCM.