Neurocutaneous melanosis.

Neurocutaneous melanosis (NCM) is a rare phakomatosis characterized by a focal or diffuse proliferation of melanin-producing cells in both the skin and the leptomeninges. This syndrome is believed to result from an error in the morphogenesis of embryonal neuroectoderm. Two-thirds of patients with NCM have giant congenital melanocytic nevi, and the remaining one-third have numerous lesions but no giant lesions. Patients may present with neurologic manifestations early in life secondary to intracranial hemorrhages, impairment of cerebrospinal fluid circulation, or malignant transformation of the melanocytes. The prognosis of patients with symptomatic NCM is poor.