Leptomeningeal melanocytosis in an adult male without large congenital nevi: a rare and atypical case of neurocutaneous melanosis.

Leptomeningeal melanocytosis is a primary melanocytic lesion of the central nervous system that is characterized by diffuse melanocytic infiltration of the leptomeninges. It is seen almost exclusively in children with large congenital nevi and together the findings form a dermatologic syndrome known as neurocutaneous melanosis. We report a rare and atypical case of a 31-year-old adult male with no evident congenital melanocytic lesions who presented with neurologic symptoms and was found to have leptomeningeal melanocytosis. The brain biopsy demonstrated a conspicuous but benign-appearing melanocytic infiltrate that was discordant with the severity of the patient's symptoms. Ultimately, the patient was suspected to represent a case of former fruste neurocutaneous melanosis. Herein the relevant clinical and histopathologic features are discussed along with a brief review of the literature.