Neurocutaneous melanosis in an adult patient with diffuse leptomeningeal melanosis and a rapidly deteriorating course: case report and review of the literature.

Neurocutaneous melanosis (NCM) rarely begins in adulthood. Due to the late onset of neurologic symptomology, a prompt diagnosis is often misleading or delayed, particularly in patients with pure leptomeningeal involvement. We describe herein a 25-year-old patient with congenital giant melanocytic nevi at birth, presenting with diffuse leptomeningeal melanocytic involvement, particularly within the basilar region of the brain. He developed a rapid increase in the size of the lesion over a short period of time, leading to rapid deterioration and death. The neuroradiologic feature in this case was unusual compared with previously reported adult cases of NCM. This case illustrates the importance of considering the likelihood of underlying NCM when evaluating adult patients with neurologic symptoms and cutaneous melanosis.