Neurocutaneous melanocytosis

Neurocutaneous melanocytosis (NCM), also known as neurocutaneous melanosis, is a rare congenital condition characterized by the presence of large or multiple congenital melanocytic nevi on the skin combined with melanocytic proliferation (melanosis or melanoma) within the central nervous system, particularly the leptomeninges (the membranes surrounding the brain and spinal cord). It is considered a congenital neurocristopathy, arising from errors in the development and migration of melanocyte precursor cells from the neural crest during embryonic development. The condition primarily affects the skin and the central nervous system. Patients typically present at birth with large or giant congenital melanocytic nevi, often located on the trunk (described as "bathing trunk" nevi) or the scalp, frequently accompanied by numerous smaller satellite nevi. Neurological symptoms may develop in infancy or early childhood and can include hydrocephalus (increased fluid pressure in the brain), seizures, developmental delay, cranial nerve palsies, and signs of increased intracranial pressure such as headache and vomiting. Leptomeningeal melanocytosis can be detected by MRI, which may show areas of T1-weighted hyperintensity in the brain parenchyma, leptomeninges, or spinal cord. Symptomatic NCM carries a poor prognosis, particularly when associated with leptomeningeal melanoma. There is no curative treatment for neurocutaneous melanocytosis. Management is primarily supportive and symptomatic. Hydrocephalus may be treated with ventriculoperitoneal shunting, and seizures are managed with anticonvulsant medications. Surgical removal of cutaneous nevi may be performed for cosmetic reasons or to reduce the risk of cutaneous melanoma, but it does not affect the intracranial disease. Somatic mutations in the NRAS gene (particularly the p.Gln61Lys variant) have been identified in many cases, and research into targeted therapies such as MEK inhibitors is ongoing. Regular neurological monitoring and MRI surveillance are recommended for patients with large congenital melanocytic nevi.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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