Diffuse leptomeningeal melanocytosis

Diffuse leptomeningeal melanocytosis (DLM) is an extremely rare and serious condition characterized by the widespread proliferation of melanin-producing cells (melanocytes) within the leptomeninges — the thin membranes (pia mater and arachnoid mater) that surround the brain and spinal cord. It belongs to the spectrum of primary leptomeningeal melanocytic neoplasms. DLM predominantly affects the central nervous system and is frequently associated with neurocutaneous melanocytosis (NCM), a condition in which large or multiple congenital melanocytic nevi of the skin are accompanied by melanocytic deposits in the leptomeninges. The ICD-10 classification (C70.9) reflects its malignant potential, as DLM can undergo transformation to diffuse leptomeningeal melanomatosis, a highly aggressive malignancy. Clinical features typically arise from the effects of melanocytic infiltration on the brain and spinal cord. Key symptoms include increased intracranial pressure leading to headaches, nausea, and vomiting; hydrocephalus (accumulation of cerebrospinal fluid); seizures; cranial nerve palsies; and progressive neurological deterioration. In children, the condition often presents in the first two years of life with signs of raised intracranial pressure, developmental regression, or irritability. Diagnosis is supported by MRI findings showing leptomeningeal enhancement and by cerebrospinal fluid analysis, which may reveal melanin-laden cells. The prognosis for diffuse leptomeningeal melanocytosis is generally poor, particularly when malignant transformation occurs. Treatment options are limited and largely palliative. Management may include surgical placement of shunts to relieve hydrocephalus, radiation therapy, and systemic or intrathecal chemotherapy, though responses are often temporary. More recently, targeted therapies directed against NRAS or BRAF mutations — which are frequently identified in these melanocytic proliferations — have been explored in clinical settings, but evidence remains limited. There is currently no established curative treatment, and multidisciplinary care involving neurology, oncology, and neurosurgery is essential.

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

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