Sudden death associated with primary leptomeningeal melanocytosis without features of neurocutaneous melanosis syndrome

Background

Leptomeningeal melanocytosis is a rare, benign melanocytic proliferation of the central nervous system, typically associated with neurocutaneous melanosis. Isolated forms without cutaneous involvement are extremely uncommon, especially in adults, and pose significant diagnostic and medicolegal challenges.

Case report

We report the sudden death of a 29-year-old man with no known medical history, found unresponsive in a prone position. External examination revealed no traumatic injuries, and toxicology was negative. Gross and microscopic examination of the brain demonstrated diffuse leptomeningeal melanocytic infiltration over the frontotemporoparietal cortex and cerebellum. Histologically, the lesion was composed of bland melanocytes containing fine melanin pigment without mitotic activity or atypia. No primary or metastatic melanoma was identified elsewhere in the body. The findings were consistent with primary diffuse leptomeningeal melanocytosis.

Discussion

Although histologically benign, leptomeningeal melanocytosis may affect critical CNS regions, potentially leading to seizures, autonomic dysregulation, or sudden death. This case emphasizes the importance of thorough neuropathological investigation in unexplained deaths. The location and extent of melanocytic infiltration suggest a possible seizure-related terminal event, highlighting a rare but important differential diagnosis in forensic practice.

Conclusion

This case underscores the forensic significance of isolated primary leptomeningeal melanocytosis as a potential cause of sudden death. Early recognition of this rare entity requires a combination of detailed autopsy, histopathology, and awareness of its variable clinical presentations, especially in the absence of cutaneous signs. These findings are of particular relevance to forensic pathologists investigating sudden, unexplained deaths.