Pediatric Primary Diffuse Leptomeningeal Melanomatosis: A Case Report and Literature Review.

Primary diffuse leptomeningeal melanomatosis (PDLM) is an exceptionally rare and aggressive pediatric central nervous system (CNS) malignancy that often presents with nonspecific symptoms, leading to delayed diagnosis. We report a seven-year-old boy who initially presented with recurrent focal neurologic episodes and headaches that were attributed to migraine before progressive visual changes and signs of elevated intracranial pressure (ICP) prompted further evaluation. Cerebrospinal fluid (CSF) cytology and meningeal biopsy confirmed PDLM with diffuse leptomeningeal involvement. Despite rapid neurologic decline after initiation of immunotherapy, urgent cranial and later spinal radiotherapy resulted in meaningful functional recovery, allowing temporary stabilization, return to school, and preservation of quality of life. Disease progression ultimately occurred, and he died 16 months after symptom onset. This case highlights the diagnostic challenges of PDLM and highlights the potential role of radiotherapy in providing neurologic improvement and symptomatic benefit, even in the setting of limited overall survival.