Primary Diffuse Leptomeningeal Melanomatosis: Case Report and Review of the Literature.

BACKGROUND: Primary diffuse leptomeningeal melanomatosis (PDLM) is an extremely rare pathologic condition that can mimic several other neurologic disease states.

METHODS: We report a rare case of PDLM without evidence of a primary focus. Additionally, we performed a comprehensive review of the literature to describe all previously reported cases of PDLM.

RESULTS: In the presented case, making the diagnosis of PDLM was difficult. A brain and frontal dural biopsy was nondiagnostic. A CT chest, abdomen, and pelvis was also obtained that did not demonstrate any distinct solitary mass. After a PET scan was performed that showed lumbar sacral enhancement, lumbar dorsal rootlet biopsy was initiated, which was diagnostic of PDLM. Our literature review demonstrated 32 previously reported cases of PDLM. Sixteen cases (48.5%) had a distinct focus or mass discovered on imaging workup. The presenting case was the 17th reported case of PDLM without a distinct focus or mass found on imaging workup.

CONCLUSIONS: PDLM is an extremely rare disease, and diagnosis is difficult due to nonspecific clinical, radiographic, and laboratory findings. In approximately half of cases, no distinct mass is demonstrated on imaging workup, which may further complicate diagnosis. PDLM should be on the differential diagnosis for cases of diffuse dural enhancement. Neurosurgical intervention is often limited to ventriculoperitoneal shunting for increased intracranial pressure, and dural and cranial biopsy to obtain diagnosis. If the initial biopsy is nondiagnostic, hypermetabolic activity as seen on PET scan may be helpful to find an alternate biopsy site.