RESUMO
A 46-year-old male experienced progressive neurocognitive decline, weight loss, intermittent headaches, and weakness over 6 months. Magnetic resonance imaging of the brain revealed hydrocephalus and the spinal cord imaging showed diffuse leptomeningeal enhancement with prominent nerve root involvement. Intradural biopsy of lumbar arachnoid tissue found mixed inflammatory infiltrate consisting predominantly of histiocytes, S100 and CD68 positivity, and lymphocytophagocytosis (emperipolesis) consistent with extranodal Rosai-Dorfman disease. Rosai-Dorfman disease, a non-Langerhans cell histocytic disorder, can mimic the appearance of neurosarcoidosis and leptomeningeal carcinomatosis and should remain on the differential of a patient presenting with diffuse leptomeningeal enhancement, a common occurrence on a neurohospitalist service.