Primary intramedullary histiocytic sarcoma.

Intramedullary primary central nervous system lymphoma (PCNSL) is a rare central nervous system (CNS) malignancy affecting mostly the brain, but it may also involve the leptomeninges, eyes, and spinal cord. A 71-year-old woman presented with back pain and progressive unilateral lower extremity weakness owing to an intramedullary primary histiocytic sarcoma of the spine, a rare PCNSL subtype. To the authors' knowledge, this is the first case of an intramedullary PCNSL caused by histiocytic sarcoma.