Rheumatoid meningitis with yellowish‐white matter on the brain surface

Abstract A 68‐year‐old man presented with a 3‐month history of progressive cognitive impairment. His brain magnetic resonance imaging showed multiple hyperintense lesions in the subarachnoid space, which suggested leptomeningitis. A brain biopsy was performed, and we found a yellowish‐white matter spread on his brain surface. Although the pathological evaluation did not lead to the diagnosis, steroid therapy improved his symptoms in five weeks. However, concomitantly with steroid tapering, his cognitive dysfunction relapsed and he developed swelling of finger joints consistent with rheumatoid arthritis, and then, we finally diagnosed him with rheumatoid meningitis. The characteristic yellowish‐white matter on the brain surface might be helpful for investigating the cause of leptomeningitis with unknown etiology.