[Case of rheumatoid meningitis: findings on diffusion-weighted image versus FLAIR image]

We report a 63-year-old man with rheumatoid meningitis. At 47-years-old, he developed rheumatoid vasculitis causing arthralgia and skin ulcer. Although the patient had been treated with prednisolone and cyclosporine A, headache and recurrent focal seizures of the right upper limb and generalized seizures developed. Brain magnetic resonance imaging showed high signal intensity lesions on FLAIR MRI and associated abnormal enhancement of the leptomeninges. Part of the lesions also showed patchy high signal intensity on diffusion-weighted imaging (DWI). This features may be useful for differentiating rheumatoid meningitis from subdural empyema, because the extent of the lesions on DWI matches the lesion on FLAIR imaging in patients with subdural empyema. Cerebrospinal fluid analysis revealed monocytic pleocytosis and negative findings for infection or malignancy. After intravenous administration of methylprednisolone (1,000 mg/day for 3 days), the patient showed improvements in headache, cerebrospinal fluid findings and abnormal hyperintensity on DWI. Rheumatoid meningitis is an extremely rare neurological manifestation, but careful attention should be paid even in the inactive stage of rheumatoid arthritis. This disease tends to present with unilateral supratentorial lesions. In this case, serial diffusion-weighted and FLAIR MRI was useful for following the leptomeningeal lesions.