Epstein-Barr virus encephalitis in a patient with rheumatoid arthritis.

A 53-year-old woman with a 6-year history of rheumatoid arthritis (RA) presented with pharyngeal pain, fever, and altered mental status. The patient had been treated with methotrexate (MTX) 12 mg/week, baricitinib 4 mg/day, and tacrolimus 2 mg/day. Magnetic resonance imaging of the brain revealed diffuse high-intensity lesions in the cerebral white matter, basal ganglia, brainstem, and right cerebellar hemisphere. She was diagnosed with Epstein-Barr virus (EBV) encephalitis due to elevated levels of EBV-DNA in the cerebrospinal fluid and serum. Although MTX-associated lymphoproliferative disorders are well-known complications in patients with RA, EBV encephalitis requires careful attention for such patients undergoing treatment with multiple potent immunosuppressants.