A case of rheumatoid meningoencephalitis induced by pembrolizumab

Abstract Immune checkpoint inhibitors occasionally cause various side effects, but the occurrence of a severe immune‐related adverse event (irAE) is rare in neurology. We report on a 56‐year‐old woman who suffered from rheumatoid arthritis and recurrent uterine cancer. After treatment with pembrolizumab, she showed visual disturbance followed by acute fever and consciousness disturbance with high‐intensity lesions around the midbrain aqueduct and bilateral caudate heads on FLAIR images of a brain MRI. Her symptoms improved after steroid therapy. However, symptoms relapsed leading to an elevation of the anti‐CCP antibody index. Pembrolizumab‐induced rheumatoid meningoencephalitis was suspected, so additional steroid therapy was provided. This improved her symptoms, turning the anti‐CCP antibody index negative. The present case is the first case of rheumatoid meningoencephalitis induced by pembrolizumab. The combination of MRI findings and elevated anti‐CCP index seems useful for diagnosing rheumatoid meningoencephalitis.