A case of rheumatoid meningoencephalitis induced by pembrolizumab

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.