ABSTRACT
Vaccination is useful for the prevention of COVID-19 and is recommended for everyone, especially people with a weakened immune system. However, various neurological complications have been reported following vaccination. Here, we report the case of a 25 years-old, Japanese man, who presented with acute encephalopathy two days after the second dose of the COVID-19 vaccine. He had been treated with nivolumab, a medication used to treat cancer. He had a high fever and was confused upon admission, and the antibody test was positive for anti-myelin oligodendrocyte glycoproteins. Abnormal signal intensity at the splenium corporis callosi was observed on diffusion-weighted imaging of the brain. We diagnosed him with autoimmune encephalitis and initiated intravenous methylprednisolone, after which, the patient's symptoms rapidly subsided.