[Spontaneous Remission of Encephalitis that Developed 17 Weeks After the Last Dose of Pembrolizumab: A Case Report].

We present a 73-year-old man with a history of lung adenocarcinoma and multiple metastases. He was treated with chemotherapy, including pembrolizumab, but treatment was interrupted due to concurrent drug-induced lung injury. Seventeen weeks after the last dose of pembrolizumab, he developed encephalitis, presenting with a disturbance of consciousness and right hemiplegia. However, his symptoms gradually improved spontaneously and disappeared three weeks after their onset. Late-onset encephalitis after the administration of immune checkpoint inhibitors is rare. In addition, this is the first report of a case in which severe encephalitis recovered spontaneously without leaving sequelae. (Received April 7, 2023; Accepted July 4, 2023; Published October 1, 2023).