[A case of meningoencephalitis associated with pembrolizumab treated for squamous cell lung cancer].

A 61-year-old man with squamous cell lung cancer was admitted to our hospital because of consciousness disturbance after treated with pembrolizumab. Cerebrospinal fluid examination revealed increased protein level (209.2 mg/dl) and lymphocytic pleocytosis(79/μl). He was diagnosed as a meningoencephalitis probably caused by an immune-related adverse event (irAE) of immune checkpoint inhibitors (ICIs), and was successfully treated with 1,000 mg methylprednisolone intravenously for 3 days twice and the consequent oral 1 mg/kg prednisolone. As ICIs, which activate the immune systems, are becoming important choices of the treatments against malignancies, we should keep the possibility of irAE in mind and, when needed, start the treatment as soon as possible.