Pembrolizumab-induced autoimmune encephalitis in a patient with advanced non-small cell lung cancer: A case report

Immune checkpoint inhibitors have markedly changed lung cancer treatment and improved overall survival. However, immune checkpoint inhibitors may be associated with various adverse events, including encephalitis, although this complication is rare. We herein describe the clinical characteristics of a case of immune checkpoint inhibitor-induced encephalitis and its management. A 51-year-old man with squamous non-small cell lung cancer was receiving pembrolizumab treatment when he suddenly displayed an altered level of consciousness. Cerebrospinal fluid examination revealed elevated lymphocyte count and autoimmune encephalitis was suspected. The patient was promptly started on steroids and his consciousness immediately improved. Pembrolizumab treatment was discontinued; however, stable disease was maintained. In conclusion, encephalitis is a rare but possibly fatal adverse event of immune checkpoint inhibitors, and prompt diagnosis and treatment are mandatory.