Lambert-Eaton Myasthenic Syndrome Caused by Atezolizumab in a Patient with Small-cell Lung Cancer

We herein report a 74-year-old man who developed Lambert-Eaton myasthenic syndrome (LEMS) during atezolizumab treatment for extensive-stage small-cell lung cancer. He was started on maintenance immunotherapy with atezolizumab every three weeks after four cycles of atezolizumab plus carboplatin plus etoposide combination therapy. After 13 cycles of maintenance atezolizumab therapy, he complained of muscular weakness and fatigue. Findings from a nerve conduction study and positive findings for anti-P/Q-type voltage-gated calcium channel antibody resulted in a diagnosis of LEMS. This was a rare case of LEMS as a neurological immune-related adverse event induced by atezolizumab therapy.