Hypothyroidism as an immune-related adverse event caused by atezolizumab in a patient with muscle spasms: a case report

A 60-year-old man with a history of 4 cycles of atezolizumab treatment for non-small cell lung cancer presented to our hospital with a chief complaint of proximal muscle-dominant spasms. Blood tests showed elevated creatine phosphokinase (CPK) of 8450 U/L and hypothyroidism. There was little improvement even after stopping levetiracetam and pregabalin, and no suspicious physical findings of myositis. After levothyroxine was started for hypothyroidism, his muscle cramps and serum CPK level improved. Hypothyroidism as an immune-related adverse event can cause muscle spasms and is important in the differential diagnosis of muscle spasms in patients treated with immune checkpoint inhibitors.