A Case of Asymptomatic Immune Checkpoint Inhibitor-associated Myocarditis.

We herein report the case of a 75-year-old man with asymptomatic immune checkpoint inhibitor (ICI)-associated myocarditis diagnosed on the basis of elevated levels of creatine kinase (CK), CK-myocardial band and troponin I (TNI). He was suspected of being complicated with myasthenia gravis (MG). High-dose prednisolone (PSL) is associated with a risk of MG exacerbation; therefore, PSL therapy was gradually increased from 5 mg/day to 20 mg/day, which resulted in the normalization of the TNI level, and no PSL-related side effects occurred. MG easily complicates myocarditis as an immune-related adverse event; thus, the treatment plan should be carefully considered.