Early Diagnosis, Delayed Treatment, and Fulminant Progression of Immune Checkpoint Inhibitor-Associated Myocarditis

BACKGROUND: Prompt immunosuppressive therapy is recommended for immune checkpoint inhibitor-associated myocarditis; however, the optimal timing in asymptomatic patients remains uncertain. CASE SUMMARY: A woman in her 60s receiving adjuvant pembrolizumab for melanoma developed asymptomatic cardiac troponin I (cTnI) elevation (93 pg/mL) before her ninth cycle. Cardiac magnetic resonance imaging met diagnostic criteria for myocarditis; however, immunosuppressive therapy was withheld because of the absence of symptoms and mild cTnI elevation. One week later, she developed symptomatic myocarditis with a marked cTnI increase (4,115 pg/mL), requiring intensive care, corticosteroid pulse therapy, and temporary mechanical circulatory support. DISCUSSION: This case demonstrates that asymptomatic immune checkpoint inhibitor-associated myocarditis can progress rapidly despite seemingly low initial risk, underscoring the importance of ongoing risk assessment following diagnosis. TAKE-HOME MESSAGES: Early diagnosis alone may not be sufficient to prevent disease progression. Risk stratification and timely intervention during the presymptomatic phase may improve patient outcomes.