Delayed-Onset ICI-Associated Myocarditis: When Immunotherapy's Cardiac Consequences Outlast Treatment

Immune checkpoint inhibitors (ICIs) are increasingly used in cancer therapy, but they may cause immune-related adverse events, including myocarditis, a rare but potentially fatal complication.

A 74-year-old man with lung adenocarcinoma treated with durvalumab presented with acute-on-chronic hypoxemic respiratory failure and hypotension. He was recently diagnosed with ICI pneumonitis and was taking corticosteroids. Evaluation revealed elevated troponins, new T-wave inversions, and reduced left ventricular ejection fraction. Coronary angiography showed no obstructive disease. Cardiac magnetic resonance revealed diffuse myocardial edema with nonischemic late gadolinium enhancement. Endomyocardial biopsy confirmed lymphohistiocytic infiltrates consistent with ICI myocarditis.

ICI-associated myocarditis can mimic acute coronary syndrome or stress cardiomyopathy. Cardiac magnetic resonance and biopsy are essential for accurate diagnosis. Early recognition and initiation of high-dose corticosteroids are critical for improved outcomes.

ICI myocarditis should be considered in patients with prior ICI exposure and new cardiomyopathy. Multimodal imaging and biopsy are key to timely diagnosis and management.