A Case of Nivolumab-Induced Multiorgan Toxicity: Concurrent Myocarditis and Interstitial Pneumonia.

This is a rare case of nivolumab-induced multiorgan toxicity presenting as concurrent myocarditis and interstitial pneumonia in an 81-year-old patient with metastatic renal cell carcinoma. Immune checkpoint inhibitor (ICI)-associated myocarditis, a high-mortality immune-related adverse event (irAE), often presents with nonspecific symptoms, complicating early diagnosis, particularly when coexisting with other irAEs. In this case, the diagnosis was supported by elevated cardiac biomarkers, multimodal imaging findings (echocardiography, cardiac MRI, and coronary CT angiography), and electrocardiogram (ECG) abnormalities, including new-onset atrial fibrillation and right bundle branch block, indicative of myocardial involvement. High-dose methylprednisolone (1 g/day) was initiated on the second hospital day, followed by a gradual tapering regimen based on troponin trends and clinical improvement, leading to the resolution of myocarditis. This case underscores the importance of early recognition of ECG abnormalities as a diagnostic clue and highlights the diagnostic challenges of distinguishing myocarditis from other irAEs in patients receiving ICIs.