Myocarditis: A Rare Complication of Immune Checkpoint Inhibitor Therapy.

Immune checkpoint inhibitors (ICIs) are a class of immunotherapy agents that are often used in cancer treatment. A rare but life-threatening complication that can be seen is ICI-induced myocarditis. We discuss a case of pembrolizumab-induced myocarditis and the nuances involved in timely diagnosis and treatment. A 64-year-old female with a past medical history significant for metastatic right-sided colorectal adenocarcinoma undergoing immunotherapy with pembrolizumab presented with worsening shortness of breath and was found to be hypoxic. Initial laboratory analysis was remarkable for troponin of 0.35 ng/mL, which later peaked at 6.01 ng/mL. The electrocardiogram showed non-specific ST segment changes in the anteroseptal leads, and a subsequent echocardiogram revealed severely reduced left ventricular systolic function with an ejection fraction of 25%. Coronary angiography showed non-obstructive coronary arteries. As the patient was on pembrolizumab immunotherapy for cancer, there was high suspicion of ICI-induced myocarditis, and the patient was started empirically on steroids. Subsequently, cardiac magnetic resonance imaging was done, which confirmed the diagnosis of myocarditis. Pembrolizumab therapy was discontinued, and she was started on guideline-directed medical therapy for heart failure. While ICIs have transformed cancer therapy, healthcare providers must be vigilant for immune-related adverse events such as myocarditis. Early recognition, prompt management, and close monitoring are crucial for optimizing patient outcomes.