Abstract 4144526: A Case Presentation of Severe Left Ventricular Dysfunction from Focal Myocarditis due to Immune Checkpoint Inhibitor

Introduction: Immune checkpoint inhibitors (ICI), such as pembrolizumab, are an effective immunotherapy for several malignancies, however, have been associated with adverse events including myocarditis and accelerated atherosclerosis. ICI myocarditis is associated with a mortality rate of up to 33%. This case reports a patient on pembrolizumab with an atypical presentation. Case presentation: A 75-year-old female with a past medical history significant for lung cancer on pembrolizumab and myasthenia gravis presented to the hospital with dyspnea and mild, intermittent exertional chest discomfort. She denied nausea, radiation of pain, diplopia, weakness in extremities, or dysphagia. Workup revealed a leucocyte count of 13,500 cells/uL, pro-brain natriuretic peptide of 13,458 pg/mL, troponin of 26 ng/L, and a normal erythrocyte sedimentation rate and C reactive protein. A chest computed tomography was performed that showed mild bilateral pleural effusion and no pulmonary embolism. A nuclear stress test showed no evidence of ischemia but showed a severely reduced left ventricular ejection fraction (LVEF) at 29%. An echocardiogram confirmed that the ejection fraction was reduced at 23% (baseline LVEF was 60% from 1 year ago). Cardiac MRI revealed a mildly increased regional T2 signal in the anterolateral wall, mildly elevated extracellular volume fraction, and no late gadolinium enhancement. With ongoing clinical suspicion despite equivocal findings on cardiac MRI, an endomyocardial biopsy was done that revealed a single small aggregate of lymphocytes present in 1 of 6 tissue samples. Ultimately, with the single site of aggregated lymphocytes on biopsy, a diagnosis of ICI myocarditis was determined, and the patient was started on high-dose intravenous glucocorticoids as well as bisoprolol, empagliflozin, spironolactone, and Entresto for heart failure management as she was able to tolerate. Discussion: Myocarditis due to pembrolizumab is a rare, but potentially lethal adverse effect. Patients typically have abnormal electrocardiograms and elevated cardiac biomarkers. Cardiac MRIs have sensitivity and specificity of 68% and 91% respectively for diagnosis, and the gold standard is endomyocardial biopsy however, it is limited due to sampling error. Our patient had an unusual presentation, but with both imaging and biopsy, we found a case of focal myocarditis with severe left ventricular dysfunction, which typically is seen with fulminant myocarditis.