Eosinophilic Myocarditis: An Often-Overlooked Diagnosis in Patients Presenting with Heart Failure.

Introduction. Hypereosinophilic syndrome (HES) is a rare disease characterized by unexplained peripheral eosinophilia along with evidence of end-organ damage. Cardiac involvement is the most life-threatening consequence and is frequently underreported with a prevalence of around 5%. The gold standard for diagnosis is myocardial biopsy, but less-invasive imaging such as cardiac MR (CMR) has been frequently used to help with the diagnosis. We are presenting a unique case of a patient diagnosed with Eosinophilic myocarditis (EM) supported by CMR with rapid improvement after starting steroid treatment. Case Presentation. A 67-year-old African American female with extensive cardiovascular disease history presenting with chest pain was diagnosed with EM secondary to hypereosinophilic syndrome (HES). Lab workup revealed absolute eosinophils of 4.70 × 10³/μL (normal 0-0.75 × 10³/μL). Transthoracic echocardiography showed mild reduction in left ventricular function and a large obliterating thrombus in the right ventricular apex. CMR showed increased signal intensity at the left ventricular and right ventricular apex, consistent with myocardial edema. Subsequently, the patient was placed on dexamethasone 10 mg daily with significant symptomatic improvement. Discussion. EM is a rare complication of hypereosinophilic syndrome and can mimic common cardiovascular diseases such as acute exacerbation of heart failure or myocardial infarction. A high index of suspicion is essential especially in the setting of suggestive lab workup. CMR is a promising noninvasive and cost-effective alternative for myocardial biopsy in diagnosis.