Eosinophilic Myocarditis: A Challenging Diagnosis.

Eosinophilic myocarditis (EM) is a rare subtype of myocarditis that is characterized by eosinophilic infiltration of the myocardium and is associated with peripheral eosinophilia in most cases. The diagnosis is suspected in the presence of acute myocarditis and peripheral eosinophilia and is usually confirmed by endomyocardial biopsy (EMB) before starting steroid therapy. Here, we present a case of severe idiopathic eosinophilic myocarditis in a young man with a history of asthma and peripheral eosinophilia. He was treated with high-dose steroids despite negative EMB, and we noted a dramatic improvement in cardiac function. Our case highlights the importance of cardiac magnetic resonance (CMR) and clinical judgment in establishing the diagnosis of EM irrespective of the histopathologic result.