Eosinophilic myocarditis: Magnetic resonance imaging -based study of a dramatic response to steroids

A 14-year-old boy presented with a history of dyspnea on exertion for 6 months. A clinical examination and 12-lead electrocardiogram (ECG) yielded unremarkable results. 2D-ECG revealed a large mass obliterating the left ventricular apex with tethering of the anterior mitral leaflet, moderate eccentric mitral regurgitation with moderate pulmonary arterial hypertension, and mild left ventricular dysfunction. Therefore, treatment with angiotensin converting enzyme (ACE) inhibitors, beta blockers, and low-dose diuretics was initiated. A cardiac magnetic resonance imaging (MRI) (Fig. 1a) suggested a left ventricular apical soft tissue mass with obliteration of apex. Late gadolinium enhancement (LGE) images (Fig. 1b) revealed a nonenhanced dark mass (white asterisk) overlying the bright subendocardial enhancement (white arrows) and the surrounding uniform subendocardial LGE in the apical region and papillary muscles with resultant mitral regurgitation and mild dysfunction (43%). The eosinophil count was elevated (1600 cells per mm3 ). Suspecting eosinophilic myocarditis, treatment with prednisolone at 1 mg/kg body weight was initiated. However, the patient was lost to follow-up for 8 months because he had symptomatically improved after taking the prescribed drugs within a few weeks. On the patient’s next visit, a repeat cardiac MRI was performed to reassess the disease status, which showed a significant reduction in the soft tissue mass at the left ventricular apex (Fig. 1c).