An unusual case of idiopathic hypereosinophilic syndrome presenting with myopericarditis and a polypoid cardiac mass.

Idiopathic hypereosinophilic syndrome (IHES) is a rare systemic disorder with blood eosinophilia and multiple system involvement. Commonly, there is endocardial fibrosis with overlying mural thrombus, and mitral and tricuspid valves can be involved concomitantly. Outflow tracts near the aortic and pulmonary valves are generally protected. We herein describe an atypical case of IHES with a mass on the left ventricular outflow tract (LVOT), which showed regression under steroid therapy. There are two features that make our case worthy of reporting: First, the mitral and tricuspid valves are expected to be involved in IHES, and outflow tracts near the aortic and pulmonary valves are generally protected. Second, within one month of steroid therapy, the vegetation had reduced dramatically in size and signs of myocarditis and pericarditis had also disappeared.