Abstract Background Loeffler’s endocarditis is a serious manifestation of hypereosinophilia, and it is associated with endomyocardial fibrosis, thrombus formation, valvular dysfunction, and, rarely, intracardiac mass lesions. Case summary A 28-year-old male patient had progressive dyspnoea, facial oedema, and fatigue for 2 years. A 2D trans-thoracic echocardiogram revealed a 24 × 15 mm mobile echogenic mass attached to the mitral valve, associated with severe mitral regurgitation. Blood counts showed hypereosinophilia. Cardiac MRI showed subendocardial fibrosis. Bone marrow examination showed increased hypercellularity, and molecular testing was positive for FIP1L1–PDGFRA fusion, confirming a myeloid neoplasm with hypereosinophilia. The patient was treated with corticosteroids, anticoagulation, and Imatinib. Following initiation of therapy, the mass size reduced, and the patient improved symptomatically. Discussion This case emphasizes the importance of a thorough diagnostic workup, including genetic testing in Loeffler’s Syndrome, to guide therapy. Recognizing molecularly driven eosinophilic disorders is essential, as targeted treatment can significantly improve prognosis. The presence of the Fip1-Like1-platelet-derived growth factor receptor alpha (FIP1L1–PDGFRα) fusion gene is a rare cause of hypereosinophilic syndrome requiring a distinct therapeutic approach.
Rao et al. (2026) studied this question.