Abstract
BACKGROUND: Eosinophilic myocarditis and restrictive cardiomyopathy (Loeffler syndrome) are rare but severe manifestations of hypereosinophilic syndromes, especially in myeloid/lymphoid neoplasms with tyrosine kinase gene rearrangements. CASE SUMMARY: A 40-year-old man presented with progressive dyspnea, constitutional symptoms, and marked eosinophilia. Imaging showed apical thrombi, restrictive physiology, and pericardial effusion. Bone marrow studies confirmed an FIP1L1-platelet-derived growth factor receptor α-positive myeloid/lymphoid neoplasm. Treatment with corticosteroids and imatinib led to clinical and echocardiographic improvement, eosinophil normalization, and molecular remission within 3 months. DISCUSSION: This case illustrates eosinophilic cardiomyopathy secondary to a specific genetic neoplasm. Early recognition, multimodality cardiac imaging, and targeted therapy are essential to improve outcomes. TAKE-HOME MESSAGES: Cardiac involvement in hypereosinophilic syndromes requires multidisciplinary management combining cytoreductive therapy, anticoagulation when thrombus is present, and serial cardiac magnetic resonance. Testing for FIP1L1-platelet-derived growth factor receptor α is disease-defining and therapy-guiding given the marked response to imatinib.