Loeffler Syndrome in FIP1L1-PDGFRA-Positive Myeloid Neoplasm.

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. 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. This case illustrates eosinophilic cardiomyopathy secondary to a specific genetic neoplasm. Early recognition, multimodality cardiac imaging, and targeted therapy are essential to improve outcomes. 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.