Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions (FIP1L1::PDGFRA) complicated by Loeffler's endocarditis leading to stroke.

Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions (MLN-TK) represent a distinct category of hematologic malignancies characterized by eosinophil-rich proliferations driven by specific gene rearrangements. Among these, the FIP1L1::PDGFRA fusion is one of the most clinically relevant due to its exquisite sensitivity to imatinib. Loeffler's endocarditis, a complication of eosinophil-mediated endomyocardial damage, can lead to thromboembolic events including ischemic stroke. We report a case of a 56-year-old male who presented with acute onset of right homonymous hemianopia. Neurological evaluation revealed acute infarction in the left occipital lobe and thalamus. Subsequent workup demonstrated marked eosinophilia (absolute eosinophil count 3.05 × 10⁹/L, 43.4%), echocardiographic findings consistent with Loeffler's endocarditis with left ventricular thrombus, and bone marrow eosinophilia (27.5%). Molecular testing confirmed the presence of FIP1L1::PDGFRA fusion, leading to a diagnosis of MLN-TK with FIP1L1::PDGFRA. Treatment with low-dose imatinib (100 mg daily) and enoxaparin resulted in rapid normalization of eosinophil counts and reduction in thrombus size. This case highlights the importance of recognizing eosinophil-associated cardiac and neurologic complications and underscores the diagnostic and therapeutic value of molecular testing in patients with unexplained stroke and eosinophilia.