Abstract
Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase fusions (M/LN-eo-TK) are uncommon but highly treatable disorders. Among them, FIP1L1::PDGFRA-driven disease is distinguished by marked eosinophilia and multisystem involvement that can rapidly reverse with targeted therapy. We describe a 50-year-old man with uncontrolled diabetes who presented with progressive dyspnea, abdominal discomfort, and painful necrotic scrotal ulcers. Laboratory testing revealed leukocytosis with a striking absolute eosinophil count of 22.1 × 10³/µL, while imaging showed pulmonary infiltrates, small-bowel inflammation, and splenomegaly. Bone marrow examination demonstrated hypercellularity with prominent eosinophilic proliferation. Fluorescence in situ hybridization confirmed a PDGFRA rearrangement with CHIC2 deletion, establishing the diagnosis of FIP1L1::PDGFRA-positive M/LN-eo-TK. Imatinib was initiated at 400 mg daily, later reduced to 200 mg, leading to a rapid normalization of eosinophil counts and resolution of systemic and dermatologic manifestations within 2 weeks. The case highlights how delayed recognition of clonal eosinophilia can permit extensive organ injury, whereas early molecular testing and prompt initiation of imatinib yield dramatic clinical and hematologic remission. Persistent hypereosinophilia, particularly with cutaneous or gastrointestinal involvement, should prompt evaluation for PDGFRA-rearranged disease to enable early intervention and prevent irreversible tissue damage.