Neoplastic Hypereosinophilia Syndrome: When To Suspect?

Abstract

Chronic Eosinophilic Leukemia (CEL) and myeloid neoplasms with FIP1L1-PDGFRA rearrangements are rare clonal disorders. In resource-limited settings, distinguishing these from reactive eosinophilia (allergic or parasitic) is challenging but critical, as targeted therapy can prevent irreversible organ damage. This  27-year-old male presented with recurrent vomiting and high TLC 33,000/mm³ with absolute eosinophilia (60%). The patient was diagnosed with a Myeloid Neoplasm with tyrosine kinase fusion (per WHO/ICC 2022) and achieved rapid clinical improvement on Imatinib 400mg.This case highlights that molecular screening should be prioritized over exhaustive allergy/infectious workups in patients with unexplained eosinophilia and splenomegaly, even when morphology appears mature. Early identification of the FIP1L1-PDGFRAmutation is life-saving and cost-effective, as it allows for highly successful, targeted treatment with Imatinib and preventing irreversible end organ damage.