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Hypereosinophilic Syndrome — RACP Adult Medicine MCQ

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HardHaematologyHypereosinophilic SyndromeRACP Adult Medicine

A 50-year-old man presents with persistent eosinophilia (15 × 10⁹/L) for 6 months without identifiable cause. He has developed endomyocardial fibrosis with restrictive cardiomyopathy. Parasites, drugs, and allergies have been excluded. FIP1L1-PDGFRA fusion gene is positive. What is the most likely cause of eosinophilia?

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Correct answer: E — Hypereosinophilic syndrome

Persistent marked eosinophilia (>1.5 × 10⁹/L for >6 months) with organ damage (endomyocardial fibrosis) and FIP1L1-PDGFRA fusion is myeloid-type hypereosinophilic syndrome. This specific fusion responds dramatically to low-dose imatinib (100 mg/day). Without treatment, eosinophilic infiltration causes progressive cardiac, pulmonary, GI, and neurological damage.

Reference: WHO – 2022 – Eosinophilic Neoplasms; ELN 2024