Fulminant Idiopathic Hypereosinophilic Syndrome Presenting with Cardiac, Neurologic and Haematologic Involvement.

Introduction: Hypereosinophilic syndrome (HES) is a rare condition characterised by persistent peripheral eosinophilia and associated with multi-organ damage. The most common sources of both morbidity and mortality in HES patients relate to cardiac or neurologic complications, necessitating early recognition and intervention. Case description: A 44-year-old male was admitted with acute chest pain followed by progressive encephalopathy which worsened, indicating the need for intubation. Laboratory studies were significant for marked hypereosinophilia, massive troponin elevation and profound thrombocytopenia. Brain magnetic resonance imaging (MRI) revealed bilateral watershed infarcts. Despite normal ventricular function and mobility on echocardiography, the onset of peak troponin levels concurrently with eosinophilia, resolving promptly after treatment, led us to consider probable acute eosinophilic myocarditis (EM). Thorough workup excluded secondary (parasitic, autoimmune) clonal causes, thus fulfilling consensus-defined criteria for idiopathic HES. High-dose intravenous corticosteroids (methylprednisolone 1 g/day × 3 days) resulted in rapid, synchronous normalisation of eosinophilia, troponin levels and platelet counts, confirming a steroid-responsive, eosinophil-driven pathology. The patient was left with persistent severe neurologic deficits. Conclusion: This case highlights the destructive potential of acute eosinophil degranulation across multiple organs. The rapid improvement with corticosteroids underscores the importance of early recognition and immediate immunosuppressive therapy to limit organ damage. Clinicians should maintain high suspicion for HES in adults with unexplained eosinophilia and multi-organ involvement. LEARNING POINTS: Maintain suspicion for HES in unexplained eosinophilia with multi-organ dysfunction.Eosinophilic myocarditis may present with high troponin despite normal echocardiogram.Bilateral watershed infarcts reflect microvascular hypoperfusion due to eosinophilic endothelial injury.Thrombocytopenia often resolves rapidly with corticosteroids.Early immunosuppression prevents irreversible organ damage.