Hypereosinophilic syndrome (HES) is a heterogeneous group of conditions that is defined at its core by hypereosinophilia (HE) (blood eosinophil count of >1.5×10(9)/L) and organ damage directly attributable to the HE. Cardiac dysfunction occurs frequently in all forms of HES and is a major cause of morbidity and mortality. Once a significantly elevated eosinophil count is identified, it must be confirmed on repeat testing and the aetiology for the HE must be rigorously sought out with a focus on identifying whether organ dysfunction is occurring. Echocardiography is routinely performed to assess for cardiac involvement, looking for evidence of left ventricular and/or right ventricular apical obliteration or thrombi or a restrictive cardiomyopathy. Cardiac magnetic resonance imaging and CT are often useful adjuncts to establish the diagnosis but endomyocardial biopsy remains the gold standard. To decrease the degree of eosinophilia, treatment can include corticosteroids and/or imatinib based on the aetiology. Anticoagulation, standard heart failure therapy for a restrictive cardiomyopathy and finally cardiac transplantation may be indicated in the treatment algorithm.
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