Refractory Idiopathic Hypereosinophilic Syndrome Presenting with Myocarditis and Responding to Imatinib: A Case Report.

Idiopathic hypereosinophilic syndrome (HES) is a rare disorder characterized by persistent hypereosinophilia leading to multi-organ dysfunction. Its clinical manifestations vary widely; however, cardiac and neurological involvement are the leading causes of morbidity and mortality. Corticosteroids are the initial treatment of choice, but in idiopathic HES resistant to corticosteroids, second-line therapy should be considered. Imatinib is usually reserved for patients with a positive platelet-derived growth factor receptor A (PDGFR-A) mutation; however, its use in idiopathic HES with a negative PDGFR mutation is debatable given that such patients usually respond well to high doses of corticosteroids. Here, we present a case of a young male with corticosteroid-refractory idiopathic HES successfully treated with imatinib. The patient presented with features suggestive of acute coronary syndrome and confusion. A coronary angiogram was normal. Echocardiography showed an ejection fraction of 37%, and brain imaging showed evidence of multifocal cerebral thromboembolic infarcts. During the hospital stay, the patient developed diffuse alveolar hemorrhage. Biochemically, it was noted that the patient had hypereosinophilia. Through thorough workup, a diagnosis of idiopathic HES was established. The patient was started on high-dose corticosteroid (500 mg intravenous methylprednisolone daily) followed by a maintenance dose of prednisolone (0.5 mg/kg/day), but had no response. Second-line therapy with imatinib (400 mg per oral daily for 4 days and then down-titrated to 100 mg daily) was initiated, which resulted in drastic biochemical and clinical improvements. This case report supports the efficacy of imatinib as a second-line agent in corticosteroid-resistant idiopathic HES with a negative PDGFR mutation.