Obstructive Prosthetic Mitral Valve Thrombosis in Idiopathic Hypereosinophilic Syndrome: A Case Report and Review of the Literature Michael W. Hii, Frank C. Firkin, Andrew I. MacIsaac, Michael Yii St. Vincents Hospital Melbourne, Victoria, Australia The idiopathic hypereosinophilic syndrome (HES) is an uncommon condition characterized by an unex- plained elevation of absolute eosinophil count (AEC) to 1.5×10 9 /l, or above, for period of at least six months. The condition is frequently associated with eosinophil- mediated end organ damage (1). Idiopathic HES, as with secondary HES and primary hypereosinophilic clonal hematopoietic disorders (2), has a high incidence of myocardial, pulmonary, neurological and other organ injury. Myocardial fibroelastosis and valvular lesions are common, and successful treatment with valve replacement or resection of fibrotic myocardium has been reported. Herein is described the case of a patient with idiopathic HES and multi-organ complica- tions, including severe mitral valve disease, in whom a functionally obstructive thrombosis of a newly inserted prosthetic mitral valve occurred despite adequate war- farinization, at a time when the AEC was profoundly elevated. Recurrent thrombosis has not occurred over a substantial period following reduction of the AEC with corticosteroid treatment, and subsequent maintenance of the AEC at normal levels. Case report A 32-year-old asthmatic female presented with cough and dyspnea due to moderate cardiac failure. Over the previous 12 years she had experienced five episodes of facial palsy which was diagnosed as multi- ple sclerosis, in spite of negative investigations. She had been admitted to hospital eight weeks previously for a similar episode of dyspnea that had responded to anti-asthma treatment, including corticosteroids. A full blood examination at the time of admission showed a mild hypereosinophilia (eosinophil count 1.5×10 9 /l). Echocardiography and cardiac catheterization on admission showed severe mitral stenosis (mean gradi- ent >20 mmHg) and severe pulmonary hypertension (right ventricular systolic pressure 70 mmHg), but excluded coronary artery disease. Transesophageal echocardiography (TEE) revealed restriction of the posterior leaflet of the mitral valve, and fusion of ante- rior and posterior leaflets at the posteromedial com- missure. The patient was commenced on therapy with frusemide, metoprolol and digoxin as treatment for cardiac failure. On admission to the authors’ institution, the AEC was normal, but two days later the patient developed a self-limiting widespread urticaria, which was attrib- uted to a drug reaction. Despite replacing the patient’s drugs with alternative agents, and resolution of the Address for correspondence: Dr. Michael Hii, Unit 2, Level 17, 15 Collins St., Melbourne 3000, Australia e-mail: mickhii@hotmail.com © Copyright by ICR Publishers 2006 Idiopathic hypereosinophilic syndrome (HES) is an uncommon condition characterized by an unex- plained elevation of absolute eosinophil count (AEC) to ≥1.5×10 9 /l for at least six months, and is frequently associated with eosinophil-mediated end organ dam- age. Idiopathic HES, as with secondary HES and pri- mary hypereosinophilic clonal hematopoietic disorders, has a high incidence of myocardial, pul- monary, neurological and other organ injury. Myocardial fibroelastosis and valvular lesions are common, and successful treatment with valve replacement or resection of fibrotic myocardium has been reported. The case is described of a patient with idiopathic HES and multi-organ complications including severe mitral valve disease, in whom a functionally obstructive thrombosis of a newly inserted prosthetic mitral valve occurred despite ade- quate anticoagulation, when the AEC was profound- ly elevated. Recurrent thrombosis has not occurred over a substantial period following AEC reduction with corticosteroids, and subsequent maintenance at normal levels. The Journal of Heart Valve Disease 2006;15:721-725