Unique presentation of hypereosinophilic syndrome: recurrent mitral prosthetic valve thrombosis without endomyocardial disease.

Hypereosinophilic syndrome (HES) is defined as a prolonged, unexplained peripheral eosinophilia in a patient presenting with end-organ damage. The heart is frequently involved, resulting in eosinophilic endomyocardial disease, which is characterized by mural thrombus formation and endocardial fibrosis. Thromboembolic complications in HES are mediated by material released from eosinophilic granules. Herein is reported the case of a patient who presented, 15 years after valve replacement with a mechanical prosthesis, with clinical signs of recurrent prosthetic valve thrombosis that was caused by missed hypereosinophilia. The unique feature of the case was that the mitral prosthetic valve obstruction was the result of an eosinophilic thrombus, though no tissue infiltration or inflammation had been detected by random biopsy of the left ventricular myocardium. After nine years of effective treatment of HES there were no cardiac or extracardiac complications.