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The hypereosinophilic syndrome is a disease process characterized by a persistently elevated eosinophil count (≥ 1500 eosinophils/mm3) in the blood for at least six months without any recognizable cause after a careful workup, with evidence of involvement of either the heart, nervous system, or bone marrow.
There are two forms of the hypereosinophilic syndrome: Endomyocardial fibrosis and Loeffler's endocarditis. Endomyocardial fibrosis (also known as Davies disease) is seen in Africa and South America, while Loeffler's endocarditis does not have any geographic predisposition.
In both forms of the hypereosinophilic syndrome, the eosinophilia causes infiltration of the myocardium of the heart, which leads to fibrotic thickening of portions of the heart. The portions of the heart most effected by this disease are the apex of the left and right ventricles. Because of the infiltrative nature of the disease process, the cavity of the ventricles of the heart diminish in size, causing an obliterative cardiomyopathy and restriction to the inflow of blood in to the chambers of the heart.