The hypereosinophilic syndrome in acute lymphocytic leukemia.

A 21-year-old white man presented with marked peripheral blood eosinophilia that later evolved into acute lymphocytic leukemia (FAB2 ALL). He died precipitously from refractory congestive heart failure immediately after antileukemic therapy was started. Autopsy revealed multiorgan infiltration with eosinophils and the typical cardiac findings of Löfflers endocarditis. Clinical and pathologic features of this and the 14 other cases of ALL and the hypereosinophilic syndrome (HES) reported in the English-language literature are described. The eosinophilia in these cases is reactive and resolves with successful leukemia remission induction. Hydroxyurea is effective in rapidly lowering eosinophil counts. Early use of hydroxyurea in this disease may improve patient survival and decrease the risk of sudden cardiac death.