Clinical overview of hypereosinophilic syndromes.

Hypereosinophilic syndrome (HES) or syndromes are disorders characterized by chronic peripheral blood hypereosinophilia with damage to various organs due toeosinophilic infiltration and release of mediators. HES is most accurately described as a collection of heterogeneous disorders, with some similarities in clinical features, but many differences. Based on recent advances in molecular and genetic diagnostic techniques and increasing experience with differences in clinical features and prognosis, some subtypes of HES have been defined, such as myeloproliferative variants, including chronic eosinophilic leukemia, and lymphocytic variants, but other subtypes remain undefined. Recent evidence suggests that, in addition to differences in clinical features, the range of complications, treatment options, and prognoses differs significantly among the myeloproliferative, lymphocytic, and undefined variants of HES.