Evaluation and differential diagnosis of marked, persistent eosinophilia

Hyperosinophilic syndromes (HES) are a group of heterogeneous disorders many of which remain ill-defined. By definition, the HES must be distinguishedfrom other disorders with persistently elevated eosinophilia with a defined cause. Although marked eosinophilia worldwide is most commonly caused by helminth (worm) infections, the diagnostic approach must include noninfectious (nonparasitic) causes of marked eosinophilia as well.