ABSTRACT
Eosinophilia is defined as elevation in the absolute eosinophil count (AEC), with severity divided into mild (AEC 500–1500 cells/μL), moderate (AEC 1500–5000 cells/μL), and severe (AEC >5000 cells/μL). Other definitions include hypereosinophilia, which is defined as blood eosinophilia ≥1500 cells/μL on at least two occasions or evidence of prominent tissue eosinophilia associated with marked blood eosinophilia. Hypereosinophilic syndrome (HES) is defined by the association of hypereosinophilia with eosinophil-mediated organ damage and/or dysfunction, provided other potential causes of the damage have been excluded. Causes of eosinophilia include medications, infections, allergic diseases, hematologic/neoplastic diseases, and HES, among other causes. HESs are classified into myeloproliferative (subdivided into myeloproliferative HES and chronic eosinophilic leukemia), lymphocytic HES, familial HES, overlap disorders, associated HES, and undefined (subdivided into hypereosinophilia of undetermined significance and other). Clinical manifestations/complications of HES are based on organ/system involvement such as hematologic, cutaneous, cardiovascular, pulmonary, gastrointestinal, rheumatologic, and neurologic systems. Diagnosis of HES and investigations include general tests, specific tests to screen for end-organ involvement, and others such as imaging. Management options of HES include corticosteroids, hydroxyurea, interferon-α, tyrosine kinase inhibitors, immunomodulatory agents, cytotoxic therapy, and allogenic stem cell transplantation.
