[Hypereosinophilic syndrome--recent developments in diagnosis and treatment]

In case of eosinophilia persisting for more than 6 months a diagnosis of hypereosinophilic syndrome (HES) should be considered if secondary causes of eosinophilia ca be ruled out. Recent studies on the pathogenesis of HES revealed that the syndrome previously coined "idiopathic HES" is comprised of pathogenetically distinct subtypes which are defined by molecular, immunophenotypic or clinical markers. Eosinophilia in HES can be caused by increased production or survival of eosinophils due to cytokines such as interleukin-5 (IL-5) or clonal expansion due to mutations. Distinction of these pathogenetically different subtypes of HES is clinically relevant as new targeted treatment approaches are available for some of these subtypes, such as tyrosine kinase inhibitors for the FIP1L1-PDGFRA-positive myeloproliferativer subtype, immunomodulators such as interferon-alpha or monoclonal antibodies against IL-5 for FIP1L1-PDGFRA-negative patients.