Hypereosinophilic syndromes

Hypereosinophilic syndromes (HES) comprise a heterogeneous group of uncommon diseases that are characterized by peripheral blood eosinophilia (> 1,500/mm(3); > 1.5 G/l), as well as tissue eosinophilia associated with organ dysfunction without other identifiable causes such as allergic diseases, drug hypersensitivity, infections, tumors or lymphomas. By means of modem diagnostic tools including immunologic and molecular methods, 2 main subgroups of HES, the myeloproliferative and lymphocytic variants, have been identified in the last decade. In addition, HES include the familial variant, the episodic type, the benign asymptomatic blood eosinophilia as well as disorders with blood eosinophilia and single organ involvement. Several complex disorders although fulfilling the criteria of HES, e.g. Churg-Strauss syndrome, are still considered as separate entities. Therapeutic options are corticosteroids, but also immunomodulators, cytostatic agents, monoclonal antibodies as well as bone marrow transplantation. Recently, the description of the HES-causing fusion gene FIP1L1-PDGFRA coding a tyrosine kinase gained attention because these patients respond to the tyrosine kinase inhibitor imatinib. In this review, we discuss current concepts of the classification, diagnostic procedures and therapy of HES.