The idiopathic hypereosinophilic syndrome: clinical presentation, pathogenesis and therapeutic strategies.

The idiopathic hypereosinophilic syndrome (HES) is a heterogenous disease entity characterized by persistent unexplained hypereosinophilia generally complicated by end-organ damage. Correct diagnosis and management are important in order to prevent long-term complications. Furthermore, it appears that HES represents a premalignant state in some patients, and close follow-up is necessary to detect early signs of malignant transformation. Previous studies of patient cohorts have led to the identification of a subgroup of patients with various clinical and biological features of primitive myeloproliferative disease. Patients in this subgroup have a clinically more aggressive disease in terms of organ damage and eventually develop acute myeloid leukemia. Among the remaining patients, it appears that some present an underlying T-cell disorder characterized by overproduction of Th2-type cytokines in vivo. Indeed, lymphocytes belonging to the Th2 subset are implicated in the maturation, activation and recruitment of eosinophils, essentially through the production of IL-5. Such patients appear to present a more benign disease at short term; however, they may develop T-cell lymphoma years after initial diagnosis. Therapy of HES includes glucocorticoids, hydroxyurea and more recently, interferon-alpha. Prednisone is generally recommended initially, followed by hydroxyurea in case of treatment failure. Until now, interferon-alpha has been reserved for refractory cases of HES. Our proposal for a new treatment strategy, based on current understanding of the pathogenesis of different subgroups of HES and on the mechanisms of action of the proposed therapeutic agents, which will be discussed in detail. Moreover, prevention of malignant transformation has become a new subject of concern when considering the beneficial effects of drugs.