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Diagnosis of hypereosinophilia Volume 12, issue 3, Juin 2006

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Service de médecine interne, hôpital Foch, 40, rue Worth, 92151 Suresnes Cedex

Hypereosinophilia (> 0,5 x 10 9/L) is a common clinical finding that can be secondary to a large variety of diseases. Hypereosinophilia always needs to be elucidating, especially because it can reveal malignancies. The history (travels) and the clinical conditions with an increased total IgE level could suggest helminth infections. Others usual diagnoses include allergic diseases and drug reactions. In a second time, rarer causes must be suspected: specific organ-disease (chronic eosinophilic pneumoniae, bullous pemphigoid…), malignancies (solid tumors, leukemia, and lymphoma) or systemic diseases (vasculitis). When evaluation of a chronic hyperéosinophilie fails to reveal an underlying disease, the diagnosis of hypereosinophilic syndrome (HES) is evocated. HES is defined by unexplained prolonged hypereosinophilia, which can be associated with heterogeneous haematological conditions, mainly myeloproliferative and lymphocytic disease. The myeloproliferative variant can be (but not only) consecutive to a fusion between Fip1-like1 (FIP1L1) and Platelet-derivated growth factor receptor α (PDGFRα) genes, inducing increased tyrosine kinase activity of PDGFRα. Imatinib, a tyrosine kinase inhibitor, is dramatically effective in presence of this fusion product. In the lymphocytic variant, hypereosinophilia is secondary to a primitive Th2 lymphoid disorder, overproducing interleukin 5 (IL-5). Corticosteroids are then considered as the first line therapy. Mepolizumab, an anti IL-5 monoclonal antibody, currently in course of evaluation, is promising, but have only a suspensive action. Despite these recent findings, about 50 % of HES remain unexplained.