[Investigation of chronic hypereosinophilia: new perspectives].

In some circumstances and despite investigations, no aetiology is found for hypereosinophilia. This becomes of particular concern when hypereosinophilia is elevated and persistent. While some chronic hypereosinophilias signal the onset of malignant haemopathies, others remain unexplained for up to several years. But all may cause severe complications to the viscera, among which cardiopathies, and in particular endomyocardial fibrosis, are predominant. New data on chronic unexplained hypereosinophilia point to regulation defects in eosinophils or more often in T lymphocytes. Thanks to simple investigations such as flow cytometry, along with other more sophisticated procedures, we should soon be better equipped to classify chronic hypereosinophilia and, in the long term, to define more adequate strategies for treatment.