REVIEW ARTICLE The Idiopathic Hypereosinophilic Syndrome

T HE IDIOPATHIC hypereosinophilic syndrome (HES) is a leukoproliferative disorder, or more likely disorders, marked by a sustained overproduction of eosinophils. The distinctiveness of the syndrome, in addition to its eosino-philia, is its marked predilection to damage specific organs, including the heart. Such cardiac pathology is not unique to the idiopathic HES, because it may develop with eosinophilia associated with other diseases with identifiable etiologies. Conversely, yet enigmatically, not all patients with hypereo-sinophilia develop the organ damage characteristic of the HES. There are no specific tests diagnostic of the HES rather, the syndrome is defined by the combination of unexplained prolonged eosinophilia and evidence of organ involvement. We first review the more common and variable hematologic and clinical manifestations of this disorder because these are the features encountered clinically and that must be ex