[Diagnostic approach to hypereosinophilia]

Blood hypereosinophilia is a common finding in medical practice requiring further investigation. There are a wide range of potential causes including atopic disorder, drug allergy, parasitic infection, certain forms of immune deficiency, inflammatory process, hemopathy, and malignant disease. Diagnosis of persistent hypereosinophilia not associated with parasitic infection is one of the major diagnostic dilemmas in medicine. If through investigation fails to achieve diagnosis, idiopathic hypereosinophilia may be suspected including the possibility of essential hypereosinophilic syndrome or Chusid syndrome. The primary determination for diagnosis of hypereosinophilia involves the presence or absence of parasitic infection. If parasitic infection is ruled out, it is often difficult to distinguish benign, self-limiting forms from severe forms requiring careful surveillance and subsequent treatment. From a pathophysiological standpoint, one may ask if some eosinophilic conditions are not due to deregulation of immunologic mechanisms that normally protect the organism against parasitic infection.