[Practical approach to hypereosinophilia]

Hypereosinophilia is a common clinical finding, and is generally associated with an underlying disease, mainly parasitosis, atopic disorders, drug hypersensitivity, and certain solid and haematological malignancies. Appropriate therapeutic management requires identification of the cause, through careful clinical examination and various technical investigations. Occasionally, thorough diagnostic work-up fails to identify an underlying disorder; the term hypereosinophilic syndrome is used when moderate or severe hypereosinophilia is associated with multi-organ involvement. Indeed, whatever its cause, when the blood eosinophil level is greater than 1500 per microfiter, there is a significant risk of complications directly related to the presence of eosinophils in tissues. The major target organs are the skin, lungs, digestive system, nervous system, and the heart. Reduction of blood eosinophil levels becomes an aim in itself in such cases, and recent studies on pathogenesis of hypereosinophilic syndrome have had an impact on the choice of therapeutic agents used to this end. Imatinib has become first line treatment for a disease variant associated with a somatic mutation involving pluripotent hematopoietic stem cells that generates autonomous tyrosine kinase activity, leading to clonal expansion of eosinophils. For all other patients, gluco-corticoids remain first choice. In case of cortico-resistance or if a cortico-sparing agent is required, options include interferon-alpha, hydroxyurea, or mepolizumab, a monoclonal anti-IL-5 antibody that has recently shown efficacy as a cortico-sparing agent for hypereosinophilic syndrome in a well-conducted clinical trial.