Eosinophilic disorders in various diseases.

Peripheral and tissue eosinophilia are usually associated with a variety of inflammatory, malignant, and infectious conditions. As the presence of eosinophils in the tissues may cause significant cellular damage to vital organs such as the heart, tissue eosinophilia should be diagnosed and treated promptly. One operative way to evaluate eosinophilic disorders is to classify them into extrinsic and intrinsic. While extrinsic eosinophilic disorders are usually due to the production of eosinopoietic factors derived from T cells or tumor cells, the intrinsic types generally are the result of genetic mutations in the eosinophilic lineage. As we understand more the biology of eosinophils, only a few eosinophilic disorders remain idiopathic. The purpose of this article is to help the clinician classify in an operational manner most eosinophilic disorders, using the extrinsic and intrinsic model. This may facilitate not only a better understanding of the role of eosinophils in these disorders, but also help the systematic clinical work-up and potential treatment of affected patients.