Eosinophilic disorders

Classification of eosinophilic disorders. Eosinophilia is either mediated by cytokines (in particular IL-5) or a consequence of mutations in hematopoietic stem cells leading to predominant eosinophil differentiation. Interestingly, even patients with idiopathic (hyper)eosinophilia can be integrated in this simple scheme as soon as information regarding cytokine expression and/or the imatinib response is available.

A proposed algorithm to diagnose eosinophilic disorders. In the first step (step 1), patients should be screened for common triggers of eosinophilia. If no likely cause of eosinophilia is identified, a potential involvement of eosinophil hematopoietins should directly be investigated (step 2). Unfortunately, if no cytokine levels can be detected in serum, an extrinsic eosinophilic disorder cannot be excluded, and no routine assays are currently available regarding in vitro cytokine production by T cells (∗). If there is evidence for a cytokine-driven process, specialized laboratories (immunology-oriented) should be contacted to identify the cytokine-producing cell, and a tumor should be excluded (step 3). Similarly, if the cytokine analysis is negative, further diagnostic procedures should also be performed by specialized laboratories (hematology-oriented) to answer the question whether a stem cell disorder might be the underlining cause of eosinophilia (step 3).