Chapter 23 - Evaluating patients with eosinophilia and eosinophilic disorders

Abstract

Eosinophilia can pose a diagnostic challenge for the clinician whether it is found incidentally, in the context of a drug reaction, or as part of evaluation for specific organ-associated signs or symptoms. Eosinophils have complex and multifaceted roles, which include but are not limited to immune regulation, inflammatory responses, and response to infections. Eosinophils are a subset of white blood cells with a short circulating half-life and are primarily considered tissue leukocytes. Although peripheral eosinophil counts of greater than 450–550cells/µL are generally considered elevated, it is important to realize that tissue eosinophilia can be seen without peripheral eosinophilia. The degree of eosinophilia may serve as a guide to the differential diagnosis although does not usually help pinpoint the exact cause of eosinophilia. For instance, although mild eosinophilia may suggest atopic disease, more severe eosinophilia does not necessarily exclude those conditions. On the other hand, severe eosinophilia may suggest a myeloid neoplasm but could also be seen in the context of parasitic infestations, inflammatory responses, or drug reactions. Secondary etiologies of eosinophilia, such as allergies/atopy, drugs, and infections, should always be investigated, as treatment of these conditions generally results in symptom improvement. If evaluation for secondary causes of persistent eosinophilia is nonrevealing, workup for hypereosinophilic syndrome should be pursued. This heterogenous group of disorders includes several variants of which the two main ones are myeloproliferative and lymphocytic. The potential for organ damage should be continuously considered throughout evaluation and management of patients with eosinophilia as there is a broad spectrum of clinical manifestations associated with eosinophilia ranging from asymptomatic presentations to potentially fatal complications, such as persistent organ damage, thromboembolism, and malignant transformations.