ICON: Eosinophil disorders

Eosinophil disorders and related syndromes are a heterogeneous group of conditions characterized by marked persistent blood eosinophilia and involvement of one or more organ systems. The hypereosinophilic (HE) state is defined by a persistent eosinophil count exceeding 1.5 · 10⁹/L blood. Several different neoplastic, paraneoplastic, infectious, and allergic disorders may underlie HE. Eosinophil-induced organ damage with more or less typical symptoms may develop in these patients. The final diagnosis is based on clinical, molecular, and histopathologic criteria, and the presence of signs and symptoms indicative of HE-induced organ damage, the latter often manifesting as hypereosinophilic syndrome. The clinical course, prognosis, and response to certain drugs vary greatly among patients and among disease variants. During the last few years, several new markers and targets have been identified, improving diagnosis, prognostication, and therapy for patients with HErelated disorders. Moreover, several attempts have been made to establish robust disease-related criteria and a global classification for HE-related diseases. However, the pathogenesis and mechanisms of HE and of HE-induced organ damage are complex, and expert opinions remain divided. In light of the increasing burden of allergic diseases, the World Allergy Organization; the American Academy of Allergy, Asthma & Immunology; the European Academy of Allergy and Clinical Immunology; and the American College of Allergy, Asthma & Immunology have come together to increase the communication of information about allergies and asthma at a global level. Within the framework of this collaboration, termed the International Collaboration in Asthma, Allergy and Immunology, a series of consensus documents called International Consensus ON (ICON) are being developed to serve as an important resource and support physicians in managing different allergic diseases. This ICON provides an updated proposal for a global nomenclature and classification of HE-related disorders and conditions. The proposal is based on the currently available literature and merges previously published proposals and the classification proposal of the World Health Organization. The International Collaboration in Asthma and Allergy initiated an international coalition among the American Academy of Allergy, Asthma & Immunology; European Academy of Allergy and Clinical Immunology; World Allergy Organization; and American College of Allergy, Asthma and Immunology on eosinophilic disorders. An author group was formed and then divided into individual committees. Within the committee, teams of authors were created to generate content for specific sections of the article. Content was derived from literature searches, relevant published guidelines, and clinical experience. After a draft of the document was assembled, it was collectively reviewed and revised by the authors. Where evidence was lacking or conflicting, the information presented represents the consensus expert opinion of the group.