Background: Hypereosinophilic syndromes (HES) are a heterogenous group of eosinophilic disorders. To date, only retrospective studies of limited sample-size and/or follow-up duration are available.
Methods: The COHESion study is a national prospective multicenter multidisciplinary cohort recruiting both adults or children with the spectrum of eosinophilic disorders (including reactive HE/HES [HE/HES-R], idiopathic HES [HES-I], lymphocytic HES [HES-L], neoplastic HE/HES [HE/HES-N], HE of unknown significance [HE-US], as well as IgG4-related disease [IgG4RD] or ANCA-negative eosinophilic granulomatosis with polyangiitis [EGPA] overlaps). Patients are followed-up yearly. All data about final diagnosis, organ involvement assessments, and outcome profiles in HES-I were captured and analyzed centrally by HES expert centers.
Results: From May 2019 to November 2023, 779 patients were included. For this preliminary analysis, 550 cases were available for centralized review (mean ± SD age: 56 ± 18 years, 42% of female patients). The final diagnoses were HES-I (47%), HE/HES-R (16%), HE-US (15%), HE/HES-N (7%), HE/HES-L (6%), IgG4RD (2%), and ANCA-negative EGPA (7%). In the 258 HES-I patients, outcome profiles were classified as follows: 16.3% had a "single-flare" without further relapse, 28.3% had a "relapsing-remitting" disease when there was at least a 6-month period free of symptoms between two flares, 46.1% had a "persistent disease" requiring continuous treatment to avoid relapses (9.3% remained unclassified because of insufficient follow-up).
Conclusions: The COHESion cohort is the first nationwide prospective multicenter study collecting data on the full spectrum of HE/HES disorders. This preliminary analysis confirms that idiopathic HES patients have various outcome profiles, suggesting different underlying pathophysiological mechanisms and the need of patient-specific management.
Trial registration: ClinicalTrials.gov identifier: NCT04018118.
Keywords: eosinophil; eosinophilic granulomatosis with polyangiitis; hypereosinophilia; hypereosinophilic syndrome.
© 2025 European Academy of Allergy and Clinical Immunology and John Wiley & Sons Ltd.