Hypereosinophilia and Hypereosinophilic Syndromes: First Findings From a Nationwide Multicenter Cohort

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. 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. 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). 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. ClinicalTrials.gov identifier: NCT04018118.