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

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).