Ourania Papaioannou Theodoros Karampitsakos Fotios Sampsonas Argyrios Tzouvelekis ^*

• Department of Respiratory Medicine, General University Hospital of Patras, Pátrai, Greece

Background: Hypereosinophilic syndrome (HES) is a heterogeneous group of rare disorders defined by the presence of marked eosinophilia resulting in end organ damage. Treatment goals include reduction of flares and eosinophils with minimal drug related side-effects. The aim of this study was to present clinical, laboratory, functional features and outcomes in patients with idiopathic HES treated with biologic agents targeting eosinophils.Patients with idiopathic HES treated with anti-eosinophilic agent between 01/10/2019 and 01/10/2023 were retrospectively included in the study.Results: Eleven patients (n=11) with diagnosis of idiopathic HES were included in the study [M/F: 6/5, median age: 54 (95% CI: 38.2 to 68.5), smokers/never smokers: 5/6]. Asthma was present in majority of them (n=8, 72.7%,), four patients (n=4, 36.4%) presented with eosinophilic pleural effusions, two patients (n=2, 18.2%) with cardiac arrhythmias and one with bilateral eyelid angioedema. Eight patients (72.7%) were treated with mepolizumab (300 mg/month) and 3 (27.3%) with benralizumab (30 mg/4 weeks). Median values of eosinophils at baseline and 12 months after initiation of biologic agent were 3000 (95% CI: 2172 to 11365) K/μL and 50 (95% CI: 3 to 190) K/μL, respectively. All patients with concomitant asthma (n=8) experienced elimination of asthma flares, asthma control (ACQ<0.75), functional improvement (mean ΔFEV1: 857 ± 594 ml) and 82% reduction in oral corticosteroids.Biologic agents in patients with idiopathic HES are both safe and effective sparing toxicity of immunosuppressive agents. Real-life data from larger registries are greatly anticipated.