Introduction: Hypereosinophilic syndromes (HES) are 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.

Aim:  To present clinical, laboratory, functional features and outcomes in patients with idiopathic HES treated with biologic agents targeting eosinophils.

Methods: Patients with idiopathic HES treated with anti-eosinophilic agent between 01/10/2019 and 02/02/2023 were included in the study.

Results: Eight patients with diagnosis of idiopathic HES were included in the study [M/F: 4/4, mean age ± SD =52.1 ± 20.1, smokers/never smokers: 3/5]. Asthma was present in all (100%, n=8) patients, 4 patients (50%) presented with eosinophilic pleural effusions and one with bilateral eyelid angioedema. Six patients (75%) were treated with mepolizumab (300 mg/month) and 2 (25%) with benralizumab (30 mg/8 weeks). Mean value of eosinophils ± SD at baseline and 6 months post-treatment were 7179 ± 5599/?l and 72 ± 89/?l, respectively. All patients (n=8) experienced elimination of asthma flares, asthma control (ACQ<0.75), functional improvement (mean ?FEV1: 857 ± 594 ml) and 75% reduction in oral corticosteroids. No-treatment related adverse events were noticed.

Conclusion: 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.