Three-year sustained remission with mepolizumab in a rare eosinophilic disease: idiopathic chronic eosinophilic pneumonia.

Background: Idiopathic chronic eosinophilic pneumonia (ICEP) is a rare eosinophilic lung disease with a high relapse rate and substantial oral corticosteroid (OCS) burden. While mepolizumab, an anti-IL-5 monoclonal antibody, has shown promise in case reports and small series, evidence from long-term follow-up studies remains limited. Methods: We conducted a single-centre, registry-based prospective observational study including a small case series of patients with ICEP and concomitant severe eosinophilic asthma who were treated with mepolizumab (100 mg every 4 weeks) for at least 36 months. Data were extracted from the Ege Severe Asthma Registry ESAR, a dynamic real-world database. ICEP relapses, asthma exacerbations, peripheral eosinophil counts, radiological findings, annual cumulative methylprednisolone dose and OCS use duration were evaluated longitudinally before and after mepolizumab initiation. Results: During the two-year inclusion period, 150 new severe asthma patients were registered in the Ege Severe Asthma Registry ESAR; among them, six patients (n:6/150) were initiated on monthly 100 mg mepolizumab based on coexisting diagnoses of severe asthma and relapsing ICEP. All patients had a history of corticosteroid-responsive disease with frequent relapses. After completing a three-year follow-up under regular mepolizumab treatment, significant reductions were observed in oral corticosteroid (OCS) use duration ( Conclusion: To our knowledge, this study represents one of the longest real-world follow-up reports of patients with the rare disease ICEP receiving Anti-IL-5 mepolizumab at the severe asthma treatment dose. Our results indicate that, over a three-year course, mepolizumab 100 mg monthly provided sustained relapse control and markedly reduced OCS dependency in ICEP, a disease well known for its frequent relapses.