Chronic Rhinosinusitis With Nasal Polyposis in EGPA: A Real-Life Multidimensional Analysis Through Mepolizumab Dosing and Role of Adjunctive Endoscopic Sinus Surgery (ESS)

Background: Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare necrotizing vasculitis involving upper- and lower-airways. Despite biologics, sinonasal disease often persists. Evidence on ENT trajectories under anti-IL5 treatment and role of endoscopic sinus surgery (ESS) remains limited and is often described without standardized assessment tools. This study provides a systematic, multidimensional evaluation of sinonasal outcomes under biologic therapy and analyzes the role of ESS in a real-life cohort. Methods: We retrospectively analyzed 52 EGPA patients with a 24-month follow-up on mepolizumab. Sinonasal disease was assessed by Nasal Polyp Score (NPS), Lund–Kennedy Score (LKS), Lund–Mackay score (LMK), and SNOT-22, while systemic activity was assessed by Birmingham Vasculitis Activity Score (BVAS). Patients were stratified by mepolizumab regimen (100 mg, 300 mg, and step-down). Predictors of adjunctive ESS were explored through multivariate logistic regression. Results: Systemic remission occurred in >90% of patients, with marked eosinophil suppression (median 700 → 59.5 cells/µL) and BVAS = 0. Conversely, NPS and LKS remained stable [IQR]: (NPS 4 [3–5] → 4 [2–5]; LKS 6 [4–8] → 5 [2–7.75]. Polyps persisted in 64% and mucosal edema/discharge in 92% of population. Continuous 100 mg therapy showed the greatest endoscopic improvement. Higher baseline sinonasal burden, more extensive surgical history, and mepolizumab dose variation were associated with adjunctive ESS (28.8%), whereas BVAS and eosinophils showed no correlation with ENT severity. Conclusion: Sinonasal disease may persist despite systemic remission, suggesting a partially independent inflammatory niche. Comprehensive assessment should combine systemic markers with dedicated ENT evaluation, while management may require integrated biologic–surgical strategies in chronic structural disease.