International Rhinologic Society Rhinology 0300-0729 2026 03 23 Effect of corticosteroids on tissue eosinophilia in chronic rhinosinusitis: a systematic review and meta-analysis EN N.R. SchläpferDepartment of Otorhinolaryngology / Head and Neck Surgery, University Hospital Zurich, University of Zurich, Switzerland Department of Surgery, Division of Plastic Surgery, University of Rochester Medical Center, Rochester, New York, United States M.B. Soyka Department of Otorhinolaryngology / Head and Neck Surgery, University Hospital Zurich, University of Zurich, Switzerland R. Liechti Department of Surgery, Division of Plastic Surgery, University of Rochester Medical Center, Rochester, New York, United States C.M. Meerwein Department of Otorhinolaryngology / Head and Neck Surgery, University Hospital Zurich, University of Zurich, Switzerland Journal Article 3385 10.4193/Rhin25.097 INTRODUCTION: This systematic review and meta-analysis evaluated the effect of oral corticosteroid (CS) treatment on tissue eosinophil count (EC) in chronic rhinosinusitis (CRS) patients. METHODOLOGY: A comprehensive database search identified 16 studies with 1,003 patients for the systematic review. Nine studies with 493 patients reporting mean tissue EC per high-power field (HPF) with 400x magnification were included in the meta- analysis. Within-subject (pre- vs. post CS treatment) and controlled comparisons (oral CS vs. no CS or topical CS) were analyzed. RESULTS: Results showed a significant reduction in tissue EC following oral CS treatment in both within-subject analyses and controlled trials. A similar effect was found when comparing oral vs. topical CS treatment. Meta-regression showed a significant negative association between cumulative CS dose and post-treatment EC/HPF. CONCLUSION: These findings provide strong evidence that oral CS significantly reduces tissue eosinophilia in CRS, including comparisons with topical CS. The effect was consistent across study designs and should be considered when assessing endotypes in CRS with nasal polyps.