Incidence of Chronic Rhinosinusitis in Patients Who Receive Rituximab.

OBJECTIVE: Rituximab causes B-cell depletion and hypogammaglobulinemia, increasing risk for infections. This study aims to determine the incidence of chronic rhinosinusitis (CRS) in patients following rituximab therapy. STUDY DESIGN: Retrospective cohort study using chart review of patients prescribed rituximab between January 2019 and January 2025. SETTING: Multisite study across Mayo Clinic Enterprise locations in Arizona, Florida, Minnesota, and Wisconsin. METHODS: Patients with documented rituximab use were included; those with pre-existing CRS were excluded. Demographic and clinical data-including timing and duration of rituximab therapy, CRS diagnosis, comorbidities (asthma, allergic rhinitis, GERD), and need for sinus surgery-were collected. Descriptive statistics summarized patient characteristics. Group comparisons were performed using t-tests, Mann-Whitney U, and chi-square tests. Analyses were conducted using SPSS v28. RESULTS: Among 17,851 patients prescribed rituximab (median age 64.0 years, M:F ratio 1.1:1), 1105 (6.2%) developed CRS, with an annual incidence of 1.03% (1032 cases per 100,000 person-years). The median duration of rituximab therapy for those diagnosed with CRS was 5.9 months (IQR, 0.5-42.6). Most CRS cases occurred after rituximab discontinuation (62.7%, n = 693) compared to during active treatment (37.3%, n = 412). The median delay between rituximab discontinuation and CRS diagnosis was 17.0 months (IQR, 4.3-41.7). CONCLUSIONS: This study demonstrates an annual incidence of 1.03% for CRS diagnoses following rituximab. While prior studies report varying CRS incidences in the general population (0.25%-0.73%), our findings suggest increased risk among rituximab users. Most CRS diagnoses occurred after rituximab discontinuation, emphasizing the need for a comprehensive medication history review during CRS evaluation.