Rethinking the relationships between chronic rhinosinusitis and asthma severity

Background: Previous authors have endorsed the need for prospective studies on the effect of treatment of chronic rhinosinusitis on asthma outcomes. Although common pathophysiology for asthma and chronic rhinosinusitis (CRS) has been suggested with the unified airway theory, there is limited data to support the claim and our study does not support the theory. Methods: This case-control study involved adult patients with a primary diagnosis of asthma in 2019 who were identified from the electronic medical records and divided into those with and without an associated CRS diagnosis. For each asthma encounter, the asthma severity classification, oral corticosteroid (OCS) use and ox-ygen saturation scores were tabulated and compared between asthma patients with CRS versus control patients after 1:1 matching on age and sex. We determined the association between asthma and chronic rhinosinusitis when evaluating proxies for disease severity: oral corticosteroid use, average oxygen saturation and minimum oxygen saturation. We identified 1321 clinical encounters for asthma associated with CRS and 1321 control encounters for asthma without CRS. Results: OCS prescription rates at the asthma encounter were not statistically different between the groups (15.3 % and 14.6 %, respectively; p = 0.623). Asthma severity classification was higher in those with CRS versus those without (38.9 % and 25.7 % classified as severe, respectively; p < 0.001). We identified 637 asthma with CRS and 637 matched control patients. There was no significant difference in mean recorded O2 saturations between asthma patients with CRS versus control patients (mean O2 saturations, 97.2 % and 97.3 %, respectively; p = 0.816) nor in minimum oxygen saturation (96.8 % and 97.0 %, respectively; p = 0.115). Conclusion: Among patients with a primary diagnosis of asthma an increasing severity of asthma classification was significantly associated with an associated diagnosis of CRS. In contradistinction, the presence of CRS co -morbidity in asthma patients was not associated with increased OCS use for asthma. Similarly, average oxygen saturation and minimum oxygen saturation did not seem differ according to CRS comorbidity. Our study does not support the unified airway theory that suggests a causative relationship between the upper and lower airway.