Olfactory function in patients with obstructive sleep apnea and the effect of positive airway pressure treatment: a systematic review and meta-analysis

Objectives To investigate olfactory function (OF) in patients with obstructive sleep apnea (OSA) and evaluate whether or not the use of positive airway pressure (PAP) treatment has an impact on olfactory performance. Methods All studies published in English that gave satisfactory data regarding the assessment of OF in patients with OSA were included in this review. First, a baseline assessment of OF in patients with OSA who had not received any treatment was examined. Second, the effect of PAP therapy on OF was assessed to be able to make before and after comparisons. The primary outcome of this study was the threshold-discrimination identification (TDI) scores, obtained from the Sniffin’ Sticks test. Results The database search identified 552 articles. According to the exclusion criteria, 11 studies involving 557 patients diagnosed with OSA were included in this meta-analysis. The general rate of olfactory dysfunction was 73% (95% CI: 56.481–87.057) among the patients with OSA. The patients with OSA had lower TDI scores compared to the control group and the difference was statistically significant ( p < 0.001). PAP treatment significantly improved the TDI scores in patients with OSA ( p < 0.001). There was a significant negative correlation between the severity of apnea-hypopnea index and TDI scores ( p = 0.001, z = −3.377, r = −0.438) and between age and TDI scores ( p = 0.007, z = −2.695, r = −0.236). Conclusion This meta-analysis demonstrates that OSA impairs OF, while PAP treatment can reverse the olfactory performance of patients with OSA.