Purpose: This meta-analysis study was designed to analyze the olfactory function in obstructive sleep apnea patients (OSA).
Methods: A comprehensive review of the English language literature regarding OSA patients and olfactory function/dysfunction was performed. The papers assessing olfactory dysfunction with Sniffin' Sticks test were taken into consideration.
Results: A total of 420 OSA patients were judged eligible for the study. The average TDI score was found to be 24.3 ± 5.6. The olfactory identification (OD), the olfactory discrimination (OD), and the olfactory threshold (OT) average values were calculated resulting 9.9 ± 2.1, 9.8 ± 1.5, and 5.3 ± 2, respectively. There were 161 healthy control subjects in this meta-analysis. The average TDI of the control group was 30.7 ± 6.0 showing a statistical difference with the group of OSA patients (p = 0.03). A linear correlation between Apnea-Hypopnea Index (AHI) increase and TDI decrease (R2 = 0.1, p = 0.05) was detected. Finally, the average values of TDI of 151 patients classified as mild-moderate OSA and 159 patients considered as severe OSA were calculated. The difference between these two groups resulted not statistically significant (p = 0.3).
Conclusion: The comparison between OSA patients and healthy subjects using Sniffin' Sticks test showed lower values of the various olfactory parameters. Although a linear correlation between AHI increase and olfactory dysfunction was observed, no statistical difference between mild-moderate and severe OSA patients in terms of the severity of olfactory dysfunction could be proved.
Keywords: Cholinergic disorders; Obstructive sleep apnea; Olfactory function; Sniffin’ Sticks test.