The Effect of Obstructive Sleep Apnea on Olfactory Functions

Objectives/Hypothesis: The aim of this study was to investigate the effect of obstructive sleep apnea (OSA) on the parameters of olfactory functions (odor threshold, odor discrimination, and odor identification tests) for orthonasal olfaction, retronasal olfactory testing, and olfactory bulb (OB) volumes. Study Design: Prospective clinical study. Methods: This study was carried out in 78 volunteers between the ages of 20 and 60 years. The mean age of the patients was 46 +/- 10.1 years. Patients were divided into three groups according to polysomnography results: 1) a control group, 2) a mild to moderate OSA group, and 3) a severe OSA group. Clinical features of the participants were evaluated with the Epworth Sleepiness Scale. Orthonasal and retronasal olfactory testing were performed with Sniffin' Sticks olfactory testing and retronasal olfactory testing, respectively. Olfactory bulb volumes were measured by planimetric manual contouring on magnetic resonance imaging (MRI). Results: The current investigation produced four major findings: 1) The apnea-hypopnea index had a significant and strong negative correlation with odor threshold scores and odor discrimination scores; 2) The apnea-hypopnea index was significantly negatively correlated with odor identification score and both right and left OB volumes; 3) retronasal olfactory scores were not significantly affected by OSA; and 4) continuous O-2 saturation had a significant positive correlation on orthonasal olfactory functions, particularly the odor threshold and discrimination scores. Conclusions: This study demonstrated that OSA had significant negative effects on all orthonasal olfactory tasks, especially on threshold and discrimination. MRI also revealed volumetric shrinkage of OB volumes.