Inter-nostril olfactory asymmetry in nasal septal deviation: a controlled cross-sectional study

Introduction Nasal septal deviation may be associated with side-specific differences in olfactory performance. This study aimed to compare side-specific olfactory function and absolute inter-nostril asymmetry between people with nasal septal deviation and healthy controls and to evaluate the association between the severity of global subjective nasal obstruction and directional olfactory asymmetry. Methods A prospective single-center controlled cross-sectional study was conducted, including 61 patients with nasal septal deviation and 48 controls comparable in age and sex. Side-specific TDI scores (Sniffin' Sticks threshold, discrimination, and identification tests) for each nasal cavity were collected. The absolute inter-nostril asymmetry (|ΔTDI|) was calculated based on the side-to-side difference in TDI scores. Subjective nasal obstruction was assessed using a visual analog scale (VAS). Results Composite TDI scores of patients with septal deviation were significantly lower on the deviated side than on the wider side (26.81 ± 5.49 vs. 31.77 ± 3.36, respectively; mean difference, 4.96 points; 95% confidence interval, 3.34–6.58; p < 0.001), whereas no significant side-to-side difference was found in controls ( p = 0.236). Absolute inter-nostril asymmetry was significantly higher in patients than in controls (median [interquartile range] = 6.00 [2.25–9.50] vs. 2.13 [0.75–3.81]; p < 0.001). The correlation between the VAS score and directional olfactory asymmetry was positive in patients (Spearman's ρ = 0.561; p < 0.001). Conclusion People with nasal septal deviation demonstrated decreased TDI scores on the deviated side and increased absolute inter-nostril asymmetry compared to controls. The clinical implications of these findings require further study.