Discussion
The following are the significant findings among CRS patients from this study: 1) When compared to non-OT patients, those who received OT showed statistically significant improvements in both total TDI score and identification score. 2) Differences in KVSS-II scores were independent of age, sex, LM score, and duration of disease and 3) Patients with anosmia at baseline assessment showed a significantly higher increase in the KVSS-II score compared with the other patients.
In this study, the patients who underwent sinonasal surgery with OT showed a significant improvement in TDI scores after 3 months. The subset analysis of the TDI scores showed that the odor threshold, discrimination, and identification scores increased significantly in the OT group. The non-training group also showed improvement in the threshold score compared with the other scores, but the difference was not statistically significant. According to a study of 20 trials published since 1991, olfaction generally improved following functional ESS. However, there has been limited research on the impact of OT on individuals with sinonasal disorders.16 There are also controversies about whether olfactory function improves with ESS in CRS patients. According to one prospective study, the University of Pennsylvania Smell Identification Test (UPSIT) score in the Chronic rhinosinusitis with nasal poloyp (CRSwNP) subgroup improved considerably following endoscopic sinus surgery. The evaluated UPSIT olfactory function improved after surgery in 46.0% of patients, did not change after surgery in 12.7% of patients, and worsened in 41.3% of patients.17 A 5-year prospective research with 75% of the participants having CRSwNP found a considerable improvement in measured olfaction at 2 years after surgery, however this became non-significant at 5 years.18 There were also studies that reported negative olfactory outcomes after ESS. One study reported that the mean postoperative T&T recognition threshold test of the eosinophilic CRS group declined after 12 months.19From another study, 34% of patients had a decline in olfactory function after sinonasal surgery20 According to a meta-analysis of olfactory outcomes after ESS for CRS, ESS improved subjective and objective olfactory parameters, with patients with nasal polyposis and prior olfactory dysfunction showing the greatest benefits.21
We also observed significantly higher total TDI and identification scores in the OT group compared to non-OT patients. In our analysis, with the exception of the initial KVSS-II score, the difference in KVSSII score was independent of age, sex, LM score, and duration of disease. There were no significant differences between the OT and non-OT groups in terms of age, sex distribution, or duration of the condition in our prior study on PIOD patients. 5 This is another significant difference compared to previous studies.
In this study of sinonasal patients, only the total TDI and identification score increased significantly. Our previous study on PIOD patients showed a significantly increased total TDI score, threshold score, and identification score after OT. The majority of prior research found that OT improved composite TDI, discrimination and identification scores in people with PIOD. The majority of prior research found that OT improved composite TDI, identification, and discrimination scores in people with PIOD.22
The odor threshold appears to be relatively unimpaired in central sources of olfactory dysfunction and is poorly connected with cognitive tests, therefore the threshold score is more strongly tied to peripheral abnormalities in the olfactory system.4 In this study, sinonasal surgery was performed in both groups and the surgical procedure improved the peripheral olfactory function and conduction of olfactory molecules. This could lead to improved threshold scores. Another KVSS-II score (total, identification) was significantly increased in the OT group, similar to our previous study on patients with PIOD.
The group with anosmia at baseline showed significantly higher improvements in KVSS-II score compared to the other patients. Long-term exposure to various odors enhances the survival of newly generated interneurons2 and odor memory,11indicating that adult neurogenesis can play a role in olfactory memory. OT based on repeated stimulation by odors could promote the survival of immature new neurons and eliminate more mature neurons.23 Based on this mechanism, patients with lower olfactory function could improve significantly after OT.
There were some limitations to this study. First of all, only a small number of patients is involved. To better understand the effects of OT, larger studies are needed. Second, those who had less severe OD in the preoperative state could have been included in the non-OT group. This can be considered a selection bias. Third, OT was applied for only 12 weeks. Therefore, it is unclear if long-term OT exposure is helpful to olfactory function.
In conclusion, OT patients exhibit significantly higher total TDI scores than non-OT patients after sinonasal surgery. In particular, odor identification scores were different between the two groups. According to the findings, a 12-week course of repeated short-term exposure to various odors could be useful in enhancing olfactory function in patients who had sinonasal surgery for sensory-neural OD.