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.