Introduction
Olfactory dysfunction (OD) can be classified into conductive and
sensorineural types, although these are not mutually exclusive. In
conductive losses, such as nasal polyps and chronic rhinosinusitis
(CRS), inspired odorants are unable to enter the olfactory cleft in the
nasal cavity. In sensorineural loss, the damage of olfactory receptor
neurons or their central projection contribute to OD.1Attempted treatments have included medical (topical and systemic
steroids, zinc, etc.) and surgical treatment. Hummel et al.2 studied the effectiveness of olfactory training(OT)
in a group of patients with olfactory loss due to post-infectious,
post-traumatic, or idiopathic etiologies. OT has shown promise as an
alternative treatment modality for several causes of OD, with the
exception of sinonasal disease.
Previous research found that exposing various odors in patients with
post-infectious and post-traumatic OD for 16 weeks increased their
olfactory function.3 According to a recent
meta-analysis, OT is a promising clinical therapy for patients with OD,
and many other trials have shown that OT has good olfactory outcomes
with no serious side effects. 4 Recently, we reported
that OT resulted in olfactory improvement reflected in the total
threshold, discrimination and identification (TDI) score, threshold
score, and identification score in patients with post-infectious
olfactory dysfunction (PIOD) as compared to a control group using five
odorants familiar to Koreans.5 Moreover, OT can be
considered for patients with persistent COVID-19-related OD because this
therapy is inexpensive and has negligible adverse
effects.6
In patients with chronic rhinosinusitis (CRS), OD is a common
complaint.7-9 Although the main mechanism of
CRS-induced OD is unclear, it is thought to be a combination of
mechanical obstruction from edematous mucosa or polyposis, as well as
sensorineural damage from chronic inflammatory injury to the olfactory
neuroepithelium.10 Endoscopic sinonasal surgery (ESS)
is used to improve sinus function and access to topical medical
treatment in patients with medically refractory CRS. However, olfactory
function after ESS can be unpredictable.11-12 An early
study endorsed the effect of ESS in reducing CRS-related OD. However,
several recent studies on the outcomes of OD after ESS have reported
conflicting results.13 A study found that OT improved
the olfactory activity of sinonasal patients, but did not evaluate the
effects of OT on post-sinonasal-operative patients. A separate study
reported that no significant changes in individual component values of
TDI scores were observed in sinonasal patients. However, that research
did not include a control group.14 Therefore, the
effectiveness of OT in CRS patients who experienced mixed (conductive
and sensorineural) olfactory dysfunction after resolving the conductive
cause by sinonasal surgery has not been investigated.