Clinical Features of Olfactory Dysfunction in COVID-19 Patients

Abstract

Background The aim of this study was to evaluate the subjective and objective olfactory function in coronavirus disease 2019 (COVID-19) patients and the effect of olfactory training. Methods A prospective cohort study was performed in 53 patients who recovered from COVID-19 and visited our tertiary hospital. Subjective olfactory function was evaluated using the 11-point Likert scale (0–10) and the Korean version of the Questionnaire of Olfactory Disorders (QOD). Objective olfactory function was evaluated using Cross-Cultural Smell Identification Test (CC-SIT). Confirmed patients were followed up after 2 months of olfactory training. Results The median, interquartile range (Q1–Q3) score of subjective olfactory function significantly deteriorated in patients with olfactory dysfunction (OD) than in those without OD, even after 3 months of onset (11-point Likert scale, 8, 6–9 vs. 10, 10–10; short version of QOD-negative statements, 19, 16–21 vs. 21, 21–21; QOD-visual analogue scale, 7, 1–13 vs. 0, 0–0; all P < 0.001). However, the objective olfactory function was not significantly different between the two groups (median, interquartile range; 11, 9–11 vs. 11, 9–11, P = 0.887). The percentage of patients with objective hyposmia (CC-SIT ≤ 10) was also not significantly different (47.4% vs. 40%, P = 0.762). OD in COVID-19 was normalized after 2 months of olfactory training in 70% of patients even after 3 months of olfactory impairment. Conclusion Although subjective olfactory function is significantly decreased in the OD group, the objective olfactory function was not significantly different. Moreover, olfactory training is effective in COVID-19 patients with OD.

Kampo Medicine Promotes Early Recovery From Coronavirus Disease 2019-Related Olfactory Dysfunction: A Retrospective Observational Study

“…COVID-19-related OD was previously considered to recover on its own with progress in time. However, recent studies revealed that nearly 50% of patients had OD more than 3 months after COVID-19 based on subjective and objective evaluation ( Bussière et al, 2021 ; Seo et al, 2021 ). OD affected daily life activities ( Temmel et al, 2002 ) and had a negative influence on psychological status ( Valsamidis et al, 2020 ).…”

“…Previous studies reported the recovery from OD in many patients within a month following the onset of OD ( D’Ascanio et al, 2021 ; Lechien et al, 2020 ). However, some studies have reported long-term persistence of OD ( Bertlich et al, 2021 ; Bussière et al, 2021 ; Seo et al, 2021 ). OD results in reduced quality of life ( Temmel et al, 2002 ); however, effective treatments are limited ( Addison et al, 2021 ).…”

Treatment and Prognosis of COVID-19 Associated Olfactory and Gustatory Dysfunctions

“…In another study, recently published by our authors, regarding the effect of olfactory training in patients with olfactory dysfunction even after three months of symptom onset, 10 patients underwent olfactory training for 8 weeks using four Korean odorants: pine, peppermint, cinnamon, and lemon. It was found that the objective olfactory function score using the Cross-Cultural Smell Identification Test (CC-SIT) was significantly increased after olfactory training, with 70% of patients reporting a recovery to normal olfactory function [ 25 ].…”

“…Several studies have reported the clinical course of COVID-19-associated olfactory and gustatory dysfunctions [ 21 , 22 , 23 , 24 , 25 , 26 ]. According to these results, approximately 8.57–25% of these patients did not have improved subjective olfactory function at 1–2 months after symptom onset, and 11.2% did not have improved subjective olfactory dysfunction at 6 months after symptom onset.…”

“…Using an objective assessment of olfactory function recovery, these studies showed that 15.3% and 5% of patients did not recover to normal olfactory function at 2 and 6 months after symptom onset, respectively. Furthermore, a recent article by our authors, including 53 patients who recovered from COVID-19, showed that among 38 patients who experienced olfactory dysfunction, 92.1% of them reported the subjective normalization of olfactory function, although only 52.6% of them were confirmed to have normal olfactory function via CC-SIT score evaluation at 3 months after symptom onset [ 25 ]. In addition, according to a prospective study of 183 adult COVID-19 patients, 110 patients complained of the sudden onset of olfactory dysfunction subjectively.…”