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. 2023 Dec 8;21(1):490.
doi: 10.1186/s12916-023-03205-x.

One-year psychophysical evaluation of COVID-19-induced olfactory disorders: a prospective cohort study

Emma J A Schepens  1   2 , Wilbert M Boek  3 , Sanne Boesveldt  4 , Robert J Stokroos  5   6 , Inge Stegeman  5   6 , Digna M A Kamalski  5   6
Affiliations

One-year psychophysical evaluation of COVID-19-induced olfactory disorders: a prospective cohort study

Emma J A Schepens et al. BMC Med. .

Abstract

Background: Olfactory disorders are common in COVID-19. While many patients recover within weeks, a notable number of patients suffer from prolonged olfactory disorders. Much research has focused on the acute phase of olfactory disorders in COVID-19; however, there is still inconsistency regarding the prognosis. We aim to assess both objective and subjective olfactory function in patients with persisting olfactory disorders following COVID-19, 1 year after diagnosis.

Methods: We objectively measured olfactory function in 77 patients who initially had COVID-19-induced smell disorders, 1 year after confirmed diagnosis. These patients previously underwent two objective measurements at approximately 3 and 6 months after COVID-19, in the context of the COCOS trial (COrticosteroids for COvid-19-induced loss of Smell). The main outcome measurement was TDI score (threshold-discrimination-identification) on Sniffin' Sticks Test (SST). Secondary outcomes included objective gustatory function on Taste Strip Test (TST), self-reported olfactory, gustatory and trigeminal function on a visual analogue scale (VAS) and outcomes on questionnaires about quality of life, and nasal symptoms.

Results: The findings of this study show that 1 year following COVID-19, the median TDI score increased to 30.75 (IQR 27.38-33.5), regarded as normosmia. The median TDI score started at 21.25 (IQR 18.25-24.75) at baseline and increased to 27.5 (IQR 23.63-30.0) at 6 months following COVID-19. The increase of 9.5 points on the TDI score between baseline and 1 year after COVID-19 marks a clinically relevant improvement. Regarding the self-reported VAS score (1-10) on sense of smell, it increased from 1.2 (IQR 0.4-3.0) at baseline to 3.2 (IQR 1.4-6.0) at 6 months and further improved up to 6.1 (IQR 2.7-7.5) after 1 year. Objective gustatory function increased with 2 points on TST a year after diagnosis. Self-reported olfactory, gustatory, and trigeminal functions also improved over time, as did quality of life.

Conclusions: Objective and self-reported olfactory function continued to improve 1 year after COVID-19. The median TDI score of 30.75 (IQR 27.38-33.5) is regarded as normosmia, which is a favorable outcome. However, the rate of improvement on TDI score reduces over time.

Keywords: COVID-19; Olfactory disorders; Prognosis; Smell.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Study design. TDI score, threshold-discrimination-identification score; SST, Sniffin’ Sticks Test; TST, Taste Strip Test
Fig. 2
Fig. 2
Participant flow chart
Fig. 3
Fig. 3
TDI scores over time
See this image and copyright information in PMC

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