Supplementary Material for: Real-world outcomes of 3-month olfactory training on post-COVID-19 parosmia

Introduction
Post-COVID-19 parosmia can be protracted and psychologically distressing. The effect of olfactory training (OT) on parosmia is still unclear. The primary objective was to investigate the effect of 3 months of OT on COVID-19-related parosmia. The secondary objectives were to study whether improvement in olfactory quantitative function and compliance to OT influenced improvement in parosmia.

Methods
This prospective cohort study was conducted from 5 October 2022 to 7 February 2023 at a tertiary smell and taste clinic. Patients with persistent post-COVID-19 parosmia were instructed to perform OT twice daily for 3 months. Improvement in parosmia was measured using self-rated intensity and pleasantness scales, a structured parosmia questionnaire and the Sniffin’ Sticks Parosmia Test (which measures hedonic direction and range). Quantitative olfactory function was measured with Sniffin’ Sticks to determine the threshold, discrimination and identification (TDI) score. Pre- and post-OT assessment of parosmia and quantitative olfactory function was performed. Compliance to OT was calculated as a percentage of the number of OT sessions performed over the expected number of training sessions over 3 months.

Results
Thirty-eight patients (mean age 41.8 [±13.3] years, 12 [31.6%] males) were recruited. After 3 months, 52.6% (n=20) reported perceived improvement in parosmia. There was improvement in perceived pleasantness (-2.0 [-3.0 to -1.0] vs. -3.0 [-4.0 to -2.0], p=0.027), hedonic range 2.4 [±1.3] vs. 1.9 [±1.6], p=0.023) and TDI (27.9 [±7.4] vs. 25.2 [±7.2], p=0.001) from baseline. All measures of parosmia did not differ significantly between patients who achieved the minimum clinically important difference (MCID) of ≥5.5 in TDI scores versus those who did not. Patients who had >70% compliance to OT displayed more significant improvements in hedonic range (1.1 [±1.1] vs. 0.2 [±1.3] p=0.04) compared to those who were less compliant.

Conclusion
COVID-19 related parosmia and olfactory dysfunction improved with OT over 3 months. Improvement in olfactory function does not necessarily improve parosmia perception. However, compliance with OT appears to have an effect on improvement in parosmia.