Effectiveness of olfactory training in COVID-19 patients with olfactory dysfunction: a prospective study

Objectives To investigate effectiveness of olfactory training (OT) in COVID-19 patients with persistent olfactory dysfunction (OD). Methods From March 2020 to March 2022, COVID-19 patients with OD were prospectively followed in three European medical centers for a period of 18 months. A standardized OT protocol were recommended to patients. Patient-reported outcome questionnaires and psychophysical evaluations were used to evaluate olfaction at baseline, 6, 12, and 18 months after the start of OT. The evolution of olfactory outcome was compared according to the adherence to the OT protocol. Results Fifty-seven patients completed the evaluations. Thirty-two patients fully adhered to the OT, while 25 did not adhere. The psychophysical scores significantly improved from baseline to 6-month post-infection in both groups. In the OT group, the psychophysical scores continued to significantly improve from 6 to 12 months after the start of OT (p = 0.032). The mean duration of OT was 15.4 weeks. The mean delay of patient recovery perception was comparable between groups (27.4 weeks). The occurrence of cacosmia (35.1%) and parosmia (43.9%) throughout the follow-up period was comparable between groups. There proportion of phantosmia was higher in training (34.4%) compared with no-OT (16.0%; p = 0.007) group. The baseline Sniffin'Sticks tests was positively associated with the 6-month Sniffin'Sticks tests (r(s) = 0.685; p < 0.001) and negatively associated with the time of recovery (r(s) = - 0.369; p = 0.034). Conclusions The adherence to an OT protocol was associated with better mid-term improvement of psychophysical scores. Future large-cohort randomized-controlled studies are needed to confirm the effectiveness of OT in COVID-19 patients.

Automated summary

This study investigated the effectiveness of olfactory training (OT) in COVID-19 patients with persistent olfactory dysfunction (OD). The findings showed that adhering to the OT protocol was associated with better mid-term improvement of psychophysical scores. Larger randomized-controlled studies are needed to confirm the effectiveness of OT in COVID-19 patients.