Olfactory training in long COVID-19 patients with lasting symptoms including olfactory dysfunction

INTRODUCTION. Two-thirds of patients with COVID-19 developed smell and taste dysfunction, of whom half experienced improvement within the first month. After six months, 5-15% still suffered from significant olfactory dysfunction (OD). Before COVID-19, olfactory training (OT) was proved to be effective in patients with post-infectious OD. Therefore, the present study aimed to investigate the progress of olfactory recovery with and without OT in patients with long COVID-19. METHODS. Consecutive patients with long COVID-19 referred to the Flavour Clinic at Godstrup Regional Hospital, Denmark, were enrolled. The diagnostic set-up at the first visit and follow-up included smell and taste tests, questionnaires, ENT examination and instructions in OT. RESULTS. From January 2021 to April 2022, 52 patients were included due to long COVID-19-related OD. The majority of patients complained of distorted sensory quality, in particular, parosmia. Two-thirds of the patients reported a subjective improvement of their sense of smell and taste along with a significant decline in the negative impact on quality of life (p = 0.0001). Retesting at follow-up demonstrated a significant increase in smell scores (p = 0.023) where a minimal clinically important difference (MCID) in smell scores was found in 23% of patients. Full training compliance was significantly associated with the probability of MCID improvement (OR = 8.13; p = 0.04). CONCLUSIONS. The average effect of OT is modest; however, full training compliance was significantly associated with an increased probability of a clinically relevant olfactory improvement.