Long term effects of olfactory training in patients with post-infectious olfactory loss

Background: There is evidence of the effectiveness of repeated exposure to odours on short-term olfactory function. The aim of this study was to assess the long-term effects of olfactory training. Methods: We conducted a prospective study of 111 patients with post-infectious olfactory dysfunction. Two groups of patients performed olfactory training for 16 and 56 weeks, respectively, and were compared with a control group. The training was performed twice daily using four odours (phenyl ethyl alcohol, eucalyptol, citronellal, eugenol). Olfactory testing was performed by means of theSniffin'Stickstest as a baseline assessment and then every 8 weeks for 56 weeks. Subjective ratings were performed using a visual analogue scale (0-100). Results: Both training groups presented significantly higher scores than the controls. The long-term group had better results than the short-term group. Short-term training patients sustained their improvement within the follow-up period. Subsets analysis showed that training patients mainly increased identification and discrimination. Subjective ratings were in accordance with the olfactory test results. Conclusion: Long-term olfactory training seems to be associated with better results in patients with post-infectious olfactory loss than a short-term scheme. Short-term training provides sustainable results at 56 weeks follow-up assessment.