People who have COVID-19–related loss of smell may benefit from visual-olfactory training using patient-preferred essential oils, according to a clinical trial published late last week in JAMA Otolaryngology-Head & Neck Surgery.
Washington University researchers in St. Louis randomly assigned 275 adults aged 18 to 71 years who reported post-COVID loss of smell to undergo either unimodal olfactory training using four physician-assigned essential oils or bimodal visual-olfactory training using four patient-chosen scents.
Participants sniffed the essential oils for 15 seconds each, with a 15-second rest in between, for 3 months. Bimodal patients were also shown images of their chosen oils. A control group was used to compare the efficacy of the trainings with simple monitoring.
Before and after the trainings, participants completed the University of Pennsylvania Smell Identification Test (UPSIT), the Clinical Global Impressions-Improvement (CGI-I) scale, and the Olfactory Dysfunction Outcomes Rating (ODOR) questionnaire.
Loss of smell was defined as an UPSIT score of less than 34 for men and 35 for women for 3 months or longer. Participants enrolled from Feb 1 to May 27, 2021.
No significant differences
Five (24%) participants in the control group saw clinical improvement on UPSIT, compared with 18 (53%) in the bimodal arm (difference, 29 percentage points). Four (19%) controls reported improvement on the CGI-I, compared with 12 (35%) in the bimodal arm (difference, 16 percentage points). The average change in ODOR score from before to after the intervention was a clinically unimportant 11.6 points.
There were no differences between arms, the authors said, "but when exploring within-patient change in UPSIT as well as self-reported impression of improvement, active interventions were associated with larger improvement than controls with a potential advantage of bimodal intervention."
Active interventions were associated with larger improvement than controls.
Carol Yan, MD, of the University of California San Diego, said in a related commentary that while the study was inconclusive, olfactory training could be considered in individual patient treatment plans. "Ultimately, patients' belief and satisfaction in their therapeutic plan can have substantial placebo-effect benefits that are not to be ignored," she wrote.