A 2022 study from Turkey used a randomized controlled trial to test the effectiveness of modified olfactory training in treating COVID-19-related parosmia. One group received modified olfactory training; the others received no rehabilitation therapy. Olfactory improvements were noted in both groups at three, six, and nine months, with larger improvements observed in the treatment group (Laryngoscope. 2022;132:1433–1438).
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May 2023“Doing olfactory training is worthwhile,” said Eric Holbrook, MD, MS, an associate professor at Harvard Medical School and division chief of rhinology at Massachusetts Eye and Ear in Boston, “but it’s unlikely to restore a sense of smell to a patient whose olfactory dysfunction is a complete loss and has persisted for a year or more. Still, it’s worth a try, as olfactory training is relatively cheap and generally well-tolerated.”
Some studies have suggested that combining olfactory training with budesonide irrigation may improve outcomes (Int Forum Allergy Rhino. 2018;8:977–981). It’s difficult to determine the real-world utility of steroid irrigation in treating long COIVD, however.
“It’s very difficult to conduct proper clinical trials for smell loss because there’s a natural regenerative process that occurs. To compare efficacy of placebo versus treatment, large numbers are needed,” said Dr. Holbrook, noting that most studies to date have been small. “I ask patients with smell loss to use budesonide irrigation only if I see evidence of inflammation in the nasal cavity and olfactory cleft. Otherwise, I have them concentrate on training,” he said.
Small studies also suggest that certain supplements—specifically, omega-3 fish oil and palmitoylethanolamide and luteolin (PEA-LUT)—may help patients regain their sense of smell. Early in the pandemic, Dr. Iloreta participated in a randomized controlled trial of omega-3 fatty acid supplementation for the treatment of COVID-19-related olfactory dysfunction (Trials. 2020;21:942). “We saw a trend toward improvement in the sense of smell in patients who took 2000 milligrams of omega-3 fish oil capsules daily for six weeks,” Dr. Iloreta said. “The findings weren’t statistically significant.”
A small German study, however, found that adding omega-3 supplementation to olfactory training resulted in improved olfactory scores in adult patients with post-viral olfactory dysfunction. Fifty-eight patients (25 men, 33 women) were included in the study, and more improvement in odor thresholds was noted in the group that received both olfactory training and omega-3 supplementation than in the group that underwent only olfactory training (Rhinology. 2022;60:139–144).
Another study compared the effectiveness of olfactory training plus daily oral ultramicronized PEA-LUT supplementation to olfactory training plus placebo and found improvements in olfactory discrimination and identification in 92% of the patients who received the supplement versus 42% of those who received olfactory training and placebo (Curr Neuropharmacol. 2022;20:2001–2012).