Efficacy of the adjunctive use of photobiomodulation therapy in olfactory disorders in post-COVID-19 patients: A randomized controlled trial

Objectives: Photobiomodulation Therapy (PBMT) is a non-invasive treatment that uses photons from the red to infrared spectrum to modulate cellular processes with anti-inflammatory and regenerative properties. This study aimed to evaluate the use of PBMT applied intranasally in patients with an impaired sense of smell after COVID19. Methods: This proof-of-concept study was a randomized, placebo-controlled clinical trial that recruited 81 patients with olfactory disorders after SARS-CoV-2 infection (1-12 months), randomly assigned to 3 groups: controls, red light and infrared light exposure groups. PBMT was applied twice a week for five weeks, associated with prednisolone 40 mg for five days and olfactory training for 90 days from the first day of laser application. UPSIT (R) and subjective chemosensory scores were the outcomes collected before the first session and three months thereafter. Results: Compared to controls, patients undergoing infrared PBMT showed more improvement in UPSIT (R) scores (+4.6 points, 95% CI: 1.5-7.8, p = 0.004) and a tendency towards reporting a better subjective smell score at the three-month follow-up. Response rates were 26.1% (95% CI: 6.7-45.5), 43.5% (95% CI: 21.6-65.4), and 68% (95% CI: 48.3-87.7) in the control, red and infrared groups, respectively. No major adverse events were reported. Conclusion: Therapy with PBMT in the infrared frequency appears to be a safe option in treating post-COVID olfactory disorders when combined with a five-day use of systemic corticosteroid and 90 days of olfactory training. Level of evidence: 2.