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

• PBMT with steroids and training improved post-COVID olfaction, especially infrared. • Infrared had a 68% response rate, surpassing red light (43.5%) and control (26.1%). • PBMT with steroids and olfactory training was safe for treating smell disorders. 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 COVID-19. 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® and subjective chemosensory scores were the outcomes collected before the first session and three months thereafter. Compared to controls, patients undergoing infrared PBMT showed more improvement in UPSIT® 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. 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. 2.