Comparative Effects of Three Active Laser Therapy Protocols and a Sham Protocol on Neurophysiological and Functional Outcomes in Patients with Bell's Palsy: A Four-Arm Randomized Controlled Trial.

Abstract

Background/Objectives: Although laser therapy is commonly used to manage Bell's palsy, optimal treatment parameters have not been established. The present randomized controlled trial compared three active laser therapy protocols with a sham-control protocol for neurophysiological and functional recovery in patients with acute Bell's palsy. Methods: The primary analysis included all 104 randomized participants (26 per group) and used multiple imputation for missing six-week outcomes, followed by baseline-adjusted pooled treatment comparisons. In this four-arm trial (NCT07519421), 104 patients were randomized (26 per group) to receive either a sham laser, 808 nm low-level laser therapy (LLLT), 980 nm LLLT, or 1064 nm high-intensity laser therapy (HILT). All participants received standard care, including corticosteroids, electrical stimulation, and facial exercises. Interventions were administered three times per week for six weeks. Compound muscle action potential (CMAP) amplitude was the primary outcome; distal motor latency and the physical and social Facial Disability Index subscales (PFDI/SFDI) were additional outcomes. Eighty patients (20 per group) completed the six-week assessment and constituted the supporting complete-case analysis population. Results: In the primary intention-to-treat analysis, overall between-group differences were significant for CMAP amplitude (Wald χ²(3) = 1844.49), distal motor latency (χ²(3) = 284.90), PFDI (χ²(3) = 359.44), and SFDI (χ²(3) = 842.37; all p < 0.001). The Group C complete treatment protocol was superior to the sham, Group A, and Group B protocols on all four six-week outcomes in Bonferroni-adjusted pairwise comparisons (all p < 0.001). The 80-participant complete-case analysis supported the general direction of these findings. An additional baseline-adjusted complete-case sensitivity analysis showed broadly concordant treatment estimates and pairwise inference. No adverse events were reported. Conclusions: Among the complete treatment protocols evaluated, the 1064 nm HILT protocol was associated with the greatest short-term improvements at six weeks. Because the active protocols differed in multiple treatment parameters beyond wavelength, these findings should not be interpreted as demonstrating superiority of the 1064 nm wavelength itself. Longer-term multicenter trials are needed to confirm durability and generalizability. The ITT estimates rely on a missing-at-random assumption for the 24 participants without six-week outcome assessments. Post-imputation diagnostic checks identified departures from regression assumptions, particularly for functional outcomes; inferential results should therefore be interpreted cautiously.