Supplementary Material for: Low-Level Laser Therapy for Allergic Rhinitis: A Systematic Review and Meta-analysis

Background: Allergic rhinitis (AR) is a common allergic disorder that impairs social and physical functioning as well as quality of life. It is characterized by sneezing, rhinorrhea, congestion, and itching which respond sub-optimally to drug therapy. Low-level laser therapy (LLLT) has anti-inflammatory and immunosuppressive properties that have shown promise in some studies.
Objective: We aim to systematically review LLLT’s effectiveness in treating AR and meta-analyze our findings.
Methods: A systematic search of PubMed, Scopus, and Web of Science was conducted on November 24th, 2023. All studies investigating LLLT on AR were included, and a pre-post meta-analysis of nasal symptoms (rhinorrhea, nasal congestion, nasal itching, and sneezing) in the LLLT treated arm was conducted. Rhinoconjuctivitis quality of life questionnaire (RQLQ) scores before and after LLLT were also meta-analyzed alongside a pairwise meta-analysis of LLLT with placebo, acupuncture, steroids/antihistamines, and ultraviolet lasers. A random effects model was used with a conservative pre-post correlation of 0.4 and standardized mean difference as the effect size.
Results: 16 studies were included in this review, and we found that nasal symptoms are alleviated post LLLT in people with AR (SMD: -1.4, 95 CI (-2.07 - -1.13), p-value<0.001). RQLQ scores were also reduced after LLLT (SMD= -0.72, 95 CI (-0.94 - -0.50), p-value<0.001), and very few adverse events were reported. This meta-analysis however, had significant publication bias and heterogeneity. When compared to a placebo, LLLT did not significantly improve nasal symptoms (SMD: -0.69, p-value=0.167), which might mean the post LLLT nasal symptom alleviation is due to a placebo effect. Comparisons to other treatment modalities were too few to deduce anything meaningful, although it does appear that LLLT is less effective than UV lasers.
Conclusion: LLLT is most likely effective at alleviating nasal symptomology and has a low likelihood of adverse events incidence, yet more high quality studies with larger sample sizes are needed to compare LLLT to a placebo to ensure its superiority to the placebo effect, as well as non-inferiority clinical trials to compare it to standard treatments.