The Immediate, Short-Term and Long-Term Effects of Photobiomodulation on Chronic Post-Surgical Pain After...

Introduction: Photobiomodulation (PBM) is one of the alternatives to opioid analgesics to reduce post-operative pain. The aim of this study was to investigate the immediate, short-term, and long-term effects of PBM on chronic post-surgical pain after tympanomastoidectomy. Methods: A total of 138 subjects who had undergone tympanomastoidectomy were selected randomly and divided into two groups: PBM and control. Patients in the PBM group (n=64) received laser therapy (energy density of 8 j/cm2, wavelength of 980 nm, and power of 50 mW in 8 points behind the ear during ten sessions every day) with routine drug therapy, while patients in the control group (n=64) received only routine drug therapy (Dexamethasone, cephalexin 500 mg, acetaminophen 500 mg). The visual analogue scale (VAS) and the headache subscale of the neck disability index (NDI) were provided to both groups to assess pain intensity before the intervention, after sessions one and five, and at one- and three-month follow-ups. The between-group comparison was made through the Mann-Whitney U test, and the within-group comparison was performed using the Friedman test with pairwise comparisons. Results: No significant differences in all variables were observed between the two groups at baseline (P>0.05). The between-group comparison showed significantly lower VAS scores in PBM compared to the control group at all four time points of the study, resulting in a very large effect size at session 5, month 1, and month 3. Also, the PBM group had significantly lower NDI scores at session 5, month 1, and month 3 (P<0.001). The effect size was large at session 5 and very large thereafter. Conclusion: The combined effects of PBM and drugs may reduce pain intensity in short-term and long-term follow-ups in patients after tympanomastoidectomy. Nevertheless, PBM did not show immediate effects on pain. The trial registration number: IRCT200808310011138N28.