Effectiveness of Botulinum Toxin Type A Injection on Scars: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Scars can cause pain as well as long-term physical dysfunction and psychological harm. Botulinum toxin type A (BoNT-A) is one of the treatment choices for scars. However, further evidence is needed to confirm its efficacy. Methods: This systematic review included randomized controlled trials (RCTs) that investigated the effectiveness of BoNT-A on scars. We extracted the mean and standard deviation for the Vancouver scar scale (VSS), Stony Brook Scar Evaluation Scale (SBSES), Visual Analog Scale (VAS) for appearance evaluation, VAS for scar pain evaluation and scar width. Subgroup analysis was performed to understand the effect of active control. Results: Overall, 21 RCTs met the inclusion criteria. VSS results revealed that the BoNT-A group had a lower score than the saline group [standardized mean difference (SMD): −0.82, 95% confidence interval (CI): −1.24 to −0.39, I 2 = 65%, P = 0.0002], whereas the BoNT-A group had a higher score than the steroid group (SMD: 0.85, 95% CI: 0.27 to 1.43, P = 0.004). Moreover, the BoNT-A group exhibited a higher grade than the saline group in SBSES (SMD: 1.42, 95% CI: 0.83 to 2.20, I 2 = 48%, P < 0.00001). VAS for appearance evaluation revealed significantly higher scores in the BoNT-A group than in the saline group (SMD: 1.25, 95% CI: 0.77 to 1.74, I 2 = 72%, P < 0.00001). Moreover, VAS for scar pain evaluation revealed that the BoNT-A group had a significantly lower score than the steroid group (SMD: −2.57, 95% CI: −4.40 to −0.74, I 2 = 95%, P = 0.006). Furthermore, the scar width was significantly shorter in the BoNT-A group than in the control group (SMD: −1.19, 95% CI: −1.49 to −0.89, I 2 = 0%, P < 0.00001) Conclusion: BoNT-A injection is more effective in treating scars than saline injection, although steroids may exhibit higher potency. Therefore, BoNT-A can be considered an alternative in patients not amenable to steroid treatment.