Botulinum toxin type A for the treatment of head and neck chronic myofascial pain syndrome: A systematic review and meta-analysis.

[BACKGROUND] The authors conducted a systematic review to study the efficacy of botulinum toxin type A (BoTN-A) in the treatment of myofascial pain syndrome.

[TYPES OF STUDIES REVIEWED] The authors identified randomized, double-masked, placebo-controlled studies on June 1, 2016, from PubMed, Web of Science, and the Cochrane Library. Three of the authors assessed the studies for risk of bias. Outcomes included pain reduction on a visual analog scale, the number of responders, and the posttreatment pain threshold to applied pressure using algometry.

[RESULTS] The initial search strategy yielded 253 unduplicated references, which the authors reduced to 13 relevant studies. The authors included 11 studies in the meta-analyses as the investigators of those studies had reported similar outcomes. Pooled results showed a nonsignificant improvement in the posttreatment intensity of pain in the BoTN-A group compared with the placebo group at 4 to 6 weeks (standardized difference in means [SDM], -0.110; 95% confidence interval [CI], -0.344 to 0.124; P = .356) and a significant improvement at 2 to 6 months (SDM, -0.360; 95% CI, -0.623 to -0.096; P = .008). The number of study participants who responded to treatment was not statistically significantly different between the groups (risk ratio, 1.346; 95% CI, 0.922-1.964; P = .123) nor was the increase of pain threshold to pressure (algometry) at 2 months (SDM, 0.131; 95% CI, -0.178 to 0.440; P = .405). The study investigators reported no major adverse events.

[CONCLUSIONS AND PRACTICAL IMPLICATIONS] Pain was reduced significantly in the group that received BoTN-A compared with the placebo group at 2 to 6 months but not at 4 to 6 weeks (with moderate quality of the evidence). Additional studies with larger numbers of participants are needed to confirm these results.