Botulinum Toxin A as a Treatment for Provoked Vestibulodynia: A Randomized Controlled Trial.

Objective: To evaluate pain reduction after two injections of 50 units botulinum toxin A compared with placebo for provoked vestibulodynia.

Methods: We conducted a double-blinded, placebo-controlled randomized trial of 50 units botulinum toxin A or placebo injected in the bulbocavernosus muscles twice, 3 months apart, in women with provoked vestibulodynia. Primary outcome was self-reported dyspareunia or pain at tampon use on a visual analog scale (VAS, 0-100). Secondary outcomes were pain at weekly tampon insertion (VAS score), reduction of pelvic floor hypertonicity (measured with a vaginal manometer), adverse events, and sexual function and distress. A sample size of 38 participants for each group was calculated to achieve a statistical power of 80% based on an effect size of 20 VAS units (0-100) (mean score range 56-76±31 SD).

Results: Between May 2016 and June 2018, 124 women with provoked vestibulodynia were assessed, and 88 were randomized to botulinum toxin A (BTA group, n=44) or placebo (placebo group, n=44). Primary outcome showed a lower but statistically nonsignificant pain rating by 7 VAS units (95% CI -15.0 to 0.4) in the BTA group compared with the placebo group. Secondary results showed a significant decrease in pain at weekly tampon insertion by 11 VAS units (95% CI -16.6 to 6.0) with botulinum toxin A injection. The vaginal manometer measured lower maximum contraction strength by 7 mm Hg (95% CI -12.7 to -2.4) and lower 10-second endurance strength by 4 mm Hg (95% CI -7.72 to -1.16) in the BTA group compared with the placebo group. No changes were observed for sexual function and distress, but there was a significant increase in women attempting vaginal intercourse in the BTA group (0.27, 95% CI 0.06-0.48). No severe adverse events were reported.

Conclusion: Twice-repeated injections of 50 units of botulinum toxin A in women with provoked vestibulodynia did not reduce dyspareunia or pain at tampon use, but secondary outcomes suggested positive effects of the treatment. Clinical trial registration: ClinicalTrials.gov, NCT02773641.