Subcutaneous botulinum toxin type A injections for provoked vestibulodynia: a randomized placebo-controlled trial and exploratory subanalysis

Background: Previous studies using botulinum toxin type A (BT) to treat provoked vestibulodynia (PVD) reported conflicting findings, possibly attributable to singular injections or low doses. We assessed PVD treatment effectiveness with high-dose single injections of BT (50 or 100 units) versus placebo, and then repeat BT 100 U injections over 6 months.

Methods: This was a randomized, double-blind, three-arm, placebo-controlled study with 33 PVD patients. BT 50 U (arm A), 100 U (arm B) or saline (arm C) were injected subcutaneously into the dorsal vulvar vestibulum and pain was assessed after 3 months. The investigation proceeded as an unblinded exploratory analysis, in which symptomatic patients received a BT 100 U injection. Symptomatic patients in arm C received a second BT 100 U injection at the 6-month visit. Symptoms were measured at 3-month cycles using: (1) cotton swab-provoked visual analogue scale (VAS), (2) von Frey filaments, and (3) Marinoff dyspareunia scale.

Results: The three groups were comparable in terms of demographics and baseline clinical characteristics. Three months after the initial injection, no significant differences in pain were observed among the study arms, yet significant improvements occurred within all groups using the von Frey filaments test. Results from the exploratory analyses showed repeat injections of 100 U BT over 6 months led to significant pain reduction (VAS and von Frey filaments). Fifty-eight percent (7/12) of patients assessable after repeat injections were symptom-free or had ≥ 2 VAS reduction. Adverse events were minor and no serious adverse events occurred during the RCT or exploratory analysis.

Conclusions: PVD symptoms after one subcutaneous injection of BT (50 or 100 units) did not significantly differ compared to placebo, yet all three study arms experienced a reduction in pain 3 months after a single injection. Exploratory analyses indicated that repeat high-dose BT injections may significantly reduce pain over 6 months.

Trial registration: This trial was registered with the Swiss Medical Agency (reference number: 2007DR2102) in 2007.