A randomized, double-blind, placebo-controlled trial of onabotulinumtoxin A trigger point injections for myofascial pelvic pain.

Background: Pelvic pain is estimated to effect 15% of women, and onabotulinumtoxin A is used to treat a variety of pain disorders. However, the data on the use of onabotulinumtoxin A for the treatment of women with myofascial pelvic pain are limited.

Objective: The objective of the study was to compare the effect of onabotulinumtoxin A vs placebo injections to the pelvic floor muscles in women with myofascial pelvic pain.

Study Design: This was a double-blind, randomized, placebo-controlled trial in women with myofascial pelvic pain. Women ≥18 years were eligible if they reported pain ≥6 on a 10 point visual analog scale ≥50% of the time and had pain on palpation ≥6 on the visual analog scale in ≥1 of 6 pelvic floor muscle groups. Participants were randomly allocated to a pelvic floor injection of 200 units of onabotulinumtoxin A or 20 mL of saline. All participants started 8 weeks of physical therapy 4 weeks after the injection. Participants completed validated questionnaires at baseline, 2, 4, and 12 weeks after injection. At each visit, a urogynecologist who was blinded to treatment arm performed a clinical examination with palpation of the left and right sides of 6 pelvic floor muscle groups. The primary outcome was change in participant-reported pain on palpation of the most painful pelvic floor muscle at 2 weeks. Analyses were intention to treat.

Results: We consented 60 women. One participant was lost to follow-up after she was consented; therefore, we randomized 59 women. The groups had similar demographic and clinical characteristics. With regard to the primary outcome, there was no significant difference between the intervention and placebo groups in the change in participant-reported pain on palpation of the most painful pelvic floor muscle at 2 weeks. There were no significant differences in participant-reported pain on palpation for any muscle group at 4 or 12 weeks. At 4 and 12 weeks, participants in the intervention group reported greater declines in overall pelvic pain on the visual analog scale compared with the placebo group, although these differences were not statistically significant (both P = .16). Using the Patient Global Impression of Improvement index, participants in the intervention group were more likely to report their symptoms were improved at 4 and 12 weeks compared with the placebo group, although this difference was significant only at 4 weeks (P = .03 and P = .10, respectively). At 2 weeks, the placebo group had a significant improvement in the Pelvic Floor Distress Inventory score compared with the intervention group (P = .01); however, this difference did not persist at 4 (P = .19) or 12 weeks (P = .11). At 2 weeks, the most common adverse event was constipation in the intervention and placebo groups, with 10.1% reporting de novo constipation. This was followed by urinary incontinence in the intervention group (22%) and urinary tract infection (9%) in the placebo group.

Conclusion: Pelvic floor onabotulinumtoxin A injections for myofascial pelvic pain were not more effective than saline injections at decreasing muscle pain on palpation. Despite this, participants who received onabotulinumtoxin A were more likely than those who received saline to report improvement, albeit not statistically significant, in their overall pelvic floor pain at 4 and 12 weeks.