Background and objectives Many women with endometriosis continue to have pelvic pain despite optimal surgical and hormonal treatment; some also have palpable pelvic floor muscle spasm. We describe changes in pain, spasm, and disability after pelvic muscle onabotulinumtoxinA injection in women with endometriosis-associated pelvic pain, a specific population not addressed in prior pelvic pain studies on botulinum toxin.

Methods We present an open-label proof-of-concept case series of women with surgically diagnosed endometriosis. Under conscious sedation and with topical anesthetic, 100 units of onabotulinumtoxinA was injected transvaginally into pelvic floor muscle spasm areas under electromyography guidance. Changes in pain intensity, muscle spasm, disability, and pain medication use were assessed at periodic visits for up to 1 year after injection.

Results Thirteen women underwent botulinum toxin injection and were followed for at least 4 months. Before injection, 11 of the 13 women had spasm in >4/6 assessed pelvic muscles and reported moderate pain (median visual analog scale (VAS): 5/10; range: 2–7). By 4–8 weeks after injection, spasm was absent/less widespread (≤3 muscles) in all (p=0.0005). Eleven rated their postinjection pain as absent/mild (median VAS: 2; range: 0–5; p<0.0001); 7/13 reduced pain medication. Disability decreased in 6/8 women with at least moderate preinjection disability (p=0.0033). Relief lasted 5–11 months in 7 of the 11 patients followed for up to 1 year. Adverse events were mild and transient.

Conclusions These findings suggest pelvic floor spasm may be a major contributor to endometriosis-associated pelvic pain. Botulinum toxin injection may provide meaningful relief of pain and associated disability.

Trial registration number NCT01553201