In women who have endometriosis, which is an inflammatory condition in which endometrial-like tissue grows outside the uterus on other organs, pelvic floor spasms are a common source of discomfort. Using botulinum toxin injections at the site of these spasms can help alleviate the pain, in part because it relaxes the muscles, according to a study conducted by the National Institute of Neurological Disorders and Stroke (NINDS). On July 8, 2019, a small study published in Regional Anesthesia & Pain Medicine was made available online.

Examining Injections and Pain Associated with Endometriosis

Following the removal of endometrial lesions, researchers used botulinum toxin to treat women who continued to suffer from pain despite receiving the best standard of care for endometriosis treatment. There was no intention to treat the disease with these injections. At the time of the injection, none of the women required surgery. While participating in the study, the women who were able to tolerate hormone therapy were given medication to reduce their menstrual cycle.

Botulinum toxin A (onabotulinumtoxinA) is just one of the many brands of botulinum toxin that are currently available for purchase in the United States, according to one of the study’s lead authors, neurologist and NINDS program director Barbara Karp, MD.

The Exclusion Rate for Women with Endometriosis in the Study

Women with endometriosis who had not undergone surgery to remove lesions were not included in the research. When a woman’s pain is found to be associated with spasms in her pelvic floor muscles during an examination, it may be worthwhile to look into. This is true for women who do not meet the requirements for surgery. Dr. Karp believes that there are other sources of pain that must be thoroughly investigated and dealt with as well.

Endometriosis Treatment Can Cause Pelvic Floor Pain

In the absence of a cure, treatments and therapies can alleviate the symptoms of endometriosis. For a variety of reasons, the NIH team concentrated on women with endometriosis. In many cases, even after undergoing all of the standard endometriosis treatment options, women with endometriosis still experience chronic pelvic pain (surgery, hormones, pain medications). These women’s pain was reproduced when we touched or pressed on the areas of their pelvic floor muscles where we found spasms in this study. Botulinum toxin, which is used to treat muscle spasms, appeared to Karp to be a reasonable treatment option. Furthermore, despite the fact that Botox has been used to treat pelvic pain in the past, there have only been a handful of controlled studies and those focused on women with endometriosis.

Two months after the Injection of Botox, Pelvic Pain Decreased

For four months, thirteen women were given the injections and then followed up with them. When asked about pain two months after receiving injections, almost everyone reported that it had decreased, with some even reporting that their pain was now mild to nonexistent. Half of those who took part in the study said they had cut back on their use of pain medications. Eight participants said moderate to severe disability prior to receiving the injections; six participants reported improvement over the course of the study.

What is the Duration of the Botulinum Toxin’s Effects?

Muscle contraction is not inhibited by botulinum toxin; rather, it prevents the release of an important chemical messenger molecule (acetylcholine) by nerve cells, which instructs the muscle to contract. Muscles relax when the nerves that control them are unable to communicate with them. This is probably not the only way it works. Pain signals are sent by chemical messages that are blocked by botulinum toxin.

In the majority of cases, when botulinum toxin is used to treat neurological conditions such as spasticity or dystonia, the effects of the toxin last three months or longer. This is because the average interval between injections for the majority of these conditions is three months. As demonstrated in some of the patients we studied, the benefit can last for a more extended period of time in some patients and for specific pain conditions.