Widely used by doctors to soften forehead wrinkles and reduce uncontrollably sweaty armpits, researchers are exploring botulinum toxin as a potential therapy for osteoarthritis (OA) pain.
“The Botox story is very intriguing,” says David Felson, MD, MPH, professor of medicine and epidemiology at Boston University School of Medicine. “It isn’t just muscles. It can paralyze nerves. Just like celebrities injecting it into wrinkles, it could have the same effect on a hip muscle. Botox could paralyze the muscle that is transmitting pain.”
This toxin may eventually be used to treat OA patients whose pain is not sufficiently controlled by traditional medicines like NSAIDs or analgesics, and for patients who may experience adverse effects from those medicines, says Dr. Felson.
One of the more recent studies was reported at the 2013 European League Against Rheumatism (EULAR) conference. In the study, 45 patients were injected with either hyaluronic acid (HA) alone or a combination of HA plus Botox and monitored at one, three, and six months. After one month, the Botox group showed a significant decrease in WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) pain and physical function scores that sustained through six months.
Blocks Pain Signals
In the same action that botulinum toxin flattens wrinkles for up to six months, the substance “blocks the neuromuscular junction, so the nerve can’t transmit signals to the muscle and it prevents contraction,” says Eric Hsu, MD, a pain specialist at Ronald Reagan-UCLA Medical Center in Los Angeles.
Although the studies conducted so far are small and look at short-term results, the results of these recent studies are “impressive,” says Dr. Felson.
He points to a Minneapolis-based study published in the Journal of Rheumatology in 2010 that looked at 54 patients experiencing chronic pain after total knee arthroplasty. Some were injected with botulinum toxin A and some were given a placebo. The results were significant: 71 percent of those injected with botulinum toxin achieved clinically meaningful reduction in pain and improved, measurable physical function in the joint compared to 35 percent of those receiving the placebo shot.
Another study published in the PMR, the Journal of Injury, Function and Rehabilitation in 2010 looked at 60 patients aged 40 years or older with painful osteoarthritis of the knee who had failed physical therapy, medications and/or injection therapy. After an 8-week treatment of botulinum toxin A, they showed statistically significant improvements in WOMAC scores for pain, stiffness and function that lasted for six months.
An Italian study published in the Journal of Rehabilitative Medicine in 2010 looked at the effectiveness of botulinum toxin A injections in the thigh muscles of patients experiencing pain due to hip OA. All patients experienced improvements in hip function and pain at two, four and 12 weeks after the injections.
Possible Treatment for Inflammation?
Another study has raised further interest by suggesting that botulinum toxin might someday be used to treat inflammation as well. Published in the journal Biochemistry in 2011, it explored a future use of botulinum toxin: Treating chronic inflammation, not just temporarily relieving pain. Felix Yeh, PhD, who led the study and is now working in the private sector in San Francisco, said the focus of the study was to learn how toxins get into neurons, something he calls “a Trojan horse strategy.”
Using botulinum toxin type B, a relatively new product on the market, on laboratory mice, Yeh and his colleagues showed that the neurotoxin could be retargeted to inhibit the release of tumor necrosis factor alpha, a key cytokine that is one of the possible causes of inflammation in autoimmune diseases like rheumatoid arthritis.
Physicians Urge Caution
Physicians treating patients with serious chronic joint pain see botulinum toxin as potentially useful, but urge caution at this point. Although studies haven’t shown serious adverse effects, Dr. Felson speculates that injecting it into large muscles supporting weight-bearing joints, such as the thigh, might impair one’s ability to walk, for example.
So far, the results look promising, so Dr. Hsu is hopeful. “I think things like this, which do not cause the systemic, multi-organ side effects of other treatments, are potentially an option for us to help our patients.”