An Italian study published in the Journal of Rehabilitative Medicine in 2010 looked at the efficacy of botulinum toxin type-A injections in the thigh muscles of patients experiencing pain due to hip OA. Each subject received two injections of the solution for a total of 400 units: 250 units in the adductor longus muscle and 150 units in the adductor magnus muscle of the thigh on the same side of the body as the affected hip. Results were equally promising. The patients were evaluated to measure hip function, pain, and overall well-being and quality of life before the study, and all saw improvements in these areas in follow-up evaluations at two, four and 12 weeks after the injections.

Another study conducted by University of Wisconsin researchers published in the journal Biochemistry in 2011 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.

“Toxins cannot naturally get into non-neural cells,” says Yeh. “But we found if we coated our toxins with antibodies, we could drive them through.” The re-engineered toxins could enter cells and cleave to SNAREs, key proteins that play a role in the secretion of inflammation-causing substances. In their mouse study, the researchers measured about a 50-percent decrease in TNF-alpha release after treating the tissue with the engineered toxin, without significantly affecting other cells. “Since we were able to inhibit its secretion, we were able to lower overall inflammatory phenotypes,” says Yeh. “We saw the potential for all toxins. All of these could be retargeted to non-neural cells for therapeutic use.”

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.”