Widely used by doctors to soften forehead wrinkles and reduce uncontrollably sweaty armpits, researchers now are exploring botulinum toxin as a potential therapy for osteoarthritis (OA) pain.

Although botulinum toxin (Botox, Dysport, Myobloc) has been studied since the 1950s, recent studies on its use in osteoarthritis pain suggest it could be a new analgesic option for a group of patients that’s been hard to treat.

“The Botox story is very intriguing,” says David Felson, MD, professor of medicine and epidemiology at Boston University. “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.”

A powerful neurotoxin produced by a bacterium that can cause deadly botulism poisoning at higher doses, botulinum toxin has an anticholinergic effect, meaning it can block the delivery of the neurotransmitter acetylcholine to the central nervous system, an action which can cause the body to produce chronic pain signals. The substance can temporarily paralyze muscles for a few months, easing painful spasms and tightness in muscles around OA-affected joints. It can also have an antinociceptive effect, meaning it can block nociceptors, or pain receptors, from sending a pain signal up the spinal cord to the brain.

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.

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.

These early, small studies on the pain-fighting potential of botulinum toxin are promising for people who have chronic osteoarthritis pain due to muscle spasms and tightness, or myofascial pain, says Dr. Hsu. Doctors don’t know why some people have this type of chronic muscular pain that never shuts off, he notes. “It’s still a controversial issue and we can’t pinpoint the reason, but there is a theory that chronic inflammation can trigger primary or secondary muscle spasm. This induces the neurotransmitters to be consistently aroused, and it triggers the central nervous system” to send continuous pain signals to the joint.

Botulinum toxin, which can block the transmission of these neurotransmitters for several months at a time, might be a useful treatment for this type of pain, says Dr. Hsu.