Spinal Botox injection reduces pain

Dec 22 2010

Botulinum neurotoxin type A (BoNT/A)—better known as Botox—reduces responses to an inflammation-related pain stimulus when injected into the spinal canal in mice, reports a study in the January issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS).

"BoNT/A, with its long-lasting antinociceptive effect, may be a useful analgesic in inflammatory pain," according to the new research, led by Won-Ho Lee, MSD, PhD, of Seoul National University.

Spinal BoNT/A Injection Provides Lasting Reduction in Pain Responses

The researchers used a standard experimental model of pain in mice to examine the effects of spinal (intrathecal) BoNT/A injection. In this model, a chemical called formalin is injected into the paw, producing a predictable two-phase inflammatory pain response. Pain behaviors were monitored for up to four weeks in mice that did and did not receive spinal Botulinum neurotoxin.

Even a single spinal injection of Botulinum neurotoxin produced a pain-reducing effect: mice receiving the injection exhibited significantly fewer pain behaviors, particularly during the second phase of the pain response. These effects were not accompanied by any movement abnormalities, suggesting that Botulinum neurotoxininjection did not adversely affect spinal cord function.

The pain-reducing effect of a single injection of Botulinum neurotoxin peaked at 10 days, then decreased up to 14 days. Mice treated with Botulinum neurotoxin also had significant reductions in certain neurotransmitters involved in various types of pain conditions.

Although 'Botox' is most familiar from its use in cosmetic plastic surgery, it is also used for treatment of various neuromuscular disorders. Over the past decade, Botulinum neurotoxin has been successfully used to treat certain types of chronic pain syndromes, including tension-type and migraine headaches and low back pain. Since Botulinum neurotoxin causes temporary muscle paralysis, these pain-reducing effects have been attributed to muscle relaxation. However, recent studies have suggested that other analgesic mechanisms may be operating as well.

By showing that Botulinum neurotoxin reduces pain even when injected into the spinal canal, the new experiments suggest that it has a "central analgesic effect" on inflammatory pain. The pain-reducing effect lasts for some time, but eventually wears off—as it does in other medical procedures for which Botulinum neurotoxin is used.

The observed differences between the first and second phases of the pain response, and the effects on neurotransmitter levels, may provide future researchers with important clues as to the exact mechanism of BoNT/A's analgesic effect. More research will be needed to further explore these effects—as well as the potential uses of spinal Botulinum neurotoxin injections for specific types of pain problems in humans.

"This study draws attention to the many unexplored therapeutic avenues to help us control chronic pain," says Dr. Steven Shafer, Editor-in-Chief of Anesthesia & Analgesia. "Only by finding new approaches to attenuating pain transmission can we create therapeutic options to free future generations from the scourge of chronic pain."

SOURCE Anesthesia & Analgesia