ACR: Botox Is New Wrinkle In Osteoarthritis

WASHINGTON, Nov. 13 -- Botox, best known for ironing out aging wrinkles, may also relieve severe pain from osteoarthritis of the knee, a researcher reported here.

In interim data from a randomized placebo-controlled trial, injections of botulinum toxin type A significantly reduced severe pain and improved function, according to Maren Mahowald, M.D., of Minneapolis VA Medical Center.

"We're very excited," Dr. Mahowald said before she presented her data at the American College of Rheumatology meeting here.

The trial, Dr. Mahowald said, grew out of clinical observations in conditions such as painful spasticity, in which investigators noticed that pain often lessened before a decline in muscle contractions.

"This suggested an independent analgesic effect of botulinum toxin," she said. So she and colleagues conducted an open-label study, in which they found 10 of 15 patients had an improvement in pain of 50% or greater.

In the current study, investigators enrolled 37 patients who were not candidates for joint replacement, and are evaluating their response at one, three, and six months to injections of either 100 units of botulinum toxin plus lidocaine or saline plus lidocaine, she said.

All patients have now been evaluated at the one-month mark, Dr. Mahowald said, and the researchers saw no effect among the 17 patients with initially moderate pain scores on the Western Ontario McMaster (WOMAC) osteoarthritis index.

However, among the patients with severe pain on the WOMAC index:

• The mean pain score among patients getting Botox fell 29% from baseline (from 62 to 42), which was statistically significant at P=0.006.
• The mean function score among patients getting Botox fell 25% from baseline (from 62 to 47), which was statistically significant at P=0.033.
• The mean pain score among patients getting placebo fell 17% over baseline, but the difference was not statistically significant.

Dr. Mahowald said 33% of the placebo patients reported at least a 30% improvement in pain and the same percentage reported at least a 50% improvement (no statistical significance data provided).

In contrast, 55% of the Botox patients reported at least a 30% improvement and 44% reported a 50% improvement or better, she said (no statistical significance data provided).

There were no significant adverse events, she said. In other clinical applications, the most common adverse event is muscle weakness, but "since we were not injecting into muscle, we didn't see any weakness of the limb."

The study is "one of the most provocative things that have come down the pike for the treatment of osteoarthritis in a long time," said Robert Wortmann, M.D. of the University of Oklahoma College of Medicine in Tulsa, who was not part of the research.

"The possibility of having something that's non-toxic and would really alter the symptomology of a disease that is not curable would be fantastic," Dr. Wortmann commented.

But he cautioned that the study - while "exciting" -- is not complete and clinicians will have to await the final results. He added that doctors will have to look closely at variations in response among patients that might be masked by averages reported in a clinical trial.