CHICAGO (AP) - A botulism toxin treatment sometimes used to smooth wrinkles can also improve tiptoe-walking common in children with cerebral palsy, new research shows.

Injections of the food-poisoning toxin cause muscle weakness and are becoming an increasingly popular but little publicized treatment for stiff muscles in cerebral palsy.

The new study, involving 155 children treated for at least a year at nine centers, is one of the largest and longest-running to examine the treatment's effectiveness.

Children aged 2 to 18 received calf-muscle injections about three times a year for up to two years. Nearly half - about 49 percent - displayed less walking on their tiptoes six weeks after the first treatment and continued to show improvement for two years post-treatment.

The toxin enabled some children to walk without braces and ride tricycles, said Dr. L. Andrew Koman, the lead researcher and an orthopedic surgery professor at Wake Forest University.

The study is published in November's issue of Pediatrics. The toxin was first approved in 1989 for treatment in adults of two rare nerve disorders that cause crossed eyes and involuntary eye-shutting. Doctors noticed reduced facial wrinkling, and the toxin became popular in plastic surgery.

It since has been used to treat cerebral palsy, even though it is not federally approved for such use, said Dr. Michael Sussman, president of the American Academy for Cerebral Palsy and Developmental Medicine.

"It's kind of a hot area in cerebral palsy treatment right now," Sussman said.

The preparation studied is called Botulinum toxin type A or BTX-A, sold as Botox by manufacturer Allergan, Inc., which funded the research.

Cerebral palsy is caused by brain damage, usually before birth, that impairs the ability to control muscle movement. An estimated 500,000 U.S. children and adults are afflicted.

Surgery is often done on the calf tendons to help treat the tiptoe-walking, but Botox injections, usually coupled with leg braces, can help give children time to develop a more normal walking pattern and may avert surgery, said Dr. Lisa Thornton, who uses Botox to treat cerebral palsy patients at Chicago's La Rabida Children's Hospital and Research Center.

Paul Greene, a Columbia University neurologist, noted that 28 percent of the children studied developed antibodies to the toxin, which can render it useless in treating the nerve disorders for which it is approved and which are common in cerebral palsy patients.

The researchers said Botox was still effective in many patients who developed antibodies, but Greene said that could reflect the strong placebo effect often found with Botox injections in adult patients.

Koman said the newest form of Botox contains fewer proteins than the preparation studied and is less likely to cause the antibody response.

He also said the placebo effect is an unlikely explanation for the results since improvement lasted sometimes years after treatment.

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