Botulinum toxin appears no better than placebo for treatment of jerky and tremulous functional movement disorders, neurologists say after conducting a randomised controlled trial.

The Dutch study of 48 patients at a single clinic has found a marked placebo response, however, suggesting a substantial potential for recovery among even chronically ill patients, researchers say.

The trial participants were randomised to receive intramuscular botulinum toxin A injections or sterile saline at baseline and three months, followed by a 10-month open-label extension study in which most patients received up to another four injections.

Around 60% of patients in both the active and control groups showed improvement in motor symptoms after the trial, with no statistically significant difference between them, the researchers said.