Botox could be used to relieve writers' cramp, a study has suggested.
The painful contractions of writers' cramp can affect the fingers, hand or arm
The toxin is usually used to treat wrinkles, but the Dutch research suggests it can also stop muscles in the arms, hands or fingers seizing up.
It has previously been shown to be helpful in treating other forms of muscle spasm, known as dystonia.
A UK neurologist said the work, in Journal of Neurology Neurosurgery and Psychiatry, could help but would not be a permanent cure.
Writer's cramp can be an extremely painful condition, which in its most severe forms turns the hand into a claw.
It involves spasmodic muscle contractions of the fingers, hand, or arm during writing, but can also occur during other manual tasks.
The condition affects around three to seven in every 100,000 people.
There is no cure. Some of those afflicted learn to write with their other hand.
But in one in four cases, the condition affects both hands, and the condition is difficult to treat.
Relaxation techniques, hypnosis, acupuncture, and 'writing re-education exercises' have all been used by patients, but none offers brings sustained relief. No drugs have been shown to be effective against the disorder.
In this study carried out at the Academic Medical Centre in Amsterdam, 40 people with writer's cramp were either given a course of botox injections or a dummy (placebo) version in two doses, usually into two muscles, over a period of 12 weeks.
Of the 20 people given botox treatment, 14 said that their condition had significantly improved, and that they wished to continue treatment.
Scientists confirmed there had been improvements using recognised disability and pain measures.
Only six of the 19 people in the group who received the dummy injection felt that their condition had improved. One person dropped out of the trial.
One person who received the dummy injection at the first session and botox at the second, also registered an improvement in symptoms.
A year after the study was carried out, half of all those who took part were still receiving botox injections, and were finding them helpful.
On average, people needed repeat injections every four months.
The botox injections are given into the particular muscle which goes into spasm in the patient.
It works by blocking the chemical message from a nerve to a muscle which makes it contract unnecessarily, and so the muscle is relaxed.
Writing in the Journal of Neurology Neurosurgery and Psychiatry, the research team led by Dr Jose Kruisdijk said: "Writers' cramp remains difficult to treat, but our results show that botox injections are safe and efficient compared with placebo.
"Further investigation of combination treatment seems a promising and challenging task."
Dr Charles Clarke, a neurologist at the National Hospital for Neurology and Neurosurgery, said: "This is certainly not a cure. It's a way of paralysing the muscle and so stopping the spasm. Freezing the muscle would work just as well."
He added: "Writers' cramp is a horrible condition. Anything that relieves it is welcome and this could help some people."