[Problems of treating writer's cramp with botulinum toxin injections: results from 10 years of experience]

We studied the efficacy of botulinum toxin (BTX-A) injections in 167 patients, from a large cohort of 259 patients, presenting with writer's cramp (WC) and followed up to 10 years. The selection of the muscle was based on a careful physical examination, using up to 6 manoeuvres whilst attempting to write in order to bring out the original dystonic posture. The injection technique had to be precise, under EMG guidance, with a hollow recording needle to detect muscle or finger fascicle. The results showed a good efficacy and tolerance of this treatment in the long term with recovery of normal writing in 46 per cent, partial benefit in 10 per cent, failure in 21 per cent, and loss to follow-up after the first injection in 23 per cent. Among the responders, 27 per cent carried on the treatment every 9 months on average, with a duration of benefit of 6 months with follow-up between 3 and 9 years. Mirror dystonia had no prognostic value. Secondary dystonia, tremulous WC, long duration WC and progressive WC were associated with poor outcome.