Evolution of dose and response to botulinum toxin A in cervical dystonia: a multicenter study

Botulinum neurotoxin (BoNT) is an effective treatment for cervical dystonia (CD). Long-term changes of several variables, including the dose of BoNT, in these patients is largely unknown. We reviewed the clinical charts of 275 patients with CD treated with BoNT type A (BoNT-A) for at least 5 years since 1989 at ten tertiary centers. The mean dose of BoNT-A per session during the first 5 years of treatment was calculated and the appearance of resistance was noted. The dose of BoNT-A for the whole group showed a significant trend to increase over time (year 1: 180 ± 65 U; year 5: 203 ± 63 U; ANOVA: p