Botulinum neurotoxins have been shown to be a safe and effective therapeutic option for most forms of
focal dystonia, and are now considered to provide the best symptomatic treatment in these disorders. However, only a few papers addressed the long-term efficacy and safety of repeated treatments with this
drug. This article reviews the data from clinical trials that have assessed the long-term results of
botulinum neurotoxin type A (
BoNT-A) and type B in the treatment of the different forms of focal craniocervical
dystonia, cervical dystonia (CD),
blepharospasm, oromandibular, and laryngeal
dystonia. Studies on the long-term effects of
BoNT-A therapy have demonstrated that the majority of patients comply with this repeated treatment because they experience a positive and stable effect over time. It is still unclear whether in patients with
focal dystonia the mean dose of
BoNT-A changes over time. In spite of the wide spectrum of side effects reported to be associated with
BoNT-A treatment, there is no evidence of specific side effects due exclusively to the long-term use of such drugs. The only exception to these positive long-term findings is the occurrence of a subgroup of patients with CD who fail to maintain a sustained response after the first or second effective treatment, partly owing to the development of
neutralizing antibodies against the toxin. Longitudinal studies aimed at defining the risk factors for this abnormal pattern of response to
botulinum toxin treatment are currently being conducted.