Use of botulinum toxin type A in the treatment of cervical dystonia.

Botulinum toxin is the most neurotoxic substance known, with a specific action at cholinergic synapses. Acting as a zinc endopeptidase, botulinum toxin cleaves specific proteins involved in vesicle fusion, thereby preventing release of acetylcholine. The therapeutic effect of the toxin taken up presynaptically at the neuromuscular junction is to weaken muscle. Botulinum toxin type A (BTX-A) has been shown to be safe and effective in the treatment of cervical dystonia (CD; also known as spasmodic torticollis). In patients with CD, injections of botulinum toxin dampen or eliminate involuntary muscle activity and improve control of neck movement, pain, and range of motion. To successfully use botulinum toxin as a therapeutic modality, targeting the dystonic muscles, injecting a sufficient quantity of toxin and minimizing diffusion into uninvolved muscle collectively provide the best outcome with the fewest adverse reactions. EMG guidance may allow more precise injections. To maintain responsiveness to the toxin over repeated injections, using the lowest dose at the longest dosing interval has been suggested.