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Botulinum Toxin for Treatment of Dystonia
by Paul G. Wasielewski, Division of Neurology/Movement Disorders
Dystonia is an abnormal movement characterized by sustained muscle contractions, frequently causing twisting and repetitive movements or abnormal postures. Dystonia can involve any part of the body. According to the site of involvement, dystonia is classified as (1) focal, such as torticollis or blepharospasm; (2) segmental- when two or more contiguous body parts are involved, such as blepharospasm and oromandibular dystonia (i.e. Meige's syndrome); (3) multifocal- when two or more noncontiguous body parts are involved; (4) hemidystonia; and (5) generalized.
Occurrences of Dystonia
Generalized dystonia tends to occur in children, usually occurring first in the foot and, over time, progressing to involve other body parts. Hemidystonia always warrants a search for a structural lesion in the contralateral cerebral hemisphere or brain stem. Focal dystonias occur predominantly in adults, the majority being idiopathic, i.e., idiopathic adult-onset focal dystonia (IAOFD). Hence, it is the focal dystonias which the primary care physicians, internists, and general neurologists should be aware of.
Idiopathic Adult-Onset Focal Dystonia (IAOFD)
The common IAOFD seen clinically include the following:
(1) cervical dystoniaãalso known as spasmodic torticollis. This consists of any combination of abnormal turning, tilting, and/or forward, backward, or lateral shift of the head and neck;
(2) blepharospasmãwhich consists of excessive blinking or prolonged contraction (i.e. closure of) the eyelids, rendering the patient functionally blind;
(3) limb dystoniaãthese typically represent specific action dystonias, such as when writing, i.e., writer's cramp, or playing a musical instrument, such as a violin;
(4) oromandibular dystoniaãwhich consists of spasms involving the muscles of the jaw and lower face;
(5) laryngeal dystoniaãor spasmodic dysphonia, in which the patient demonstrates a strained, choked, or strangled voice.
Botulinum Toxin and the Treatment of Dystonia
Treatment of dystonia is initiated with medications, the most successful being either a benzodiazepine, such as clonazepam (Klonopin), or an anticholinergic such as trihexyphenidyl (Artane). Efficacy with such medications varies, being about 50%. However, the introduction of Botulinum Toxin type A (BOTOX) in the late 1980s revolutionized the treatment of dystonia.
Harvested from the bacteria Clostridium botulinum, it is one of the most potent biological toxins known to man. When the toxin is injected locally into a contracting muscle (as occurs in dystonia) the toxin diffuses 1-2 inches and enters nerve terminals and prevents the release of acetylcholine. This will than stop any ongoing muscle contraction, relieving the dystonic movement. Onset of the maximal effect of the toxin typically takes a few weeks, and the effects can last several months. Efficacy tends to be 70%. Typically, injections are given no more frequently than every 3 months. Adverse effects include excessive local weakness, which if occurs in the neck region, can impair swallowing ability. A small percentage of patients may develop antibodies to the toxin following repeated injections, thus rendering the toxin ineffective; such patients than have to be treated with another type of the toxin.
In addition to the focal dystonias, Botulinum toxin is very effective for the treatment of hemifacial spasm (with nearly 100% efficacy), and also spasticity following stroke or due to multiple sclerosis or cerebral palsy. Its uses outside of neurological conditions continues to expand as well.
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