Dystonia Background

Dystonia is a neurological movement disorder characterized by involuntary muscle contractions, which force certain parts of the body into abnormal, sometimes painful, movements or postures. Dystonia can affect any part of the body including the arms and legs, trunk, neck, eyelids, face, or vocal cords. If dystonia causes any type of impairment, it is because muscle contractions interfere with normal function. Features such as cognition, strength, and the senses, including vision and hearing are normal. While dystonia is not fatal, it is a chronic disorder and prognosis is difficult to predict.

It is the third most common movement disorder after Parkinson's Disease and Essential Tremor, affecting more than 300,000 people in North America. Dystonia does not discriminate - affecting all races and ethnic groups.

Surgery for Dystonia

Surgery for Dystonia may be considered when patients fail to achieve desired relief from other treatments. Although some forms of surgery may lose its effect over the years, it can provide some temporary relief. The goal of this type of surgery is to interrupt various pathways of the nervous system that are responsible for the abnormal movements. Some operations intentionally damage small regions of the thalamus (thalamotomy), globus pallidus (pallidotomy), or other deep centers in the brain. Recently, chronic deep brain stimulation (DBS) has been tried with increasing success (click on Twisted icon on this page for more information).

Other surgical approaches include cutting nerves going to the nerve roots deep in the neck close to the spinal cord (anterior cervical rhizotomy) or removing the nerves at the point they enter the contracting muscles (selective peripheral denervation). There are a number of factors that may influence the success of the operation. Each patient is unique, and the muscles involved vary from one patient to another. It is for this reason that pre-operative evaluation by a movement disorders expert is essential.

What is deep brain stimulation and what role does it play in the treatment of dystonia?

It is clear that dystonia results from abnormal and excessive or reduced neuronal activity respectively, in specific nuclei (e.g., the globus pallidus) in the basal ganglia. With advances in neuroimaging (e.g., MRI) and the ability to physiologically map (e.g., microelectrode recording) the brain, the surgeon is now able to more accurately pinpoint the desired target. As a result the technique of deep brain stimulation (DBS) has been used in place of the conventional approach of lesioning or ablation. DBS entails placing a permanent stimulating electrode in the brain which is connected to a pulse generator implanted in the chest wall. Where as ablation causes permanent destruction of the targeted area, DBS acts reversibly to inactivate the area. It offers the further advantage of being adjustable in terms of frequency and amplitude of the current pulses, thus specifying the area influenced.

Although the thalamus has been the most common target to ablation in dystonia, the pallidum has been targeted recently because of better observed efficacy. The preliminary results are encouraging, although typically not as immediate or dramatic as the results seen in patients suffering from Parkinson’s disease and essential tremor.

Bilateral pallidal DBS produces significant benefit in dystonia with average impovements of about 50-60% in the Burke-Fahn-Marsden dystonia rating scale. Some primary generalized patients have been reported to have upto 90% improvment. DBS has also been performed on persons with secondary dystonias, cervical dystonia, segmental dystonia, and myoclonic dystonia with encouraging results.