Dystonia
Dystonia (literally, "abnormal muscle tone") is a generic term used to describe a neurological movement disorder involving involuntary, sustained muscle contractions. Dystonia may effect muscles throughout the body (generalised), in certain parts of the body (segmental), or may be confined to particular muscles or muscle groups (focal).
Causes
Primary dystonia is caused by a pathology of the central nervous system, likely originating in those parts of the brain concerned with motor function, such as the basal ganglia. The precise cause of primary dystonia is unknown. In many cases it probably involves some genetic predisposition towards the disorder combined with environmental conditions.
Secondary dystonia refers to dystonia brought on by some identified cause, usually involving brain damage or chemical imbalance. Some cases of (particularly focal) dystonia are brought on after trauma, are induced by certain drugs (tardive dystonia), or may be the result of diseases of the nervous system such as Wilson's disease.
Symptoms
Symptoms vary according to the kind of dystonia involved. In all cases, dystonia tends to lead to abnormal posturing, particularly on movement. For many sufferers, pain is also a feature of the condition.
Types of Dystonia
- Generalised
- Segmental
- Focal
The Focal Dystonias
These are the most common dystonias and tend to be classified as follows:
- Cervical dystonia (spasmodic torticollis). This effects the muscles of the neck, causing the head to rotate to one side, to pull down towards the chest, or back, or a combination of these postures.
- Blepharospasm. This effects the muscles around the eyes. The sufferer experiences rapid blinking of the eyes or even their forced closure causing effective blindness.
- Oramandibular dystonia. This effects the muscles of the jaw and tongue, causes distortions of the mouth and tongue.
- Spasmodic dysphonia. This effects the muscles of the larynx, causing the voice to sound broken or reducing it to a whisper.
Treatment
Drugs, such as anticholinergics which act as an inhibitor of the neurotransmitter acetylcholine, may provide some relief. However, for most sufferers their effects are limited. Botulinum toxin injections into effected muscles have proved quite successful in providing some relief for around 3-6 months, depending on the kind of dystonia. The injections have to be repeated and around 15% of recipients develop immunity to the toxin. Surgery, such as the denervation of selected muscles, may also provide some relief. Recently, the procedure of deep brain stimulation has proved successful in a number of cases of severe generalised dystonia.