Dystonia (literally, "abnormal muscle tone") is a generic term used to describe a neurological movement disorder involving involuntary, sustained muscle contractions. Dystonia may affect muscles throughout the body (generalised), in certain parts of the body (segmental), or may be confined to particular muscles or muscle groups (focal).. . Contents [hide]. 1 Causes . 2 Symptoms . 3 Types of Dystonia . 4 The Focal Dystonias . 5 Treatment . 6 References . 7 External links . . . . [edit]. 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 by some unidentified cause such as 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.. . [edit]. 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.. . [edit]. Types of Dystonia. Generalised . Segmental . Intermediate . [edit]. The Focal Dystonias. These are the most common dystonias and tend to be classified as follows:. . Cervical dystonia (spasmodic torticollis). This affects 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 affects the muscles around the eyes. The sufferer experiences rapid blinking of the eyes or even their forced closure causing effective blindness. . Oromandibular dystonia. This affects the muscles of the jaw and tongue, causes distortions of the mouth and tongue. . Spasmodic dysphonia. This affects the muscles of the larynx, causing the voice to sound broken or reducing it to a whisper. . The combination of blepharospasmodic contractions and oromandibular dystonia is called Meige's syndrome.. . [edit]. Treatment. Drugs, such as anticholinergics which act as an inhibitor of the neurotransmitter acetylcholine, may provide some relief. Clonazepam, an anti-seizure medicine, is also sometimes prescribed. However, for most sufferers their effects are limited. Botulinum toxin injections into affected 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. There is a Type A and Type B toxin approved for treatment of dystonia; often those that develop resistance to Type A may be able to use Type B.. . 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.. . One type of dystonia, dopa-responsive dystonia can be completely treated with regular doses of carbidopa/levodopa (Sinemet). Although this doesn't remove the condition, it does alleviate the symptoms most of the time.