Dystonia
What are the symptoms?
Primary focal dystonia
These are the commonest forms of dystonia. For instance cervical dystonia or spasmodic torticollis affects around twelve thousand people in the UK and blepharospasm, some five to six thousand.
- Spasmodic Torticollis or Cervical Dystonia affects the neck muscles. The neck and head can be twisted forward, backwards, to one side or even held in one specific position. Head tremor can also occur.
- Blepharospasm affects the muscles around the eyes leading to constant blinking or closure of the eyes, especially in strong light. In some cases the frequency of the spasm can be such that the eye remain shut resulting in the affected person being unable to see despite having normal vision.
- Writer's Cramp affects the muscles of the hand and arm when writing. Other dystonias of the hand muscles are typist's cramp and sport and musician's cramps.
- Oromandibular Dystonia affects the mouth, jaw and tongue muscles. Speech and swallowing are sometimes affected as the dystonia causes the mouth to remain closed or open.
- Cranial Dystonia (also known as Breughel or Meige syndrome) is a combination of Oromandibular Dystonia and Blepharospasm.
- Laryngeal Dystonia affects the speech muscles of the throat and can lead to the voice becoming strained or forced, or in some cases only being able to speak in a whisper.
Generalised and segmental dystonia
Generalised dystonia usually starts in childhood, with onset in a limb which spreads to other parts of the body. It is often familial and can be very disabling. The commonest form has been shown to be caused by a mutation in a specific gene known as DYT1.
- DYT1 Dystonia is inherited in an autosomal dominant fashion, although many family members who carry the abnormal gene may only be mildly affected or not at all. Typically the condition causes onset of dystonia in an arm or leg in childhood or early teens which then spreads to involve the trunk and other limbs (generalised dystonia). Drug therapy is not particularly helpful but in recent years there have been reports of useful benefit from the neurosurgical procedure known as deep brain stimulation. Identification of the common mutation in the DYT1 gene means that genetic testing is available with appropriate counselling.
- Dopa-responsive Dystonia (aka Segawa's syndrome) is another genetic condition that can cause more widespread dystonia. In this condition dystonia tends to affect walking more than other activities and characteristically worsens towards the end of the day. Other members of the family may be affected, and can also show symptoms similar to Parkinson's disease. The commonest genetic cause in the UK is GTP-cyclohydrolase 1 deficiency which is usually dominantly inherited. The key point is that it usually responds well to treatment with the drug levodopa.
- Secondary or Symptomatic Dystonia is often characterised by the presence of other clinical features in addition to dystonia. Dystonia in childhood can be due to secondary causes such as a form of cerebral palsy, thought to be due to lack of oxygen to the brain around the time of birth, which damages the basal ganglia. Rare biochemical and metabolic disorders can also cause dystonia along with other cognitive and neurological features. In children and adults it is also important to exclude the possibility of drug induced dystonia. Drugs that interfere with the chemical neurotransmitter dopamine (such as anti-emetics and anti-psychotics) can cause what is referred to as tardive dystonia. Other secondary causes include structural damage to the basal ganglia from strokes, tumours and trauma.
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