One way to classify dystonia is to divide causes into idiopathic dystonia, inherited dystonia and acquired dystonia. In idiopathic dystonia there is no identifiable cause of the dystonia and no degeneration or structural damage to the brain. In inherited dystonia, the person affected is known to have inherited a gene causing dystonia but there is no other degeneration or structural damage. Most people with the commonest forms of dystonia such as neck (cervical) dystonia and eye dystonia (blepharospasm) have idiopathic dystonia. In acquired dystonias, the dystonia is caused by damage or degeneration of the brain (for example after brain injury or stroke) or exposure to particular drugs.
There are more than 50 other causes of secondary dystonia affecting many thousands of people. This article will discuss some of the main ones.
Dystonia caused by brain injury/damage
Dystonia can sometimes appear after trauma to the brain via physical injury, or stroke. Where the injury is to the head, the symptoms often affect the side of the body which is opposite to the side of the brain injured. The injury can often result in observable damage (lesions) in the brain that can be seen using neuroimaging techniques such as MRI scans. This contrasts with primary dystonia where no abnormalities of the brain can be seen.
Dystonia can also result from an injury to a part of the body other than the brain: for instance neck dystonia sometimes follows whiplash, eye dystonia (blepharospasm) can follow eye surgery and mouth dystonia (oromandibular) can follow dentistry work. Post-traumatic dystonia can sometimes be distinguished from primary dystonia because the symptoms may not respond to sensory tricks and may persist during sleep. Symptoms may also be paroxysmal which means they occur in episodes rather than being constant.
Dystonia following brain injury/damage may not appear for several months or (more rarely) several years after the injury. Treatment for posttraumatic dystonia can include medications and botulinum toxin injections.
Parkinson’s disease and dystonia
Parkinson's disease is a neurological movement disorder with a wide range of symptoms including slowness of movement, rigidity of muscles, memory impairment and others. Both Parkinson’s disease and dystonia can arise in the same person because they seem to originate in the same part of the brain: the basal ganglia. Sometimes symptoms similar to Parkinson’s disease (parkinsonism) arise together with dystonia due to a genetic defect as in the rare condition, x-linked dystonia parkinsonism.
However, the most common cause of dystonia in Parkinson’s patients is a secondary dystonia arising from the effect of treating Parkinson’s disease using the medication, Levodopa.
Levodopa is a chemical that converts into dopamine, a chemical messenger in the brain. It is a shortage of dopamine that causes Parkinson’s and dopamine is also thought to play a role in dystonia although what exactly this role is has yet to be fully clarified. Curiously, dystonia is caused both when the effect of Levodopa is too strong and too weak. Off-period dystonia occurs when the effect is the Levodopa is wearing off and the symptoms include postural changes in the hands and feet and also in the neck. On-period dystonia happens when
levodopa is at its most effective.
It is thought around a third of those on medication for Parkinson’s disease experience dystonia. As levodopa is so frequently used in treatment this will amount to many thousands of people. However, these conditions are so frequent that most doctors think of them as part of Parkinson's disease and they are not included in the Dystonia Society’s estimate of 70,000 people with dystonia.
Cerebral palsy and dystonia
Cerebral palsy is an umbrella term for a group of movement and posture disorders that occur as a result of damage to the developing foetal or infant brain. Causes can include premature delivery and birth injuries. The disorders can sometimes be accompanied by cognitive problems or epilepsy. By far the most common type of cerebral palsy is spastic cerebral palsy where the range of movement is decreased because the muscles are tight. However, a significant minority (around 15%) have a type of cerebral palsy known as dystonic (or athetoid) cerebral palsy.
Dystonic cerebral palsy is caused by damage to the basal ganglia or cerebellum and causes dystonic symptoms such as involuntary muscle spasms and slow, rhythmic, twisting movements. The condition is clearly distinct from spastic cerebral palsy because the muscle tone switches from floppy and loose to tight rather than staying tight all the time. There can also be difficulty controlling the tongue and vocal cords. As with childhood-onset primary dystonias, treatment is usually through a variety of medications and sometimes botulinum toxin. However, Deep Brain Stimulation which is often effective for primary dystonias is not generally used for secondary dystonias.
The prevalence of cerebral palsy is around 1 in 500 so the number of people affected by dystonic cerebral palsy is estimated to be at least 15,000.
Metabolic disorders and dystonia
Metabolic disorders arise when the body fails to process the chemicals in the body properly. This can result in excesses or deficiencies of materials arising in different parts of the body. Dystonia is one of the conditions that can occur when these metabolic disorders affect the brain. There are more than 50 different metabolic conditions that can cause dystonia but most of them are
Examples include Wilson’s disease which is a treatable genetic condition in which the body does not process copper properly and neuronal brain iron accumulation syndrome (NBIA) – a genetic degenerative condition in which iron is deposited in the basal ganglia.
Drug-induced dystonia (tardive dystonia)
Note: This article was prepared with the guidance of Dr Mark Edwards and using information from Parkinson's UK, Scope and the DMRF.
Last reviewed March 2012
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