Dystonia

Dystonia is a neurological movement disorder in which sustained muscle contractions cause twisting and repetitive movements or abnormal postures.^[1] The disorder may be inherited or caused by other factors such as birth-related or other physical trauma, infection or reaction to drugs.^[1]

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Causes

The cause(s) of dystonia are not yet known or understood; however, they are categorized as follows on a theoretical basis:

Primary dystonia is suspected to be 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, and the GABA (gamma-aminobutyric acid) producing Purkinje neurons. The precise cause of primary dystonia is unknown. In many cases it may involve 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.

Symptoms

Symptoms vary according to the kind of dystonia involved. In most cases, dystonia tends to lead to abnormal posturing, particularly on movement. Many sufferers have continuous pain, cramping and relentless muscle spasms due to involuntary muscle movements.

Early symptoms may include loss of precision muscle coordination (sometimes first manifested in declining penmanship, frequent small injuries to the hands, dropped items and a noticeable increase in dropped or chipped dishes), cramping pain with sustained use and trembling. Significant muscle pain and cramping may result from very minor exertions like holding a book and turning pages. It may become difficult to find a comfortable position for arms and legs with even the minor exertions associated with holding arms crossed causing significant pain similar to restless leg syndrome. Affected persons may notice trembling in the diaphragm while breathing, or the need to place hands in pockets, under legs while sitting or under pillows while sleeping to keep them still and to reduce pain. Trembling in the jaw may be felt and heard while lying down, and the constant movement to avoid pain may result in TMJ-like symptoms and the grinding and wearing down of teeth. The voice may crack frequently or become harsh, triggering frequent throat clearing. Swallowing can become difficult and accompanied by painful cramping.

Electrical sensors (EMG) inserted into affected muscle groups, while painful, can provide a definitive diagnosis by showing pulsating nerve signals being transmitted to the muscles even when they are at rest. The brain appears to signal portions of fibers within the affected muscle groups at a firing speed of about 10 Hz causing them to pulsate, tremble and contort. When called upon to perform an intentional activity, the muscles fatigue very quickly and some portions of the muscle groups do not respond (causing weakness) while other portions over-respond or become rigid (causing micro-tears under load). The symptoms worsen significantly with use, especially in the case of focal dystonia, and a "mirror effect" is often observed in other body parts: use of the right hand may cause pain and cramping in that hand as well as in the other hand and legs that were not being used. Stress, anxiety, lack of sleep, sustained use and cold temperatures can worsen symptoms.

Direct symptoms may be accompanied by secondary effects of the continuous muscle and brain activity, including disturbed sleep patterns, exhaustion, mood swings, mental stress, difficulty concentrating, blurred vision, digestive problems and short temper. People with dystonia may also become depressed and find great difficulty adapting their activities and livelihood to a progressing disability. Side effects from treatment and medications can also present challenges in normal activities.

In some cases, symptoms may progress and then plateau for years, or stop progressing entirely. The progression may be delayed by treatment or adaptive lifestyle changes, while forced continued use may make symptoms progress more rapidly. In others, the symptoms may progress to total disability, making some of the more risky forms of treatment worth considering.

An accurate diagnosis may be difficult because of the way the disorder manifests itself. Sufferers may be diagnosed as having similar and perhaps related disorders including Parkinson's disease, essential tremor (ET), carpal tunnel syndrome, TMJ, Tourette's syndrome, or other neuromuscular movement disorders.

Supposing a car represented a human body, and the wheels and axels represented the limbs, and the engine represented the brain... A simple car without a gearbox would be moving very consistently no obvious speed change and it would only stop if it runs out of petrol (resulting in sleep). A gearbox allows us to slow down that movement, speed it up and even stop it without turning off. However, if that gearbox (the globus pallidus in the brain) was faulty, the movement would be inconsistent and unpredictable and this would make going up or downhill impossible.

Classification

Types of Dystonia

• Generalized
• Segmental
• Intermediate

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.

• Oculogyric crisis. An extreme and sustained (usually) upward deviation of the eyes often with convergence causing diplopia. It is frequently associated with backwards and lateral flexion of the neck and either widely opened mouth or jaw clenching. Frequently a result of antiemetics such as the neuroleptics (e.g. prochlorperazine) or metoclopramide.

• Oromandibular dystonia. This affects the muscles of the jaw and tongue, causing distortions of the mouth and tongue.

• Spasmodic dysphonia/Laryngeal dystonia. This affects the muscles of the larynx, causing the voice to sound broken or reducing it to a whisper.

• Focal hand dystonia (also known as musician's or writer's cramp). This affects a single muscle or small group of muscles in the hand. It interferes with activities such as writing or playing a musical instrument by causing involuntary muscular contractions. The condition is "task specific," meaning that it is generally only apparent during certain activities.

The combination of blepharospasmodic contractions and oromandibular dystonia is called cranial dystonia or Meige's syndrome.

Segmental Dystonias

Segmental dystonias affect two adjoining parts of the body:

• Hemidystonia. This affects an arm and a leg on one side of the body.

• Multifocal dystonia. This affects many different parts of the body.

• Generalized dystonia. This affects most of the body, frequently involving the legs and back.

Treatment

Treatment has been limited to minimizing the symptoms of the disorder as there is yet no successful treatment for its cause. Reducing the types of movements that trigger or worsen dystonic symptoms provides some relief, as does reducing stress, getting plenty of rest, moderate exercise, and relaxation techniques. Various treatments focus on sedating brain functions or blocking nerve communications with the muscles via drugs, neuro-suppression or denervation. All current treatments have negative side effects and risks.

Physicians may prescribe a series of different medications on a trial-and-error basis in an effort to find a combination that is effective for a specific patient. Not all patients will respond well to the same medications. Drugs that have had positive results in some patients include anti-Parkinsons agents (Trihexyphenidyl), muscle relaxers (Valium), keppra, and beta-blockers including "off-label" uses for some blood pressure medications.

Drugs such as anticholinergics, which act as inhibitors 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 and side effects like mental confusion, sedation, mood swings and short-term memory loss occur.

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. Botox injections have the advantage of ready avalibility (the same form is used for cosmetic surgery) and the effects are not permanent. There is a risk of temporary paralysis of the muscles being injected or the leaking of the toxin into adjacent muscle groups causing weakness or paralysis in them. The injections have to be repeated as the effects wear off and around 15% of recipients will 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.^[2]

Surgery, such as the denervation of selected muscles, may also provide some relief; however, the destruction of nerves in the limbs or brain is not reversible and should only be considered in the most extreme cases. Recently, the procedure of deep brain stimulation (DBS) has proved successful in a number of cases of severe generalised dystonia.^[3]

One type of dystonia, dopa-responsive dystonia, can be completely treated with regular doses of L-dopa in a form such as Sinemet (carbidopa/levodopa). Although this doesn't remove the condition, it does alleviate the symptoms most of the time.

A baclofen pump has been used to treat patients of all ages exhibiting muscle spasticity along with dystonia. The pump delivers baclofen via a catheter to the thecal space surrounding the spinal cord. The pump itself is placed in the abdomen. It can be refilled periodically by access through the skin.^[4]

Physical therapy can sometimes help with focal dystonia. A structured set of exercises is tailored to help the affected area.

References

See also

• Torsion dystonia
• Tardive Dyskinesia
• Edward Flatau
• Geste antagoniste