Dystonie

What is dystonia?

A dystonia is lasting unwanted (involuntary) muscle contractions that often cause repeated twisting movements or unusual body positions. The severity of the muscle contraction often changes depending on the position the person is in and whether the area of the body involved is doing something.

Sometimes the contractions may be painful. They can affect just one muscle or a group of muscles. The eyes, tongue (twisting or protrusion), face, neck, trunk, limbs (eg in-turning of the ankle), or larynx may be affected, and the contractions can be constant or fluctuating (spasmodic).

There are different ways of describing dystonias. They can be described according to what has caused the dystonia, the age the person was when they first had the symptoms, or by which parts of the body are affected. For example, when described by which parts of the body are affected, there are five types:

• Focal: a single body region is affected (for example, the eye or the hand).

• Segmental: two or more connected body regions are affected.

• Multifocal: two or more non-connected body regions are affected.

• Generalised: the trunk and at least two other body regions are affected (this may or may not include the legs).

• Hemidystonia: all of one side of the body is affected.

What causes dystonia?

The cause of dystonia is not fully understood. There seems to be an underlying problem with the region of the brain called the basal ganglia which helps co-ordinate movements.

The causes of dystonia are described as primary or secondary.

Primary dystonia

Primary means the dystonia has been passed down through your genes and you were born with it. Many people will want to know if their child will inherit the dystonia. In some types of dystonia the genes responsible have been identified. Currently 13 inheritable forms of dystonia have been identified.

Most primary or generalised dystonias that develop in childhood are inherited in a dominant manner. This means that if a parent has this type of dystonia, there is a 1 in 2 chance of passing the affected gene on to their child. However, inheriting the gene does not always mean you will develop dystonia.

This is known as reduced penetrance and it reduces the ability of the gene to produce a dystonia in the person who has inherited it. About 3 or 4 people out of 10 who inherit the gene, develop signs of dystonia. If you are told you have a primary or generalised dystonia, it may be useful to see a genetic counsellor who will advise you about the risks in your family.

It can be difficult to identify other family members who may have only a mild form of dystonia. They may have never sought medical advice.

Secondary dystonia

Secondary means the dystonia has been caused by another condition or by something which has happened to you. It is not caused by your genetic make-up. Some neurological conditions can cause dystonia such as:

• la maladie de Parkinson.

• AVC.

• Maladie de Wilson.

• Maladie de Huntington.

When it occurs in children it is nearly always because of la paralysie cérébrale.

Certains medications such as those used in certain psychiatric conditions and some poisons can also cause it.

How common is dystonia?

This is not precisely known; however, it is thought that at least 70,000 people in the UK are affected by dystonia. This is about 1 person in 900.

Dystonia symptoms

These can vary greatly according to the type of dystonia and how many muscles are affected. Some examples of types of dystonia are as follows.

Dystonia of the eye

Dystonia of the eye is called blepharospasm. It involves recurrent spasms of eye closing, which can make the person look like they are blinking repeatedly.

Crampes de l'écrivain

Writer's cramp is a type of dystonia. It is the inability to write (or use any hand-held instrument) because of spasms of the hand and arm muscles.

As both blepharospasm and writer's cramp involve a particular area of the body, they are called focal dystonias.

Dystonia of the neck

Another type of focal dystonia is torticollis, which is spasm of the neck muscles. It is also called cervical dystonia. The symptoms vary but may include the feeling that the neck/head is being pulled to one side, backwards or forwards, or difficulty turning the neck/head one way. There may also be an associated tremblement of the head.

Dystonia of the voice muscles

Muscle spasms can also affect the voice box (laryngeal muscles). It may show as being an effort to speak or the voice having a strangled quality or a feeling of choking on words. The voice can be like a whisper, with difficulty being heard in noisy environments.

Dystonia affecting many muscles

One very severe but rare type (called primary pure dystonia) usually first happens in children, with spasms of the legs when walking, and sometimes of the arms, body or neck. It normally progresses to affect the whole body, making the child severely disabled within about ten years.

How is dystonia diagnosed?

Your doctor will ask you questions which may include when your problems started, which parts are affected and if other family members have similar problems. They may examine you. There are no specific tests for dystonias. If your doctor suspects that you might have dystonia, they will refer you to see a local neurologist.

Dystonia treatment

There is currently no cure for dystonia. The treatments that are offered help to relieve the spasms. The type of treatment will vary depending on the type of dystonia.

Injections de toxine botulique

Focal dystonias - like writer's cramp - are best treated with an injection of botulinum toxin. Botulinum toxin is produced by the bacterium Clostridium botulinum. It is usually associated with causing food poisoning (botulism). However, when it is used in controlled doses, it is safely used to relax excessive muscle contraction. This injection is given every three months and starts to work within a few days.

Selective denervation surgery

If botulinum toxin isn't effective, selective denervation surgery may be tried. This has been used to treat neck dystonia (spasmodic torticollis) for a number of years. It is a surgical operation where the nerves controlling the overactive muscles (that are causing the symptoms of dystonia) are cut. The aim of the operation is to introduce a permanent paralysis to the muscles causing the problems.

Médicaments

More generalised or childhood forms may be treated with medication such as levodopa, diazepam or baclofen:

• Levodopa (co-béneldopa ou co-carélopa) is a medicine that may also be used in Parkinson's disease. It replaces a brain chemical which helps to control movements.

• Anticholinergic medicines (for example, trihexyphenidyl ou procyclidine) work by blocking a chemical called acetylcholine, which can cause muscle spasms for some people with dystonia.

• Diazepam creates a generalised relaxation. It can also make you feel drowsy.

• Baclofène is an anti-spasm medication that is also used in conditions such as multiple sclerosis and cerebral palsy.

The response to these medications can vary. Although some people with dystonia find one or other of these medicines helpful, side-effects may be a problem and there is no strong evidence to support their use as a routine treatment for dystonia.

Deep brain stimulation

If medications do not work you may be considered for deep brain stimulation. This is a surgical procedure where two fine electrodes are inserted into the brain. They are connected to a power source that sits just under the skin. It delivers a constant, painless signal which aims to block the signals that cause the symptoms of dystonia.

Physiothérapie

If the dystonia results in abnormal positions of your limbs, which are difficult to overcome, a physiotherapist may be able to help. They can use massage therapies and exercises to help re-train the limb muscles.

Quel est le pronostic ?

Dystonia is very rarely a cause of death. If dystonia develops in childhood and starts in the legs, it may spread to other parts of the body, and can become generalised. This can be severely disabling. Dystonia in adults is usually limited to one part of the body (focal dystonia). Spreading is unlikely but usually affects only one other area, which is commonly the nearest muscle group.

Dystonia is unpredictable and the severity of symptoms can vary from day to day. There may be worsening over a period of time but it can be difficult to say how long this will last. A focal dystonia tends to worsen very gradually over a five-year period but then often stays the same. Sometimes a dystonia may improve or disappear altogether for no apparent reason. The chances of this happening have been estimated as somewhere between 1 in 10 and 1 in 20. Sometimes the dystonia comes back, but at other times it will disappear completely.