Dystonia: Causes, biological mechanisms, symptoms, diagnosis and treatment

Dystonia is a rare disease that affects around 20,000 people in France, the majority of whom are women. It can occur at any age and is characterised by long-lasting involuntary muscle contractions resulting in abnormal postures. A distinction is made between primary dystonia caused by genetic mutations and secondary dystonia, the cause of which may be another neurological condition or a drug. When only one part of the body is affected, the condition is known as focal dystonia; if two adjacent parts of the body are affected by contractions, the condition is known as segmental dystonia; finally, some patients may present with generalised dystonia if the trunk and two different parts of the body are affected.
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The causes and biological mechanisms of dystonia

Primary or idiopathic dystonia is due to a genetic mutation, either familial (i.e. inherited) or sporadic, and generally begins in childhood. Secondary dystonia results from brain damage caused by a severe lack of oxygen to the brain at birth or later, from another neurological pathology such as multiple sclerosis or stroke, or from a side effect of drugs such as antipsychotics or antiemetics (anti-nausea drugs).

Dystonia is caused by hyperactivity in certain areas of the brain. These include the deep structures of the brain, the basal ganglia, which control part of the motor system, the cortex and the cerebellum.

 

Symptoms and diagnosis of dystonia

Dystonia manifests itself as involuntary, long-lasting contractions of the muscles in one part of the body, causing long-term changes in the position of the affected limb and trunk.

Any muscle in the body can be affected. A distinction is made between generalised dystonia, which is very rare, and focal dystonia, which is more common:

  • Neck dystonia: spasmodic torticollis, usually laterocollis (to the side) but sometimes antecollis (forward) or retrocollis (backward).
  • Dystonia of the hand: writers’ cramp which occurs when writing.
  • The larynx: spasmodic dysphonia or tightening of the vocal cords
  • Blepharospasm, repeated involuntary contractions of the eyelids
  • Foot dystonia

Diagnosis of dystonia can be difficult. It is essentially based on a clinical examination of the symptoms. MRI brain imaging can help to establish the diagnosis. The clinician looks to see if triggering factors such as another neurological disease or hypoxia are at the root of the dystonia. A family investigation is also carried out if the disease appears without a primary cause. In the presence of a family history or without an identified cause, sequencing of the patient’s DNA is necessary to search for the genetic mutation causing the disease.

 

Treatments for dystonia

The different types of dystonia – focal, segmental and generalised – do not require the same treatments.

In generalised dystonia, treatment is based on muscle relaxants or anticholinergics. Severe forms can also be treated with non-invasive transcranial magnetic stimulation or deep brain stimulation. In some very severe cases, ablative surgery of an area of the brain may be considered. Treatments for focal or segmental dystonia The basic treatment consists of injections of botulinum toxin.

 

Last updated May 2024.