Hemidystonia is a form of dystonia that affects only the left OR right side of the body. It is characterised by abnormal movements in either the left leg, left arm sometimes left side of the face; OR the right arm, right leg and sometimes right side of the face.

The symptoms can include:

  • Twisting postures of the leg and arm
  • Turning in of the foot and/or leg and/or arm
  • Muscles spasms in the face or mouth causing unusual movements
  • In Hemidystonia, all dystonic symptoms occur on only the one side of the body.

Causes of hemidystonia

Most cases of hemidystonia are caused by another underlying conditions, such as stroke, tumor, problems at birth (cerebral palsy), head injuries, a problem with blood vessels and even multiple sclerosis (MS). Hemidystonia can result when one of the above conditions causes damage to only one of side of the brain (the side of the brain opposite to the side of the body with hemidystonia) commonly within an area called the basal ganglia. Such cases are called Acquired, Secondary, or Symptomatic Hemidystonia.

There can be a significant delay between the onset of the underlying condition and the subsequent development of hemidystonia, particularly in the case of perinatal and head injury. The speed of development varies by individual and the hemidystonia can either appear immediately after the damage to the basal ganglia or weeks to months and even years later. Frequently, the longest delay between event and development of hemidystonia is seen in perinatal injury and head injury.

Usually acquired hemidystonia occurs in the side of the body opposite to the side where the brain is damaged. The most common cause of the damage is believed to be stroke, closely followed by brain insult around birth and head injury.
If there is no underlying condition or identifiable trigger for hemidystonia, it is given the term Idiopathic Hemidystonia. In these cases, there is no detectable abnormality on any brain scans/investigations so it is uncertain both why the dystonia has appeared and why it is only on one side of the body.

How is hemidystonia different from other dystonias?

Hemidystonia affects just the one side of the body whereas generalised dystonia affects both sides of the body. 
Segmental dystonia affects two areas of the body that are next to each other, such as facial and neck muscles; muscle groups of the neck and upper arm. It does not usually involve the leg. Multifocal dystonia affects two or more non-adjacent unrelated areas of the body, such as eyelids and neck or hand.

In segmental or multifocal dystonia, the leg is most commonly unaffected, whereas in hemidystonia the leg is affected together with the arm and sometimes the face.

Does hemidystonia spread?

Because acquired hemidystonia develops following damage to the brain, symptoms are often expected to be relatively static. The first symptoms are frequently a sudden onset of weakness on one side of the body. Dystonia may then appear as the weakness recovers – but the dystonia does not tend to spread after this initial onset period.
Idiopathic hemidystonia may spread more slowly. Symptoms may spread through the affected side during the first few months to years, followed by an eventual plateau and stabilisation. However, with no identifiable lesion in the brain, there is no understanding/reason as to why the dystonia only affects one half on the body.


Hemidystonia is treated similarly to generalised dystonia – primarily using a range of oral medications. An anti-cholinergic drug such as trihexyphenidyl can often be helpful in controlling muscle spasms and tremor. Second line treatments may include clonazepam (a strong muscle relaxant) or tetrabenazine (helps to control tremor and involuntary spasm) and baclofen (an effective muscle relaxant). A combination of medications is often advised by the neurologist. These drugs can have side effects which you should discuss with your doctor.

Botulinum toxin injections may be helpful in easing the symptoms in some isolated areas but it is more difficult to use such injections to treat larger areas such as the leg as there are often too many muscles responsible for the abnormal movements that would need to be injected. Injecting all these muscles is neither practical nor feasible as only a certain number of units of Botulinum toxin may be injected at any one time. For this reason, injections tend to be restricted to smaller more specific areas such as the face, wrist, hand, fingers, ankle, foot, toes etc.

The surgical procedure, deep brain stimulation (DBS), may be helpful in some cases but is more likely for be suitable for idiopathic hemidystonia rather than acquired hemidystonia. It works by inserting fine electrodes in the brain to damp down the spurious signals causing the muscle spasms. Selection of patients is done carefully with extensive testing to ensure the patient’s condition is likely to benefit from the surgery.

To read case studies of individuals with hemidystonia that have been featured in Dystoniamatters! click on the links below:

Fiona MacKinnon

Last reviewed October 2014
