Most cases are caused by another underlying condition, such as:

  • stroke
  • tumour
  • problems at birth (cerebral palsy)
  • head injuries
  • a problem with blood vessels and even multiple sclerosis (MS).

Hemidystonia can occur when one of these conditions causes damage to just one of side of the brain (the side of the brain opposite to the side of the body with hemidystonia).

In idiopathic hemidystonia there is no detectable abnormality on any brain scans or investigations so it is uncertain both why the dystonia has appeared and why it is only on one side of the body.