The cause of dystonia is not yet fully understood, in some cases at least it can be attributed to a chemical imbalance in the part of the brain called the basal ganglia, a part which helps to control movement.

The basal ganglia regulates the numerous muscle contractions that are necessary to move the body and if this part of the brain is damaged in some way, that means the wrong muscles contract when you try to move or that the muscles contract even when you are not meaning to move, causing uncontrollable twitching, tremor and contractions. These spasms are known as dystonic movements.

This imbalance can be:

inherited – a dystonia caused by mutations in a specific gene
acquired (secondary) – a dystonia that appears to have a specific cause such as drug reaction, brain injury, or as a symptom of another neurological or metabolic disorder or;
idiopathic – a dystonia with no known or clear cause.