What is Dystonia?
Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often, repetitive movements, postures, or both.
The movements are typically twisting and turning movements or patterned movements. There may be tremulous or tremor-‐like movements superimposed, but usually the tremulous movements are irregular or jerky. Although some abnormal movements may persist at rest, the abnormal movements are generally worsened by voluntary movement. The patient may also have movement overﬂow in which abnormal movements are triggered by voluntary movement of a distant part of the body not aﬀected by dystonia. The sustained twisting movement may cause muscular pain and even secondary orthopedic injury to patients. These latter two features are most common in patients who have dystonia involving, or cervical dystonia.
It may be diﬃcult to diﬀerentiate dystonia from other movement disorders. Amongst the most common diﬃculties is diﬀerentiating dystonia from tics. Individuals may have repetitive jerky movements sometimes with sustained abnormal postures as part of a tic disorder. Unlike dystonia, the tics are usually produced in response to an urge to make the movement and many patients can at least brieﬂy suppress tics voluntarily unlike dystonic movements. Tics are often multi-‐focal, occurring in one part of the body and then another. Tics tend to wax and wane. Patients may have motor tics in which abnormal movements are made and they may have vocal tics in which either formed words or said or other utterances occur such as sniﬃng or grunting. Most commonly, tics occur as part of Tourette syndrome which is a chronic motor and vocal tic disorder occurring with onset before the age of 18. Occasionally, tics can begin in adulthood and may be a purely motor disorder without vocal tics in which case the diﬀerentiation from dystonia can sometimes be more diﬃcult.
Dystonia can often result in jerky, tremulous-‐type movements and it is important to diﬀerentiate dystonic tremor from other forms of tremor. Tremor is generally deﬁned as a rhythmic oscillatory movement produced by alternating contractions of opposite acting muscles. Dystonic tremor is usually irregular, unlike most other forms of tremor, and is usually produced by simultaneous or co-‐contraction of opposite acting muscles. The most common forms of tremor are those seen as part of essential tremor and parkinsonian tremor. Patients with dystonic tremor usually have superimposed abnormal posture of the aﬀected body part in addition to the tremulous movements. Isolated head tremor without tremor elsewhere in the body is usually due to cervical dystonia and dystonic tremor but is commonly misdiagnosed as essential tremor.