Dystonia is generally classified based on its cause, the age at which symptoms first occur, and the regions of the body affected.
Based on the cause, dystonia is classified as primary, or secondary. Primary dystonia is a condition in which dystonia is the only clinical feature. There is no evidence of cell death or a known cause. It is also known as idiopathic torsion dystonia. The primary dystonias are often inherited from a parent. In non-primary or secondary dystonia, an acquired or exogenous cause is identified. This can be a prior stroke, a birth injury or exposure to certain drugs. Secondary dystonia may also represent one symptom of other neurological disorders, such as Parkinson’s disease.
Based on age of onset, dystonia is classified as early-onset, if it develops before age 21, or late onset, after age 21. The age at onset is an important indicator of whether the dystonia is more likely to spread to other body regions. The younger the patient is at dystonia onset, the higher the likelihood that the dystonia may involve other areas. In patients with primary late-onset dystonia, dystonia often begins in the upper body, such as the neck, head, neck, or an arm.
Based on regions of the body affected, dystonia is classified as:
- Generalized Dystonia: is the most widespread form of dystonia; it affects the legs or one leg and the trunk, plus other regions, most commonly the arms.
- Focal Dystonia: involves only one region of the body, such as the neck, vocal cords or hand. Focal dystonia includes blepharospasm, oromandibular dystonia, cervical dystonia (or spasmodic torticollis), laryngeal dystonia (also called spasmodic dysphonia) and limb dystonia.
- Hemidystonia: affects one half of the body.
- Segmental Dystonia: affects two or more adjacent body regions, such as the neck and an arm.
- Multifocal Dystonia: affects two or more distant regions of the body, such as the upper face and the hand.
For even more information on dystonia, please visit our "What is Dystonia" page.