Dystonia
Classification of Dystonia
Dystonia is generally classified in three ways:
- Age of onset
- Bodily distribution of symptoms
- Cause
Age of Onset
The symptoms of dystonia may begin during childhood (i.e., early onset), adolescence, or adulthood (e.g., 30s to 50s or later, known as late-onset dystonia). For example, the symptoms of generalized dystonia or dopa-responsive dystonia (DRD) may begin during childhood or adolescence. Most cases of early-onset dystonia are thought to occur as the result of an inherited defect in a gene. Other cases may result from a spontaneous change in a gene. Certain focal dystonias such as cervical dystonia (spasmodic torticollis), blepharospasm, writer's cramp, and spasmodic dysphonia are examples of late-onset dystonias. Unlike early-onset dystonia, the causes of late-onset dystonia are variable. The age of onset may be a factor in determining the probability of disease progression. Generally, the earlier the onset of symptoms, the more likely the chance of progression with advancing age.
Bodily Distribution of Symptoms
Dystonia may also be classified as follows, according to the bodily distribution of symptoms:
- Focal dystonia
- Segmental dystonia
- Multifocal
- Generalized
Focal Dystonia
Symptoms may be focal or limited to one region of the body, such as the neck or an arm or a leg. There are many different types of focal dystonia.
Blepharospasm is marked by involuntary contraction of the muscles that control the movement of the eyelids. Symptoms may range from intermittent, painless, increased blinking to constant, painful, eye closure leading to functional blindness.
In patients with cervical dystonia (CD), also known as spasmodic torticollis, muscle spasms of the head and neck may be painful and cause the neck to twist into unusual positions or postures. Spasms may be intermittent or constant.
Oromandibular and lingual dystonia are characterized by forceful contractions of the muscles of the lower face causing the mouth to open or close. Chewing and unusual tongue movements may also occur.
In spasmodic dysphonia (SD), also known as laryngeal dystonia, the muscles in the larynx are affected. SD is marked by difficulties in either opening or closing the vocal cords. This causes the voice to have either a strained, hoarse, strangled, or whispering quality.
In limb dystonia, there are involuntary contractions of one or more muscles in the arm, hand, leg, or foot. These types of focal dystonias include writer's cramp, musician's cramp, and other occupational dystonias.
Segmental
Symptoms affect two adjacent areas of the body, such as the head and neck or arm and trunk.
Multifocal
Symptoms affect two areas of the body that are not next to each other, such as the two arms, or an arm and a leg.
Generalized
Symptoms begin in an arm or a leg and advance, becoming more widespread. Eventually, the trunk and the rest of the body are involved.
