Dystonia

Dystonia is a neurological movement disorder characterized by involuntary or unintended muscle contractions that cause slow repetitive movements or abnormal postures that can sometimes be painful. There are several different forms of dystonia that may affect only one muscle, groups of muscles or muscles throughout the body. The affected areas and severity of symptoms varies from person to person.

Dystonia can occur on its own or be the result of another condition, some of which may be hereditary. Some forms of dystonia are genetic. The disorder typically is not associated with problems thinking or understanding. Dystonia is not fatal, but problems related to conditions that may result from dystonia may be life-threatening.

There are several different forms of dystonia that may affect only one muscle, groups of muscles or muscles throughout the body. The affected areas and severity of symptoms varies from person to person. 

Dystonia is classified along two distinct axes.

• Axis I is based on clinical features which include age at onset, body region affected, specific features and whether there are associated clinical problems.
• Axis II is based on the cause of dystonia. This classification includes dystonia that doesn't have a known cause as well as dystonia caused by genetics or abnormalities in the brain. 

There are many different forms of dystonia. Within Axis I, some are grouped by the regions of the body which they affect:

• Generalized dystonia affects most or all of the body
• Focal dystonia is localized to a specific part of the body
• Multifocal dystonia involves two or more unrelated body parts
• Segmental dystonia affects two or more adjacent parts of the body
• Hemidystonia involves the arm and leg on the same side of the body

Some of the more common forms that involve a specific part of the body are:

Cervical dystonia, also called spasmodic torticollis or torticollis, is the most common of the focal dystonias. It affects the muscles in the neck that control the position of the head, causing the head to turn to one side or to be pulled forward or backward. Sometimes the shoulder is pulled up. Cervical dystonia can occur at any age, although for most individuals it first occurs in midlife. It often begins slowly and usually reaches a plateau over a few months or years. About 10 percent of those with torticollis may experience a spontaneous remission, but it may not be lasting.

Blepharospasm, the second most common focal dystonia, is the involuntary, forcible contraction of the muscles controlling eye blinks. The first symptoms may be increased blinking, and usually both eyes are affected. Spasms may cause the eyelids to close completely resulting in “functional blindness” even though the eyes are healthy and vision is normal.

Cranial dystonia affects the muscles of the head, face and neck. The term Meige syndrome is sometimes applied to cranial dystonia accompanied by blepharospasm. 

Oromandibular dystonia affects the muscles of the jaw, lips and tongue. It may cause difficulties with opening and closing the jaw, and speech and swallowing can be affected. 

Spasmodic dysphonia, also called laryngeal dystonia, involves the muscles that control the vocal cords, resulting in strained or breathy speech.

Task-specific dystonias tend to occur only when undertaking a particular repetitive activity. Examples include writer's cramp that affects the muscles of the hand and sometimes the forearm and only occurs during handwriting. Similar focal dystonias have also been called typist's cramp, pianist's cramp and musician's cramp. Musician's dystonia is a term used to classify focal dystonias affecting musicians, specifically their ability to play an instrument or to perform. It can involve the hand in keyboard or string players, the mouth and lips in wind players or the voice in singers.

Researchers believe that dystonia results from an abnormality in or damage to the basal ganglia or other brain regions that control movement. There may be abnormalities in the brain's ability to process a group of chemicals called neurotransmitters that help cells in the brain communicate with each other. There also may be abnormalities in the way the brain processes information and generates commands to move. In most cases, no abnormalities are visible using magnetic resonance imaging or other diagnostic imaging.

The dystonias can be divided into three groups: idiopathic, genetic and acquired.

Idiopathic dystonia refers to dystonia that does not have a clear cause. Many instances of dystonia are idiopathic. 

Genetic dystonia is caused by inheriting an abnormal gene. Symptoms may vary widely in type and severity even among members of the same family. In some instances, a person who inherits the defective gene may not develop dystonia. Dystonia can be a symptom of other diseases, some of which may be hereditary. Known genetic forms of dystonia include:

• DYT1 dystonia is a rare form of dystonia that typically begins in childhood, affects the limbs first and continues to worsen, often causing significant disability
• Dopa-responsive dystonia (DRD), also known as Segawa's disease, typically begins during childhood and may cause progressive difficulty with walking. Symptoms characteristically fluctuate and are worse late in the day and after exercise. Some forms of DRD are due to mutations in the DYT5 gene. People living with this disorder have dramatic improvements in symptoms after treatment with levodopa, a medication commonly used to treat Parkinson's disease.

Other genes that are known to cause dystonia include:

• DYT3, which causes dystonia associated with parkinsonism (has Parkinson-like symptoms such as tremor, muscle stiffness and slow movement).
• DYT6, which affects muscles in the head, neck and arm (and sometimes a leg).
• DYT11, which causes dystonia associated with myoclonus (brief contractions of muscles).
• DYT12, which causes rapid onset dystonia associated with parkinsonism.
• DYT28, which is associated with childhood onset dystonia.

Acquired dystonia, also called secondary dystonia, results from environmental or other damage to the brain, or from exposure to certain types of medications. Some causes of acquired dystonia include birth injury (including hypoxia, a lack of oxygen to the brain, and neonatal brain hemorrhage), certain infections, reactions to certain drugs, heavy metal or carbon monoxide poisoning, trauma or stroke. Acquired dystonia often plateaus and does not spread to other parts of the body. Dystonia that occurs as a result of medications often ceases if the medications are stopped quickly.

Researchers believe that dystonia results from an abnormality in or damage to the basal ganglia or other brain regions that control movement. There may be abnormalities in the brain's ability to process a group of chemicals called neurotransmitters that help cells in the brain communicate with each other. There also may be abnormalities in the way the brain processes information and generates commands to move. In most cases, no abnormalities are visible using magnetic resonance imaging or other diagnostic imaging.

Dystonia can occur at any age, but some forms are often divided as either early (childhood) or adult onset.

• Early onset dystonia often begins with symptoms in the arms and legs and may progress to involve other regions of the body. Some symptoms tend to occur after periods of exertion and/or fluctuate over the course of the day.
• Adult-onset dystonia usually is located in one or adjacent parts of the body, most often involving the neck and/or facial muscles. Some dystonias can affect other regions of the body.