Dystonia is a general term used to describe disorders characterized by involuntary spasms and muscle contractions that cause abnormal movements and postures. An estimated 250,000 North Americans have this non-contagious disorder. Primary dystonia - that is, dystonia that isn't a symptom of some other nervous system disorder - does not affect the patient's consciousness, sensation or intellectual function.

More information about dystonias

• What are the types of dystonia?
• Who gets dystonia, and what causes it?
• What are the treatments for dystonia?

What are the types of dystonia?

There are a wide range of different types of dystonias. Generalized dystonia affects most or all of the body. Focal dystonia involves one body part, multifocal dystonia involves two or more unrelated body parts, and segmental dystonia affects two more or adjacent parts of the body.

Hemidystonia, often the result of a stroke, involves the arm and the leg on the same part of the body. Dystonia is sometimes a symptom of other diseases of the central nervous system, such as cerebral palsy.

Some types of dystonia are defined as specific syndromes, including the following:

• Spasmodic torticollis: Spasmodic torticollis is the most common type of focal dystonia, affecting the muscles in the neck that control the position of the head. The muscles cause the head to twist and turn, from side to side or forwards and backwards. It most often strikes middle-aged people, beginning slowly.
• Benign essential blepharospasm: Blepharospasm, the involuntary closure of the eyelids, is the second most common type of focal dystonia.

Often, the syndrome begins with uncontrollable blinking affecting one or both eyes. The disease can progress to the point that patients become functionally blind, although there is nothing wrong with their eyes.

• Meige syndrome: This form often occurs together with benign essential blepharospasm. It affects the lower face, mouth, tongue, throat and neck.
• Spasmodic dystonia: Sometimes called laryngeal dystonia, this form of dystonia affects muscles that control the vocal cords, resulting in wavery, halting speech patterns. Sometimes, the patient has difficulty breathing.
• Generalized dystonia (idiopathic torsion dystonia): This rare, progressive form of dystonia begins in childhood and is characterized by strange postures, awkward gait and contractions of many different muscle groups.

Who gets dystonia, and what causes it?

Some forms of dystonia, such as idiopathic torsion dystonia, are most common in children, appearing first between the ages of five and 16.

Often, the dystonia affects a hand or foot first, and later involves other parts of the body. Dystonias that begin in childhood tend to get worse as the patient gets older. In other individuals, dystonia appears in the late teen years, usually with a slower progression of symptoms.

Dystonias that first begin in adulthood generally affect only one part of the body. Many forms of dystonia, including generalized dystonia, are genetically linked. However, the symptoms of dystonia can vary widely among family members - for example, if a parent has dystonia affecting the neck, the child may have an completely different form of dystonia.

Some types of dystonia are called secondary dystonias, resulting from brain trauma caused by stroke, disease or injury. These types of dystonias tend to remain static - that is, they don't get worse.

The cause of most primary dystonias is unknown. However, researchers have identified abnormalities in a part of the brain called the basal ganglia, which is where the messages to begin muscle contractions are believed to originate. Also, the brains of dystonia patients appear to have problems processing chemicals - neurotransmitters - that help cells in the brain communicate with each other. All of this helps explain some of the symptoms, but no one knows why these abnormalities occur.

What are the treatments for dystonia?

No one treatment is effective for all forms of dystonia, and some forms respond better than others to drug therapy. Several types of drugs that help correct imbalances in neurotransmitter levels can be helpful. Some forms of dystonia respond particularly well to dopamine-increasing drugs, and occasionally anticonvulsants are prescribed. It can take time to find which drugs and what dosage work best for each individual. Side effects of drug therapy can occur, sometimes becoming a significant problem in the treatment of the disorder. Symptoms of focal dystonias can sometimes be relieved for several months through injections of a tiny amount of botulism toxin, which blocks spasms by slightly weakening the affected muscles.

A few patients may undergo surgery when drug therapy is unsuccessful or side effects become too severe, although this form of treatment is risky and unpredictable. People with advanced generalized dystonia can be helped by the surgical destruction of parts of the thalamus, a structure in the brain that controls movement. This type of surgery can be risky, however. Speech disturbances can occur because areas of the brain important to speech are located very close to the thalamus. Unfortunately, the effects of surgery are sometimes temporary.

Some dystonias can be helped by surgeries that cut one or more of the contracting muscles in the neck. Other surgical procedures cut nerve roots near the spinal cord or remove nerves at the point where they enter the contracting muscles.