The dystonias are movement disorders in which sustained muscle contractions cause twisting and repetitive movements or abnormal postures. The movements, which are involuntary and sometimes painful, may affect a single muscle; a group of muscles such as those in the arms, legs, or neck; or the entire body. Those with dystonia usually have normal intelligence and no associated psychiatric disorders.
Investigators believe that the dystonias result from an abnormality in an area of the brain called the basal ganglia where some of the messages that initiate muscle contractions are processed. Scientists suspect a defect in the body's ability to process a group of chemicals called neurotransmitters that help cells in the brain communicate with each other.
Some of these neurotransmitters include:
- GABA (gamma-aminobutyric acid), an inhibitory substance that helps the brain maintain muscle control.
- Dopamine, an inhibitory chemical that influences the brain's control of movement.
- Acetylcholine, an excitatory chemical that helps regulate dopamine in the brain. In the body, acetylcholine released at nerve endings causes muscle contraction.
- Norepinephrine and serotonin, inhibitory chemicals that help the brain regulate acetylcholine.
Acquired dystonia, also called secondary dystonia, results from environmental or disease-related damage to the basal ganglia. Birth injury (particularly due to lack of oxygen), certain infections, reactions to certain drugs, heavy-metal or carbon monoxide poisoning, trauma, or stroke can cause dystonic symptoms. Dystonias can also be symptoms of other diseases, some of which may be hereditary.
About half the cases of dystonia have no connection to disease or injury and are called primary or idiopathic dystonia. Of the primary dystonias, many cases appear to be inherited in a dominant manner; i.e., only one carrier parent need contribute the dystonia gene for the disease to occur, each child having a 50/50 chance of being a carrier. In dystonia, however, a carrier may or may not develop a dystonia and the symptoms may vary widely even among members of the same family.
The product of one defective gene appears to be sufficient to cause the chemical imbalances that may lead to dystonia; but the possibility exists that another gene or genes and environmental factors may play a role.
Some cases of primary dystonia may have different types of hereditary patterns. Knowing the pattern of inheritance can help families understand the risk of passing dystonia along to future generations.
Dystonia can affect many different parts of the body. Early symptoms may include a deterioration in handwriting after writing several lines, foot cramps, and/or a tendency of one foot to pull up or drag; this may occur "out of the blue" or may occur after running or walking some distance. The neck may turn or pull involuntarily, especially when the patient is tired or stressed.
Sometimes both eyes will blink rapidly and uncontrollably, rendering a person functionally blind. Other possible symptoms are tremor and voice or speech difficulties. The initial symptoms can be very mild and may be noticeable only after prolonged exertion, stress, or fatigue. Over a period of time, the symptoms may become more noticeable and widespread and be unrelenting; sometimes, however, there is little or no progression.
How are the dystonias classified?
One way to classify the dystonias is according to the parts of the body 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 patterns of dystonia are defined as specific syndromes:
Torsion dystonia, previously called dystonia musculorum deformans or DMD, is a rare, generalized dystonia that may be inherited, usually begins in childhood, and becomes progressively worse. It can leave individuals seriously disabled and confined to a wheelchair. Genetic studies have revealed an underlying cause in many patients - a mutation in a gene named DYT1.
And it has been discovered that this gene is related not only to generalized dystonia, but also to some forms of focal dystonia. Note, however, that most dystonia, of any type, is not due to this gene and has an unknown cause.
Cervical dystonia, also called spasmodic torticollis, or torticollis, is the most common of the focal dystonias. In torticollis, the muscles in the neck that control the position of the head are affected, causing the head to twist and turn to one side. In addition, the head may be pulled forward or backward.
Torticollis can occur at any age, although most individuals first experience symptoms in middle age. It often begins slowly and usually reaches a plateau. About 10 to 20 percent of those with torticollis experience a spontaneous remission, but unfortunately the remission may not be lasting.
Blepharospasm, the second most common focal dystonia, is the involuntary, forcible closure of the eyelids. The first symptoms may be uncontrollable blinking. Only one eye may be affected initially, but eventually both eyes are usually involved. The spasms may leave the eyelids completely closed causing functional blindness even though the eyes and vision are normal.
Cranial dystonia is a term used to describe dystonia that affects the muscles of the head, face, and neck. Oromandibular dystonia affects the muscles of the jaw, lips, and tongue. The jaw may be pulled either open or shut, and speech and swallowing can be difficult.
Spasmodic dysphonia involves the muscles of the throat that control speech. Also called spastic dysphonia or laryngeal dystonia, it causes strained and difficult speaking or breathy and effortful speech. Meige's syndrome is the combination of blepharospasm and oromandibular dystonia and sometimes spasmodic dysphonia. Spasmodic torticollis can be classified as a type of cranial dystonia.
Writer's cramp is a dystonia 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. Dopa-responsive dystonia (DRD), of which Segawa's dystonia is an important variant, is a condition successfully treated with drugs. Typically, DRD begins in childhood or adolescence with progressive difficulty in walking and, in some cases, spasticity.
In Segawa's dystonia, the symptoms fluctuate during the day from relative mobility in the morning to increasingly worse disability in the afternoon and evening as well as afterexercise. The diagnosis of DRD may be missed since it mimics many of the symptoms of cerebral palsy.
Doctors don't know exactly what causes most cases of dystonia, but a few factors may be involved.
Altered nerve cell communication
Dystonia has been linked to altered communication between nerve cells located in the basal ganglia — an area of the brain involved in initiating muscle contractions.
Researchers have also discovered a number of genetic changes associated with certain inherited forms of dystonia and also with other forms of dystonia. However, most cases of adult-onset focal dystonias have not been linked to genes.
Sometimes dystonia is but one symptom of a more pervasive disorder that affects the basal ganglia, such as:
- Parkinson's disease.
- Huntington's disease.
- Traumatic brain injury.
- Brain tumor.
- Oxygen deprivation.
- Infections, such as tuberculosis or encephalitis.
- Reactions to certain drugs.
- Heavy metal or carbon monoxide poisoning.
No one treatment has been found universally effective. Instead, physicians use a variety of therapies aimed at reducing or eliminating muscle spasms and pain.
Several classes of drugs that may help correct imbalances in neurotransmitters have been found useful. But response to drugs varies among patients and even in the same person over time. The most effective therapy is often individualized, with physicians prescribing several types of drugs at different doses to treat symptoms and produce the fewest side effects. Note that not all of the medications mentioned below are currently available for patients in the United States.
Frequently, the first drug administered belongs to a group that reduces the level of the neurotransmitter acetylcholine. Drugs in this group include trihexyphenidyl, benztropine (Cogentin), and procyclidine HCl. Sometimes these medications can be sedating, especially at higher doses, and this can limit their usefulness.
Drugs that regulate the neurotransmitter GABA may be used in combination with these drugs or alone in patients with mild symptoms. GABA-regulating drugs include the muscle relaxants diazepam (Valium), lorazepam (Ativan), clonazepam (Klonopin) and baclofen (Lioresal).
Other drugs act on dopamine, a neurotransmitter that helps the brain fine-tune muscle movement. Some drugs which increase dopamine effects include levodopa/carbidopa (Sinemet) and bromocriptine (parlodel). DRD has been remarkably responsive to small doses of this dopamine-boosting treatment.
On the other hand, patients have occasionally benefited from drugs that decrease dopamine, such as reserpine or the investigational drug tetrabenazine. Once again, side effects can restrict the use of these medications.
Anticonvulsants including carbamazepine (Tegretol), usually prescribed to control epilepsy, have occasionally helped individuals with dystonia.
Botulinum toxin (Botox).
Minute amounts of this familiar toxin can be injected into affected muscles to provide temporary relief of focal dystonias. First used to treat blepharospasm, such injections have gained wider acceptance among physicians for treating other focal dystonias. The toxin stops muscle spasms by blocking release of the excitatory neurotransmitter acetylcholine. The effect lasts for up to several months before the injections have to be repeated.
Surgery and other treatments. Surgery may be recommended for some patients when medication is unsuccessful or the side effects are too severe. In selected cases, advanced generalized dystonias have been helped, at least temporarily, by surgical destruction of parts of the thalamus, a structure deep in the brain that helps control movement.
Speech disturbance is a special risk accompanying this procedure, since the thalamus lies near brain structures that help control speech. Surgically cutting or removing the nerves to the affected muscles has helped some focal dystonias, including blepharospasm, spasmodic dysphonia and torticollis. The benefits of these operations, however, can be short-lived. They also carry the risk of disfigurement, can be unpredictable, and are irreversible.
Some patients with spasmodic dysphonia may benefit from treatment by a speech-language pathologist. Physical therapy, splinting, stress management, and biofeedback may also help individuals with certain forms of dystonia.