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. Diminished intelligence and emotional imbalance are not usually features of the dystonias.
Causes of Dystonia
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 that 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.
Signs and Symptoms of Dystonia
Early symptoms may include a deterioration in handwriting after writing several lines, foot cramps, and a tendency of one foot to pull up or drag after running or walking some distance. The neck may turn or pull involuntarily, especially when tired. 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.
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Medical Content Last Updated on 07/12/2008
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