Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 91. Movement Disorders

Topics: Introduction | Myoclonus | Tremor | Parkinson's Disease | Progressive Supranuclear Palsy | Shy-Drager Syndrome | Tics | Chorea and Athetosis | Huntington's Disease | Dystonia | Coordination Disorders

Coordination Disorders

The cerebellum is the part of the brain most responsible for coordinating sequences of movements; it also controls balance and posture. Anything that damages the cerebellum can lead to incoordination (ataxia).

Prolonged alcohol abuse is the most common cause of damage to the cerebellum. Other causes include strokes, tumors, bleeding (hemorrhage) in the brain, repeated head injuries, multiple sclerosis, birth defects of the brain, an underactive thyroid gland (hypothyroidism), a high fever, certain toxic substances (such as carbon monoxide and heavy metals), and undernutrition. Several rare hereditary disorders, such as Friedreich's ataxia and ataxia-telangiectasia, may also damage the cerebellum.

People with ataxia cannot control the position of their arms and legs or their posture, so they stagger and make broad, zigzag movements with their arms. There are several specific types of ataxia. People with dysmetria cannot control the accuracy of body movements. For example, in attempting to reach for an object, people with dysmetria may reach beyond the object. People with dysarthria have poor coordination of speech muscles, causing slurred speech and uncontrolled fluctuations in volume. Such people may also exaggerate movement of the muscles around the mouth. Damage to the cerebellum can cause intention tremor.

In Friedreich's ataxia, a progressive disorder, walking becomes unsteady between the ages of 5 and 15. Then arm movements become uncoordinated, and speech becomes slurred and hard to understand. Vibration sense, position sense (knowing where the arms and legs are), and reflexes are lost. Mental function may decrease. By their late 20s, people with this disorder may be confined to a wheelchair. Death, often due to an abnormal heart rhythm or heart failure, usually occurs by middle age.

For the hereditary disorders, such as Friedreich's ataxia and ataxia-telangiectasia, there is no treatment. Ataxia due to use of alcohol or a drug such as phenytoin can be treated by withdrawing that substance.