What causes a tremor?
Tremor occurs when the muscles relax and contract repeatedly. While most people experience a tremor at some time, usually because of fear or excitement, a number of neurological diseases that destroy nerve tissue cause uncontrollable tremor. These include Parkinson's disease and multiple sclerosis. Other causes include stroke or head injury; Wilson's disease, a hereditary disorder in which toxic levels of copper accumulate in the tissues; mercury poisoning; an over-active
thyroid gland; and liver encephalopathy. Tremor can occur as a side effect of drugs including amphetamines, antidepressants, antipsychotics, caffeine, and lithium, and as a result of withdrawal from alcohol or addictive drugs.
Some types of tremor are signs of an underlying condition. About a million and a half Americans have Parkinson's disease, a disease that destroys nerve cells. Severe shaking is the most apparent symptom of Parkinson's disease. This coarse tremor features four to five muscle movements per second. These movements are evident at rest but decline or disappear during movement. Other disorders that cause tremor are multiple sclerosis, Wilson's disease, mercury poisoning, thyrotoxicosis, and liver encephalopathy. A tremor that gets worse during body movement is called an "intention tremor." This type of tremor is a sign that something is amiss in the cerebellum, a region of the brain concerned chiefly with movement, balance and coordination.
Tremors are classified according to the type of shaking, how often it occurs, and how severe it is. A tremor that gets worse when a person is moving is called an intention tremor. Intention tremors signal a problem in the cerebellum, the part of the brain responsible for movement, balance, and coordination. These usually occur in people with multiple sclerosis, who have had a stroke, or suffer from alcoholism. Essential tremors are a type of tremor that begin in early adulthood and have no known cause. When essential tremors begin in older people, they are called senile tremors. Research has shown that essential tremor is in an inherited condition in over 50 percent of all cases. Children of a parent with essential tremor have a 50% chance of also having this condition. Essential tremors do not indicate any underlying disease. Tremors that occur when the muscles are at rest may be a sign of Parkinson's disease. These types of tremors are called resting tremors or Parkinsonian tremors.