Tremor is an unintentional (involuntary), rhythmical alternating movement that may affect the muscles of any part of the body. Tremor is caused by the rapid alternating contraction and relaxation of muscles and is a common symptom of diseases of the nervous system (neurologic disease).
Occasional tremor is felt by almost everyone, usually as a result of fear or excitement. However, uncontrollable tremor or shaking is a common symptom of disorders that destroy nerve tissue such as Parkinson's disease or multiple sclerosis. Tremor may also occur after stroke or head injury. Other tremor appears without any underlying illness.
Causes & symptoms
Tremor may be a symptom of an underlying disease or it may be caused by drugs. It may also exist as the only symptom (essential tremor).
Some types of tremor are signs of an underlying condition. About 1.5 million 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.
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.