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What is tremor?

Tremor is an unintentional, somewhat rhythmic, muscle movement involving to-and-fro movements (oscillations) of one or more parts of the body. It is the most common of all involuntary movements and can affect the hands, arms, head, face, vocal cords, trunk, and legs. Most tremors occur in the hands. In some people, tremor is a symptom of another neurological disorder. The most common form of tremor, however, occurs in otherwise healthy people. Although tremor is not life-threatening, it can be embarrassing to some people and make it harder to perform daily tasks.

What causes tremor?

Tremor is generally caused by problems in parts of the brain that control muscles throughout the body or in particular areas, such as the hands. Neurological disorders or conditions that can produce tremor include multiple sclerosis, stroke, traumatic brain injury, and neurodegenerative diseases that damage or destroy parts of the brainstem or the cerebellum. Other causes include the use of some drugs (such as amphetamines, corticosteroids, and drugs used for certain psychiatric disorders), alcohol abuse or withdrawal, mercury poisoning, overactive thyroid, or liver failure. Some forms of tremor are inherited and run in families, while others have no known cause.

What are the characteristics of tremor?

Characteristics may include a rhythmic shaking in the hands, arms, head, legs, or trunk; shaky voice; difficulty writing or drawing; or problems holding and controlling utensils, such as a fork. Some tremors may be triggered by or become exaggerated during times of stress or strong emotion, when the individual is physically exhausted, or during certain postures or movements.

Tremor may occur at any age but is most common in middle-aged and older persons. It may be occasional, temporary, or occur intermittently. Tremor affects men and women equally.

A useful way to understand and describe tremors is to define them according to the following types. Resting or static tremor occurs when the muscle is relaxed and the limb is fully supported against gravity, such as when the hands are lying on the lap. It may be seen as a shaking of the limb, even when the person is at rest. This type of tremor is often seen in patients with Parkinson's disease. An action tremor occurs during any type of movement of an affected body part. There are several subclassifications of action tremor. Postural tremor occurs when the person maintains a position against gravity, such as holding the arms outstretched. Kinetic (or intention) tremor occurs during purposeful voluntary movement, such as touching a finger to one's nose during a medical exam. Task-specific tremor appears when performing highly skilled, goal-oriented tasks such as handwriting or speaking. Isometric tremor occurs during a voluntary muscle contraction that is not accompanied by any movement.