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.

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.

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. The most common form of tremor occurs in otherwise healthy people. However, in some people a tremor is a symptom of another neurological disorder or condition, including:

• Multiple sclerosis
• Stroke
• Traumatic brain injury
• 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.

Characteristics may include:

• A rhythmic shaking in the hands, arms, head, legs, or trunk
• Shaky voice
• Difficulty writing or drawing
• 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.

Although tremor is not life-threatening, it can be embarrassing to some people and make it harder to perform daily tasks.

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.

Tremor is most commonly classified by clinical features and cause or origin. Some of the better known forms of tremor are:

• Essential tremor (sometimes called benign essential tremor) – the most common of the more than 20 types of tremor
• Parkinsonian tremor – caused by damage to structures within the brain that control movement
• Dystonic tremor – occurs in individuals of all ages who are affected by dystonia, a movement disorder in which sustained involuntary muscle contractions cause twisting and repetitive motions and/or painful and abnormal postures or positions
• Cerebellar tremor – caused by lesions in or damage to the cerebellum resulting from stroke, tumor, or disease such as multiple sclerosis or some inherited degenerative disorder
• Psychogenic tremor (also called hysterical tremor) – many patients with psychogenic tremor have a conversion disorder (defined as a psychological disorder that produces physical symptoms) or another psychiatric disease
• Orthostatic tremor – characterized by rhythmic muscle contractions that occur in the legs and trunk immediately after standing
• Physiologic tremor – occurs in every normal individual and has no clinical significance

There is no cure for most tremors. The appropriate treatment depends on accurate diagnosis of the cause. Some tremors respond to treatment of the underlying condition. For example, in some cases of psychogenic tremor, treating the patient’s underlying psychological problem may cause the tremor to disappear.

Symptomatic drug therapy is available for several forms of tremor. Eliminating tremor “triggers” such as caffeine and other stimulants from the diet is often recommended. Physical therapy may help to reduce tremor and improve coordination and muscle control for some patients. Surgical intervention such as thalamotomy and deep brain stimulation may ease certain tremors. These surgeries are usually performed only when the tremor is severe and does not respond to drugs.