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A tremor is an involuntary, rhythmic, shaking movement produced when muscles repeatedly contract and relax.

Everyone has a tremor to some degree. For example, when held outstretched, the hands usually tremble slightly. Such slight, rapid tremor, called physiologic tremor, is normal and reflects the precise moment-by-moment control of muscles by nerves. In most people, the tremor is too slight to be noticed.

Factors that can make a normal tremor more noticeable include stress, anxiety, fatigue, withdrawal of alcohol or certain other drugs (such as opioids), an overactive thyroid gland (hyperthyroidism), consumption of caffeine, and use of certain drugs, including theophylline Some Trade Names
BRONKODYL
THEOLAIR
and beta-adrenergic agonists such as albuterol Some Trade Names
PROVENTIL
VENTOLIN
(which are used to treat asthma), corticosteroids, and valproate Some Trade Names
DEPARENE
(an anticonvulsant).

Types of Abnormal Tremors

There are several types of abnormal tremor. Tremors are classified according to the following:

• How fast the shaking movements are (frequency)
• How wide (amplitude) they are, ranging from fine to coarse
• How often the tremors occur
• How severe they are
• What triggers them, such as rest or movement
• What causes them

Tremors triggered by rest are called resting tremors. Tremors triggered or made worse by movement are called action tremors. Action tremors can be classified as intention tremors (triggered by aiming for a target) or postural tremors (triggered by holding a limb in one position). Causes are classified as physiologic, essential, cerebellar, or secondary. Secondary tremors are caused by disorders or drugs.

Resting Tremor: This tremor occurs when muscles are at rest, making an arm or a leg shake even when a person is completely relaxed. The tremor becomes less noticeable or disappears when the person moves the affected muscles. Resting tremors are often slow and coarse.

These tremors develop when collections of nerve cells at the base of the cerebrum (including the basal ganglia) are disturbed. Such disturbances usually result from Parkinson's disease. Antipsychotic drugs are another common cause of resting tremors.

Resting tremors may be socially embarrassing but typically do not interfere with daily activities, such as drinking a glass of water.

Intention Tremor: This tremor occurs when a person ends a purposeful movement (such as pressing a button) or aims for a target (as when reaching for an object with the hand). The person may miss the targeted object because of the tremor. Intention tremors are relatively slow and coarse.

These tremors may result from damage to the cerebellum or its connections. Thus, cerebellar tremors and intention tremors may be used synonymously. Multiple sclerosis is a common cause. Stroke, Wilson's disease, alcoholism, and overuse of sedatives or anticonvulsants can cause the cerebellum to malfunction, resulting in an intention tremor.

Postural Tremor: This tremor occurs when an arm or a leg is held in one position against gravity, as when a person holds the arms outstretched in front of the body.

If the tremor develops gradually, it is usually a physiologic or essential tremor. If a postural tremor starts more suddenly, the cause may be a toxin, a disorder (such as hyperthyroidism), withdrawal of alcohol or a drug, or use of certain drugs.

Essential Tremor: This tremor usually begins in early adulthood but can begin at any age. The tremor slowly becomes more obvious and becomes more noticeable as people age. Thus, it is sometimes incorrectly called senile tremor. It is usually rapid and fine but may be slow, coarse, or both.

Some forms of essential tremor, called benign hereditary tremor, run in families. What causes essential tremors is unknown, but these tremors (while they can be disabling if severe) do not indicate a serious disorder.

Essential tremor can affect the hands, head, and voice. Usually, the tremor stops during rest and worsens when the limbs are held in uncomfortable positions. The tremor often becomes obvious when the limbs are outstretched. For example, a tremor of the hand or wrist may become obvious when the wrist is bent upward and the fingers are spread apart. The tremor typically affects both sides of the body but may affect one side more than the other. Sometimes the head trembles and bobs, and the voice becomes shaky.

Any factor that makes normal (physiologic) tremors worse (such as stress, fatigue, or consumption of caffeine) can make essential tremors more noticeable. Drinking alcohol usually makes the tremor less noticeable.

Usually, essential tremor remains mild. However, it can be troublesome and embarrassing. It can affect handwriting and make using utensils difficult. In some people, the tremor gradually worsens over time, eventually resulting in disability.

Asterixis: Asterixis resembles a tremor but is not one. Asterixis occurs when a group of contracted muscles suddenly and temporarily goes limp. For example, when the arms and hands are outstretched, the hands suddenly drop, then resume their original position. The movements are repetitive, coarse, slow, and not rhythmic.

Asterixis commonly results from liver failure and so has been called liver flap. Asterixis may also result from kidney failure, use of certain drugs, or brain damage (encephalopathy) due to a metabolic disorder. It is often accompanied by tremors and myoclonus (see Movement Disorders: Myoclonus).

Did You Know... Everyone has tremors to some degree. Simple, common-sense measures can make functioning with noticeable tremors easier.

Diagnosis

If a noticeable tremor develops, it should be evaluated by a doctor. A doctor can usually identify the type of tremor by its characteristics. The type of tremor determines which diagnostic tests are done.

• Resting tremor: A complete neurologic evaluation is done to check for Parkinson's disease. Computed tomography (CT) or magnetic resonance imaging (MRI) of the brain may be done.
• Intention tremor: An imaging procedure, such as CT or MRI, is often done to look for damage to the brain, especially the cerebellum.
• Postural tremor: If symptoms develop suddenly, the doctor asks about the drugs the person is taking, and tests may be done to check for other disorders, such as thyroid disorders. CT or MRI may also be done.
• Essential tremor: The doctor asks what drugs the person is using, whether the person is experiencing anxiety or stress, and whether an alcoholic beverage makes the tremor less noticeable. A blood test to check for hyperthyroidism is done.
• Asterixis: Blood tests are done to determine whether a liver, kidney, or metabolic disorder is the cause.

Treatment

For mild tremor, no treatment is needed. If tremors become bothersome, some simple measures can help:

• Grasping objects firmly and holding them close to the body to avoid dropping them
• Avoiding uncomfortable positions
• Not eating soup in public
• Using assistive devices, as instructed by an occupational therapist

Assistive devices may include rocker knives, utensils with large handles, and, particularly if the tremor is severe, button hooks, Velcro fasteners (instead of buttons or shoe laces), zipper pulls, straws, and shoe horns.

For physiologic or essential tremor, eliminating or minimizing the trigger may lessen the tremor. For example, treating hyperthyroidism may help. Drinking alcohol in moderation may lessen the tremor. However, heavy drinking followed by stopping it suddenly makes the tremor worse. If many daily activities (such as using utensils and drinking from a glass at mealtime) become difficult or if the person's work requires steady hands, drugs are used. Treatment may include a beta-blocker (such as propranolol Some Trade Names
INDERAL
), the anticonvulsant primidone Some Trade Names
MYSOLINE
, or both.

If due to Parkinson's disease, a resting tremor is treated as part of that disease. Drugs with anticholinergic effects such as trihexyphenidyl Some Trade Names
ARTANE
and benztropine Some Trade Names
COGENTIN
usually help control the tremor.

Intention tremors are difficult to treat, but if the condition affecting the cerebellum can be corrected, the tremor may resolve. If the condition cannot be corrected, a therapist may put wrist and ankle weights on the affected limb to reduce the tremor. Or people may be taught to brace the limb during activity. These measures sometimes help.

Deep Brain Stimulation: Tiny electrodes are placed in the area of the brain involved in tremors. The electrodes deliver a painless shock to block the impulses causing tremors. Deep brain stimulation is sometimes done when drugs cannot control a severe, disabling essential tremor or a resting tremor. For essential tremors, the thalamus (a collection of nerve cells at the base of the brain) is stimulated. For resting tremors, the thalamus or subthalamic nucleus (located below the thalamus) is stimulated. Such procedures are available only at special centers.

Last full review/revision August 2007 by David Eidelberg, MD; Michael Pourfar, MD