Tremors are involuntary, purposeless movements of a body part around a fixed plane in space. A tremor can be classified on the basis of whether it occurs with a certain posture, at rest, or during movement. It can be localized to the affected body part and characterized by what makes the tremor better or worse.
A physiological tremor is a variation of what is normal while a pathological tremor is not. The two most common types of pathological tremors are essential tremors and tremors associated with Parkinson’s disease. In addition, disease in the cerebellum of the brain may also cause a tremor of intention (i.e., with movement). Other less common causes of tremor include alcohol withdrawal or diseases of the peripheral nerves.
An essential tremor is also known as a benign tremor. It is about ten to twenty times more common than the tremor of Parkinson’s disease. It is most noticeable when a person holds their hands outstretched or makes fine movements. By contrast with the tremor of Parkinson’s disease, essential tremor tends to disappear when the hands and arms are relaxed. Sixty percent of essential tremors are inherited and are known as familial tremors.
Parkinson’s disease occurs in about 1 percent of people aged sixty-five years or older, increases to 2.5 percent of persons over eighty years of age. The hallmark of Parkinson’s disease is an asymmetrical tremor that occurs at rest. A relatively low frequency and medium amplitude characterize the tremor. Classically, it is described as a pill rolling tremor of the hands (a term of distant origin, referring to the days when pharmacists made pills on site) yet it can also affect the chin. Typically, this tremor only rarely affects the neck or voice. This tremor diminishes with purposeful movements and therefore it usually does not cause motor disability. Parkinson’s disease does not evolve from essential tremors.
Cerebellar tremors tend to be related to movement and increase in severity as the extremity approaches its target, often resulting in the extremity moving part of its object (so-called pist points) and having to rely on visual input ultimately to find the target. They are associated with other signs of cerebellar malfunction such as abnormalities of gait, speech, and eye movements. A postural tremor may also be associated with damage to the cerebellum. Causes of cerebellar postural tremor are diseases like multiple sclerosis, tumors, stroke or nonspecific neurodegenerative disease of the brain.
Drugs used for treatment of essential tremor include beta-adrenergic blockers, benzodiazepines, or anticonvulsants. Small doses of alcohol have been found to provide temporary relief of essential tremors although excess alcohol intake is strongly discouraged and can make them worse, especially as the blood level is reduced.. Replacement of dopamine is used for treatment of Parkinson’s disease and therapy can be augmented with anticholinergic agents or dopamine agonists. Thalamotomy (or the surgical disruption of a deep brain structure known as the thalamus) is a surgical procedure used to treat patients with severe, drug resistant essential tremor or patients with Parkinson’s disease who have severe, disabling, predominantly unilateral tremor. Pallidotomy (surgical destruction of the globus pallidus) is an alternative to thalamotomy in the treatment of parkinsonian tremor. Implantation of an electrode in the thalamus can suppress some tremors. All surgical therapies should only be considered for patients who have debilitating symptoms that persist despite adequate medical therapy.
Tremor is an important sign in aging, which can occur in the absence of disease. Although, sometimes embarassing, essential tremor on its own is neither disabling nor a sign of impending brain disease.
Philip E. Lee B. Lynn Beattie
See also Parkinsonism.
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Charles, P. D.; Esper, G. J.; Davis, T. L.; Maciunas, R. J.; and Robertson, D. ‘‘Classification of Tremor and Update on Treatment.’’ American Family Physician 59, no. 6 (15 March 1999): 1565–1572.
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Louis E. D.; Ottman R.; and Hauser W. A. ‘‘How Common Is the Most Common Adult Movement Disorder? Estimates of Essential Tremor Throughout the World.’’ Movement Disorder 13 (1998): 5–10.
Uitti, R. J. ‘‘Tremor: How To Determine if the Patient Has Parkinson’s Disease.’’ Geriatrics (May 1998): 30–36.
Yahr, M. D., and Pang, S. W. H. ‘‘Movement Disorders’’ (Chapter 84). In The Merck Manual of Geriatrics. Edited by William B. Abrams and Robert Berkow. Whitehouse Station, N.J.: Merck and Co. Inc., 1990. Pages 981–982.
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.
Drugs and tremor
Several different classes of drugs can cause tremor as a side effect. These drugs include amphetamines, antidepressant drugs, antipsychotic drugs, caffeine , and lithium. Tremor also may be a sign of withdrawal from alcohol or street drugs.
Many people have what is called "essential tremor," in which the tremor is the only symptom. This type of shaking affects between three and four million Americans.
The cause of essential tremor is not known, although it is an inherited problem in more than half of all cases. The genetic condition has an autosomal dominant inheritance pattern, which means that any child of an affected parent will have a 50% chance of developing the condition.
Essential tremor most often appears when the hands are being used, whereas a person with Parkinson's disease will most often have a tremor while walking or while the hands are resting. People with essential tremor will usually have shaking head and hands, but the tremor may involve other parts of the body. The shaking often begins in the dominant hand and may spread to the other hand, interfering with eating and writing. Some people also develop a quavering voice.
Essential tremor affects men and women equally. The shaking often appears at about age 45, although the disorder may actually begin in adolescence or early adulthood. Essential tremor that begins very late in life is sometimes called "senile tremor."
Close attention to where and how the tremor appears can help provide a correct diagnosis of the cause of the shaking. The source of the tremor can be diagnosed when the underlying condition is found. Diagnostic techniques that make images of the brain, such as computed tomography scan (CT scan) or magnetic resonance imaging (MRI), may help form a diagnosis of multiple sclerosis or other tremor caused by disorders of the central nervous system. Blood tests can rule out metabolic causes such as thyroid disease. A family history can help determine whether the tremor is inherited.
Neither tremor nor most of its underlying neurological causes can be cured. Tremor caused by medications or by drug withdrawal, can sometimes be lessened with herbs that relax the nerves and muscle tissue, such as skullcap (Scutellaria laterifolia ), valerian (Valeriana officinalis ), and Jamaican dogwood (Piscidia piscipula ).
Patients suffering from Parkinson's disease-related tremors may benefit from mucuna seeds (Mucuna pruriens ). Practitioners of Ayurveda, or traditional Indian medicine, have prescribed mucuna to treat Parkinson's disease (or Kampavata ) for over 4,000 years. Mucuna contains a natural form of l-dopa, a powerful antiParkinson's drug.
Most people with essential tremor respond to drug treatment, which may include propranolol, primidone, or a benzodiazepine. People with Parkinson's disease may respond to anti-Parkinson's drugs.
Research has shown that about 70% of patients treated with botulinus toxin (Botox) have some improvement in tremor of the head, hand, and voice. Botulinus is derived from the bacterium Clostridium botulinum. This bacterium causes botulism, a form of food poisoning . It is poisonous because it weakens muscles. A very weak solution of the toxin is used in cases of tremor and paralysis to force the muscles to relax. However, some patients experience unpleasant side effects with this drug and cannot tolerate effective doses. For other patients, the drug becomes less effective over time. Medications do not produce any tremor relief in about half of all patients.
Tremor control therapy
Tremor control therapy is a type of treatment that uses mild electrical pulses to stimulate the brain. These pulses block the brain signals that trigger tremor. In this technique, the surgeon implants an electrode into a large oval area of gray matter within the brain that acts as a relay center for nerve impulses and is involved in generating movement (thalamus). The area that is particularly targeted for relief of tremor associated with PD is called the ventralis intermedius nucleus of the thalamus. The electrode is attached to an insulated wire that runs through the brain and exits the skull where it is attached to an extension wire. The extension is connected to a generator similar to a heart pacemaker. The generator is implanted under the skin in the chest, and the extension is tunneled under the skin from the skull to the generator. The patient can control his or her tremor by turning on the generator with a hand-held magnet to deliver an electronic pulse to the brain.
Some patients experience complete relief with this technique, but others receive no benefit at all. About 5% of patients experience complications from the surgical procedure, including bleeding in the brain. The procedure causes some discomfort, because patients must be awake while the implant is placed. Batteries must be replaced by surgical procedure every three to five years.
Other surgical treatments
A patient with extremely disabling tremor may find relief with a surgical technique called thalamotomy, in which the surgeon destroys part of the thalamus. However, the procedure produces such side effects as numbness, balance problems, or speech problems in a significant number of cases.
Pallidotomy is another type of surgical procedure sometimes used to decrease tremors from Parkinson's disease. In this technique, the surgeon destroys part of a small structure within the brain called the globus pallidus internus. The globus is part of the basal ganglia, another part of the brain that helps control movement. This surgical technique also carries the risk of permanent disabling side effects.
Fetal tissue transplantation (also called a nigral implant) is a controversial experimental method to treat Parkinson's disease symptoms. This method implants fetal brain tissue into the patient's brain to replace malfunctioning nerves. Unresolved issues include how to harvest the fetal tissue and the moral implications behind using such tissue, the danger of tissue rejection; and the amount of tissue required. Although initial studies using this technique looked promising, there has been difficulty in consistently reproducing positive results. More promising is the development of dopamine-producing cells from neuronal stem cells for transplantation into the brains of patients with PD. A method for producing these dopaminergic cells was patented in 2001.
Small amounts of alcohol may temporarily (sometimes dramatically) ease the shaking. Some experts recommend a small amount of alcohol (especially before dinner). The possible benefits, of course, must be weighed against the risks of alcohol abuse.
Essential tremor and tremor caused by neurologic disease (including Parkinson's disease) slowly get worse and can interfere with a person's daily life. While the condition is not life-threatening, it can severely disrupt a person's everyday experiences. One recent finding is that Parkinson's patients are more concerned about the limitations imposed on their functioning and social life by the tremor than they are by the symptom itself.
- Intention tremor
- —A rhythmic purposeless shaking of the muscles that begins with purposeful (voluntary) movement. This tremor does not affect muscles that are resting.
Essential tremor and tremor caused by a disease of the central nervous system cannot be prevented. Avoiding use of such stimulant drugs as caffeine and amphetamines can prevent tremor that occurs as a side effect of drug use.
Fauci, Anthony S. et al., eds. Harrison's Principles of Internal Medicine. New York: McGraw-Hill, 1998.
Eskandar, Emad N., G. Rees Cosgrove, Leslie A. Shinobu. "Surgical Treatment of Parkinson Disease. (Contempo Updates Linking Evidence and Experience). " Journal of the American Medical Association 286 (December 26, 2001): 3056-3059.
"Neuralstem Patents Methods for Generating Dopamine-Producing Neurons from Neural Stem Cells." Stem Cell Week (December 31, 2001): 13.
Whetten-Goldstein, K., et al. "Patients' Perceptions of Living with Parkinson's Disease." Gerontologist (October 15, 2001): 281.
American Academy of Neurology. 1080 Montreal Ave., St. Paul, MN 55116. (612) 695-1940. http://www.aan.com/public/con.html.
American Parkinson Disease Association. 1250 Hylan Boulevard, Suite 4B, Staten Island, NY 10305-1946. (800) 223-2732. http://www.apdaparkinson.com/.
International Tremor Foundation. 7046 West 105th Street, Overland Park, KS 66212. (913) 341-3880.
Rebecca J. Frey, PhD
The extent to which the fingers shake varies with the person's psychological circumstances; there are many references in the Bible and in Shakespeare to the association with fright and strong emotion. This is due to the liberation of the hormone adrenaline at these times. Musicians and others making public appearances may suffer from stage fright, and excessive tremor is then often seen. High levels have been observed in air squadron cadets learning to fly light aircraft, and unusually high levels have been observed after bungee jumping.
Physiological tremor is usually rhythmic, the peak of the oscillations being at about 10 cycles per second. Whilst its size may vary widely from moment to moment, the rate remains much the same. Each muscle is controlled by the nerve impulse activity in a number of nerve fibres, each of which is responsible for controlling the contraction of a number of individual muscle fibres. The number of muscle fibres controlled by a single nerve fibre (forming a motor unit) varies considerably in different muscles. In those of the trunk it is large, but is smaller in the small muscles of the hand where high precision of control is needed. The nerve impulses occur usually at a rate of 5–20 cycles per second. This is not fast enough to cause the muscle elements to produce a smooth contraction; these facts about the behaviour responsible for our posture and its disturbances have been established by animal and human experiments. Our posture is thus based on many small, jerky sources of force. We are not usually aware of these discontinuities, because the different motor units are operating out of step with one another so that overall there is a large measure of smoothing in the force acting through the tendons. An analogue would be soldiers falling out of step when marching over a bridge. These bumpy forces are applied across our joints.
In general, limbs are under-damped, that is, they oscillate preferentially at a certain rate: the resonant frequency. It so happens that the resonant frequency of the human wrist is about 10 cycles per second for small movements — close to the rate of discharge of the nerve fibres to the muscles of the arm. It is the combination of these two factors which is mainly responsible for physiological tremor.
In disease the discharges of the individual nerve fibres may become unusually closely timed to one another; they are then said to be synchronized. There is then a prominent tremor. This is the situation in pathological tremors such as that seen in Parkinsonism. This lower frequency tremor at 4–6 cycles per second can be widespread, involving the forearms and even the head and trunk.
After a stroke, the foot on the affected side may at times jerk rhythmically, in response to ankle displacement, in a powerful and disturbing manner. Strictly speaking this is classed as clonus rather than tremor.
Movements and posture are regulated by the cerebellum. This part of the brain is responsible for organizing the motor programmes. The correct timing of the multiplicity of muscle actions needed in performing everyday tasks is a problem of great magnitude. If the cerebellum or its pathways are not capable of fully normal action, as in Freidrich's Ataxia, movements will be poorly co-ordinated and there will be an ‘intention tremor’: when picking something up, the hand may oscillate to and fro at the end of the motion, under-reaching and over-reaching, instead of coming to rest neatly in the correct position. These pathways are also after impaired in multiple sclerosis. Some people, who are otherwise quite healthy, have unusually prominent shaking. This is called essential tremor. Sometimes it is hereditary. In northern Sweden the population moved little for hundreds of years, and very good church records exist. From this region and certain other areas very extensive family trees have been prepared, which show the mode of inheritance of some forms of the condition. If severe, essential tremor can be a serious disability as it interferes with skilled movements such as writing. This can be socially embarrassing, and the person may falsely be believed to be an alcoholic — whereas small amounts of alcohol may actually suppress tremor. Tremor associated with alcoholism occurs the morning after rather than at the time of the drinking. With excessive intake the person may show widespread shaking, the Latin name for this being delirium tremens — a very serious condition. Many other drugs also can give rise to shaking. Adolph Hitler had a prominent tremor, perhaps due to the stimulant amphetamine (purple hearts), which he was taking. Some people find that coffee brings out tremor; this is due to the presence of caffeine, which is an excitant; these effects are not, however, universal.
As to treatment, there is no panacea. For tremors associated with anxiety, drugs which block the action of adrenaline can be of use, but there may be side actions. Very severe and incapacitating tremors are sometimes treated by surgical operations on the brain. Important and interesting human and animal research is currently being conducted on tremor mechanisms and the possibilities of refining treatment.
E. Geoffrey Walsh
Walsh, E. G. (1992). Muscles, masses and motion. Mackeith/Cambridge University Press.
See also cerebellum; movement; skeletal muscle.
trem·or / ˈtremər/ • n. an involuntary quivering movement: a disorder that causes tremors and muscle rigidity. ∎ (also earth tremor) a slight earthquake. ∎ a sudden feeling of fear or excitement: a tremor of unease. ∎ a tremble or quaver in a person's voice.