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).
Description
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).
Underlying disease
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.
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."
Diagnosis
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.
Treatment
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.
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 bacteriumClostridium 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.
Expected results
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.
KEY TERMS
Intention tremor
—A rhythmic purposeless shaking of the muscles that begins with purposeful (voluntary) movement. This tremor does not affect muscles that are resting.
Prevention
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.
BOOKS
Fauci, Anthony S. et al., eds. Harrison's Principles of Internal Medicine. New York: McGraw-Hill, 1998.
PERIODICALS
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.
ORGANIZATIONS
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.
