Deep brain stimulation in movement disorders
Jun. 09, 2020
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What is tremor?
Tremor is an involuntary, rhythmic muscle contraction leading to shaking movements in one or more parts of the body. It is a common movement disorder that most often affects the hands but can also occur in the arms, head, vocal cords, torso, and legs. Tremor may be intermittent (occurring at separate times, with breaks) or constant. It can occur sporadically (on its own) or happen as a result of another disorder.
Tremor is most common among middle-aged and older adults, although it can occur at any age. The disorder generally affects men and women equally.
Tremor is not life threatening. However, it can be embarrassing and even disabling, making it difficult or even impossible to perform work and daily life tasks.
What causes tremor?
Generally, tremor is caused by a problem in the deep parts of the brain that control movements. Most types of tremor have no known cause, although there are some forms that appear to be inherited and run in families.
Tremor can occur on its own or be a symptom associated with a number of neurological disorders, including:
Some other known causes can include:
What are the symptoms of tremor?
Symptoms of tremor may include:
Some tremor may be triggered by or become worse during times of stress or strong emotion, when an individual is physically exhausted, or when a person is in certain postures or makes certain movements.
How is tremor classified?
Tremor can be classified into two main categories:
Resting tremor occurs when the muscle is relaxed, such as when the hands are resting on the lap. With this disorder, a person’s hands, arms, or legs may shake even when they are at rest. Often, the tremor only affects the hand or fingers. This type of tremor is often seen in people with Parkinson’s disease and is called a “pillrolling” tremor because the circular finger and hand movements resemble rolling of small objects or pills in the hand.
Action tremor occurs with the voluntary movement of a muscle. Most types of tremor are considered action tremor. There are several sub-classifications of action tremor, many of which overlap.
What are the different categories or types of tremor?
Tremor is most commonly classified by its appearance and cause or origin. There are more than 20 types of tremor. Some of the most common forms of tremor include:
Essential tremor. Essential tremor (previously also called benign essential tremor or familial tremor) is one of the most common movement disorders. The exact cause of essential tremor is unknown. For some people this tremor is mild and remains stable for many years. The tremor usually appears on both sides of the body, but is often noticed more in the dominant hand because it is an action tremor.
The key feature of essential tremor is a tremor in both hands and arms, which is present during action and when standing still. Additional symptoms may include head tremor (e.g., a “yes” or “no” motion) without abnormal posturing of the head and a shaking or quivering sound to the voice if the tremor affects the voice box. The action tremor in both hands in essential tremor can lead to problems with writing, drawing, drinking from a cup, or using tools or a computer.
Tremor frequency (how “fast” the tremor shakes) may decrease as the person ages, but the severity may increase, affecting the person’s ability to perform certain tasks or activities of daily living. Heightened emotion, stress, fever, physical exhaustion, or low blood sugar may trigger tremor and/or increase its severity. Though the tremor can start at any age, it most often appears for the first time during adolescence or in middle age (between ages 40 and 50). Small amounts of alcohol may help decrease essential tremor, but the mechanism behind this is unknown.
About 50 percent of the cases of essential tremor are thought to be caused by a genetic risk factor (referred to as familial tremor). Children of a parent who has familial tremor have greater risk of inheriting the condition. Familial forms of essential tremor often appear early in life.
For many years essential tremor was not associated with any known disease. However, some scientists think essential tremor is accompanied by a mild degeneration of certain areas of the brain that control movement. This is an ongoing debate in the research field.
Dystonic tremor. Dystonic tremor occurs in people who are affected by dystonia—a movement disorder where incorrect messages from the brain cause muscles to be overactive, resulting in abnormal postures or sustained, unwanted movements. Dystonic tremor usually appears in young or middle-aged adults and can affect any muscle in the body. Symptoms may sometimes be relieved by complete relaxation.
Although some of the symptoms are similar, dystonic tremor differs from essential tremor in some ways. The dystonic tremor:
Cerebellar tremor. Cerebellar tremor is typically a slow, high-amplitude (easily visible) tremor of the extremities (e.g., arm, leg) that occurs at the end of a purposeful movement such as trying to press a button. It is caused by damage to the cerebellum and its pathways to other brain regions resulting from a stroke or tumor. Damage also may be caused by disease such as multiple sclerosis or an inherited degenerative disorder such as ataxia (in which people lose muscle control in the arms and legs) and Fragile X syndrome (a disorder marked by a range of intellectual and developmental problems). It can also result from chronic damage to the cerebellum due to alcoholism.
Psychogenic tremor. Psychogenic tremor (also called functional tremor) can appear as any form of tremor. It symptoms may vary but often start abruptly and may affect all body parts. The tremor increases in times of stress and decreases or disappears when distracted. Many individuals with psychogenic tremor have an underlying psychiatric disorder such as depression or post-traumatic stress disorder (PTSD).
Physiologic tremor. Physiologic tremor occurs in all healthy individuals. It is rarely visible to the eye and typically involves a fine shaking of both of the hands and also the fingers. It is not considered a disease but is a normal human phenomenon that is the result of physical properties in the body (for example, rhythmical activities such as heart beat and muscle activation).
Enhanced physiologic tremor. Enhanced physiological tremor is a more noticeable case of physiologic tremor that can be easily seen. It is generally not caused by a neurological disease but by reaction to certain drugs, alcohol withdrawal, or medical conditions including an overactive thyroid and hypoglycemia. It is usually reversible once the cause is corrected.
Parkinsonian tremor. Parkinsonian tremor is a common symptom of Parkinson’s disease, although not all people with Parkinson’s disease have tremor. Generally, symptoms include shaking in one or both hands at rest. It may also affect the chin, lips, face, and legs. The tremor may initially appear in only one limb or on just one side of the body. As the disease progresses, it may spread to both sides of the body. The tremor is often made worse by stress or strong emotions. More than 25 percent of people with Parkinson’s disease also have an associated action tremor.
Orthostatic tremor. Orthostatic tremor is a rare disorder characterized by rapid muscle contractions in the legs that occur when standing. People typically experience feelings of unsteadiness or imbalance, causing them to immediately attempt to sit or walk. Because the tremor has such a high frequency (very fast shaking) it may not visible to the naked eye but can be felt by touching the thighs or calves or can be detected by a doctor examining the muscles with a stethoscope. In some cases the tremor can become more severe over time. The cause of orthostatic tremor is unknown.
How is tremor diagnosed?
Tremor is diagnosed based on a physical and neurological examination and an individual’s medical history. During the physical evaluation, a doctor will assess the tremor based on:
The doctor will also check other neurological findings such as impaired balance, speech abnormalities, or increased muscle stiffness. Blood or urine tests can rule out metabolic causes such as thyroid malfunction and certain medications that can cause tremor. These tests may also help to identify contributing causes such as drug interactions, chronic alcoholism, or other conditions or diseases. Diagnostic imaging may help determine if the tremor is the result of damage in the brain.
Additional tests may be administered to determine functional limitations such as difficulty with handwriting or the ability to hold a fork or cup. Individuals may be asked to perform a series of tasks or exercises such as placing a finger on the tip of their nose or drawing a spiral.
The doctor may order an electromyogram to diagnose muscle or nerve problems. This test measures involuntary muscle activity and muscle response to nerve stimulation.
How is tremor treated?
Although there is no cure for most forms of tremor, treatment options are available to help manage symptoms. In some cases, a person’s symptoms may be mild enough that they do not require treatment.
Finding an appropriate treatment depends on an accurate diagnosis of the cause. Tremor caused by underlying health problems can sometimes be improved or eliminated entirely with treatment. For example, tremor due to thyroid hyperactivity will improve or even resolve (return to the normal state) with treatment of thyroid malfunction. Also, if tremor is caused by medication, discontinuing the tremor-causing drug may reduce or eliminate this tremor.
If there is no underlying cause for tremor that can be modified, available treatment options include:
Focused Ultrasound. A new treatment for essential tremor uses magnetic resonance images to deliver focused ultrasound to create a lesion in tiny areas of the brain’s thalamus thought to be responsible for causing the tremors. The treatment is approved only for those individuals with essential tremor who do not respond well to anticonvulsant or beta-blocking drugs.
Surgery. When people do not respond to drug therapies or have a severe tremor that significantly impacts their daily life, a doctor may recommend surgical interventions such as deep brain stimulation (DBS) or very rarely, thalamotomy. While DBS is usually well tolerated, the most common side effects of tremor surgery include dysarthria (trouble speaking) and balance problems.
What is the prognosis?
Tremor is not considered a life-threating condition. Although many cases of tremor are mild, tremor can be very disabling for other people. It can be difficult for individuals with tremor to perform normal daily activities such as working, bathing, dressing, and eating. Tremor can also cause “social disability.” People may limit their physical activity, travel, and social engagements to avoid embarrassment or other consequences.
The symptoms of essential tremor usually worsen with age. Additionally, there is some evidence that people with essential tremor are more likely than average to develop other neurodegenerative conditions such as Parkinson’s disease or Alzheimer’s disease, especially in individuals whose tremor first appears after age 65.
Unlike essential tremor, the symptoms of physiologic and drug-induced tremor do not generally worsen over time and can often be improved or eliminated once the underlying causes are treated.
What research is being done?
The mission of the National Institute of Neurological Disorders and Stroke (NINDS) is to seek fundamental knowledge about the brain and nervous system and to use that knowledge to reduce the burden of neurological disease. The NINDS is a component of the National Institutes of Health (NIH), the leading supporter of biomedical research in the world.
Researchers are working to better understand the underlying brain functions that cause tremor, identify the genetic factors that make individuals more susceptible to the disorder, and develop new and better treatment options.
Brain functioning. It can be difficult to distinguish between movement disorders such as Parkinson's disease and essential tremor. These debilitating movement disorders have different prognoses and can respond very differently to available therapies. NINDS researchers are working to identify structural and functional changes in the brain using non-invasive neuroimaging techniques to develop sensitive and specific markers for each of these diseases and then track how they change as each disease progresses.
Other researchers are using functional magnetic resonance imaging technology to better understand normal and diseased brain circuit functions and associated motor behaviors. Scientists hope to design therapies that can restore normal brain circuit function in diseases such as Parkinson's disease and tremor.
Genetics. Research has shown that essential tremor may have a strong genetic component affecting multiple generations of families. NINDS researchers are building on previous genetics work to identify susceptibility genes for familial early-onset (before age 40) essential tremor. Researchers are focusing on multigenerational, early onset families to better detect linkages.
Additionally, NINDS scientists are researching the impact of genetic abnormalities on the development of essential tremor. Previous research that has shown a link between essential tremor and possible genetic variants on chromosome 6 and 11; ongoing research is targeting the impact of other genetic variations in families.
Medications and other treatment methods. While drugs can be effective for some people, approximately 50 percent of individuals do not respond to medication. In order to develop assistive and rehabilitative tremor-suppressing devices for people with essential tremor, researchers are exploring where and how to minimize or suppress tremor while still allowing for voluntary movements.
Many people with essential tremor respond to ethanol (alcohol); however, it is not clear why or how. NINDS researchers are studying the impact of ethanol on tremor to determine the correct dosage amount and its physiological impact on the brain and whether other medications without the side effects of ethanol can be effective.
Other NIH researchers hope to identify the source of essential tremor, study the effects of currently available tremor-suppressant drugs on the brain, and develop more targeted and effective therapies.
Where can I get more information?
For more information on neurological disorders or research programs funded by the National Institute of Neurological Disorders and Stroke, contact the Institute's Brain Resources and Information Network (BRAIN) at:
P.O. Box 5801
Bethesda, MD 20824
More information about tremor research supported by NINDS and other NIH Institutes and Centers can be found using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies. RePORTER also includes links to publications and resources from these projects.
Information on tremor also is available from the following organizations:
International Essential Tremor Foundation
P.O. Box 14005
Lenexa, KS 66285-4005
14425 Coachway Drive
Centreville, VA 20120
National Ataxia Foundation
2600 Fernbrook Lane North, Suite 119
Minneapolis, MN 55447-4752
Tremor Action Network
P.O. Box 5013
Pleasanton, CA 94566-5013
"Tremor Fact Sheet", NINDS, Publication date May 2017. NIH Publication No. 17-4734.
Office of Communications and Public Liaison
National Institute of Neurological Disorders and Stroke
National Institutes of Health
Bethesda, MD 20892
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