Tremor is an unintentional, somewhat rhythmic, involuntary muscle movement involving to-and-fro movements (oscillations) of one or more parts of the body.
Tremor is generally caused by problems in parts of the brain or spinal cord that control muscles throughout the body or in particular areas, such as the hands. Neurological disorders or conditions that can produce tremor include multiple sclerosis, stroke, traumatic brain injury and neurodegenerative diseases that damage or destroy parts of the brainstem or the cerebellum. Other causes include the use of some drugs (such as corticosteroids, and drugs used for certain psychiatric disorders), alcohol abuse or withdrawal, mercury poisoning, liver failure.
Some of the more common forms of tremor, with their symptoms, include the following.
Essential tremor (sometimes called benign essential tremor) is the most common of the more than 20 types of tremor. Although the tremor may be mild and nonprogressive in some people, in others, the tremor is slowly progressive, starting on one side of the body but affecting both sides within 3 years. The hands are most often affected but the head, voice, tongue, legs, and trunk may also be involved. Head tremor may be seen as a “yes-yes” or “no-no” motion. Essential tremor may be accompanied by mild gait disturbance. Tremor frequency 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 tremors and/or increase their severity. Onset is most common after age 40, although symptoms can appear at any age. It may occur in more than one family member. Children of a parent who has essential tremor have a 50 percent chance of inheriting the condition. Essential tremor is not associated with any known pathology.
Parkinsonian tremor is caused by damage to structures within the brain that control movement. This resting tremor, which can occur as an isolated symptom or be seen in other disorders, is often a precursor to Parkinson's disease (more than 25 percent of patients with Parkinson's disease have an associated action tremor). The tremor, which is classically seen as a “pill-rolling” action of the hands that may also affect the chin, lips, legs, and trunk, can be markedly increased by stress or emotions. Onset of parkinsonian tremor is generally after age 60. Movement starts in one limb or on one side of the body and usually progresses to include the other side.
Parkinsonian tremor can also be due to drugs, such as anti-psychotics, that have anti-dopaminergic actions.
Dystonic tremor is the second most common (after Parkinsonian) tremor to be misdiagnosed as essential tremor. It is characterized by a "nonrhythmic tremor that was restricted to the body region affected by dystonia". Dystonic tremor may affect any muscle in the body and is seen most often when the patient is in a certain position or moves a certain way. The pattern of dystonic tremor may differ from essential tremor. Dystonic tremors occur irregularly and often can be relieved by complete rest. Touching the affected body part or muscle may reduce tremor severity (a geste antagoniste). The tremor may be the initial sign of dystonia localized to a particular part of the body.
Cerebellar tremor (also known as "intention tremor") is a slow, broad tremor of the extremities that occurs at the end of a purposeful movement, such as trying to press a button or touching a finger to the tip of one’s nose. Cerebellar tremor is caused by lesions in or damage to the cerebellum resulting from stroke, tumor, or disease such as multiple sclerosis or some inherited degenerative disorder. It can also result from chronic alcoholism or overuse of some medicines. In classic cerebellar tremor, a lesion on one side of the brain produces a tremor in that same side of the body that worsens with directed movement. Cerebellar damage can also produce a "wing-beating" type of tremor called rubral or Holmes' tremor — a combination of rest, action, and postural tremors. The tremor is often most prominent when the affected person is active or is maintaining a particular posture. Cerebellar tremor may be accompanied by other manifestations of ataxia, including dysarthria (speech problems), nystagmus (rapid, involuntary rolling of the eyes), gait problems and postural tremor of the trunk and neck.
Physiologic tremor occurs in every normal individual and has no clinical significance. It is rarely visible to the eye and may be heightened by strong emotion (such as anxiety or fear), physical exhaustion, hypoglycemia, hyperthyroidism, heavy metal poisoning, stimulants (amphetamines and caffeine), alcohol withdrawal or fever. It can be seen in all voluntary muscle groups and can be detected by extending the arms and placing a piece of paper on top of the hands. Enhanced physiologic tremor is a strengthening of physiologic tremor to more visible levels. 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.
- Psychogenic tremor (also called hysterical tremor) can occur at rest or during postural or kinetic movement. The characteristics of this kind of tremor may vary but generally include sudden onset and remission, increased incidence with stress, change in tremor direction and/or body part affected, and greatly decreased or disappearing tremor activity when the patient is distracted. Many patients with psychogenic tremor have a conversion disorder or another psychiatric disease.
- Rubral tremor is characterized by coarse slow tremor which is present at rest, at posture and with intention. This tremor is associated with conditions which affect the red nucleus in the midbrain, classically unusual strokes.
Tremor can result from other conditions as well. Alcoholism, excessive alcohol consumption, or alcohol withdrawal can kill certain nerve cells, resulting a tremor known as asterixis. Conversely, small amounts of alcohol may help to decrease familial and essential tremor, but the mechanism behind this is unknown. Tremor in peripheral neuropathy may occur when the nerves that supply the body’s muscles are traumatized by injury, disease, abnormality in the central nervous system, or as the result of systemic illnesses. Peripheral neuropathy can affect the whole body or certain areas, such as the hands, and may be progressive. Resulting sensory loss may be seen as a tremor or ataxia (inability to coordinate voluntary muscle movement) of the affected limbs and problems with gait and balance. Clinical characteristics may be similar to those seen in patients with essential tremor.
Distinguishing different types of tremor is very difficult. One third of patients referred for neurological evaluation may have been incorrectly diagnosed by their referring doctor. Diagnostic criteria have been proposed for essential tremor and for Parksonson's Disease. Regarding Parkinson's Disease, appropromately 75% of patients with this diagnosis do not have confirmatory findings at autopsy.
The degree of tremor should be assessed in four positions. The tremor can then be classified by which position most accentuates the tremor:  Only about 75% of patients diagnosed with Parkinson's disease have confirmatory findings at autopsy.
|At rest||Resting tremors||Tremors that are worse at rest include Parkinsonian syndromes and essential tremor if severe. This includes drug-induced tremors from blockers of dopamine receptors such as haloperidol and other antipsychotic drugs.|
|During contraction (eg a tight fist while the arm is resting and supported)||Contraction tremors||Tremors that are worse during supported contraction include essential tremor and also cerebellar and exaggerated physiologic tremors such as a hyperadrenergic state or hyperthyroidism. Drugs such as adrenergics, anti-cholinergics, and xanthines can exaggerate physiologic tremor.|
|During posture (eg with the arms elevated against gravity such as in a 'bird-wing' position)||Posture tremors||Tremors that are worse with posture against gravity include essential tremor and exaggerated physiologic tremors.|
|During intention (eg finger to nose test)||Intention tremors||Intention tremors are tremors that are worse at during intention and the patient's finger approaches a target include cerebellar disorders.|
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:
- Parkinsonian tremor drug treatment involves levodopa and/or dopamine-like drugs such as pergolide mesylate, bromocriptine mesylate and ropinirole. Other drugs used to lessen parkinsonian tremor include amantadine hydrochloride and anticholinergic drugs.
- Essential tremor may be treated with propranolol, nadolol or other beta blockers and primidone, an anticonvulsant drug.
- Cerebellar tremor typically does not respond to medical treatment.
- Rubral tremor patients may receive some relief using levodopa or anticholinergic drugs.
- Dystonic tremor may respond to Valium, anticholinergic drugs, and intramuscular injections of botulinum toxin. Botulinum toxin is also prescribed to treat voice and head tremors and several movement disorders.
- Enhanced physiologic tremor is usually reversible once the cause is corrected. If symptomatic treatment is needed, beta blockers can be used.
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. A physical therapist will evaluate the patient for tremor positioning, muscle control, muscle strength, and functional skills. Teaching the patient to brace the affected limb during the tremor or to hold an affected arm close to the body is sometimes useful in gaining motion control. Coordination and balancing exercises may help some patients. Some therapists recommend the use of weights, splints, other adaptive equipment, and special plates and utensils for eating.
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.
Thalamotomy, involving the creation of lesions in the brain region called the thalamus, is quite effective in treating patients with essential, cerebellar, or parkinsonian tremor. This in-hospital procedure is performed under local anesthesia, with the patient awake. After the patient’s head is secured in a metal frame, the surgeon maps the patient’s brain to locate the thalamus. A small hole is drilled through the skull and a temperature-controlled electrode is inserted into the thalamus. A low-frequency current is passed through the electrode to activate the tremor and to confirm proper placement. Once the site has been confirmed, the electrode is heated to create a temporary lesion. Testing is done to examine speech, language, coordination, and tremor activation, if any. If no problems occur, the probe is again heated to create a 3-mm permanent lesion. The probe, when cooled to body temperature, is withdrawn and the skull hole is covered. The lesion causes the tremor to permanently disappear without disrupting sensory or motor control.
Deep brain stimulation (DBS) uses implantable electrodes to send high-frequency electrical signals to the thalamus. The electrodes are implanted as described above. The patient uses a hand-held magnet to turn on and turn off a pulse generator that is surgically implanted under the skin. The electrical stimulation temporarily disables the tremor and can be “reversed,” if necessary, by turning off the implanted electrode. Batteries in the generator last about 5 years and can be replaced surgically. DBS is currently used to treat parkinsonian tremor and essential tremor.
The most common side effects of tremor surgery include dysarthria (problems with motor control of speech), temporary or permanent cognitive impairment (including visual and learning difficulties), and problems with balance.
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