Tremor is a rhythmic, involuntary, smooth oscillation of a body part. Tremors can occur alone or as a symptom of another disorder such as Parkinson's disease. Tremors are not to be confused with tics, which are rapid, involuntary movements of the body. All true tremors are greatly reduced or disappear altogether during sleep.
Tremors are classified into three categories: intention tremors, rest tremors, and postural (or physiological) tremors. Intention tremors occur when a person makes a purposeful movement, such as reaching for a glass. The tremor subsides when the movement ceases. Rest tremors, which are characteristic of Parkinson's disease, occur while the body is at rest, and disappear when the person moves. Postural tremors occur when the limbs are outstretched.
Tremors that usually begin in early adulthood, slowly become more pronounced, and have no known cause are called essential tremors. Essential tremors are postural tremors that can occur at any age, and may become progressively more severe with time. Over half of essential tremor cases are inherited. While essential tremors usually remain mild and do not indicate serious disease, they can become a nuisance, as handwriting and utensil use can be affected. Essential tremors usually stop when the arms or legs are resting, but become obvious when the limbs are outstretched or held in uncomfortable positions. These tremors usually affect one side of the body more than the other, but may involve both sides of the body. If the vocal cords are affected, the voice will shake and quiver. Drinking alcohol reduces the severity of the tremor, but leads to rebound tremors.
Senile tremors are essential tremors that begin in old age. Familial tremors are essential tremors that occur in families.
Over 50% of essential tremors are hereditary. The remaining essential tremors have no known cause. Up to half of essential tremors are inherited as autosomal dominant disorders. This means that the gene for tremor is located on a chromosome other than the sex chromosomes, and that if a parent has the gene for tremor, there is at least a 50% chance that a child of that parent will develop a tremor as well.
A person's tremor, however, can vary in type and severity from that of an affected parent, and may affect different parts of the body.
Some tremors occur as a result of other diseases, and are called symptomatic tremors. Diseases such as Parkinson's disease, Wilson's disease, and peripheral neuropathy may cause symptomatic tremors. Multiple sclerosis, chronic alcoholism, cerebellar damage, or stroke are other conditions that can also cause tremor.
Some tremors have no known origin. Tremors with no known origin are called idiopathic tremors, and include postural tremors and task-specific tremors.
Classic symptoms of tremors include rhythmic shaking of the head, hands, legs, or trunk Table 01. Rhythmic shaking often results in loss of manual dexterity or clumsiness. Voice tremors give speech a shaky, quivering quality. Other symptoms include slow voluntary movements and unsteadiness or shaking legs while standing.
Tremors are categorized according to their symptoms Table 02. Tremors vary according to their speed, severity, frequency, and whether they occur while resting or during directed movement. Substances such as caffeine may exacerbate postural tremors.
Table 1. Characteristics of Tremors
Slow, rhythmic movements involving the fingers, hands, arms, legs, head, or trunk. Onset of early adulthood, but occasionally later adulthood. Quivering or shaky voice Difficulty writing or handling utensils Symptoms occur only at rest and stop during movement, or only during movement and stop at rest Symptoms become milder or disappear after consuming alcohol Symptoms exacerbated by stressful situations, such as before speaking in front of a crowd
Table 2. Tremor Classifications
Enhanced physiologic tremor Essential tremor Intention tremor Rest tremor Fine tremors with a frequency of 8 to 12 HzOccurs during movement or when holding a fixed position (postural tremor)Does not normally produce symptomsMovement may not be apparent until it is exaggerated by anxiety, coffee consumption, hyperthyroidism, or drugs such as lithium and tricyclic antidepressantsAmplitude and frequency vary among different people and within same person at different times Occurs on both sides of bodyOccurs during movement or when holding a fixed position (postural tremor)Often involves the head and voice, and can involve the hands, legs, or trunk.Can occur in the absence of stimuliApproximately half are inherited, and half are sporadicConsumption of alcohol can reduce these tremorsTremors are most noticeable when head or hands are held outstretched against gravity, and least prominent at restTremors can be exacerbated by tasks requiring precision, such as writing Large, irregular, and slow tremors of 2-4 HzOccur when person makes a purposeful motionCan be caused by damage to the cerebellum Usually associated with Parkinson's diseaseTremor in a relaxed, supported limb, usually beginning in the fingers and later involving the arms and legsInvolves a characteristic ?pill-rolling? movementParkinsonian tremor is slow, approximately 3-8 Hz, and can be suppressed by voluntary movement
Having a family history of tremor puts you at risk for developing a tremor yourself. Essential tremors can cluster in families, and when they do, are called familial tremors. Up to 50% of essential tremors are inherited disorders.
Certain underlying diseases cause tremor. Neurological diseases such as Parkinson's disease, multiple sclerosis, chronic alcoholism, cerebellar damage, or stroke can all cause tremor. Parkinson's disease is characterized by rest tremors, whereas multiple sclerosis, chronic alcoholism, stroke, and cerebellar damage cause intention tremors.
As rest tremors and essential tremors require different treatment and have different outcomes, your doctor will take a careful history to determine the cause of your tremor. Your doctor will ask if your tremor occurs while you are resting or while you are moving purposefully. The doctor will also want to know if your tremor lessens when you drink alcohol, or if it becomes worse when you consume caffeine. Tell your doctor if you have a family history of tremor, as up to half of essential tremors are inherited disorders. In addition, tell your doctor about other conditions you may have (i.e. Parkinson's or multiple sclerosis) or about any medications you are taking that may be causing your tremor. Your doctor will also want to know where your tremor occurs, and if you also have problems with muscle stiffness, sluggishness, depression, clumsiness, handwriting changes, or sleep disturbances
Your doctor will perform a physical examination to help determine the cause of your tremor. Your doctor will watch for tremor while you are resting and while engaged in purposeful movement, and will note the location of your tremor. The doctor will also make note of the frequency and severity of your tremor.
Examining your feet and hands for sensory loss, atrophy and weakness, or decreased reflexes can help the doctor determine if another disease such as multiple sclerosis or peripheral neuropathy is causing your tremor.
Other signs, such as fluttering eyes, slurred speech, or coordination problems will indicate to your doctor that your tremor may be caused by cerebellar damage.
An electromyogram (EMG) test may be used to reveal which muscle groups are working to make a particular movement occur. For example, the EMG of a Parkinsonian tremor would show alternating movement of opposing muscle groups.
Your doctor may run blood tests to help uncover the cause of tremor. Abnormal levels of glucose, thyroid-stimulating hormone (TSH), cortisol, calcium, or sodium in the blood can cause tremor. In addition, drugs like lithium and theophylline, or certain heavy metals can also cause tremor. These elements can also be detected with a blood test.
An MRI test can help determine if your tremor is a result of a structural defect in the brain. An MRI can detect tumors, abscesses, or trauma from an injury, all of which can cause tremor.
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