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What are the different categories of tremor?
Tremor is most commonly classified by its appearance and cause or origin. Some of the better-known forms of tremor, with their symptoms, include the following:
Essential tremor (sometimes called benign essential tremor) is the most common of the forms of abnormal tremor. Although the tremor may be mild and nonprogressive in some people over a long period of time, in others, the tremor is slowly progressive, starting on one side of the body but affecting both sides within a few years. The hands are most often affected but the head, voice, tongue, legs, and trunk may also be involved, typically to a lesser extend than the hands. Tremor of the hands is typically present as an action tremor. 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. A variant in the gene LINGO1 has been identified as a risk gene, although not all individuals with essential tremor carry this variant--which also can be present in people without essential tremor. While essential tremor was thought not to be associated with any known pathology over many years, recent studies suggest that there is a mild degeneration of certain parts of the cerebellum in individuals with essential tremor.
Parkinsonian tremor is caused by damage to structures within the brain that control movement. This tremor, which appears characteristically as a resting tremor, can occur as an isolated symptom or be seen in other disorders and is often the first symptom of 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.
Dystonic tremor occurs in individuals of all ages who are affected by dystonia, a movement disorder in which sustained involuntary muscle contractions cause twisting and repetitive motions and/or painful and abnormal postures or positions, such as twisting of the neck (torticollis) or writer's cramp. 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. The tremor may be the initial sign of dystonia localized to a particular part of the body.
Cerebellar tremor is a slow tremor of the extremities that occurs at the end of a purposeful movement (intention tremor), 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 dysarthria (speech problems), nystagmus (rapid involuntary movements of the eyes), gait problems, and postural tremor of the trunk and neck.
Psychogenic tremor (also called functional tremor) can appear as any form of tremor 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 individual is being distracted. Many indviduals with psychogenic tremor have a conversion disorder (defined as a psychological disorder that produces physical symptoms) or another psychiatric disease.
Orthostatic tremor is characterized by rhythmic muscle contractions that occur in the legs and trunk immediately after standing. The person typically perceives orthostatic tremor as unsteadiness rather than actual tremor. Because of its high tremor frequency, often the tremor cannot be seen, but sometimes be heard when putting a stethoscope to the thigh muscles. No other clinical signs or symptoms are present and the unsteadiness ceases when the individual sits, is lifted off the ground, or starts walking.
Physiologic tremor occurs in every normal individual. 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, alcohol withdrawal, caffeine, or fever. It can occur 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.
Tremor can result from other conditions as well. Alcoholism, excessive alcohol consumption, or alcohol withdrawal can kill certain nerve cells, resulting in tremor, especially in the hand. (Conversely, small amounts of alcohol may even help to decrease essential tremor, but the mechanism behind this is unknown. Doctors may use small amounts of alcohol to aid in the diagnosis of certain forms of tremor but not as a regular treatment for the condition.) 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 individuals with essential tremor.