All people have some degree of tremor during movement. This shaking normally involves mainly the hands. Stress, fatigue, anger, fear, caffeine, and cigarettes may temporarily worsen this type of tremor to the point that it becomes visible to the naked eye. Essential tremor is the most common form of abnormal tremor. It resembles an exaggerated shaking. Essential tremor is worsened by the same factors that enhance normal tremors. Although the cause is unknown, new research shows that one part of the brain, called the cerebellum, does not appear to function properly in patients with essential tremor. The cerebellum is the part of the brain that coordinates muscle movements and provides accuracy and harmony to voluntary movement. Nevertheless, no brain lesions have been identified in patients with this form of tremor. There is evidence of several different types of essential tremor (such as young-onset essential tremor or essential tremor with head tremor). These types differ in their response to treatment. If an essential tremor occurs in more than one member of a family, it is called a familial tremor. It appears that essential tremor has some genetic basis, not only because of the hereditary pattern observed in some families, but also because an identical twin (who shares the same genes) of a person with essential tremor is twice as likely as a fraternal twin (who has different genes) to have essential tremor. Since some identical twins do not share this condition, environmental factors must play a role as well. Essential tremors can occur at any age but are most common in people older than 65. Essential tremor is a relatively benign condition, affecting movement or voice quality, but with no other effects. It involves a rhythmic, moderately rapid tremor of voluntary muscles. Purposeful movements may make the tremors worse, while avoiding hand movements may suppress the tremors completely. There may be difficulty holding or using small objects (such as silverware or writing utensils). Over time, the tremors may affect the hands, arms, head, voice box, eyelids, or other muscles. An essential tremor rarely involves the legs or feet. It may start in one body part but can progress to include other parts.
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