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Essential tremor

Essential tremor is a neurological disorder characterized by shaking of hands (and sometimes other parts of the body including the head), evoked by intentional movements. The incidence is unknown, but is estimated to be as common as one person in 20, and it is the most common type of tremor and also the most commonly observed movement disorder.

Essential tremor (ET) generally presents as a rhythmic tremor (4-12 Hz) that is present only when the affected muscle is exerting effort (i.e., it is not present at rest). Any sort of physical or mental stress will tend to make the tremor worse, often creating the false impression that the tremor is of somatic origin. It is typical for the tremor to be worse in "performance" situations, such as when making out a check at a checkout stand. This is due to the increased stress in such situations.

Essential tremor is often found in more than one member of a family (familial tremor), in which case it is usually dominant in inheritance, or it may occur with no family history. The tremor may start as any age, from birth through advanced ages (senile tremor). Any voluntary muscle in the body may be affected, though it's most commonly seen in the hands and arms and slightly less commonly in the larynx, tongue and eyelids. A resting tremor is sometimes present, despite the common misunderstanding that a resting tremor is proof of Parkinson's Disease. ET is usually painless, although in some cases tremor of the head or neck may cause pain, and writing can become painful quickly for a person with hand tremors who grips a pen tightly in a struggle to maintain control over penmanship.

The cause of the disease is unknown (idiopathic), and there is no identifiable structural abnormality in the nervous system of the those who are affected, although prominent researchers including Elan D. Louis are searching actively for neurochemical and brain structure abnormalities that might be commonplace among people with ET. Usually the diagnosis is established on clinical grounds, but when suspicion exists, other diseases causing tremor (excessive caffeine consumption, drugs, hyperthyroidism) should be excluded. The tremors can worsen in response to fatigue, strong emotions, hunger, cold, or other factors and may lessen with alcohol. However, using small amounts of alcohol for treatment may cause alcohol addiction.

There is ongoing controversy as to whether ET is related to Parkinson's disease and whether essential tremor should properly be considered a kind of parkinsonism. Although some statistics seem to indicate that there is an increased chance of developing Parkinson's for people with ET, this statistical finding may be due to people with Parkinson's being initially misdiagnosed with ET. Members of a family known as the "Iowa Kindred" develop either parkinsonism or symptoms that are indistinguishable from ET; their pattern of inheritance is associated with PARK4.

ET does sometimes occur in combination with other neurological disorders such as dystonia and benign fasciculation syndrome. However, there is no clear evidence that having ET predisposes a person to one of these diseases. Conflicting research results have so far made it difficult for medical researchers to say with certainty that people with ET are more likely than the general population to experience hearing loss and a reduction or complete loss of olfaction, among a wide assortment of other non-tremor symptoms, but it is commonly assumed among researchers that tremors are not the only symptom of ET.

While ET may be progressive (sometimes rapidly, sometimes very slowly), and can in severe cases be disabling, it is not life-threatening and does not appear to shorten lifespan. (Some research suggests that people with ET actually live longer than average.) In disabling cases, ET can interfere with a person's ability to perform tasks of daily living, including feeding, dressing, and activities of personal hygeine.

Treatment of ET may or may not be attempted, depending on the severity of the tremor and the physical and social handicaps that implies. Drug treatment may include tranquilizers, beta-blockers, and antiepileptic drugs. Surgical treatments (which are generally reserved for the most severe cases) include botulism toxin injections into the affected muscles, thalotomy , and deep brain stimulation – the insertion of a "pacemaker" into the brain.

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