|Classification and external resources|
Essential tremor (ET) is a progressive neurological disorder whose most recognizable feature is a tremor of the arms that is apparent during voluntary movements such as eating and writing. This type of tremor is often referred to as "kinetic tremor." The tremor may also occur in the head (neck), jaw and voice as well as other body regions, with the general pattern being that the tremor begins in the arms and then spreads to these other regions in selected patients. Women are more likely to develop the head tremor than are men. Other types of tremor may also occur, including postural tremor of the outstretched arms, intentional tremor of the arms and rest tremor in the arms. Some patients may have unsteadiness and problems with gait and balance that are above and beyond that due to normal aging. In addition to these motor problems, a variety of non-motor features have recently been linked with ET. These include anxiety and depressive symptoms as well as cognitive difficulty. Recent studies have demonstrated that old-onset ET (onset > age 65) may be associated with an increased risk of developing dementia. ET is one of the most common neurological diseases, with a prevalence of approximately 4% in persons age 40 and older and considerably higher among persons in their 60s, 70s, 80s, and 90s. Aside from enhanced physiological tremor, it is the most common type of tremor and one of the most commonly observed movement disorders. Essential tremor was also previously known as "benign essential tremor", but the adjective "benign" has been removed in recognition of the sometimes disabling nature of the disorder. Although often mild, patients with severe tremor have difficulty performing many of their routine activities of daily living.
The underlying etiology is not clear but many cases seem to be familial. It has been estimated that approximately one-half of the cases are due to a genetic mutation and the pattern of inheritance is most consistent with autosomal dominant transmission. As of yet, no genes have been identified but genetic linkage has been established with several chromosomal regions. A number of environmental factors, including toxins, are also under active investigation and these may play a role in disease etiology. In terms of pathophysiology, clinical, physiological and imaging studies point to an involvement of the cerebellum and/or cerebellothalamocortical circuits. Recent postmortem studies have demonstrated the presence of degenerative changes in the ET brain, with these changes including Purkinje cell axonal swellings and Purkinje cell loss in the majority of cases and brainstem Lewy bodies in the remainder. These studies suggest that the disease is both heterogeneous and degenerative. In other words, ET might be a family of degenerative diseases rather than a single disease.
Usually the diagnosis is established on clinical grounds. Tremors can start at any age, from birth through advanced ages (senile tremor). Any voluntary muscle in the body may be affected, although the tremor is most commonly seen in the hands and arms and slightly less commonly in the neck (causing the patient's head to shake), tongue, and legs. A resting tremor of the hands is sometimes present.
ET does sometimes occur in combination with other neurological disorders such as dystonia. In addition, there may be a link between ET and Parkinson's disease, with one study showing ET patients having an approximately 4 times greater likelihood of developing Parkinson's disease.
Essential tremor generally presents as a rhythmic tremor (4–12 Hz) that is present only when the affected muscle is exerting effort (in other words, 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 psychosomatic origin.
Tremor intensity can worsen in response to fatigue, strong emotions, low blood sugar, cold, caffeine, lithium salts, some antidepressants or other factors. It is typical for the tremor to worsen in "performance" situations, such as when making out a check at a checkout stand.
ET-related tremors do not occur during sleep, but patients sometimes complain of an especially coarse tremor upon awakening that becomes noticeably less coarse within the first few minutes of wakefulness.
In mild cases, ET can manifest as the inability to stop the tongue or hands from shaking, the ability to only sing in vibrato, and difficulty to do small precise tasks such as threading a needle. In disabling cases, ET can interfere with a person's ability to perform tasks of daily living, including feeding, dressing, and activities of personal hygiene.
Drug treatment may include tranquilizers, beta-blockers, or antiepileptic drugs. Surgical treatments (which are generally reserved for the most severe cases) include thalamotomy and deep brain stimulation. A trial of the benzodiazepine-anticonvulsant Clonazepam (Klonopin, Rivotril) was found not to be an effective treatment; however, it is still recommended in some cases .
The two medications that are prescribed most commonly for control of ET symptoms are the anticonvulsant Primidone (Mysoline) and the beta-blocker propranolol (Inderal). Self medication with small amounts of alcohol has been shown to give short term relief from tremor.
Minor cases of ET can be treated with physical therapy and development of the muscles in the sections of the body that are severe in their shaking.
The International Essential Tremor Foundation (IETF) provides information, services and support to individuals and families affected by essential tremor (ET). The organization encourages and promotes research in an effort to determine the causes, treatment and ultimately the cure for ET. The IETF is a worldwide organization dedicated to meeting the needs of those whose daily lives are challenged by ET. IETF, an international non-profit 501(c)(3) organization that derives its support entirely from its membership and the general public, was founded in 1988 and is guided by a board of directors and a medical advisory council. The organization's membership consists of patients, physicians, educators, parents, relatives and volunteers who provide education, community services and funding to help support tremor research.
The National Tremor Foundation(NTF), founded in 1992, is a British friendly organisation based in Essex, England, an affiliate of the International Tremor Foundation, which was founded in 1988. The organisation's primary work is production of a quarterly informational newsletter. The NTF also maintains a list of ITF medical advisors, and facilitates the formation of self-help groups. NTF was granted charitable status in 1994.
Tunic Software has released software to help people with essential tremor, Parkinson's disease, and other causes of hand tremor control their computer mouse. The software, MouseCage, automatically smooths mouse cursor motion to reduce the effects of unsteady or shaky hands.
IBM created a peripheral device that filters out tremoring movements of the hand. The hardware adapter, termed AMA, is connected between the computer and the input device. It is switched on or off and adjusted on the device for tremor severity.
Other tools have also been adapted for people with tremors; for example, eating utensils which are weighted to help damp out tremor.