Essential tremor

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Essential tremor
ICD-10 G25.0
ICD-9 333.1
OMIM 190300 602134
MedlinePlus 000762
MeSH D020329

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

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 exact incidence is unknown, but it is presumed to be the most common type of tremor and also the most commonly observed movement disorder. 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.

Cause

Half of the cases are due to gene mutation and transmitted dominantly. There are two main loci: ETM1 and ETM2.[1] The rest are idiopathic. No identifiable and consistent structural abnormality has yet been demonstrated to exist in the nervous system of every person with ET.

A French kindred study found that the Ser9Gly variant of the dopamine receptor D3 (DRD3) was strongly associated with ET in 23 out of 30 families studied.[2]

Diagnosis

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, though it's most commonly seen in the hands and arms and slightly less commonly in the neck (causing the patient's head to shake), eyelids, larynx, tongue, trunk, and legs. A resting tremor of the hands is sometimes present.

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 disorders.

Symptoms

Essential tremor (ET) generally presents as a rhythmic tremor (4-12Hz) 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 psychosomatic origin. 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. Tremor intensity can otherwise worsen in response to fatigue, strong emotions, low blood sugar, cold, caffeine, lithium salts, some antidepressants or other factors.

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.

ET is usually painless, although in some cases tremor of the head or neck causes 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.

Sometimes people with ET develop a raspy speaking voice while their ET symptoms worsen over time. When this dysphonia occurs, it is true even in cases where the person's tremor symptoms were first noticeable during early childhood and, so, is unlikely to be related to commonplace reductions in quality that can gradually affect the speaking voices of some elderly people.

People with ET often report a progressive decline in their sense of balance and their fine motor skills.

ET is clearly progressive in most cases (sometimes rapidly, sometimes very slowly), and can be disabling, but significant disability is rare.

Treatment

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, thalamotomy, pallidotomy, and deep brain stimulation – the insertion of a brain pacemaker.

The two medications that are prescribed most commonly for control of ET symptoms are the anticonvulsant Primidone (Mysoline) and the beta-blocker propranolol (Inderal).

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.

Other potential sources of tremor (excessive caffeine consumption, recreational drug use, medications, hyperthyroidism) should be excluded if possible

Support groups

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.

Help with Technology

Tunic Software has released software to help people with essential tremor, Parkinson's Disease, and other causes of hand tremor control their computer mouse. Called 'MouseCage', the software automatically smooths mouse cursor motion to reduce the effects of unsteady or shaky hands.- anti-tremor mouse software

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 for tremor severity right on the device.

IBM also offer a free smoothing mouse driver for windows 2000 and XP which uses the same technology that helps steady the image in a hand held camcorder. See http://www.alphaworks.ibm.com/tech/mousesmoothing

Another option is http://www.steadymouse.com/about/

Other tools have also been adapted for people with tremors; for example, eating utensils which are weighted to help damp out tremor.

References

  1. Kovach M, Ruiz J, Kimonis K; et al. (2001). "Genetic heterogeneity in autosomal dominant essential tremor". Genet Med. 3 (3): 197–9. PMID 11388761.
  2. Jeanneteau F, Funalot B, Jankovic J; et al. (2006). "A functional variant of the dopamine D3 receptor is associated with risk and age-at-onset of essential tremor". Proc Natl Acad Sci U S A. 103 (28): 10753&ndash, 8. PMID 16809426.

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