Essential tremor

# 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.

# Historic Perspective
The term essentieller Tremor (essential tremor) was first coined by Raymond (France, 1892). This term gained widespread use among neurologists during the second half of the 20th century to describe the familial cases of tremors.

# Classification
There is no system to classify essential tremor.

# Pathophysiology
The pathogenesis of essential tremor (ET) is not fully explained. There is a strong genetic component. It has an autosomal dominant pattern of inheritance, and almost 80% of patients have a family history of tremor.
The neuropathology of ET remains highly debatable, although some believe that it is localized to brainstem and cerebellum, it is a controversial theory.

# Cause
Half of the cases are due to gene mutation and transmitted dominantly. There are two main loci: ETM1 and ETM2. 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.

# Differential Diagnosis
The following table distinguishes ET from other major tremor disorders.

# Epidemilogy
ET is the most common form of action tremor, and has bimodal age at onset in the second and in the sixth decade of life. The prevalence is usually same for the both genders. The world-wide prevalence for all age is 1%.

# Risk Factors
1) Family history
2) Age: age above 40 is considered as a risk factor.

# Screening
There is no available screening test to diagnose ET.

# Natural History, Complications, and Prognosis

## Natural history
ET is a progressive disease, and it usually worsens gradually over time.

## Complications
Patients usually have psychological consequences such as anxiety and depression as they tend to avoid social events and stressful situations. Some patients usually have mild cognitive difficulties. It can affect activities of daily living such as holding tools/utensils and equipment, also writing can be significantly affected.

## Prognosis
The course of ET is usually stable, however, ET may be associated with an increased risk for developing Parkinson's disease.

# Diagnosis

## Diagnostic Criteria
The International Parkinson and Movement Disorder Society (IPMDS) task force defines ET by the following four features.
1) Isolated tremor of bilateral upper limb, without other motor abnormalities.
2) Duration: at least three years
3) Absence of other neurological signs.
4) With or without a tremor in other locations. (for example, tremors of arms, hands, or head)

## Symptoms

### Tremor Characteristics
The ET is a type of action tremor, which usually affects hands and arms. It often occurs asymmetrically and bilaterally. It can involve the face, voice, and trunk. The frequency of ET is 6-12 HZ.
Tremor is initiated by voluntary movements when arms are held in an outstretched position against gravity and is usually amplified by goal-directed movements such as drinking from a glass or finger-to-nose testing. Tremor is absent when the affected body part is fully relaxed and supported by gravity. 
Lower limb tremor is highly unusual in ET and often suggests Parkinson disease. Essential tremor (ET) generally presents as a rhythmic tremor (6-12Hz) 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.
It is often relieved by drinking alcohol. 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 tremors of the head or neck 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.
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 fine motor skills.

### Neurological signs
Sometimes individuals may show ataxia, abnormal gait, cognitive deficits, personality changes, and depression. ET affects the activities of daily living and quality of life.

## Physical Examiniation
The prominent symptom of ET is asymmetric, postural tremor affecting upper extremities. It can affect head and voice, but rarely lower extremities. Tone and reflexes are usually normal. The minority of patients may have difficulties with gait and balance.

## Laboratory findings
There is no signings lab abnormality seen in patients of ET. Routine lab tests such as Thyroid functions tests, electrolytes are done to rule out physiological tremor.

## Imaging
Structural brain imaging such as CT scan or MRI is not required in patients of ET.
Striatal dopamine transporter imaging single-photon emission computed tomography (SPECT; DaTscan) can be used to distinguish ET from parkinson disease, Lewy body dementia, and multiple system atrophy. It is usually normal in patients with ET, and it is not generally indicated to diagnose ET. However, it can be useful if it is difficult to differentiate ET from Parkinson's disease.

# 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 organization based in Essex, England, an affiliate of the International Tremor Foundation, which was founded in 1988.  The organization's primary work is the 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 offers 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 
Another option is /
Other tools have also been adapted for people with tremors; for example, eating utensils which are weighted to help damp out tremor.