Essential tremor is the most common movement disorder; its cause is unknown.
It typically involves a tremor of the arms, hands or fingers but sometimes involving the
head or other body parts during voluntary movements such as eating and writing.
It is distinct from Parkinson's disease—and often misdiagnosed as such—although some
individuals have both conditions.
Essential tremor is commonly described as an action tremor rather than a resting tremor;
rigidity, such as is seen in Parkinson’s, is usually not included among its symptoms.
Classification This type of tremor is often referred to as
"kinetic tremor".
Essential tremor has been known as "benign essential tremor", but the adjective "benign"
has been removed in recognition of the sometimes disabling nature of the disorder.
Signs and symptoms In mild cases, ET can manifest as the inability
to stop the tongue or hands from shaking, the ability to sing only in vibrato, and difficulty
to do small precise tasks such as threading a needle.
Even simple tasks like cutting in a straight line or using a ruler can range from difficult
to impossible, depending on the severity of the condition.
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.
Essential tremor generally presents as a rhythmic tremor that occurs only when the affected
muscle is exerting effort.
Any sort of physical or mental stress will tend to make the tremor worse.
The tremor may also occur in the head, 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.
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 and disease activity/intensity can worsen in response to fatigue, strong emotions,
low blood sugar, cold and heat, caffeine, lithium salts, some antidepressants, and other
factors.
It is typical for the tremor to worsen in "performance" situations, such as when writing
a check for payment at a store or giving a presentation.
Parkinson's Disease and Parkinsonism can also occur simultaneously with ET.
In those cases the degree of tremor, rigidity, and functional disability does not differ
from those people with idiopathic Parkinson's Disease.
Hand tremor predominates, and occurs in nearly all cases, followed by head tremor, voice
tremor, neck, face, leg, tongue and trunk tremor.
Most other tremors occur in association with hand tremor.
Walking difficulties in Essential Tremor are common.
About half of patients have associated dystonia, including cervical dystonia, writer's cramp,
spasmodic dysphonia, and cranial dystonia, and 20% of the patients had associated parkinsonism.
Olfactory dysfunction is common in Parkinson’s Disease, and has also been reported to occur
in patients with Essential Tremor.
A number of patients with essential tremor also exhibit many of the same neuropsychiatric
disturbances seen in idiopathic Parkinson's disease.
Cause The underlying etiology of essential tremor
is not clear but many cases seem to be familial.
Approximately one-half of the cases are due to a genetic mutation and the pattern of inheritance
is most consistent with autosomal dominant transmission.
No genes have been identified yet but genetic linkage has been established with several
chromosomal regions.
A number of environmental factors, including toxins, are also under active investigation
as they may play a role in the disease's etiology.
In terms of pathophysiology, clinical, physiological and imaging studies point to an involvement
of the cerebellum and/or cerebellothalamocortical circuits.
Changes in the cerebellum could also be mediated by alcoholic beverage consumption.
Purkinje cells are especially susceptible to ethanol excitotoxicity.
Impairment of Purkinje synapses is a component of cerebellar degradation that could underlie
essential tremor.
Recent post mortem studies have evidenced alterations in LINGO and GABA receptors in
the cerebellum of people with essential tremor.
Diagnosis Usually the diagnosis is established on clinical
grounds.
Tremors can start at any age, from birth through advanced ages.
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, tongue, and legs.
A resting tremor of the hands is sometimes present.
Tremor occurring in the legs might be diagnosable as Orthostatic Tremor.
ET does not usually occur in combination with other neurological disorders; it is thought
to be a mono-symptomatic disease.
Treatment Not all individuals with ET require treatment,
but there are many treatment options depending on symptom severity.
Caffeine and stress should be avoided, and good sleep is recommended.
When symptoms are sufficiently troublesome to warrant treatment, the first medication
choices are beta blockers such as propranolol or alternately, nadolol and timolol.
Atenolol and pindolol are not effective for tremor.
The anti-epileptic primidone is also effective for ET.
Second-line or third-line medications can be added if the first-line medications do
not control the tremor.
Second-line medications are the anti-epileptics topiramate, gabapentin and levetiracetam,
or benzodiazepines like alprazolam.
Third-line medications are clozapine and mirtazapine.
When medications do not control the tremor or the patient does not tolerate medication,
botulinum toxin, high intensity focused ultrasound, or deep brain stimulation may be considered.
Occupational therapy can be helpful.
The electrodes for deep brain stimulation are usually placed in the "tremor center"
of the brain, the ventral intermediate nucleus of the thalamus.
Prognosis Although essential tremor is often mild, patients
with severe tremor have difficulty performing many of their routine activities of daily
living.
ET is generally progressive in most cases, and can be disabling in severe cases.
Epidemiology 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.
Society and culture The actress Katharine Hepburn had an essential
tremor, which she inherited from her grandfather, that caused her head—and sometimes her hands—to
shake.
According to Dickens, the tremor was noticeable by the time of her performance in the 1979
film The Corn is Green, when critics mentioned the "palsy that kept her head trembling".
Hepburn's tremor worsened in the 1980s, when she was in her 70s to 80s.
Research directions Harmaline is a widely used model of essential
tremor in rodents.
Harmaline is thought to act primarily on neurons in the inferior olive.
Olivocerebellar neurons exhibit rhythmic excitatory action when harmaline is applied locally.
References
External links Essential tremor at DMOZ