A tremor is a fine shaking or vibratory involuntary movement of some part of the body. There are many causes, such as certain medications which cause tremor as a side-effect, or neurological disease. However, essential tremor (ET) is the most common condition in which this phenomenon occurs.
ET occurs in the absence of any other physiological condition. It may be progressive or non-progressive. In classic ET, 95% of patients have the upper limbs affected, the head in 34%, the lower limbs in 30%, the voice in 12%, the tongue, face, and trunk in only around 5%. Individuals with ET may have either a postural or kinetic tremor.
ET occurs in about 10 million people in the USA alone, but its estimated prevalence is likely to be grossly below the actual. This has many reasons, such as:
- The high rate of medication-induced tremor
- The low rate of self-reported personal or family history of tremor, with many patients and their families being genuinely unaware that they have a tremor
- Misdiagnosis, particularly as Parkinson disease or senile tremor
ET starts after the age of 40 years in the majority of cases, and commonly in people over 65 years. However, people of any age may develop ET.
It is passed on to the offspring in half of those affected, and more than one member of a family may then be affected. This is called familial essential tremor, and is inherited as a dominant trait. Both men and women have an equal incidence of ET.
The presence of ET may make routine tasks such as eating, writing or shaving difficult, as well as altering the normal gait.
Some conditions which provoke or worsen essential tremor include:
- Stress states
- Strong emotions
After a careful history is taken, the physician may ask about possible precipitating factors, such as:
- The use of tobacco or smokeless tobacco
- Alcohol withdrawal
- Overuse of caffeine
- Whether certain medicines are in use
- Existence of anxiety or stress
If any organic pathology is suspected following physical examination, the physician may advise some blood tests and brain scans.
Recent research suggests six criteria that may be obtained by neurophysiologic studies such as an electromyogram and accelerometry.
Since there is no identifiable cause for ET, it is difficult to suggest a cure. If the tremor is so violent as to disturb normal life, medications such as beta blockers may be prescribed. This includes propranolol. Side effects include bradycardia and impotence, besides orthostatic hypotension.
Another drug used to treat ET is the anticonvulsant primidone. It produces a higher initial incidence of adverse effects other than nausea and vomiting, which include ataxia, drowsiness, and vertigo.
Gabapentin is another drug which may reduce tremor in about a third of patients, and is usually free of major side effects.
Topiramate is an anticonvulsant which acts by blocking sodium channels, and also inhibits muscular excitation via GABA potentiation. Serious side effects such as anorexia and paresthesia give it a third-line status, along with the difficulty of reaching the acceptable dosage.
Other medications sometimes used in this condition include calcium-channel blockers such as nimodipine, antiepileptic drugs, and first level antidepressants such as alprazolam. They may induce dependence. Clozapine is a neuroleptic drug which has been used successfully, but can produce agranulocytosis. Pregabalin has also begun to be studied in this condition.
Symptoms may be relieved or alleviated if the patient avoids trigger factors such as caffeine and other stimulants.
Some patients may find it helpful to undergo physical and occupational therapy, which improves the muscle coordination and muscular control.
Finally, a specialized treatment called deep brain stimulation is available in a very few centers. This depends on the presence of an implanted device to send signals to the brain areas which control or regulate muscular movement. These signals are designed to block the abnormal signals or impulses which bring about the tremor. This results in a temporary cessation of tremor.
Other specialized surgical procedures such as stereotactic surgery are being investigated. The serious nature of their side effects has led to delay in their introduction.
ET is not a lethal condition. However, it can produce embarrassment. Miscommunication may occur in a few cases because the head tremor may be mistaken to convey movements of agreement (head nodding) or disagreement (head shaking). The patient may also be frustrated by the inability to perform routine daily tasks. In many patients, the tremor becomes worse though less frequent with advancing age. In others, it remains mild and manageable throughout their lives.
Reviewed by Afsaneh Khetrapal BSc (Hons)