A tremor is an involuntary rhythmic movement of a part of the body. There are different types of tremor some of which are discussed in this article.
Normal (physiological) tremor
When a limb is stretched out against gravity or is bearing a heavy load, a tremor normally develops. This can be demonstrated by putting a light piece of paper on top of the outstretched hand. However, it is not normally noticeable because it is so minor.
Therefore, a fine postural or kinetic tremor, typically affecting hands or fingers, and which is usually bilateral, is considered a normal occurrence. Physiologic tremor has a very low amplitude and frequency, approximately 6-12 Hz, and occurs as a postural or kinetic tremor.
Even though a slight tremor is normal, this may be exacerbated by factors such as:
- Extreme fatigue
- Intense emotion
- Low blood sugar (hypoglycemia)
- An overactive thyroid
- Medications such as corticosteroids, amphetamines or beta-agonists
- Heavy metal toxicity
- Stimulants such as caffeine
- Alcohol withdrawal
An exacerbated physiological tremor may become visible. However, evaluation fails to show any neurologic, metabolic, or structural cause.
Enhanced physiological tremor has a higher frequency but the same low amplitude as the normal tremor. It is visible, but is usually brought on by maintaining a specific posture. It is due to the mechanical activation of muscles by certain drugs or toxins. A clue may be offered by the presence of other clinical features of drug toxicity.
Treatment of noticeable tremor consists of identifying and correcting the reversible causes. Treatment is non-pharmacologic, and coping strategies are important. However, in certain situations it may be essential to have no tremor at all, as in the case of a professional performance. Beta-blockers can help reduce an exaggerated or drug-induced tremor, provided the optimum dosage is found beforehand.
Also called benign essential tremor, this is one of the most frequent causes of non-physiologic tremor. It is defined as a bilateral and usually symmetrical postural or kinetic tremor which affects hands and forearms. It is visible and persistent. Sometimes it may be mild and remain so throughout life. In others, it progresses from being unilateral to becoming bilateral and more severe.
This type of progression may take from years to decades. The age of onset, the rate of progression, and the ultimate severity are unpredictable in most cases, and may vary even between two members of the same family. Most cases do occur after the age of 40 years. Both men and women are affected alike.
Essential tremor is currently thought to be due to cerebellar pathology, which may be very subtle. In addition, a neurodegenerative process may underlie essential tremor, as shown by the higher incidence in relatives of patients with PD and other similar conditions caused by neuronal damage.
Essential tremor affects the hands in most individuals, but may also occur in the head, vocal cords, tongue, legs, and trunk. The hands show the most severe tremor among these, and this may become so violent as to hinder normal activities of daily living, such as writing, eating, and shaving.
Head tremors may take the shape of either nodding or shaking, which may lead to misunderstandings if taken for signs of agreement or disagreement during conversations. Hearing disability is more often associated with this group of patients than in those with other types of tremors, and correlates with the severity of tremor.
Inability to care for oneself typically leads to depressive and angry feelings.
The children of a parent with essential tremor have a 50 percent chance of developing the condition, which denotes an autosomal dominant inheritance. That is, one of two copies of a gene must be abnormal for the condition to develop.
A gene marker has been studied, namely, LINGO1, which seems to carry increased risk. However, some people with essential tremor do not have the gene, while others without any symptoms do carry it. Interestingly, alcohol consumption very often reduces or abolishes the tremor.
Some cases are associated with a mild degeneration of the cerebellum, but the vast majority of individuals with essential tremor do not show any central nervous system pathology. Methods of treatment include:
- Watchful waiting if the tremor is mild and does not appear to progress.
- Removing exacerbating factors such as caffeine, fatigue, lack of sleep, or stress.
- Medications such such as a beta-blocker an anticonvulsant, have been found to be effective in up to 75% of patients, and a marked reduction in the tremor (about 75%), rather than complete cessation, which is rarely achieved.
- Sedatives are useful in some cases.
Surgical intervention includes:
- Deep brain stimulation, using an implanted electrode inside the thalamus which is connected to a pulse generator under the skin of the chest. This produces impulses which suppress the abnormal impulses within the brain, cutting off the tremor. The frequency of impulse generation may be altered to reduce the incidence of side effects, such as nausea, dizziness, or dysarthria.
- Thalamotomy and pallidotomy are stereotactic surgical procedures which involve destroying the part of the thalamus or the globus pallidum which is responsible for the tremor.
Reviewed by Afsaneh Khetrapal BSc (Hons)