Parkinson's disease: tremor
A tremor is a form of involuntary movement (i.e. a movement that is not under conscious control). Some involuntary movements (e.g. blinking) are normal, while others are abnormal and are usually related to a particular medical condition. Similarly, tremor can be either normal (physiological) or abnormal (pathological).
Tremors have a different quality from other involuntary movements in that they are rhythmic, occurring when a particular movement is repeated regularly with no breaks between the movements. This is different from other movements such as chorea and athetosis, where there is a wide variety of movements, and the pattern of movement is constantly changing.
Tremors are described in terms of frequency and amplitude. Some tremors are extremely regular, with one frequency dominating, while others have an irregular rhythm, with no particular frequency dominating or the frequency pattern continually changing.
Similarly, some tremors may have a constant amplitude, while others, which have waves of different amplitudes, appear to be less regular.
Classification of tremor
There are 2 clear categories of tremor, normal and abnormal, and a number of different ways of classifying abnormal tremor.
Probably the simplest classification is according to the situation in which it occurs, rather than according to the underlying mechanism. The following tremors are listed alphabetically rather than by classification.
Action tremor
Also called postural tremor or (sometimes) cerebellar tremor, this is a class of tremor that occurs when parts of the body are held in certain positions (e.g. when the arms are held outstretched and while they are being moved) but is not present when the limbs are relaxed or fully supported. It involves the outstretched hand, the head and, less often, the lips and tongue. It occurs with voluntary movement and may increase a little during the movement as it becomes more precise, but does not become as severe as intention tremor. Actions such as handwriting and speech are generally not affected.
This category of tremor is seen in a wide range of disorders and includes a number of variants of normal tremor such as exaggerated physiological tremor, adrenaline tremor, anxiety tremor, thyrotoxic tremor, tremor of fatigue and benign essential tremor.
Adrenaline tremor
Injections of adrenaline produce a tremor of normal frequency but greater amplitude. It is absent at rest, but apparent in all parts of the body when muscular activity is undertaken or posture maintained. It is significant in that it is probably the underlying cause of variants of physiological tremor such as anxiety tremor, thyrotoxic tremor and the tremor of fatigue.
Anxiety tremor
People who are anxious or under stress often develop a fine tremor, most obvious in the fingers of the outstretched hands. If it is not visible to the naked eye, it can be seen by placing a sheet of paper on the fingers. It has been suggested that it is the result of the secretion of adrenaline that increases the amplitude of the normal tremor.
Ataxic tremor
(See intention tremor.)
Benign essential tremor
Benign or hereditary essential tremor is one of the most common tremors and about 30 per cent of people have an affected family member. It is more common in females. It is one of the postural tremors which is absent at rest, appearing bilaterally when the muscles begin to move and is not influenced by loading the muscles. It may begin in childhood, but normally it develops later, persisting throughout adult life, usually starting with the hands and possibly affecting the head, chin (in 80 per cent) and voice.
It progresses slowly, and at varying rates for different people, affecting each side of the body to a different extent, which may result in subtle postural control problems. The tremor is worse when the person is under observation and may become a source of embarrassment, as well as sometimes affecting the ability to perform normal tasks. It is easily distinguished from the tremor of PD and usually appears with no latency period. It may increase during writing, drinking and eating. One or 2 drinks of alcohol may abolish the tremor, which comes back when the effects have worn off. Deep brain stimulation is being used as a treatment.
Cerebellar tremor
(See intention tremor.)
Drug-induced tremor
Tremor is a common side effect of a wide range of drugs. Various types of tremor can be produced by drugs, although most are postural in nature. Withdrawal of drugs (e.g. alcohol) can produce tremor.
Essential tremor
(See benign essential tremor.)
Exaggerated physiological tremor
Also called enhanced physiological tremor, this is a tremor of greater than normal amplitude but normal frequency. It is absent at rest, present when maintaining posture and persists but does not intensify during movement. It is common in anxiety states and a number of metabolic disorders and is similar to postural or action tremor.
Familial tremor
(See benign essential tremor.)
Hepatic tremor
Tremor in severe liver disease was first described in 1949; it is now recognised that it also occurs in other metabolic disorders. There are probably several different types of involuntary movement involved, the most common being asterixis or 'flap', which is absent when the limbs are at rest or during movement, but can be seen when the arms are outstretched. The hands drop and are immediately pulled back to their original position. The other types of movement involved are an oscillating tremor of the fingers and random individual movements of the fingers.
Hereditary essential tremor
(See benign essential tremor.)
Intention tremor
This kind is usually seen in association with diseases of the cerebellum or its connections and may occur together with cerebellar ataxia.
It is not seen when the limb is at rest and supported, but only during movement. It is absent during the first part of a voluntary movement. But as the movement becomes more precise, jerky side-to-side movements develop, which become exaggerated as the movement ends and sometimes continue for a second or 2 after the target has been reached. It is exhibited in such situations as the 'finger to nose' test, where a person is asked to touch their nose, and can seriously interfere with a person's ability to perform skilled tasks. It can improve with training by an occupational therapist or physiotherapist.
Sometimes there is an intention component to other types of tremor such as parkinsonian tremor. The removal of visual feedback can improve movement in intention tremor, whereas in Parkinson's disease (PD) this can cause the tremor to deteriorate.
Normal tremor
Normal tremor is the normal rhythmic oscillation of all body parts.
Parkinsonian tremor
Parkinsonian or resting tremor occurs in a majority of people with PD and is a 'pill-rolling' tremor which is present at rest but temporarily suppressed by movement and increased loading, recurring if the person tries to hold still. The frequency of the tremor does not increase with age or progression of the disease but it usually begins in one hand and extends to other parts of the body as the disease progresses. Emotional stress aggravates the tremor and most people find that the tremor, while not the most disabling aspect of PD, is the most embarrassing.
Deep brain stimulation and thalamic surgery have been shown to decrease this type of tremor.
Physiological tremor
(See normal tremor.)
Postural tremor
(See action tremor.)
Resting tremor
(See parkinsonian tremor.)
Tardive dyskinesia
This is an abnormal condition characterised by involuntary, repetitious movements of the muscles of the face, the limbs, and the trunk. This disorder most commonly affects older people who have been treated for extended periods with phenothiazine. The involuntary movements associated with the condition may slacken or disappear after weeks or months and have been significantly reduced in some individuals by the administration of cholinergic drugs.
Thyrotoxic tremor
This tremor is similar to physiological tremor except in amplitude and is readily seen in the fingers of the outstretched hands. It is possibly an effect of the action of adrenaline on the person's normal tremor.
Tremor of fatigue
The stress of excessive fatigue causes a tremor of normal frequency, but the amplitude is sufficient to be observed by the naked eye. The suggestion is that the tremor is caused by increased circulation of adrenaline.
Last Reviewed: 24 June 2002
