Tremors are non-intentional rhythmic movements of a body part, which are the result of alternating or irregular synchronous contractions of muscles that have an opposite effect on a joint. For example, muscles that, when contracted, result in flexion of the wrist are stimulated synchronously with muscles that result in extension of the wrist. The result is a rhythmic flexion and extension of the wrist. This phenomenon can happen in any part of the body. It is this rhythmic quality that defines and distinguishes tremors from any other abnormal movements.
Two main categories can be recognized:
- normal (also called physiologic)
- abnormal (or pathologic)
The normal or physiological tremor is a fine, almost imperceptible, tremor that is difficult to see by the naked eye and does not interfere with activities. It can be seen in the fingers when the arms are outstretched. The frequency of the contractions is in the area of 8 to 13 cycles per minute. The cause of this tremor is not known, but it is not considered to be associated with any disease process.
The abnormal or pathological tremor it is more obvious and more visible to the naked eye. As such, it does interfere with everyday activities. The frequency of the contractions is in the area of 4 to 7 cycles per minute. In many instances this tremor is associated with defined medical conditions.
Most often the abnormal tremor is observed in the distal parts of the limbs (hands, fingers); however, every part of the body (such as the head, the tongue, the vocal cords, or the trunk) can be affected by the tremor.
The clinical distribution of the tremor might be different depending upon the medical condition associated with it and some individual factors. However, in a particular individual the quality and distribution of the tremor is very constant.
These abnormal tremors can be subclassified into the following categories:
- A resting tremor (also call Parkinsonian tremor) is observed in a body part that is not active and is completely supported against gravity. It is a coarse, rhythmic tremor, often localized in the hands and forearms, but less frequently seen in other parts of the body and is observed when the limb is in a position of rest. Intentional movement might decrease the intensity of the tremor. However, the tremor disappears when the limbs are in extreme rest, as it is the case when the patient is sleeping. This phenomenon is common to most of the tremors. In the hands, the tremors result in a peculiar "pill rolling" movement of the fingers, more obvious between the thumb and the index finger. Other parts of the body might also be affected. For example, the eyelids tend to flutter, and the jaw and the lips can flicker. When the legs are impaired it might result in gait (walking) problems. This tremor is most often seen as a manifestation of the Parkinson's syndrome.
- Postural, or action tremor, is observed when muscles voluntarily contract. This tremor is exhibited with any attempt to keep the limbs or trunk in a particular position, for example to keep the arms outstretched. This type of tremor becomes worse when the limb is actively moved, for instance, when trying to drink from a cup. However, no tremor is observed when the limb is fully relaxed. This tremor is most often seen as a manifestation of essential tremor.
- Intention (ataxic) tremor can be a very disabling type of tremor. It has some of the characteristics of the action tremor in the sense that it is triggered by movement; however, its main feature is that it occurs at the end of an action, when a fine, precise adjustment is needed. For example, when a person is asked to touch the tip of the nose, the early part of the action does not elicit the tremor, but as soon as the finger is near the nose and has to zero in on the tip of the nose, an irregular, rhythmic tremor with a frequency of 2 to 4 oscillations per minute is seen. Unlike action and resting tremor, the oscillations are in different planes and may persist even after the task is achieved. This type of tremor is mostly seen in conditions associated with the cerebellum or its neurological connections.
- Rubral tremor is characterized by intense, violent movement. With this type of tremor, a patient's slight movement of the arms or attempts to maintain a static posture, like trying to keep the arms outstretched, results in an intense rhythmic "wing-beating" movement. It is also associated with some interruptions of the cerebellar connections. This type of tremor is seen most often, among other conditions, in persons with multiple sclerosis.
In general, one particular tremor type is predominant and sometimes the only tremor present in a defined clinical condition, for example, resting tremor in Parkinson's disease or postural tremor in essential tremor. However, there are several individual variations, and it is not unusual for a patient with a defined clinical condition, for example Parkinson's disease, to have, besides the resting tremor typical of the disease, some degree of postural tremor.
Medically Reviewed by a Doctor on 12/11/2014
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