Tremors are involuntary, purposeless movements of a body part around a fixed plane in space. A tremor can be classified on the basis of whether it occurs with a certain posture, at rest, or during movement. It can be localized to the affected body part and characterized by what makes the tremor better or worse.
A physiological tremor is a variation of what is normal while a pathological tremor is not. The two most common types of pathological tremors are essential tremors and tremors associated with Parkinson’s disease. In addition, disease in the cerebellum of the brain may also cause a tremor of intention (i.e., with movement). Other less common causes of tremor include alcohol withdrawal or diseases of the peripheral nerves.
An essential tremor is also known as a benign tremor. It is about ten to twenty times more common than the tremor of Parkinson’s disease. It is most noticeable when a person holds their hands outstretched or makes fine movements. By contrast with the tremor of Parkinson’s disease, essential tremor tends to disappear when the hands and arms are relaxed. Sixty percent of essential tremors are inherited and are known as familial tremors.
Parkinson’s disease occurs in about 1 percent of people aged sixty-five years or older, increases to 2.5 percent of persons over eighty years of age. The hallmark of Parkinson’s disease is an asymmetrical tremor that occurs at rest. A relatively low frequency and medium amplitude characterize the tremor. Classically, it is described as a pill rolling tremor of the hands (a term of distant origin, referring to the days when pharmacists made pills on site) yet it can also affect the chin. Typically, this tremor only rarely affects the neck or voice. This tremor diminishes with purposeful movements and therefore it usually does not cause motor disability. Parkinson’s disease does not evolve from essential tremors.
Cerebellar tremors tend to be related to movement and increase in severity as the extremity approaches its target, often resulting in the extremity moving part of its object (so-called pist points) and having to rely on visual input ultimately to find the target. They are associated with other signs of cerebellar malfunction such as abnormalities of gait, speech, and eye movements. A postural tremor may also be associated with damage to the cerebellum. Causes of cerebellar postural tremor are diseases like multiple sclerosis, tumors, stroke or nonspecific neurodegenerative disease of the brain.
Drugs used for treatment of essential tremor include beta-adrenergic blockers, benzodiazepines, or anticonvulsants. Small doses of alcohol have been found to provide temporary relief of essential tremors although excess alcohol intake is strongly discouraged and can make them worse, especially as the blood level is reduced.. Replacement of dopamine is used for treatment of Parkinson’s disease and therapy can be augmented with anticholinergic agents or dopamine agonists. Thalamotomy (or the surgical disruption of a deep brain structure known as the thalamus) is a surgical procedure used to treat patients with severe, drug resistant essential tremor or patients with Parkinson’s disease who have severe, disabling, predominantly unilateral tremor. Pallidotomy (surgical destruction of the globus pallidus) is an alternative to thalamotomy in the treatment of parkinsonian tremor. Implantation of an electrode in the thalamus can suppress some tremors. All surgical therapies should only be considered for patients who have debilitating symptoms that persist despite adequate medical therapy.
Tremor is an important sign in aging, which can occur in the absence of disease. Although, sometimes embarassing, essential tremor on its own is neither disabling nor a sign of impending brain disease.
PHILIP E. LEE B. LYNN BEATTIE
See also PARKINSONISM.
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