Tremor is an involuntary movement, roughly rhythmic and sinusoidal, although some tremors (e.g., dystonic) are irregular in amplitude and periodicity. Tremors may be classified clinically:
- Rest tremor:
present when a limb is supported against gravity and there is no voluntary muscle activation, e.g., the 3.5-7 Hz "pill rolling" hand tremor of Parkinson’s disease; midbrain/rubral tremor.
- Action tremor:
present during any voluntary muscle contraction. Various subtypes of action tremor are recognized:
- Postural tremor:
present during voluntary maintenance of a posture opposed by gravity, e.g., arm tremor of essential tremor; 6Hz postural tremor sometimes seen in Parkinson’s disease, which may predate emergence of akinesia/rigidity/rest tremor; modest postural tremor of cerebellar disease; some drug-induced tremors (including alcohol withdrawal, delirium tremens); tremor of IgM paraproteinemic neuropathy; Wing-beating tremor of Wilson’s disease.
- Kinetic tremor:
present with movement, often with an exacerbation at the end of a goal-directed movement (intention tremor), e.g., cerebellar/midbrain tremor (3-5Hz).
- Task-specific tremor:
evident only during the performance of a highly-skilled activity, e.g., primary writing tremor.
- Isometric tremor:
present when voluntary muscle contraction is opposed by a stationary object, e.g., primary orthostatic tremor (14-18Hz).
- Psychogenic tremors:
these are difficult to classify, with changing characteristics; the frequency with which such tremors are observed varies greatly between different clinics; the coactivation sign (increase in tremor amplitude with peripheral loading) is said to be typical of psychogenic tremor.
EMG may be useful for determining tremor frequency, but is only diagnostic in primary orthostatic tremor.
Various treatments are available for tremor, with variable efficacy. Essential tremor often responds to alcohol, and this is a reasonable treatment (previous anxieties that such a recommendation would lead to alcoholism seem unjustified); alternatives include propranolol, primidone, topiramate, alprazolam, flunarizine, and nicardipine. In Parkinson’s disease, tremor is less reliably responsive to levodopa preparations than akinesia and rigidity; anticholinergics, such as benzhexol, may be more helpful (but may cause confusion). Primary orthostatic tremor has been reported to respond to clonazepam, primidone, and levodopa. Cerebellar tremor is often treated with isoniazid, but seldom with marked benefit, likewise carbamazepine, clonazepam, ondansetron, limb weights; stereotactic surgery may be the optimum treatment if preliminary experimental data are confirmed.
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Barker R, Burn DJ. Tremor. Advances in Clinical Neuroscience &Rehabilitation 2004; 4(1): 13-14
Deuschl G, Bain P, Brin M and an Ad Hoc Scientific Committee. Consensus statement of the Movement Disorder Society on tremor. Movement Disorders 1998; 13(suppl3): 2-23
Findley LJ, Koller WC (eds.). Handbook of Tremor Disorders. New York: Marcel Dekker, 1995