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Ivan Donaldson

, C. David Marsden

, Susanne A. Schneider

, and Kailash P. Bhatia

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date: 20 May 2022

Tremor is an involuntary periodic oscillation of a part of the body. The rhythmic sinusoidal appearance distinguishes this abnormal movement. At times, however, it can become confused with other involuntary movements. Clonus is rhythmic but is evoked by passive stretch of muscles. Some forms of myoclonus can be rhythmic, but the resulting movement is not sinusoidal. Rhythmic myoclonus produces repetitive muscle jerks. If the frequency is fast it can masquerade as tremor. Negative myoclonus or asterixis can also cause confusion. When the electromyography (EMG) pauses are over 200 ms it is usually readily distinguished, but if they are shorter than this the appearance may be that of an irregular high-frequency tremor. Epilepsia partialis continua can also occasionally result in a similar appearance.

Tremor may be classified in a variety of ways and formal systems have been proposed to try to standardize nomenclature, particularly for use in publications. The best known of these are the classification systems of the tremor investigation group (TRIG) (Deuschl et al. 1995) and the ad hoc committee of the Movement Disorder Society (Deuschl et al. 1998).

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