Neurophysiological study of tremor.

Tremor is frequently encountered in neurologic practice, clinical examinati on supplies information regarding its approximative frequency, regularity, amplitude, topography and activation conditions. The neurophysiological stu dy helps in confirming the tremor, in differentiating it from other movemen t disorders like myoclonus, and may provide distinctive features which are important for the aetiological diagnosis. The neurophysiological investigat ion includes accelerometry, which analyses the mechanics of the movement. S pectral analysis with FFT allows the determination of frequency and amplitu de. Accelerometry is always associated with surface EMG of at least two ant agonistic muscles. It may show rhythmic bursts, their frequency, duration a nd activation pattern (alternating or synchronous). This neurophysiological approach to tremor has multiple interests. It may help in differentiating a true rest tremor from a postural tremor seemingly persisting at rest. Bri ef interruptions or rhythm breaks during distraction manoeuvers are seen in psychogenic tremors. Surface EMG may also demonstrate positive myoclonic b ursts, or brief silent periods corresponding to negative myoclonus, sometim es pseudorhythmic, thus appearing clinically like a tremor, but investigati ons, aetiologies and treatment are different. Several features, especially slow frequency, may suggest a midbrain tremor, thus requiring brain imagery centered around the posterior fossa. Finally, the neurophysiological exami nation is the only way to demonstrate a primary writing tremor, or a primar y orthostatic tremor, the frequency of which is pathognomonic while clinica l symptoms are rather misleading. (C) 2000 Editions scientifiques et medica les Elsevier SAS.