To the Editor.
—Orthostatic tremor has been defined by Heilman1 in the Archives in 1984 as prominent rhythmic muscle contractions of the legs and trunk occurring primarily while standing. While its distinctive phenomenology has been shown to be specific to maintaining a standing posture,2 its physiological picture among the reported cases has been sufficiently variable so as to suggest that more than one clinical entity could meet this description. Several tremor frequency ranges have been found for orthostatic tremor,2-5 and its muscle contraction pattern in agonist-antagonist groups has varied from synchronous to alternating.2,3 Some authors have considered orthostatic tremor to be no more than a variant of essential tremor3,5 while others have emphasized unique characteristics that distinguish it from other tremor types.2,4 Possibly, the lack of uniformity in physiological studies from case to case indicates that different mechanisms might account for similar clinical phenomenology.
LeWitt PA. Orthostatic Tremor: The Phenomenon of 'Paradoxical Clonus'. Arch Neurol. 1990;47(5):501–502. doi:10.1001/archneur.1990.00530050015002
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