Assessment of resting tremor in Parkinson’s disease

Abstract

Of the three cardinal features of Parkinson’s disease, rigidity, bradykinesia and tremor, it is the tremor at rest that responds least predictably to drug therapy (Boshes, 1976). The evaluation of response to drug treatment is further complicated by the difficulties encountered when attempting objective assessments of tremor magnitude. The problems of assessing the resting tremor arise because its amplitude is subject to sudden and extreme fluctuations. These fluctuations can be the result of circadian variations, alterations in anxiety level, external stresses such as those produced by difficult tasks and, of course, fluctuations in the ‘availability’ of dopaminergic agents at receptor sites. Although these factors undoubtedly contribute to the variability in the amplitude of rest tremor, the commonest observed fluctuation, i.e. the abrupt change in amplitude seen in the apparently unstimulated patient, appears to be unrelated to any of the above factors. It is such fluctuations, of unknown origin, that make the assessment of this tremor particularly difficult.