Distinguishing between physiological and essential tremor using discriminant and cluster analyses of parameters derived from the frequency spectrum

Three parameters, root mean square (rms) acceleration, frequency and shape, were calculated from the frequency spectrum in 20 patients with essential tremor. Tremor was measured in two postures (with the arms outstretched - ' postural' tremor and with the arm supported and hand relaxed - 'rest' tremo r) in the dominant and non-dominant hands using a piezo-electric accelerome ter. These data were compared with data obtained from accelerometric measur ements of physiological tremor in 81 adults. Step-wise discriminant analysi s was applied to the data to identify which variables best discriminated be tween essential and physiological tremor. K-means cluster analysis was used to identify any sub-groups within the essential tremor data. The analysis identified four variables, which together, best distinguished between physi ological and essential tremor, these were postural amplitude and frequency, and rest shape (non-dominant hand) and postural shape (dominant hand). Usi ng these variables 94.74% of cases were correctly classified into the physi ological and essential tremor groups. Cluster analysis on the amplitude val ues for postural tremor (but not for the other parameters or postures measu red) suggested that two sub-groups were present in this sample of essential tremor patients. Discriminant analysis and K-means cluster analysis on par ameters derived from the frequency spectrum of tremor measured in different postures can be used to distinguish pathological tremors from physiologica l tremor and provide a way of identifying possible sub-groups in essential tremor. (C) 2000 Elsevier Science B.V. All rights reserved. PsycINFO classi fication. 2540; 3297; 2240.