Asymmetry of tremor intensity and frequency in Parkinson’s Disease and essential tremor.pdfVIP

Asymmetry of tremor intensity and frequency in Parkinson’s disease and essential tremor Zsuzsanna Farkas, Anita Csillik, Imre Szirmai, Anita Kamondi* Department of Neurology, Semmelweis University, Balassa u. 6., 1083 Budapest, Hungary Received 14 January 2005; revised 28 June 2005; accepted 25 July 2005 Abstract We investigated the asymmetry of tremor intensity, frequency and frequency dispersion of Parkinsonian (PT) and essential (ET) tremor using accelerometry. Data of the more and less trembling hands were statistically elaborated. We found that tremor intensity was significantly asymmetric not only in PT but also in ET, while frequency and frequency dispersion were symmetric in ET but asymmetric in PT. We conclude that bilateral assessment of frequency related tremor parameters may be used for differentiation between ET and PT, and provides further details on the central organization of tremor generators. q 2005 Elsevier Ltd. All rights reserved. Keywords: Parkinson’s disease; Essential tremor; Accelerometry; Intensity; Center frequency; Frequency dispersion1. Introduction The most frequent tremor syndromes are the Parkinso- nian (PT) and essential (ET) tremor [1] that are generated by central mechanisms [2–4]. It is a clinical evidence, which has only recently been corroborated by a study using clinical score systems [5], that tremor intensity in Parkinson’s disease is asymmetric [1,6]. ET has long been considered a symmetric disorder, but it has been found by Louis et al. [7] that amplitude asymmetry is a fundamental property of ET. Although frequency/ amplitude dependency is an important characteristic of oscillating systems [8], it has not been examined, whether intensity asymmetry in PT and ET is associated with asymmetry of frequency. In studies, where amplitude and frequency were measured on one side only, this question could not be addressed [9–12]. In publications with bilateral recordings, data of the two hands were either combined, or the averages of