Background and purpose: Essential tremor (ET) is likely the most common movement disorder. The aim of the study was to carry out spectral analysis of the essential tremor recorded by an accelerometer and assess the symmetry of tremor parameters between the two hands.
Material and methods: We examined 39 patients with ET diagnosed clinically using the criteria of the Movement Disorder Society. The control group consisted of 52 healthy persons. A biaxial accelerometer mounted at the dorsal side of the hand was used. Spectral analysis was performed. Tremor intensity, frequency of spectral peaks, centre frequency, standard deviation of the centre frequency, and harmonic index were measured. The side-to-side symmetry of these parameters was analysed. The relationship of hand dominance and severity of tremor was also analysed.
Results: There was significant side-to-side asymmetry of intensity in ET. The intensity in the more affected hand was over two times higher than that in the less affected one. The tremor was more severe in the nondominant hand in 62% of patients. In spite of significant difference in tremor intensity between the two sides, tremor frequency was similar in both hands. The standard deviation of centre frequency was significantly lower and the harmonic index was significantly higher in the more trembling hand.
Conclusions: Accelerometric registration revealed that asymmetry of intensity and symmetry of frequency are characteristic features of ET. The remaining two coefficients reflecting the rhythmicity and regularity of tremor also differed considerably between the hands.