P 104 - Head and hand tremor measurement and analysis for the differentiation between essential and dystonic tremors.

Head tremor is a common clinical manifestation in essential tremor (ET) and can also occur as dystonic tremor (DT) in cervical dystonia. The clinical differentiation of head tremor due to ET and DT is not easy. Therefore, we developed instrumental methods using an accelerometer and an optical motion capture system to precisely measure and analyze head and hand tremor, and for distinguishing between ET and DT. Head tremor was measured with a Wireless XSens accelerometer and hand tremor by the Optitrack V120 Trio (MOCAP) and the tremor amplitude was computed. We included 24 patients fulfilling the criteria for ET (12 M, 12 F, mean age 58, SD 10) and 26 patients with cervical dystonia (5 M, 21 F mean age 64, SD 10). In supine position, visible head tremor disappeared in 5 out of 13 ET (38%) and in 8 out of 20 DT patients (40%). In ET patients, we found a strong correlation between the amplitudes of head tremor in sitting and supine position (rho=0.91, p<0.001). In contrast, in patients with DT, the correlation was weak (rho = 0.49, p = 0.01). Tremor of the upper limbs was significantly higher in the ET group, compared to DT (p < 0.001). Measurement of hand tremor with MOCAP confirmed the predicted difference in tremor of the upper limbs in patients with ET and DT. In the contrary, the analysis of head tremor amplitude did not confirm the hypothesis that head tremor disappears in supine position in patients with ET. The correlations show that the ET is just suppressed and depends on its amplitude. DT suppression is unpredictable. [ABSTRACT FROM AUTHOR]