The diagnostic value of tremor analysis in patients with coexisting essential tremor and Parkinson′s disease

Objective To explore the diagnostic value of tremor analysis in patients with coexisting essential tremor (ET) and Parkinson′s disease (PD). Methods A cross-sectional survey was conducted to collect 30 patients with PD, 30 patients with ET and 20 patients with ET+PD in Peking University Third Hospital from January 2015 to December 2017. Tremor analysis was performed in all the patients. Results There were statistically significant differences in age (63.0(54.8, 68.0), 49.0(26.5, 58.5), 57.0(50.0, 66.0) years, H=21.336, P<0.05), disease course (12.0(8.0, 13.3), 36.0(12.0, 87.0), 22.0(11.5, 33.0) years, H=18.233, P<0.05) and Unified Parkinson′ s Disease Rating Scale score (21.13±8.85, 8.00±3.68, 24.35±9.14, F=36.443, P<0.05) among the PD, ET and ET+PD groups. The average tremor frequencies in PD, ET and ET+PD groups at rest were (5.46±0.77), (7.11±1.80) and (6.18±1.55) Hz, respectively, with statistically significant differences among the three groups (F=5.77, P=0.006). The average tremor frequencies in the three groups at posture were (6.19±2.21), (8.23±1.96) and (6.49±1.23) Hz, respectively, with statistically significant differences (F=9.673, P<0.01). There was no statistically significant difference in tremor amplitude among the three groups at rest and posture position. In the PD, ET and ET+PD groups, the proportion of electromyography alternating contractions of the active and antagonistic muscles was 76.9% (20/26), 0/6 and 5/15 at rest (χ2=17.192, P<0.01), and 53.8% (14/26), 20.0% (6/30) and 4/15 at posture (χ2=7.564, P=0.023),both with statistically significant differences. Conclusions The clinical manifestations of patients with ET+PD have both characteristics of PD and ET, but they have their own characteristics. Tremor analysis can objectively identify the bilaterally synchronous or alternate discharges of electromyography at rest, which are different from those of typical PD and ET. Tremor analysis is helpful for the identification of this disease. Key words: Parkinson disease; Tremor; Electromyography