Upper-Extremity Disability in Essential Tremor

Experimental set-up for hand tremor recording. Subjects were seated without back support holding a box fitted with white matte surfaces. Note the recessed handle of the box permitting a precision grip between the thumb and fingers and the 2 laser displacement sensors positioned to capture horizontal and vertical movements of the box.

(A, C, E) Hand tremor data from a control subject and (B, D, F) a subject with ET-type hand tremor. (A, B) In the horizontal displacement recordings, note the large higher-frequency (5–6Hz) displacement oscillations in the recording from the ET subject. (C, D) When the displacement recordings are double differentiated and presented as an acceleration time series, the regularity and magnitude of the tremor in the subject with ET are evidenced by large acceleration fluctuations. (E, F) The power spectrum plots clearly illustrate the predominant peak frequency, which is typical of tremor recordings in people with ET. Note that the y axis for the ET subject is 1000 times greater than that for the control subject. Vertical dotted lines indicate the 1-Hz window (summed power) used to calculate tremor amplitude.

Mean BBT scores ± standard deviation (SD) for the (A) dominant and (B) nondominant hand of control subjects and 2 subgroups of ET subjects. There was a significant group effect on both the dominant and nondominant sides (bold horizontal line). Post hoc analysis showed that ET subjects with ET-type tremor in the dominant hand and those with ET-type tremor in the nondominant hand transferred fewer blocks during the 60-second trial compared with controls. *P<.05.

Mean PPT scores ± SD for the number of pegs placed in 30 seconds with the (A) dominant and (B) nondominant hands, (C) number of pairs of pegs placed using both hands in 30 seconds, and (D) number of component parts placed during the assembly task in 60 seconds. There was a significant group effect (bold horizontal line) for (B) the nondominant hand unilateral task and (C, D) both of the bilateral tasks. Post hoc analysis showed that scores from (B) ET subjects with ET-type tremor in the nondominant hand and (C, D) ET subjects with ET-type tremor in at least 1 of their hands were significantly lower than those of the control group. *P<.05.

Mean summed times for TEMPA tasks ± SD for the (A) dominant and (B) nondominant unilateral tasks and (C) bilateral tasks, and (D) the TEMPA total. There was a significant group effect (bold horizontal line) for all TEMPA score groupings (bold horizontal line). Post hoc analysis showed that scores from ET subjects with ET-type tremor in the (A) dominant and (B) nondominant hands took longer to perform the unilateral TEMPA tasks compared with controls. Note that ET subjects without ET-type tremor in the dominant hand were also slower than the control group when performing the unilateral tasks (A). ET subjects with ET-type tremor in at least 1 of their hands took longer to complete the bilateral tasks (C) and the summed total of all TEMPA tasks (D) compared with the control group. *P<.05.