Ed. Louis et al., Is essential tremor symmetric? Observational data from a community-based study of essential tremor, ARCH NEUROL, 55(12), 1998, pp. 1553-1559
Background: Essential tremor (ET) has been variably portrayed in the litera
ture both as a symmetric arm tremor and as an asymmetric arm tremor. Few qu
antitative clinical or neurophysiological data specifically address the iss
ue of tremor asymmetry in ET.
Objectives: To examine a community-dwelling cohort of subjects with ET to (
1) estimate the prevalence of tremor asymmetry and (2) quantify the magnitu
de of tremor asymmetry.
Methods: Fifty-four subjects with ET, identified in a community-based study
of ET in New York City, underwent a Tremor Interview and a videotaped Trem
or Examination. The examination included 6 tasks: sustained arm extension,
pouring water, drinking water, using a spoon, finger-to-nose movements, and
drawing spirals with each arm. Two neurologists rated the severity of trem
or using a 0 to 3 clinical rating scale and a total tremor score was calcul
ated (range, 0-36). Fourteen (25%) of 54 subjects also underwent quantitati
ve computerized tremor analysis.
Results: The prevalence of asymmetry depended on the definition of asymmetr
y; small to moderate differences between sides were common. The mean side-t
o-side difference in clinical ratings for each of the 6 tasks was 0.54 of 3
points, which represented a 1.32-fold difference between sides. Clinical r
ating scores were higher in the nondominant arm in 39 subjects (72%), highe
r in the dominant arm in 9 (17%), and equal in 6 (11%). The 2 left-handed s
ubjects had higher clinical ratings on the right. During quantitative compu
terized tremor analysis, there was a 1.71-fold mean difference between trem
or amplitudes in the dominant and nondominant sides, and in 12 subjects (86
%), the maximum tremor amplitude was in the nondominant arm.
Conclusions: Small to moderate differences between sides were common in ET.
In most community-dwelling subjects, tremor amplitude was greatest in the
nondominant arm. In contrast, clinic-based studies have reported greater tr
emor in the dominant arm; those with ET who seek medical attention are more
likely to exhibit severe tremor in their dominant arms. This study documen
ts that mild asymmetry is a fundamental property of ET and that tremor is m
ore severe in the nondominant arm.