Is essential tremor symmetric? Observational data from a community-based study of essential tremor.
BACKGROUND
Essential tremor (ET) has been variably portrayed in the literature both as a symmetric arm tremor and as an asymmetric arm tremor. Few quantitative clinical or neurophysiological data specifically address the issue of tremor asymmetry in ET.


OBJECTIVE
To examine a community-dwelling cohort of subjects with ET to (1) estimate the prevalence of tremor asymmetry and (2) quantify the magnitude 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 Tremor 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 tremor using a 0 to 3 clinical rating scale and a total tremor score was calculated (range, 0-36). Fourteen (25%) of 54 subjects also underwent quantitative computerized tremor analysis.


RESULTS
The prevalence of asymmetry depended on the definition of asymmetry; small to moderate differences between sides were common. The mean side-to-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 rating scores were higher in the nondominant arm in 39 subjects (72%), higher in the dominant arm in 9 (17%), and equal in 6 (11%). The 2 left-handed subjects had higher clinical ratings on the right. During quantitative computerized tremor analysis, there was a 1.71-fold mean difference between tremor 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 tremor in the dominant arm; those with ET who seek medical attention are more likely to exhibit severe tremor in their dominant arms. This study documents that mild asymmetry is a fundamental property of ET and that tremor is more severe in the nondominant arm.
Louis
E D
ED
Department of Neurology, College of Physicians and Surgeons, Columbia University, New York, NY, USA.
Wendt
K J
KJ
Pullman
S L
SL
Ford
B
B
D000368:Aged; D000369:Aged, 80 and over; D001132:Arm; D015331:Cohort Studies; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D012720:Severity of Illness Index; D014202:Tremor / Q000503:physiopathology*