HOW NORMAL IS NORMAL - MILD TREMOR IN A MULTIETHNIC COHORT OF NORMAL SUBJECTS

Background: While many ''normal'' subjects exhibit mild clinically det ectable tremor, the extent to which this tremor is present has receive d little attention. Objective: To characterize the prevalence and clin ical characteristics of mild, clinically detectable tremor in a multie thnic cohort of normal subjects. Methods: Normal control subjects (n=3 6) and their relatives (n=67) were enrolled in a community-based case- control study of the familial aggregation of essential tremor. Subject s underwent a tremor interview and videotaped tremor examination. Two neurologists independently rated the severity of tremor during differe nt postures and tasks, and a total tremor score (maximum score, 36) wa s calculated for each subject. Eight subjects were randomly selected t o undergo quantitative computerized tremor analysis. Results: In 103 n ormal subjects (36 control subjects and 67 relatives of control subjec ts) the mean total tremor score was 4.8 (range, 0-12.5), Ninety-nine ( 96%) of 103 subjects had tremor, as defined by a total tremor score of 0.5 or higher. For most tasks, the mean tremor score was greater in t he nondominant than in the dominant arm. The total tremor score correl ated highly with age (r=0.28; P=.004). There were no ses or ethnic dif ferences in the mean total tremor scores. On tremor analysis, the ampl itude and frequency of the tremor differed from that in a group of sim ilarly studied subjects with essential tremor. Conclusions: Normal sub jects almost uniformly have a clinically detectable tremor that is mil d and age dependent. Characterization of this tremor helps to establis h standards for normal tremor. These standards are crucial for accurat e diagnostic classification in population-based studies of essential t remor.