Tremor asymmetry: Cross-sectional and prospective, longitudinal data in essential tremor.

INTRODUCTION

Efforts to characterize the semiology of tremor have considerable value. Despite this, available data on the extent and clinical correlates of tremor asymmetry in essential tremor (ET) are surprisingly scarce. Furthermore, there are no longitudinal data.

OBJECTIVE

To enhance our understanding of tremor asymmetry in ET.

METHODS

ET cases were enrolled in a prospective, longitudinal study of older adults with ET and examined at baseline and every 18 months using a reliable and valid clinical rating scale for action tremor (range = 0 - 23 in each arm).

RESULTS

In most cases (263 of 306, 85.9%), there was some degree of tremor asymmetry. The range of tremor asymmetry (side-side difference in tremor scores) was 0 to 13.5. In 108 cases (35.3%, i.e., one in three cases) tremor asymmetry was ≥3 points (equivalent to at least a 1-point difference between sides on three tasks). In cross-sectional analyses, degree of tremor asymmetry was weakly inversely associated with tremor duration (Spearman's rho = -0.154, p = 0.007). In longitudinal analyses of 89 cases with up to 4.5 years of follow-up, degree of asymmetry was consistent across time (intraclass correlation coefficients = 0.799 - 0.840, p < 0.001).

CONCLUSIONS

Most ET cases evidenced tremor asymmetry. In one third of cases, tremor asymmetry was ≥3 points (equivalent to at least a 1-point difference between sides on three tasks). In cross-sectional analyses, there was a weak inverse association between tremor asymmetry and tremor duration. During longitudinal follow-up, tremor asymmetry remained consistent, although length of follow-up was limited.