How common is the most common adult movement disorder? Estimates of the prevalence of essential tremor throughout the world

Essential tremor (ET) is the most common adult movement disorder, as much as 20 times more prevalent than Parkinson's disease. Estimates of the crude prevalence of ET range widely from 0.08 to 220 cases per 1000 persons, a 2750-fold difference. There has been no formal attempt to synthesize these disparate results. Our purpose is to provide an overview of existing studies, to examine methodologic issues that may account for this tremendous variability in results, and to provide a more precise estimate of the prevalence of ET. Nineteen studies of the prevalence of ET were reviewed. Factors that contribute to the broad range of prevalence estimates include (a) differences in study design that influence validity and (b) differences in characteristics of study populations that influence comparability of studies. If we limit our examination to studies that (a) provided diagnostic criteria for ET, (b) defined ET as an action tremor, and (c) used community-based rather than service-based designs, then five studies remain, and the prevalence of ET is 4.1 to 39.2 cases per 1000, a 9.6-fold difference. Four of these five provided age-stratified data. Among these four, the prevalence of ET in those over the age of 60 years was 13.0 to 50.5 cases per 1000, a 3.9-fold difference.