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 m uch 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 100 0 persons, a 2750-fold difference. There has been no formal attempt to synthesize these disparate results. Our purpose is to provide an over view of existing studies, to examine methodologic issues that may acco unt for this tremendous variability in results, and to provide a more precise estimate of the prevalence of ET. Nineteen studies of the prev alence 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 pop ulations that influence comparability of studies. If we limit our exam ination to studies that (a) provided diagnostic criteria for ET, (b) d efined ET as an action tremor, and (c) used community-based rather tha n 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 th ese five provided age-stratified data. Among these four, the prevalenc e of ET in those over the age of 60 years was 13.0 to 50.5 cases per 1 000, a 3.9-fold difference.