How common is the most common adult movement disorder? Update on the worldwide prevalence of essential tremor.

Essential tremor (ET) is among the more prevalent neurological disorders, yet prevalence estimates have varied enormously, making it difficult to establish prevalence with precision. We: (1) reviewed the worldwide prevalence of ET in population-based epidemiological studies, (2) derived as precisely as possible an estimate of disease prevalence, and (3) examined trends and important differences across studies. We identified 28 population-based prevalence studies (19 countries). In a meta-analysis, pooled prevalence (all ages) = 0.9%, with statistically significant heterogeneity across studies (I(2) = 99%, P < 0.001). In additional descriptive analyses, crude prevalence (all ages) = 0.4%. Prevalence increased markedly with age, and especially with advanced age. In the meta-analysis, prevalence (age >or= 65 years) = 4.6%, and in additional descriptive analyses, median crude prevalence (age >or= 60-65) = 6.3%. In one study of those age >or= 95 years, crude prevalence = 21.7%. Several studies reported ethnic differences in prevalence, although more studies are needed. Greater than one-third of studies show a gender difference, with most demonstrating a higher prevalence among men. This possible gender preference is interesting given clinical, epidemiological, and pathological associations between ET and Parkinson's disease. Precise prevalence estimates such as those we provide are important because they form the numerical basis for planned public health initiatives, provide data on the background occurrence of disease for family studies, and offer clues about the existence of environmental or underlying biological factors of possible mechanistic importance. (c) 2010 Movement Disorder Society.