Ethnic differences in essential tremor

Background: Ethnic differences in the clinical characteristics (severity an d distribution) of essential tremor (ET) have not been studied. The presenc e of these differences suggests that ET is not a homogeneous disease and th at there is variability in disease expression under different circumstances . As part of a community-based study, we evaluated a multiethnic group of c ases. Objective: To assess whether there are ethnic differences in the clinical c haracteristics of ET. Methods: Elderly residents of Washington Heights-Inwood, New York, were enr olled in a community-based health study (N = 2117). Participants underwent a medical interview and a neurological examination conducted by a neurologi st, and subjects with ET were identified. These subjects with ET were then enrolled in a community-based study of ET and underwent a tremor interview, a videotaped tremor examination, and in some cases, a performance-based te st of function and quantitative computerized tremor analysis. A total tremo r score (range, 0-36, with 0 indicating no tremor and 36 indicating maximum tremor) was assigned to each subject based on 2 neurologists' ratings of t he termor examination. Results Among 62 subjects with ET (white [n = 16], African American [n = 18 ], and Hispanic [n = 28]), there were ethnic differences in the total tremo r score (F = 3.68, P = .03). In a multiple regression model adjusting for a ge, white subjects had a mean total tremor score that was 5.3 points lower than that of nonwhite subjects (P = .008). We divided the nonwhite group in to African American and Hispanic subgroups. In a regression model adjusting for age and duration, the white group had a mean total tremor score that w as 6,1 points lower than that of the Hispanic group (P = .07) and 7.2 point s lower than that of the African American group (P = .05). The mean perform ance-based test score was 1.7 times higher in the African American group an d 2.1 times higher in the Hispanic group compared with the white group (P = .38). No subjects ill the African American group had head tremor, while subjects: in the white group (25%) and 8 subjects in the Hispanic group (29 %) did have head tremor (chi(2) = 6.17, P=.05). Conclusions: There are ethnic differences in the expression of ET, suggesti ng that ET is not a homogeneous disorder. These differences may reflect phe notypic variability caused by genotypic differences or differences in expos ure to environmental factors that influence tremor.