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.