Screening for and Estimating the Prevalence of Essential Tremor: A Random-Digit Dialing-Based Study in the New York Metropolitan Area

Abstract

Background: There are nearly no published screening instruments for essential tremor (ET). This is a remarkable fact, given its high prevalence. Here, we assess the validity of a screening questionnaire and hand-drawn spirals and also estimate the prevalence of ET in a community sample. Methods: Four hundred nineteen study subjects living in a geographically defined area in the New York metropolitan area were contacted using a random digit telephone dialing scheme. Seven tremor screening questions were administered and each subject drew 2 spirals. A movement disorders neurologist assigned ET diagnoses based on neurological examination. Results: The spirals were a more sensitive test than the screening questions (73.7 vs. 26.3%); specificities of the 2 tests were similar (95.5 vs. 96.8%). The combination of both tests was not superior to the use of spirals alone. The positive predictive value of the spiral test was 43.8%. The crude prevalence of ET, 19 of 419 (4.53%, 95% CI 2.92-6.97), increased with age (p = 0.049). Conclusions: A screening spiral was more sensitive than a screening questionnaire for ET and was moderately sensitive. Nearly one-half of subjects who screened positive had ET; therefore, when screening a population, one can expect the number of true positives and false positives to be roughly equivalent.