Validity of a performance-based test of function in essential tremor

Background: The central factor influencing therapeutic decisions in essential tremor (ET) is the functional impact of the tremor. Neither the neurological examination nor computerized tremor analysis measures function. Questionnaires may assess function, but data are highly subjective. Performance-based tests of functional impairment provide an alternative means with which to assess the functional impact of ET. Objective: To determine the internal consistency and validity of a performance-based measure of functional impairment in ET. Methods: Subjects with ET from a community in northern Manhattan, NY, and from a clinic and control subjects each underwent a 21/2-hour evaluation including 12 screening questions for ET, a 31-item Tremor Disability Questionnaire to assess the functional impact of tremor, a 26-item Videotaped Tremor Examination that was rated by a neurologist, a 15-item, 10-minute Performance-Based Test, and Quantitative Computerized Tremor Analysis. Internal consistency was assessed with Cronbach alpha. The correlation between the Performance-Based Test and these other measures of tremor was assessed by means of correlation coefficients (r). Results: There were 50 ET cases and 51 normal control subjects. The Performance-Based Test was internally consistent (Cronbach alpha = .92). It also demonstrated validity among cases; the total score correlated with the total number of screening questions answered yes (r = 0.44; P = .001), the total score on the Tremor Disability Questionnaire (r = 0.55; P<.001), the total score on the Videotaped Tremor Examination (r = 0.71; P<.001), and multiple physiological measures recorded during Quantitative Computerized Tremor Analysis. Conclusions: A valid performance-based test was developed to objectively assess functional capacity in patients with ET. This test would be useful in therapeutic trials, where it would provide an objective means to quantify the functional impact of tremor.