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Elan D. Louis, MD, MS; Kristin J. Wendt, MPH; Steven M. Albert, MS, PhD; Seth L. Pullman, MD; Qiping Yu, PhD; Howard Andrews, PhD

Arch Neurol. 1999;56:841-846.

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 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 . 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 =.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.

From the Department of Neurology (Drs Louis, Albert, Pullman, and Yu) and the Gertrude H. Sergievsky Center (Drs Louis and Albert and Ms Wendt), College of Physicians and Surgeons, Columbia University, and the Data Management and Statistical Analysis Unit, New York State Psychiatric Institute (Dr Andrews), New York, NY.

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