Objective: To assess temporal amplitude variability in patients with essential tremor (ET).
Methods: Patients who satisfied the diagnostic criteria for probable or definite ET were enrolled in the study. Each enrolled patient was first rated using the essential tremor rating assessment scale (TETRAS). Postural and kinetic tremors of the arms were then measured using a quantitative motor assessment system (QMAS) starting at 8:00 AM (T0-baseline) every 2 h for 6 h. Subjects were videotaped performing the tasks. Single subjects consecutively performed each assessment twice during every time-interval. At the end of the study, videos were randomized and blindly rated using TETRAS.
Results: Twelve ET subjects were enrolled. QMAS and video scores were directly correlated with high test-retest reliability for each time-interval. Furthermore, the QMAS scores at T0 significantly correlated with in-person rated TETRAS scores as well as with subsequent time-intervals instrumental scores. No significant differences were detected between time-intervals QMAS average measurements using ANOVA. There was a maximal 23% absolute variation in tremor amplitude from baseline as determined by the QMAS. Test for equality of variance showed high measurement variability for subjects with high QMAS scores at T0 and throughout the 6 h of assessment.
Conclusions: Baseline measures are predictive of tremor amplitude at subsequent assessments during the day. High amplitude tremor is associated with high intra-assessment variability.
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