Tremor Research Group Essential Tremor Rating Scale (TETRAS): Assessing Impact of Different Item Instructions and Procedures

Introduction: The Tremor Research Group Essential Tremor Rating Scale (TETRAS) is a well-validated instrument to assess essential tremor. However, similar to all other tremor rating scales, specific instructions for individual tasks are based mostly on expert opinion and tradition. Several tasks have multiple possible variations that have never been compared to determine if they impact score.

Methods: Using blinded, randomized videotapes, a group of tremor experts evaluated multiple ET patients to determine: 1. whether assessments of spirals and writing samples are similar if the rater only sees the end result as opposed to actually watching the task, 2. whether arm tremor ratings (postural and wing-beating) are similar if the subjects hold both hands out concurrently vs. if they only hold one arm out at a time, 3. whether heal to shin tremor scores vary between supine and sitting, and 4. compared cursive vs script writing samples.

Results: Intraclass correlation coefficients (ICC) were excellent (>0.95) for all arm assessments. Writing tremor was rated worse if only rating the spiral/writing photos (p < 0.05) rather than also viewing the writing process, arm tremor scores were higher if each arm was rated individually (p < 0.001), heal to shin scores were higher when done sitting (p = 0.01), and cursive writing tended to be rated higher than script (p = 0.08).

Discussion: Minor procedure differences when administering the TETRAS can significantly alter results.