NEW ORLEANS—The Essential Tremor Rating Assessment Scale (TETRAS) has a high degree of inter-rater reliability for evaluating head and upper limb tremor, reported Rodger Elble, MD, at the 64th Annual Meeting of the American Academy of Neurology. TETRAS has good inter-rater reliability for evaluating voice tremor and fair inter-rater reliability for evaluating face, leg, and trunk tremor, according to Dr. Elble.
The most common scales among movement disorder specialists use subjective anchors and are not designed specifically for essential tremor, noted Dr. Elble, Professor of Neurology, Southern Illinois University School of Medicine in Springfield. He and his colleagues developed TETRAS as a simple, rapid assessment of essential tremor that uses objective, metric anchors to assign ratings on a scale of 0 to 4.
To evaluate the inter-rater reliability of TETRAS, Dr. Elble’s group videotaped 50 TETRAS exams, including assessments of 44 patients and six controls. The patients (26 men) had had essential tremor for at least six years. Ten specialists rated the patients in the videos twice. An interval of one to two months separated each pair of ratings. Of the 10 raters, six had been involved in the development of TETRAS from the beginning, and four had never used the scale.
Dr. Elble calculated the inter-rater reliability of the scale using a two-way random effects intraclass correlation (ICC) with an absolute agreement definition. The ICCs for head tremor, upper extremity tremor, postural tremor, and kinetic tremor were all approximately 0.9. For Archimedes spiral tremor, the ICC was slightly greater than 0.9. During both rating rounds, the ICC for voice tremor was approximately 0.75. The ICCs for face tremor, leg tremor, and trunk tremor were 0.64, 0.45, and 0.56, respectively. “These items contribute relatively little to the total score,” and ICCs for the total performance score did not improve significantly when these items were omitted, said Dr. Elble. In addition, ICCs did not differ statistically between experienced and inexperienced raters.
The ambiguous distinction between irregular movement and lower limb tremor could explain the lower ICCs for leg tremor, explained Dr. Elble. Also, examiners did not all perform this assessment in the same way.
The study results confirm a previous study conducted by the Tremor Research Group. In that study, one clinician examined 10 consecutive patients, and 10 group members rated each patient simultaneously. The live examinations yielded comparable ICCs.
“Most of the ratings for head tremor and upper limb tremor are anchored by specific amplitude ranges in centimeters,” Dr. Elble told Neurology Reviews. “Therefore, raters are not required to learn the meanings of ‘mild,’ ‘moderate,’ and ‘severe,’ but are simply asked to observe the tremor, estimate its maximum amplitude, and choose the corresponding rating.”
Zesiewicz TA, Elble RJ, Louis ED et al. Evidence-based guideline update: treatment of essential tremor: report of the Quality Standards subcommittee of the American Academy of Neurology. Neurology. 2011;77(19):1752-1755.