56 research outputs found
Corrigendum: Digitizing Tablet and Fahn–Tolosa–Marín Ratings of Archimedes Spirals have Comparable Minimum Detectable Change in Essential Tremor
No full textCorrigendum to: Elble RJ, Ellenbogen A. Digitizing tablet and Fahn–Tolosan–Marín ratings of Archimedes spirals have comparable minimum detectable change in essential tremor. Tremor Other Hyperkinet Mov. 2017; 7. doi: 10.7916/D89S20H
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Estimating Change in Tremor Amplitude Using Clinical Ratings: Recommendations for Clinical Trials
No full textTremor rating scales are the standard method for assessing tremor severity and clinical change due to treatment or disease progression. However, ratings and their changes are difficult to interpret without knowing the relationship between ratings and tremor amplitude (displacement or angular rotation), and the computation of percentage change in ratings relative to baseline is misleading because of the ordinal nature of these scales. For example, a reduction in tremor from rating 2 to rating 1 (0–4 scale) should not be interpreted as a 50% reduction in tremor amplitude, nor should a reduction in rating 4 to rating 3 be interpreted as a 25% reduction in tremor. Studies from several laboratories have found a logarithmic relationship between tremor ratings R and tremor amplitude T, measured with a motion transducer: logT = α·R + β, where α ≈ 0.5, β ≈ –2, and log is base 10. This relationship is consistent with the Weber–Fechner law of psychophysics, and from this equation, the fractional change in tremor amplitude for a given change in clinical ratings is derived: (Tf−Ti)/Ti=10α(Rf−(Ri)−1, where the subscripts i and f refer to the initial and final values. For a 0–4 scale and α = 0.5, a 1‐point reduction in tremor ratings is roughly a 68% reduction in tremor amplitude, regardless of the baseline tremor rating (e.g., 2 or 4). Similarly, a 2‐point reduction is roughly a 90% reduction in tremor amplitude. These Weber–Fechner equations should be used in clinical trials for computing and interpreting change in tremor, assessed with clinical ratings
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Digitizing Tablet and Fahn–Tolosa–Marín Ratings of Archimedes Spirals have Comparable Minimum Detectable Change in Essential Tremor
No full textBackground: Drawing Archimedes spirals is a popular and valid method of assessing action tremor in the upper limbs. We performed the first blinded comparison of Fahn–Tolosa–Marín (FTM) ratings and tablet measures of essential tremor to determine if a digitizing tablet is better than 0–4 ratings in detecting changes in essential tremor that exceed random variability in tremor amplitude.Methods: The large and small spirals of FTM were drawn with each hand on two consecutive days by 14 men and four women (age 60±8.7 years [mean±SD]) with mild to severe essential tremor. The drawings were simultaneously digitized with a digitizing tablet. Tremor in each digitized drawing was computed with spectral analysis in an independent laboratory, blinded to the clinical ratings. The mean peak-to-peak tremor displacement (cm) in the four spirals and mean FTM ratings were compared statistically.Results: Test–retest intraclass correlations (ICCs) (two-way random single measures, absolute agreement) were excellent for the FTM ratings (ICC 0.90, 95% CI 0.76–0.96) and tablet (ICC 0.97, 95% CI 0.91–0.99). Log10 tremor amplitude (T) and FTM were strongly correlated (logT = αFTM + β, α≈0.6, β≈–1.27, r = 0.94). The minimum detectable change for the tablet and FTM were 51% and 67% of the initial assessment.Discussion: Digitizing tablets are much more precise than clinical ratings, but this advantage is mitigated by the natural variability in tremor. Nevertheless, the digitizing tablet is a robust method of quantifying tremor that can be used in lieu of or in combination with clinical ratings.</p
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