Digitizing Tablet and Fahn-Tolosa-Marín Ratings of Archimedes Spirals have Comparable Minimum Detectable Change in Essential Tremor

Tremor Other Hyperkinet Mov (N Y). 2017 Jul 7:7:481. doi: 10.7916/D89S20H7. eCollection 2017.

Abstract

Background: 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.

Keywords: Essential tremor; minimum detectable change; rating scale; spirography.

Publication types

  • Clinical Trial, Phase II
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Computers, Handheld*
  • Diagnosis, Computer-Assisted*
  • Double-Blind Method
  • Essential Tremor / diagnosis*
  • Essential Tremor / physiopathology
  • Female
  • Humans
  • Linear Models
  • Male
  • Middle Aged
  • Motor Skills*
  • Reproducibility of Results