Get access

Validation of digital spiral analysis as outcome parameter for clinical trials in essential tremor§


  • Funding agencies: This research was conducted through funding from the NINDS Intramural Research Program, the Austrian Science Fund, FWF (Erwin Schrödinger Fellowship, project no.: J2783-B09; to D.W.), and Ariston Pharmaceuticals (to L.W.).

  • Relevant conflicts of interest/financial disclosures: Nothing to report. Dr. Toro is the developer and intellectual owner of Neuroglyphics, a freely available software, with no financial interests involved.

  • §

    Full financial disclosures and author roles may be found in the online version of this article.


Essential tremor, one of the most prevalent movement disorders, is characterized by kinetic and postural tremor affecting activities of daily living. Spiral drawing is commonly used to visually rate tremor intensity, as part of the routine clinical assessment of tremor and as a tool in clinical trials. We present a strategy to quantify tremor severity from spirals drawn on a digitizing tablet. We validate our method against a well-established visual spiral rating method and compare both methods on their capacity to capture a therapeutic effect, as defined by the change in clinical essential tremor rating scale after an ethanol challenge. Fifty-four Archimedes spirals were drawn using a digitizing tablet by nine ethanol-responsive patients with essential tremor before and at five consecutive time points after the administration of ethanol in a standardized treatment intervention. Quantitative spiral tremor severity was estimated from the velocity tremor peak amplitude after numerical derivation and Fourier transformation of pen-tip positions. In randomly ordered sets, spirals were scored by seven trained raters, using Bain and Findley's 0 to 10 rating scale. Computerized scores correlated with visual ratings (P < 0.0001). The correlation was significant at each time point before and after ethanol (P < 0.005). Quantitative ratings provided better sensitivity than visual rating to capture the effects of an ethanol challenge (P < 0.05). Using a standardized treatment approach, we were able to demonstrate that spirography time-series analysis is a valid, reliable method to document tremor intensity and a more sensitive measure for small effects than currently available visual spiral rating methods. © 2011 Movement Disorder Society