Essential tremor (ET) subjects demonstrated less improvement than controls when drawing sequential spirals, suggesting a possible motor learning deficit in ET, here captured in an affected limb, according to a recent study. Researchers utilized computerized spiral analysis, which captures multiple characteristics of Archimedean spirals and quantifies performance through calculated indices. 161 ET and 80 age-matched control subjects drew 10 consecutive spirals on a digitizing tablet. Degree of severity (DoS)—a weighted, computational score of spiral execution that takes into account spiral shape and line smoothness, previously validated against a clinical rating scale—was calculated in both groups. Tremor amplitude (Ampl), an independent index of tremor size, measured in centimeters, was also calculated. They found:
- Both groups demonstrated improvement in DoS across trials, but with less improvement in the ET group compared to controls.
- Ampl demonstrated a tendency to worsen across trials in ET subjects.
- DoS improved independently of Ampl, showing that DoS and Ampl are separable motor physiologic components in ET that may be independently mediated.
Kim CY, Luo L, Yu Q, et al. Repeated spiral drawings in essential tremor: A possible limb-based measure of motor learning. [Published online ahead of print September 11, 2018]. Cerebellum. doi:10.1007/s12311-018-0974-x.