Objective: To identify variables that can distinguish essential tremor from dystonic tremor using automated analysis of hand drawn Archimedes spirals.

Background: Spiral drawings using pen-on-paper are commonly used in the clinic to quantify action/ postural tremor. Some attributes of the spiral like spiral axis and variability were suggested to be useful in differentiating tremor subtypes. We aimed to develop an automated algorithm to analyse pen-on-paper spirals and identify objective measures to differentiate tremor subtypes, specifically essential tremor (ET, including ET plus) and dystonic tremors (DT).

Method: 32 subjects with postural/action tremor (dystonic tremors, n= 13, essential tremor, n= 19) were recruited. Each subject produced a free hand, clockwise spiral using the dominant hand on standard pen and paper. Scanned images underwent pre-processing. Inter loop distances along four axes were calculated across five turns of the spiral and mean loop width calculated for each loop. The mean loop widths (MW1, MW2, MW3, MW4, MW5) were compared between DT and ET groups using a repeated measures model with tremor type as the between-subjects factor.

Results: There was a significant main effect of tremor type on mean loop width [F(1,30)=4.45, P=0.043] (Figure 1).  Within the tremor groups DT and ET, mean widths remained relatively constant across loops [F(4,120)= 1.89, p=0.175] and there was no significant interaction between MW and tremor type [F(4,120)=0.427, p=0.574].

Conclusion: Automated analysis of pen-on-paper spirals can generate clinically relevant variables to differentiate tremor subtypes. Spiral loop width derived from hand drawn spirals may be a useful parameter to distinguish DT and ET.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/spiral-loop-width-differentiates-essential-tremor-and-dystonic-tremor/