Objective To compare spiral drawings between essential tremor (ET) and functional tremor (FT); exploring spiral size, axis, density and tremor severity score for parameters to potentially distinguish ET from FT.
Method Spiral drawing data of 29 patients with either ET or FT were acquired from ASPH using the NHs patient database and patient notes. Using a ruler spiral size was represented as the horizontal diameter, and it was also measured to 3-loops (3-turn diameter/3TD). Spiral density was determined using total loop number and the horizontal diameter of each spiral. Tremor severity score was determined using a validated tremor scale (Bain). The spirals were also rated for the presence of single or multiple axes. An independent t-test was used to compare tremor severity, 3TD and size and a Mann-Whitney test was used to compare spiral density between both groups.
Results Spirals drawn by ET patients had significantly higher tremor severity scores than FT patients (4.18 vs 2.82 p=0.03). Spiralaxis is significantly affected by tremor type (p=0.03); there was a significantly greater proportion of patients in the ET group that demonstrate a single axis on spirography compared to those in the FT group (57% vs 14.3%; p=0.02). In two patients with FT and ET there were variable degrees of change in tremor severity over time, with the change in severity in FT being greater than in ET.
Conclusion ET and FT can be distinguished by tremor severity and the presence of a single vs multiple axis on analysis of handwritten spiral drawings.
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