Shannon entropy: A novel parameter for quantifying pentagon copying performance in non-demented Parkinson's disease patients

Introduction: Impaired copy of intersecting pentagons from the Mini-Mental State Examination (MMSE), has been used to assess dementia in Parkinson's disease (PD).We used a digitizing tablet during the pentagon copying test (PCT) as a potential tool for evaluating early cognitive deficits in PD without major cognitive impairment.We also aimed to uncover the neural correlates of the identified parameters using whole-brain magnetic resonance imaging (MRI).Methods: We enrolled 27 patients with PD without major cognitive impairment and 25 age-matched healthy controls (HC).We focused on drawing parameters using a digitizing tablet.Parameters with between-group differences were correlated with cognitive outcomes and were used as covariates in the whole-brain voxelwise analysis using voxel-based morphometry; familywise error (FWE) threshold p < 0.001.Results: PD patients differed from HC in attention domain z-scores (p < 0.0001).In terms of tablet parameters, the groups differed in Shannon entropy (horizontal in-air, p = 0.003), which quantifies the movements between two strokes.In PD, a correlation was found between the median of Shannon entropy (horizontal in-air) and attention z-scores (R = -0.55,p = 0.006).The VBM revealed an association between our drawing parameter of interest and gray matter (GM) volume variability in the right superior parietal lobe (SPL).Conclusion: Using a digitizing tablet during the PCT, we identified a novel entropy-based parameter that differed between the nondemented PD and HC groups.This in-air parameter correlated with the level of attention and was linked to GM volume variability of the region engaged in spatial attention.