AbstractBackgroundPrevious studies suggest the usefulness of CDT in distinguishing between neurodegenerative diseases. The purpose of this study was to examine differences in CDT performance in individuals with AD and PD compared to normal controls.MethodsTotal of 194 participants. Four groups included in analysis: patients that met diagnostic criteria for late MCI/mild AD, moderate AD, PD with no cognitive impairment, and normal controls. All participants completed MMSE and CDT. MMSE score ≤ 23 considered moderate AD, MMSE score >24 considered mixed late MCI/mild AD, all PD patients had MMSE score >24.ResultsAn ANOVA was used to examine group differences in CDT and MMSE scores. There was a significant main effect of group for both CDT and MMSE scores (p < 0.001). Moderate AD group had significantly lower MMSE scores compared to other groups (average MMSE score of 19.4 for moderate AD compared to 26.6 for mild AD, 26.9 for Parkinson’s, and 28.2 for controls). Post‐hoc t‐tests (Bonferroni corrected for multiple comparisons) showed moderate AD group had significantly higher error scores on CDT compared to controls (p<0.001). Moderate AD group also had significantly higher error score compared to both MCI/mild AD and PD patient groups (p<0.001). No statistical significance existed in error scores between MCI/mild AD group compared to controls (p = 0.134) or to Parkinson’s disease (p = 1.000). No statistical significance in CDT error scores between the Parkinson’s group compared to controls (p = 0.904). Findings suggest executive functioning may only begin to significantly decline in advanced stages of AD.ConclusionOur findings suggest that deficits in executive functions measured by CDT is impaired in moderate AD but relatively preserved in MCI/mild AD and PD with no cognitive impairment, which is consistent with previous studies. One limitation of the study is that we did not include a copy trial for the CDT, which may support that our findings are due to executive dysfunction rather than visuospatial deficits. Future directions include increasing sample sizes, including individuals with PD with cognitive impairment, and using novel digital versions of the CDT to different variables of the CDT such as time to start and complete, visuospatial coordination, and graphic size.