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Introduction. Among the nonmotor features of Parkinson's disease (PD), cognitive impairment is one of the most troublesome problems. New diagnostic criteria for mild and major neurocognitive disorder (NCD) in PD were established by Diagnostic and Statistical Manual of Mental Disorders 5th edition (DSM-5). The aim of our study was to establish the diagnostic accuracy of widely used screening tests for NCD in PD. Methods. Within the scope of our study we evaluated the sensitivity and specificity of different neuropsychological tests (Addenbrooke's Cognitive Examination (ACE), Mattis Dementia Rating Scale (MDRS), Mini Mental State Examination (MMSE), and Montreal Cognitive Assessment (MoCA)) in 370 PD patients without depression. Results. MoCA and ACE feature the finest diagnostic accuracy for detecting mild cognitive disorder in PD (DSM-5) at the cut-off scores of 23.5 and 83.5 points, respectively. The diagnostic accuracy of these tests was 0.859 (95% CI: 0.818–0.894, MoCA) and 0.820 (95% CI: 0.774–0.859, ACE). In the detection of major NCD (DSM-5), MoCA and MDRS tests exhibited the best diagnostic accuracy at the cut-off scores of 20.5 and 132.5 points, respectively. The diagnostic accuracy of these tests was 0.863 (95% CI: 0.823–0.897, MoCA) and 0.830 (95% CI: 0.785–0.869, MDRS). Conclusion. Our study demonstrated that the MoCA may be the most suitable test for detecting mild and major NCD in PD.

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Asymmetry is one of the unique and mysterious features of Parkinson's disease (PD). Motor symptoms develop unilaterally either on the left (LPD) or the right side (RPD). Incongruent data are available whether the side of onset has an impact on cognition in PD. The objective of this study is to compare the visuospatial performance of RPD and LPD patients. Seventy-one non-demented, non-depressive and right-handed patients were categorized into RBD (n = 36) and LPD (n = 35) groups. Rey-Osterrieth Complex Figure Test (ROCF) was evaluated by both the Taylor's and Loring's scoring systems. Subsequently, we also performed subgroup analyses on patients having short disease duration (≤5 years, 15 RBD and 15 LPD patients). The standard analysis of ROCF (Taylor's system) did not reveal any differences; however, the utilization of the Loring's system demonstrated that LPD patients had significantly worse visuospatial performance than the RPD subjects (3.0 vs. 2.0 points, median, p = 0.002). Correlation between the number of spatial errors and the degree of asymmetry was significant (r = -0.437, p = 0.001). However, this difference could not be observed in PD patients with short disease duration. LPD patients had worse visuospatial performance than the RPD subjects and the number of errors tightly correlated with the degree of asymmetry and long disease duration.

This association may reflect a trait-like relationship between vitamin D and brain size possibly determined in early development.