Objective: To assess the impact of psychiatric and other non-motor symptoms on disability in Parkinson's disease (PD).
Design: A convenience sample of 114 outpatients with idiopathic PD at the Parkinson's Disease Research, Education and Clinical Center (PADRECC) at the Philadelphia VA were assessed for depression and other non-motor symptoms in the context of receiving routine neurological care.
Materials and Methods: Patients were assessed with the Geriatric Depression Scale, the Hamilton Depression Rating Scale, the Structured Clinical Interview for DSM-IV depression module, the Mini-Mental State Examination, the Apathy Scale, the Epworth Sleepiness Scale, the Unified Parkinson's Disease Rating Scale, the Hoehn and Yahr staging scale, and the Schwab and England ADL scale. Pearson correlations and partial correlations (controlling for motor function) were calculated for the chosen variables and the two functional ability scales. Categorical variables were compared using the Chi-square statistic. Student's test and analysis of variance (ANOVA) were used to compare means. Stepwise multiple regression analysis (entering only variables significantly correlated with disability using bivariate correlation) was used to determine the impact of psychiatric symptoms, non-motor symptoms, and PD clinical variables on function. P<.05 was considered to be significant for all analyses.
Results: There was a significant correlation between increasing disability, as measured by the score on the Schwab and England Scale, and the following variables: increasing age, higher Hoehn and Yahr stage, higher UPDRS motor score, higher GDS-SF Score, higher HDRS score, a current DSM-IV depression diagnosis, lower MMSE score, current psychosis, higher Epworth Sleepiness Scale score, and higher Apathy Scale Score. Duration of PD and side predominance of motor symptoms were not significantly correlated with disability. Results of a stepwise multivariate regression analysis produced a model accounting for 54.0% of the variance in disability in this population. Increasing PD severity (as measured by the Hoehn and Yahr score) was most strongly associated with functional impairment, followed by increasing depressive symptoms (as measured by the HDRS) and cognitive impairment (as measured by the MMSE). Other clinical and demographic factors did not significantly add to the variance in disability that was explained by the model.
Conclusion: Results support and extend previous findings that psychiatric and other non-motor symptoms contribute significantly to disability in PD. Further study is required to determine if identifying and treating these symptoms will improve function.
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