Objectives: To examine the effect of depression and other nonmotor symptoms on functional ability in Parkinson's disease (PD).
Design: A cross-sectional study of a convenience sample of PD patients receiving specialty care.
Setting: The Parkinson's Disease Research, Education and Clinical Center at the Philadelphia Veterans Affairs Medical Center.
Participants: One hundred fourteen community-dwelling patients with idiopathic PD.
Measurements: The Unified Parkinson's Disease Rating Scale (UPDRS); Hoehn and Yahr Stage; Mini-Mental State Examination; Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, depression module; probes for psychotic symptoms; Hamilton Depression Rating Scale; Geriatric Depression Scale—Short Form; Apathy Scale; and Epworth Sleepiness Scale. Disability was rated using the UPDRS activity of daily living (ADL) score and the Schwab and England ADL score. Multivariate analysis determined effect of depression and other nonmotor symptoms on disability.
Results: The presence of psychosis, depressive disorder, increasing depression severity, age, duration of PD, cognitive impairment, apathy, sleepiness, motor impairment, and percentage of time with dyskinesias were related to greater disability in bivariate analyses. Entering these factors into two multiple regression analyses, only the increasing severity of depression and worsening cognition were associated with greater disability using the UPDRS ADL score, accounting for 37% of the variance in disability (P<.001). These two factors plus increasing severity of PD accounted for 54% of the variance in disability using the Schwab and England ADL score (P<.001).
Conclusion: Results support and extend previous findings that psychiatric and other nonmotor symptoms contribute significantly to disability in PD. Screening for nonmotor symptoms in PD is necessary to more fully explain functional limitations. Further study is required to determine whether identifying and treating these symptoms will improve function and quality of life.