Neurocognitive Functioning in Parkinsons Disease Patients: Assessing the Unique Contributions of Depression and Fatigue While Controlling for Disease Severity
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Background: While individuals diagnosed with Parkinsons disease (PD) often experience cognitive deficits, depression, and fatigue, the relationships among these non-motor sequelae throughout the progression of the disease are unclear. Objective: To examine the relationships among disease severity, depression, and fatigue and investigate the independent contributions of depression and fatigue to a composite measure of cognitive functioning, when controlling for disease severity in PD patients. Methods: A mixed retrospective and prospective sample of PD patients completed a comprehensive neuropsychological battery, as well as self-report measures of depression and fatigue. Cognitive functioning was represented by a summary statistic, or cognitive impairment index (CII). A hierarchal linear regression model, controlling for disease severity, examined the unique contributions of depression and fatigue on cognitive functioning. A Pearson correlation examined the relationship between depression and fatigue. Results: At step one, disease severity significantly contributed to the model, F(1, 41) = 48.06, p < .001, accounting for 52.8% of the variance in cognitive functioning. Introduction of depression and fatigue explained an additional 7.2% of the variance and this change in R2 was significant F(2,39) = 4.68, p < 0.05. Only depression continued to be a significant contributor beyond disease severity, t = 2.21, = 0.24, p < 0.05 and the change in the model was significant, F(1, 40) = 4.88, p < 0.05, R2 change = 0.05Conclusions: Findings suggest that depression is uniquely associated with cognitive functioning observed in PD patients independent of disease severity or level of fatigue. Interventions targeted towards depression may improve cognitive functioning.