Individual Variability in Neuropsychological Performances Predicts Cognitive Decline in De Novo Parkinson\u27s Disease

Introduction: Parkinson’s disease (PD) is a neurodegenerative disorder that commonly results in cognitive impairments and dementia. Intraindividual variability (IIV) of neuropsychological performance is a sensitive marker of cognitive decline in other neurologic populations. Furthermore, individuals with Parkinson’s disease have higher IIV when compared to healthy controls and other neurodegenerative diseases. However, studies have not examined the longitudinal utility of IIV in predicting future cognitive impairments among individuals with PD. In the current study we hypothesize that increased IIV would predict future cognitive decline above and beyond traditional neuropsychological markers of cognitive impairment. Methods: Data was collected from the Parkinson’s Progressive Markers Initiative (PPMI). The sample included 423 newly diagnosed PD patients and 175 healthy controls, who were followed up to five years (baseline, 1st, 2nd, 3rd, 4th and 5th annual follow up). All participants underwent neuropsychological tests of learning, memory, processing speed, attention, verbal fluency and visuospatial functioning. IIV was calculated as the standard deviation of 6 neuropsychological tests at each assessment. Cognitive status (cognitive intact, mild cognitive impairment, and dementia) was classified based on previously established criteria. Multilevel models (MLMs) were computed to examine the longitudinal relationship between IIV and cognitive status. Results: Analyses revealed that increased IIV (i.e. more dispersion in neuropsychological performance) was predictive of incident cognitive decline (i.e. greater risk of transitioning from cognitively intact to mild cognitive impairment or transitioning from mild cognitive impairment to dementia) among individuals with PD. Additional analyses revealed a significant IIV by Group (PD or control) interaction, meaning that IIV was predictive of declines in cognitive functioning among PD participants only, but not healthy controls. Conclusion: Findings suggest IIV may be a harbinger for future cognitive decline among individuals with PD. Earlier detection/diagnosis may allow for earlier interventions and preserve general cognitive functions and quality of life among patients