Abstract
INTRODUCTION: Parkinson's disease (PD) is a neurodegenerative disorder that commonly results in cognitive impairments and dementia. Intraindividual variability of neuropsychological performance is a sensitive marker of cognitive decline in other neurologic populations. However, studies have not examined the longitudinal utility of intraindividual variability in predicting future cognitive impairments among individuals with PD. In the current study, we hypothesized that increased intraindividual variability would predict future cognitive decline independent of traditional neuropsychological markers of cognitive impairment. METHODS: The sample included 423 newly diagnosed PD patients and 175 healthy controls, who were followed up to 5 years (baseline, first, second, third, fourth, and fifth annual follow-up). Participants underwent tests of learning, memory, processing speed, attention, verbal fluency, and visuospatial functioning. Cognitive status (cognitive intact, mild cognitive impairment, and dementia) was classified based on previously established criteria. Multilevel models were computed to examine the longitudinal relationship between intraindividual variability, cognitive status, and general cognitive functioning. RESULTS: Analyses revealed that increased intraindividual variability was predictive of incident cognitive decline among individuals with PD. Specifically, greater dispersion in neuropsychological performance was associated with greater risk of transitioning from cognitively intact to mild cognitive impairment or transitioning from mild cognitive impairment to dementia. Additional analyses revealed a significant Intraindividual Variability × Group (PD or control) interaction, meaning that intraindividual variability was predictive of declines in cognitive functioning among PD participants only but not healthy controls. CONCLUSION: Intraindividual variability may be a harbinger for future cognitive decline among individuals with PD. (PsycINFO Database Record (c) 2020 APA, all rights reserved).