Intraindividual variability in neuropsychological performance predicts longitudinal cortical volume loss in early Parkinson's disease.

Cognitive impairment is common among individuals with Parkinson's disease (PD). Intraindividual variability (IIV) is a measure of variability across multiple tasks of cognitive functioning. Due to the limited amount of research, particularly among individuals with PD, IIV has been an underutilized metric of cognitive functioning both in research and clinical practice. Previous research demonstrated that individuals with PD have greater variability in cognitive performance relative to controls, and that IIV is predictive of future cognitive impairments. The aim of this study is to investigate the association between baseline IIV and change in cortical and subcortical volumes among individuals with PD. The present study used data from 80 newly diagnosed PD patients who were part of a longitudinal cohort study (Parkinson progression marker initiative [PPMI]). Participants completed neuropsychological measures and underwent T1 structural magnetic resonance imaging (MRI) at baseline and the first annual follow-up. Neuropsychological tests assessed attention, processing speed, visuospatial functioning, verbal fluency learning, and memory. T1 scans were processed using standard Freesurfer protocols for extraction of regional volumes. Greater IIV at baseline was predictive of change in cortical volume in posterior temporal/parietal regions over the 1-year period. Baseline IIV predicted cortical volume changes above and beyond the main effect of motor severity and the baseline statistical mean/global cognition score. Our results provide initial evidence that IIV is a marker of longitudinal cortical volume loss. Evidence is building that IIV is a sensitive marker of cognitive impairment and the underlying neurodegeneration among individuals with PD. (PsycInfo Database Record (c) 2022 APA, all rights reserved).