Predictors of Cognitive Change in Parkinson Disease: A 2-year Follow-up Study

Background: Mild cognitive impairment is common in Parkinson disease (PD-MCI). However, instability in this clinical diagnosis and variability in rates of progression to dementia raises questions regarding its utility for longitudinal tracking and prediction of cognitive change in PD. We examined baseline neuropsychological test and cognitive diagnosis predictors of cognitive change in PD. Methods: Persons with PD, without dementia PD (N=138) underwent comprehensive neuropsychological assessment at baseline and were followed up to 2 years. Level II Movement Disorder Society criteria for PD-MCI and PD dementia (PDD) were applied annually. Composite global and domain cognitive z-scores were calculated based on a 10-test neuropsychological battery. Results: Baseline diagnosis of PD-MCI was not associated with a change in global cognitive z-scores. Lower baseline attention and higher executive domain z-scores were associated with greater global cognitive z-score worsening regardless of cognitive diagnosis. Worse baseline domain z-scores in the attention and language domains were associated with progression to MCI or PDD, whereas higher baseline scores in all cognitive domains except executive function were associated with clinical and psychometric reversion to "normal" cognition. Conclusions: Lower scores on cognitive tests of attention were predictive of worse global cognition over 2 years of follow-up in PD, and lower baseline attention and language scores were associated with progression to MCI or PDD. However, PD-MCI diagnosis per se was not predictive of cognitive decline over 2 years. The association between higher executive domain z-scores and greater global cognitive worsening is probably a spurious result.