Cognition and the course of prodromal Parkinson's disease

Background Prospective data on cognitionin prodromalParkinson's disease are limited. The objectives of this study were to assess in prodromalPD (1) if baseline cognitionpredicts conversion to clinical PD, (2) if baseline dopamine transporterbinding predicts longitudinal changes in cognition, and (3) if impaired olfactionpredicts future cognitivedecline. Methods Prodromalparticipants were 136 hyposmic individuals enrolled in the Parkinson Associated Risk Study. We examined baselineneuropsychological test performance in PD converters versus nonconverters and the association between baseline dopamine transporterbinding and change in cognition. An additional 73 normosmic individuals were included in analyses of the relationship between hyposmiaand cognitivedecline. Results In prodromalparticipants, baseline cognitivescores did not significantly predict conversion, but converters performed numerically worse on 5 of the 6 cognitivedomains assessed, with the greatest differences in executive function/working memory (0.68 standard deviation lower) and global cognition(0.64 standard deviation lower). Lower baseline dopamine transporterbinding predicted greater future decline in processing speed/attention (P = 0.02). Hyposmiapredicted greater future decline in language (P = 0.005) and memory (P = 0.01) abilities. Conclusions Given hyposmiain the general population predicts cognitivedecline, the role of cognitionin predicting conversion in prodromalPD needs to be assessed in large cohorts followed long-term. The dopamine system may be associated with changes in processing speed/attention in individuals at risk for PD. © 2017 International Parkinson and Movement Disorder Society