Progression of parkinsonism and loss of cognitive function in Alzheimer disease

Objective: To assess the relation between parkinsonism and cognitive function in Alzheimer disease from cross-sectional and longitudinal perspectives. Design: Prospective cohort study with annual clinical evaluations during a 4-year period. Setting: Alzheimer disease clinic in an urban medical center. Participants: Four hundred ten persons with clinically diagnosed Alzheimer disease. Main Outcome Measures: Global and specific measures of cognitive function and parkinsonism. Results: Higher levels of parkinsonism at baseline were reliably associated with lower levels of cognitive function at baseline and with more rapid cognitive decline during the 4-year study period. However, the associations were small, with baseline parkinsonism accounting for less than 10% of the variation either in baseline cognitive function or in the rate of cognitive decline. By contrast, rates of change in parkinsonism and cognitive function were strongly correlated, with 70% or more shared variance in the rates of change in many models. The association was observed with diverse measures of cognition and parkinsonism and was not explained by demographic variables or use of neuroleptic medications. Conclusion: In Alzheimer disease, progressive worsening of parkinsonism is more strongly associated with cognitive decline than previously recognized.