Objective: To report the rates and predictors of progression from normal cognition to either mild cognitive impairment (MCI) or dementia using standardized neuropsychological methods.Methods: A prospective cohort of patients diagnosed with Parkinson disease (PD) and baseline normal cognition was assessed for cognitive decline, performance, and function for a minimum of 2 years, and up to 6. A panel of movement disorders experts classified patients as having normal cognition, MCI, or dementia, with 55/68 (80.9%) of eligible patients seen at year 6. Kaplan-Meier curves and Cox proportional hazard models were used to examine cognitive decline and its predictors.
Results:We enrolled 141 patients, who averaged 68.8 years of age, 63% men, who had PD on average for 5 years. The cumulative incidence of cognitive impairment was 8.5% at year 1, increasing to 47.4% by year 6. All incident MCI cases had progressed to dementia by year 5. In a multivariate analysis, predictors of future decline were male sex (p 5 0.02), higher Unified Parkinson's Disease Rating Scale motor score (p # 0.001), and worse global cognitive score (p , 0.001).Conclusions: Approximately half of patients with PD with normal cognition at baseline develop cognitive impairment within 6 years and all new MCI cases progress to dementia within 5 years. Our results show that the transition from normal cognition to cognitive impairment, including dementia, occurs frequently and quickly. Certain clinical and cognitive variables may be useful in predicting progression to cognitive impairment in PD. Nonmotor symptoms are common in Parkinson disease (PD), 1 including mild cognitive impairment (MCI) and dementia (PDD).2 Up to 80% of patients with PD develop dementia long-term, 3 and 20%-30% of patients with PD without dementia meet criteria for MCI. 4 Both PD-MCI and PDD impact negatively on patient quality of life, cost of care, and caregiver burden. 5,6 Longitudinal reports on patients with early PD-MCI show that more than 25% will develop dementia within 3 years, 7 and MCI at disease onset increases risk for development of dementia.
8Another study reported that up to 50% of patients with early PD developed cognitive decline within 5 years, 9 although the sample size was relatively small and lack of cognitive impairment at baseline was defined by Mini-Mental State Examination score only.Structural MRI, and plasma and CSF biomarkers, are associated with cognitive functioning and predict future cognitive decline in PD.1 However, many biomarkers are invasive, costly, and done mainly at academic centers conducting research. Demographic and clinical factors such as age, 10 motor subtypes, 11 and early visuospatial, language, and fluency deficits 12,13 have also been shown to predict future cognitive decline. However, to our knowledge, no research has focused on those patients defined as having normal cognition (NC) at baseline, which allows for examination of the course of cognitive decline from its clinical onset.