Evolution of mild cognitive impairment in Parkinson disease

Objective: We examined the development of Parkinson disease (PD)-mild cognitive impairment (MCI) in patients with newly diagnosed PD over 5 years using recently proposed consensus criteria,and we assessed the reliability of the criteria.
Methods: Patients with PD (n 5 123) underwent extensive neuropsychological testing at baseline and after 3 (n 5 93) and 5 years (n 5 59). Two neuropsychologists independently applied the PD-MCI criteria to examine the interrater and intrarater reliability.
Results: At baseline, 35% of patients had PD-MCI. Three years later, 53% of the patients had PD-MCI. At 5-year follow-up, 20 patients who had PD-MCI at an earlier assessment had converted to PD dementia and 50% of the remaining patients without dementia had MCI. The interrater reliability (kappa) was 0.91. The intrarater reliabilities were 0.85 and 0.96.
Conclusion: Approximately one-third of patients with newly diagnosed PD fulfill the consensus criteria for PD-MCI; after 5 years, this proportion is approximately 50% of patients without dementia. The criteria have good interrater and intrarater reliability.