Background: The significant variability across studies of mild cognitive impairment (MCI) in rates of progression to Alzheimer's disease (AD) and reversion to normal cognition may be due to differences in specific neuropsychological tests and thresholds used to define MCI.
Methods: We assessed 115 subjects with amnestic (AMN) or non-amnestic (NON) MCI on a standardized neuropsychological battery at baseline and after a mean follow-up of 16.4 months to determine the prevalence and persistence of deficits identified with specific tests.
Results: The prevalence of impaired performance varied widely across tests. Deficits were more persistent in the AMN group than in the NON group. Baseline deficits in Visual Reproduction II and the California Verbal Learning Test were the best predictors of persistent memory impairment. Subjects who at baseline were impaired on multiple memory tests or had poorer overall memory performance were more likely to exhibit persistent memory deficits.
Conclusions: The use of different neuropsychological tests and thresholds to diagnose MCI identified subsets of subjects with different rates of persistence of cognitive impairment. Standardization of the operational definition of cognitive impairment in MCI may result in more consistent predictions of progression to AD.