Quantification of Five Neuropsychological Approaches to Defining Mild Cognitive Impairment

Objectives: Operational definitions of cognitive impairment have varied widely in diagnosing mild cognitive impairment (MCI). Identifying clinical subtypes of MCI has further challenged diagnostic approaches because varying the components of the objective cognitive assessment can significantly impact diagnosis. Therefore, the authors investigated the applicability of diagnostic criteria for clinical subtypes of MCI in a naturalistic research sample of community elders and quantified the variability in diagnostic outcomes that results from modifying the neuropsychological definition of objective cognitive impairment. Design: Cross-sectional and longitudinal study. Setting: San Diego, CA, Veterans Administration Hospital. Participants: Ninety nondemented, neurologically normal, community-dwelling older adults were initially assessed and 73 were seen for follow-up approximately 17 months later. Measurements: Participants were classified via consensus diagnosis as either normally aging or having MCI via each of the five diagnostic strategies, which varied the cutoff for objective impairment and the number of neuropsychological tests considered in the diagnostic process. Results: A range of differences in the percentages identified as MCI versus cognitively normal were demonstrated, ranging from 10-74%, depending on the classification criteria used. A substantial minority of individuals demonstrated diagnostic instability over time and across diagnostic approaches. The single domain nonamnestic subtype diagnosis was particularly unstable (e.g., prone to reclassification as normal at follow up). Conclusion: Our findings provide empirical support for a neuropsychologically derived operational definition of clinical subtypes of MCI and point to the importance of using comprehensive neuropsychological assessments. Diagnoses, particularly involving nonamnestic MCI, were variable over time. The applicability and utility of this particular MCI subtype warrants further investigation. (Am J Geriatr Psychiatry 2009; 17: 368-375)