Occurrence of cognitive impairment after age 90: usefulness and drawbacks of four broadly used concepts.

Background Few data are available on the impact of applying different concepts to define cognitive impairment among nonagenarians and centenarians. This study explored the occurrence of four broadly used concepts in an over 90-year-old population. Design/methods We examined a community-based cohort of 34 people with a mean age (±S.D.) of 96.4 (±3.9) years, living in Bologna (Italy). We calculated the proportion of subjects that was given a diagnosis of cognitive impairment according to the following four commonly used concepts: Mild Cognitive Impairment (MCI), Age-Associated Memory Impairment (AAMI), Cognitive Impairment, No Dementia (CIND), and Questionable Dementia stage of the Clinical Dementia Rating (CDR 0.5). Results The proportion of subjects with cognitive impairment varied from 5.9%, according to CIND, to 32.4%, according to MCI. The four concepts identified different groups of subjects as having cognitive impairment, and no subject was given a diagnosis of cognitive impairment according to all four concepts. Conclusion Commonly used criteria for diagnosis of cognitive impairment can differ by a factor of five in the number of subjects they classified as impaired. Such disagreement has serious implications for prevention, as people with a mild cognitive impairment may be a suitable target group for interventions before the development of dementia.