Natural history of cognitive decline in the old old

To prospectively examine the occurrence and outcome of cognitive decline in healthy, community-dwelling elders.

Ninety-five elders (mean age 84 years) who at entry had no cognitive impairment were followed for up to 13 years. Cognitive decline was defined as obtaining either a Clinical Dementia Rating (CDR) = 0.5 or Mini-Mental State Examination (MMSE) score < 24 on two examinations.

Three outcomes of aging were determined: intact cognition, persistent cognitive decline without progression to dementia, and dementia. Whereas 49% remained cognitively intact, 51% developed cognitive decline. Mean follow-up to first CDR 0.5 was 3.8 years and age at conversion was 90.0 years. Those who remained cognitively intact had better memory at entry and were less likely to have APOE4 than those who developed cognitive decline. Of the 48 participants with cognitive decline, 27 (56%) developed dementia (CDR > or =1) a mean of 2.8 years later. Participants with cognitive decline who progressed to dementia had poorer confrontation naming at the time of their first CDR 0.5 than those with persistent cognitive decline who did not progress during follow-up.

The old old are at high risk for developing cognitive decline but many will not progress to dementia in the next 2 to 3 years or even beyond. These findings are important for understanding the prognosis of cognitive decline and for the design of treatment trials for AD. APOE genotype is a risk factor for cognitive decline.