Dementia From Alzheimer Disease and Mixed Pathologies in the Oldest Old

To the Editor: The oldest old (≥90 years of age) are the fastest growing segment of the US population and account for half of all persons with dementia. Alzheimer disease (AD) is the most common pathology underlying dementia in the old (ages 65-89 years). Recent community-based autopsy studies1,2 suggest the relationship between AD pathology and expression of dementia is attenuated in the oldest old.3 Studies may be complicated by the common coexistence of AD plus infarct and/or Lewy body (LB) pathology (mixed pathologies).4 Few data exist on mixed pathologies and dementia in the oldest old.5 We examined the relationship of AD and mixed pathologies to dementia in the oldest old compared with the old. We tested the hypothesis that the clinical expression of AD and mixed pathologies differs across age groups.