Prevalence and characterization of mild cognitive impairment and dementia among the oldest old: The WISE study

People aged 85 years and older, commonly referred to as the oldest old, comprise the fastest growing segment of the population, especially among women. Although cognitive impairment is more common with age, the prevalence of mild cognitive impairment (MCI), dementia, and their subtypes has not been well characterized among the oldest old. The objective of this study was to determine the prevalence of all-cause MCI and dementia and their subtypes among oldest old women. We studied 1299 primarily white, oldest old women (mean age 88.2 years) from the Study of Osteoporotic Fractures Women, Cognitive Impairment Study of Exceptional Aging (SOF-WISE) study. Each woman completed an extensive neuropsychological test battery. Those who screened positive for cognitive impairment (n = 634) were given a clinical cognitive diagnosis from an expert panel of clinicians; the others were considered cognitively normal. We determined the prevalence of dementia, MCI, and subtypes overall and by subgroup. The overall prevalence of dementia was 17.8% (n = 231) and of MCI was 23.2% (n = 301), for a combined cognitive impairment prevalence of 41.0%. Clinical features consistent with Alzheimer's disease and mixed dementia were most common, accounting for 39.8% of dementia cases each. Among those with MCI, amnestic multiple domain followed by non-amnestic single domain were the most common subtypes, accounting for 33.9% and 28.9% of cases respectively. The prevalence of cognitive impairment was higher among women ≥90 years compared to women 85-89 years (dementia 28.2% versus 13.9%, p < 0.0001, and MCI 24.5% versus 22.7%, p = 0.02). Cognitive impairment was also more common in women with less than high school education, a history of stroke, and prevalent depression. In this large sample of oldest old women, approximately 40% had clinically significant cognitive impairment. Cognitive impairment was particularly common among women aged ≥90 years and in those with lower education, history of stroke, or prevalent depression.