Data from 330 participants in The 90+ Study, of whom 70% were women, has revealed an overall annual incidence rate of 18.2% for dementia, rising from 12.7% per year in the 90-94 age group, to 21.2% in the 95-99 age group and 40.7% per year in the 100+ age group. 60% of the cases were attributed to Alzheimer's disease, 22% vascular dementia, 9% mixed Alzheimer’s and vascular dementia and 9% other/unknown. Unlike previous findings, rates were very similar for men and women.
Dementia rate in extreme elderly population
Reference
Corrada, M. M., Brookmeyer, R., Paganini-Hill, A., Berlau, D., & Kawas, C. H. (2010). Dementia incidence continues to increase with age in the oldest old: The 90+ study. Annals of Neurology, 67(1), 114-121. Retrieved from http://dx.doi.org/10.1002/ana.21915
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http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2813%2961570-6/fulltext