Objective: To study dementia in extreme old age. Design: Longitudinal population study.
Materials and Methods: The 95+ study includes more than 700 comprehensive neuro-psychiatric examinations of individuals from age 95 to 101 years of age. Dementia and its severity were diagnosed according to the DSM-III-R criteria, Alzheimer’s disease (AD) according to the NINCDS-ADRDA criteria and vascular dementia (VaD) according to criteria proposed by Erkinjuntti.
Results: The prevalence of dementia was 51% at age 95 (N=338) and increased to 58% at age 97 (N=167). At age 95, the prevalence was 36% for AD, 15% for VaD, including mixed dementia. The incidence of dementia between age 95 and 97 was 173/1000 person years at risk. The proportion of mild dementia was 5%. Institutionalization rate was 26% for non-demented and 85% for demented at age 95 and increased to 30% for non-demented and 95% for demented at age 97.
Conclusions: The prevalence of dementia continues to increase after age 95. The incidence rate of dementia was higher between age 95 and 97 than between age 85 and 88 (90/1000 person years at risk). In line with several other studies the proportion of mild dementia decreased from 28% at age 85, 19% at age 88 to 5% at age 95. One reason may be that DSM-III-R severity criteria are based on the need for assistance in daily living. Therefore, the higher frequency of physical co-morbidity in the extremely old will give a lower proportion of mild dementia. When a physically impaired individual reaches the threshold for dementia, the degree of severity will thus be higher than for a physically unaffected individual. Another explanation could be that the brains of extremely old individuals may be more fragile. When this is superimposed by Alzheimer encephalopathy the decline into more severe dementia may be faster than in younger groups.
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