P1-248: Cognitive decline between age 95 and 99 in relation to dementia onset

Abstract

To examine cognitive performance prior to dementia onset, and cognitive decline after onset of dementia, in a very old population. Longitudinal population study. A representative sample of 95–year–olds from the Göteborg 95+ Study was examined using a comprehensive neuropsychiatric examination and the Mini Mental State Examination (MMSE), and followed with repeated examinations at age 97 and at age 99. Dementia was diagnosed according to DSM–III–R criteria. Of 165 non–demented 95–year–olds, 67 were lost due to death or refusals, leaving 98 for re–examination at age 97. Between age 97 and 99, 56 were lost, and 42 were re–examined. Twenty–five participants developed dementia between 95 and 97 years, and 8 between 97 and 99 years. Mean MMSE at age 95 was higher among those who did not develop dementia by age 97 (N=73), than for those with dementia onset between 95 and 97 [27.1 (SD 2.6) vs 24.3 (SD 3.0), p<0.000]. Cross–sectional mean MMSE score at age 97 was higher among nondemented versus demented [26.7 (SD 3.3) vs 17.5 (SD 5.3), p<0.000]. At age 95, there was no difference in mean MMSE among those who never developed dementia to age 99 (N=28) compared to those with dementia onset between age 97 and 99 [27.6 (SD 2.6) vs 28.0 (SD 1.8), p=0.716]. At age 97, mean MMSE was nonsignificantly higher for those who never developed dementia by age 99 (N=28) compared to those with dementia onset between age 97 and age 99 [27.9 (SD 2.0) vs 26.4 (SD 3.1), p=0.097]. Cross–sectional mean MMSE score at age 99 was higher among nondemented versus demented [26.6 (SD 3.9) vs 16.6 (SD 6.7) p<0.000]. Among the oldest old, cognitive decline was detectable only during the 2 years immediately prior to clinical dementia. Very old individuals without dementia remain at a high cognitive level. Once cognitive decline begins in this very old age group, the decline seems to progress more rapidly than in younger age groups. This may also explain why we found an unexpectedly small proportion of mild dementias (9%) among all demented 95–year–olds (Börjesson–Hanson et al, Neurology 2004).