A reevaluation of the duration of survival after the onset of dementia.

Background: Dementia shortens life expectancy; estimates of median survival after the onset of dementia have ranged from 5 to 9.3 years. Previous stud ies of people with existing dementia, however, may have underestimated the deleterious effects of dementia on survival by failing to consider persons with rapidly progressive illness who died before they could be included in a study (referred to as length bias). Methods: We used data from the Canadian Study of Health and Aging to estima te survival from the onset of symptoms of dementia; the estimate was adjust ed for length bias. A random sample of 10,263 subjects 65 years old or olde r from throughout Canada was screened for cognitive impairment. For those w ith dementia, we ascertained the date of onset and conducted follow-up for five years. Results: We analyzed data on 821 subjects, of whom 396 had probable Alzheim er's disease, 252 had possible Alzheimer's disease, and 173 had vascular de mentia. For the group as a whole, the unadjusted median survival was 6.6 ye ars (95 percent confidence interval, 6.2 to 7.1). After adjustment for leng th bias, the estimated median survival was 3.3 years (95 percent confidence interval, 2.7 to 4.0). The median survival was 3.1 years for subjects with probable Alzheimer's disease, 3.5 years for subjects with possible Alzheim er's disease, and 3.3 years for subjects with vascular dementia. Conclusions: Median survival after the onset of dementia is much shorter th an has previously been estimated. (N Engl J Med 2001;344:1111-6.) Copyright (C) 2001 Massachusetts Medical Society.