Abstract
We have prospectively followed over a 5-year period 434 volunteers who were at intake ambulatory, functional, presumably nondemented, and between 75 and 85 years of age. Fifty-six (an incidence of 3.53 per 100 person-years at risk) developed a progressive dementia: 32 met diagnostic criteria for Alzheimer's disease (AD) (an incidence of 2.0 per 100 person-years at risk), 15 had vascular or mixed dementia, and 9 had other disorders or remain undiagnosed. New cases of dementia were as common as myocardial infarction and twice as common as stroke. Risk factors for both dementia and AD were age (over 80) and gender (female); other reported risk factors such as family history, prior head injury, thyroid disease, maternal age, and smoking were not risk factors for AD in this elderly cohort. Prior stroke was the major risk factor for vascular or mixed dementia; diabetes and left ventricular hypertrophy but not a history of hypertension per se were also risk factors for vascular dementia. The major predictor of the development of AD was the mental status score on entry. The 58.5% of the cohort who made zero to two errors on a 33-item mental status test had a less than 0.6% per year chance of developing AD, whereas the 16% of the cohort with five to eight errors on this test developed AD at a rate of over 12% per year. Thus, it is possible to identify a large cohort of 80-year-olds who are at low risk for AD and a smaller cohort at very high risk.
Highlights
We have prospectively followed over a 5-year period 434 volunteers who were at intake ambulatory, functional, presumably nondemented, and between 75 and 85 years of age
Because we were interested in observing the onset of dementia, we chose to study a group of subjects whose ages made it likely that a significant proportion would develop one or another of the disorders that produces dementia
Because of the relatively small number of subjects with MID/MIX, other important risk factors may not have become evident. Both prevalence C9, 231 and incidence 112, 271 of dementia rise sharply with age, with the majority of cases being attributable to Alzheimer's disease (AD)
Summary
We enroìied and evaluated 488 volunteer subjects and obtained at least one repeat evaluation on 434. The 58.5% of the cohort with an initial mental status score of zero to two errors out of 33 possible errors was at low risk for developing dementia, AD in particular, the rate of which was less than 1 case per 100 person-years (O.Ol/yr). MID/MIX occurred with an incidence rate of 0.85 per 100 person-years at risk, among the 71.2% of the initial cohort with mental status scores of O to 3. The women who developed AD had more memory complaints at intake than women who remained nondemented (22.2% vs. The most important risk factor for MID/MIX was a history of prior stroke (46.7% compared with 3.4% in the nondemented group; chi-square, p < 0.0001). MID/MIX subjects, unlike AD subjects, were more likely to have a history of depression (chi-square, p < 0.02) and
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