Development of dementing illnesses in an 80-year-old volunteer cohort

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.

Clinico-pathologic studies in dementia: nondemented subjects with pathologically confirmed Alzheimer's disease

We compared neuropsychological findings in 28 longitudinally evaluated elderly subjects with their postmortem neuropathology, including senile plaque and neurofibrillary tangle counts from standardized sections. Nine of the subjects were not demented when evaluated just prior to their death. Numerous cortical senile plaques and other changes of Alzheimer's disease (AD) occurred in six of nine nondemented old-old subjects. Five of these six subjects had shown decline on yearly neuropsychological tests but their cognitive impairment was too mild to meet clinical criteria for dementia. Whereas cortical senile plaque count did not distinguish well between demented and nondemented subjects, every subject with numerous cortical neurofibrillary tangles was demented. The nondemented subjects with Alzheimer pathology may have had "preclinical" AD, or numerous cortical plaques may occur in some elderly subjects who would never develop clinical dementia.

Alzheimer's disease. A double-labeling immunohistochemical study of senile plaques

The senile plaque is one of the histopathologic changes that characterizes Alzheimer's disease and the aging brain. The histopathology of senile plaques was studied using double-labeling immunohistochemistry and lectin histochemistry with thioflavin S fluorescent microscopy in 9 cases of Alzheimer's disease, 2 nondemented elderly individuals, and 3 individuals with non-Alzheimer primary degenerative dementias. Every plaque that was visualized with thioflavin also had amyloid, but not all thioflavin-positive plaques contained neurites that could be recognized with specific monoclonal antibodies to paired helical filament, tau, or neurofilament epitopes. Some neurofilament-positive neurites were not visualized with thioflavin, but almost all tau-positive neurites were colabeled with thioflavin. Microglia were associated with most plaques. Most plaques were also surrounded by fibrous astrocytes. These results suggest that amyloid may be the common feature that defines senile plaques, but that other elements may be more specific for Alzheimer's disease, because extensive neuritic degeneration was seen only in Alzheimer brains and not in either nondemented elderly individuals with senile plaques or in non-Alzheimer dementia cases.

Clinical, pathological, and neurochemical changes in dementia: a subgroup with preserved mental status and numerous neocortical plaques

Postmortem examination was performed on 137 residents (average age 85.5 years) of a skilled nursing facility whose mental status, memory, and functional status had been evaluated during life. Seventy-eight percent were demented using conservative criteria; 55% had characteristic Alzheimer's disease. Choline acetyltransferase and somatostatin were significantly reduced in the brains of patients with Alzheimer's disease as compared with age-matched nursing home control subjects, although the degree of the reduction was less severe than found in subjects less than 80 years of age. Ten subjects whose functional and cognitive performance was in the upper quintile of the nursing home residents, as good as or better than the performance of the upper quintile of residents without brain pathology (control subjects), showed the pathological features of mild Alzheimer's disease, with many neocortical plaques. Plaque counts were 80% of those of demented patients with Alzheimer's disease. Choline acetyltransferase and somatostatin levels were intermediate between controls and demented patients with Alzheimer's disease. The unexpected findings in these subjects were higher brain weights and greater number of neurons (greater than 90 micron 2 in a cross-sectional area in cerebral cortex) as compared to age-matched nursing home control subjects. These people may have had incipient Alzheimer's disease but escaped loss of large neurons, or alternatively, started with larger brains and more large neurons and thus might be said to have had a greater reserve.

Validation of a short Orientation-Memory-Concentration Test of cognitive impairment

A 6-item Orientation-Memory-Concentration Test has been validated as a measure of cognitive impairment. This test predicted the scores on a validated 26-item mental status questionnaire of two patient groups in a skilled nursing home, patients in a health-related facility, and in a senior citizens' center. There was a positive correlation between scores on the 6-item test and plaque counts obtained from the cerebral cortex of 38 subjects at autopsy. This test, which is easily administered by a nonphysician, has been shown to discriminate among mild, moderate, and severe cognitive deficits.