Neuropsychological characteristics of subjects with and without neocortical Alz-50 immunoreactivity.

We performed quantitative histopathology and Alz-50 staining on 8 non-demented and 16 demented subjects who had received yearly neuropsychological evaluations as part of prospective studies of dementia. Of the 8 non-demented subjects, four had begun to show signs of cognitive decline on serial neuropsychological testing. These subjects showed marked decline on the Fuld Object Memory Evaluation, a test of recent memory. Scores on IQ tests and the Blessed test of orientation, memory, and concentration showed fluctuations but not consistent declines. These old-old, retired subjects were called "cognitively impaired" but not demented because they did not show decline in activities of daily living or social interactions. Five of the non-demented subjects had numerous cortical senile plaques and met standard pathological criteria for Alzheimer's disease (AD), but only one of the five was Alz-50 positive. That subject had shown the most consistent decline on neuropsychological scores. Ten of 11 clinically demented subjects with pathological evidence of AD were Alz-50 positive. All five clinically demented subjects with non-Alzheimer dementias on pathological examination were Alz-50 negative. Alz-50 may stain plaques found in AD, but not stain plaques which accompany aging. The cognitive impairment found in the Alz-50 negative subjects may be age-associated and not indicate early AD.