Cross-sectional studies comparing patients with very mild AD to agematched, nondemented control subjects have demonstrated that a deficit in memory is the earliest and most prominent neuropsychological deficit in patients with diagnosed AD (Welsh, Butters, Hughes, Mohs, & Heyman,1991). This deficit is most pronounced on tasks for which the patients are asked to recall previously learned information (such as a short list of words) after a brief delay during which the patient engages in other cognitive activity.
Longitudinal studies of nondemented persons who are at risk for dementia have examined the question of whether there are neuropsychological deficits that are measurable before patients are impaired enough to warrant a diagnosis of AD. In these studies, baseline neuropsychological data are used to compare performance of patients who subsequently were diagnosed with AD with those who remain dementia free.
Results of these studies indicate that there are measurable deficits in memory and, to a lesser extent, in language and cognitive-processing speed at least 1 year before patients meet diagnostic criteria for dementia Our own results from the JHH study confirm that patients with a CDR score of 0.0 who convert to CDR 0.5 1 year later have baseline memory scores that are poorer than the baseline memory scores of patients who remain CDR 0.0 on follow-up. Thus, data from a variety of sources indicates that poor scores on a test of memory, particularly delayed-recall memory, are a sensitive indicator of early dementia.
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