A new EEG method for estimating cortical neuronal impairment that is sensitive to early stage Alzheimer's disease.

Objectives: To test the hypothesis that elecetroencephalographic (EEG) analysis is sensitive to cortical neuronal impairment in early stage Alzheimer's disease (AD), and that this analysis correlates with corresponding changes in cerebral blood flow.

Methods: We examined an EEG measure of neuronal impairment in the cerebral cortex in terms of its ability to detect very mild AD. This measure, the mean value of the resting state EEG alpha dipolarity (D(alpha)), approaches unity without cortical sulcal lesions, whereas brains with randomly distributed cortical sulcal lesions lower D(alpha) values well below unity. D(alpha) was evaluated in 25 patients with very mild AD, 33 patients with moderately severe AD, and 56 normal age-matched subjects. These subjects also received SPECT, and strong correlation between D(alpha) and regional cerebral blood flow (rCBF) was observed.

Results: D(alpha) values greater than 0.977 correctly classified normal subjects, but also included 10% of very mild AD. D(alpha) values less than 0.952 correctly classified very mild AD as well as moderately severe AD, but also included 10% of normal subjects. D(alpha) values also correlated positively with bilateral temporal-parietal rCBF (a characteristic finding in AD patients); both declined with increasing dementia severity.

Conclusions: Analysis of D(alpha) in this sample supports the hypothesis that early stages of AD can be discriminated from normal aging using measures of cortical neuronal impairment. Furthermore, dementia severity, as reflected by the degree of impairment, is reflected in declining D(alpha) values and increasing variance (greater spread of the D(alpha) values).