P300 in Alzheimer's disease: relationships to dementia severity and glucose metabolism.

In 45 patients (aged 48-85 years) with probable Alzheimer's disease (AD) according to current research criteria (NINCDS-ADRDA) with different stages of dementia severity (Mini Mental Status Examination (MMSE) 7-27) the auditory evoked P300 waves were mapped and regional cerebral metabolic rates of glucose were measured by positron emission tomography of 2-[18F]fluoro-2-deoxy-D-glucose. Age adjusted P300 latency was significantly correlated to dementia severity (r = -0.33, p = 0.028), but no significant relationships were found for P300 amplitudes. Dependencies existed among cortical glucose metabolic rates and MMSE with the highest correlation coefficient for the metabolic ratio of regions typically affected and non-affected in AD (r = 0.75, p = 0.0001). A significant correlation was also calculated between P300 latency and metabolic ratio (r = -0.44, p = 0.002), but no relationships were observed among P300 amplitudes and glucose metabolic rates of individual brain regions. These results indicate that P300 latency and metabolic rates but not P300 amplitudes qualify as measures of severity in AD. The lack of regional correlations among P300 amplitudes and glucose metabolism is not consistent with a cortical contribution to P300 generation.