Flash Visual Evoked Potentials of Various Derivations in Dementia of the Alzheimer Type and Vascular Dementia

Abstract

Background: Recently, evoked potentials have been used for objective monitoring of the cortical function in dementia. The aim of this study was to distinguish dementia of the Alzheimer type (DAT) from vascular dementia (VaD) using flash visual evoked potentials of various derivations. Methods: A total of 70 patients consulting Tachikawa Medical Center Kashiwazaki Kosei Hospital were divided into four groups, normal adult (29.5 ± 8.5 years, n=16), normal elderly (77.2 ± 4.7 years, n=17), VaD (81.1 ± 8.1 years, n=17) and DAT (77.4 ± 5.6 years, n=20). Red flash stimulation was provided by a pair of goggles. Visual evoked potentials (VEPs) to flash were recorded in accordance with the International 10–20 Electrode System. Results: The latencies of N130 and P190 of frontal and central derivations were significantly reduced in DAT compared with all other groups (p<0.05). The N130 and P190 latencies were markedly delayed in the normal elderly group compared with the normal adult group (p<0.05). The P3 (P100) latency of occipital derivation was significantly delayed in normal elderly, VaD and DAT groups compared with the normal adult group (p<0.05). In the DAT group, the P190 latency was shortened at central and frontal derivations compared with that at occipital derivation (p<0.05). Conclusions: The N130 and P190 latencies decreased at frontal and central derivations in DAT. While the reason is still unclear, dysfunction in the central visual system induced by the degeneration of neuronal populations in DAT may cause the apparently reduced latency. Flash VEPs of frontal and central derivations may be useful for the differential diagnosis of DAT from VaD.