Serial visual evoked potential recordings in Alzheimer's disease.

Primary presenile dementia slows the major positive component of the visual evoked potential to flash stimulation but does not affect the visual evoked potential to patterned stimulation. The progressive effect of Alzheimer's disease was followed in a 58 year old woman over three and a half years from the development of the earliest symptoms to complete mental incapacity. The pattern reversal visual evoked potential remained normal, but the flash visual evoked potential gradually slowed from 129 ms in 1981 to 153 ms in 1984. The severity of the abnormality of the flash visual evoked potential thus reflected the severity of the dementia. Electroencephalography, computed tomography, and psychometric tests indicated generalised cortical disease, but the results were not specific to dementia. The combination of a slowed flash and normal pattern visual evoked potential seems to be specific to Alzheimer's disease and supports the use of flash and pattern visual evoked potentials in routine diagnostic testing for this condition.