[Visual evoked potentials in Alzheimer's and Parkinson disease]

Harding et al. suggested at first that an increase of P2 latency in flash VEP without an increase of P2 latency in pattern reversal VEP may be a diagnostic marker of Alzheimer's disease. Up to now there is no convincing evidence for this hypothesis. The purpose of the present study was to examine this hypotheses in an extended group of patients with Alzheimer's disease (n = 36). In addition, a group of patients with Parkinson's disease (n = 8) without dementia syndrome and a group of healthy elderly controls (n = 46) was investigated in order to determine the sensitivity and specificity of these VEP parameters. The results confirmed significant group differences between patients with Alzheimer's disease and healthy controls concerning the increase of Flash P2 latency and unchanged latency of P2 in the pattern reversal VEP. No significant correlations were found between duration of illness and mental test scores. The group differences of P2 latency in the flash VEP for patients with Parkinson's disease and healthy controls were also significant. Therefore, the increase of flash P2 latency in VEP does not seem to be specific for Alzheimer's disease nor for dementia syndrome. The pathological mechanism causing the flash P2 latency increase in a remarkable number of neuropsychiatric patients should be elucidated in further experimental investigations.