Visual evoked potentials in elderly patients with primary or multi-infarct dementia

Visual evoked responses in Alzheimer's disease: a review

This review of the literature has shown that a delayed flash P2, in the presence of a normal flash P1 and pattern-reversal P100, can distinguish groups of Alzheimer's patients from groups who are healthy, psychiatrically ill, or suffering from other types of dementia. The VER's usefulness in the individual patient remains undetermined. With today's techniques, too many patients are misclassified. False negatives may result if Alzheimer's patients with visual symptoms are a distinct subgroup. Those with a normal flash VER may have cortical dysfunction outside the visual association areas. This would most likely be in the earliest stages of the disease before the atrophy becomes widespread. It may be that a VER test would only be valid in established disease. Future research should use adequate numbers of patients who are in a single category of mild, moderate or severe, so that the applicability of a VER test in the early stages of the disease can be determined. Strict diagnostic criteria such as the NINCDS-ADRDA guidelines should be used. Patients should be drug free, or at least not taking medications with anticholinergic properties. Flash VER should be obtained using a strobe light with eyes closed, and the pattern VER using a black and white television with a large pattern and high contrast.

Eye closure affects flash VEP latency in dementia

In a group of 27 demented patients (21 with DAT and 6 with MID) with normal pattern VEP (PVEP), the latencies of the main flash VEP (FVEP) components (P1, N2, P2 and N3) were assessed both with open and closed eyes. At variance from controls, demented patients showed that both P2 and N3 components are significantly delayed with closed eyes while neither P1 nor N2 timings are affected. Control studies ruled out the possibility that such an outcome might depend on a defective pupillary responsiveness and/or an impaired sensitivity to luminance changes. On these grounds it is suggested that the effect of mode of stimulation on FVEP latency in demented patients is more likely to depend on "central" than on "peripheral" mechanisms. The dependence of latency changes on closure of the eyes seems to negate the direct effect of lesions upon visual structures and suggests an impairment of the modulatory action of non-visual afferents upon the activity of the visual cortex.

Visual evoked potentials in Alzheimer's disease: investigations in a PET-defined collective

Intravital diagnosis of Alzheimer's disease (AD) based clinical and neuropsychological findings alone does not allow sufficient differentiation from other disorders such as vascular dementia. Positron emission tomography (PET) secures intravital diagnosis with high accuracy by determination of a typical metabolic pattern. Numerous publications have proposed visual evoked potentials (VEP) for the detection of AD. In a collective of 15 patients with probable AD according to NINCDS/ADRDA criteria and the typical metabolic pattern of AD, we examined pattern reversal and flash VEPs. The results were compared to those of an age-matched collective of patients without impairment of memory. Neither pattern reversal nor flash VEP were correlated to severity of dementia as determined by the mini-mental status examination (MMSE). The positive results of other investigators are probably due to different patient selection criteria which do not include findings of cerebral glucose metabolism in the definition of AD.

Neurophysiology and SPECT cerebral blood flow patterns in dementia

A series of elderly patients with dementia of Alzheimer type (AD), multi-infarct dementia (MID) and functional (non-organic) psychiatric illness (major depressive disorder) were selected by DSM III-R criteria and had the following investigations: a battery of cognitive tests, EEG with power and coherence spectral analyses of T4-T6, T3-T5, P4-O2, P3-O1 channels, visual evoked potential (flash and pattern reversal) and P300 recordings as well as single photon emission tomography (SPECT) using 99mTc HMPAO. Three subsets of patients were chosen on clinical and SPECT criteria. These were as follows: patients with a clinical diagnosis of AD and a SPECT rCBF pattern showing bilateral temporo-parietal perfusion deficits (AD type), patients with a clinical diagnosis of MID and a SPECT rCBF pattern showing single focal perfusion deficits or multiple areas of low perfusion in the cerebral cortex suggestive of ischaemic change (MID type SPECT picture) and functionally ill patients with normal rCBF (controls). The AD type group differed from the MID rCBF group in having significantly less alpha and more delta 2 (2- < 4 Hz) power. The latter had significantly lower alpha power than the controls. The 2 dementia groups with abnormal rCBF patterns did not differ in terms of coherence spectra or P300 latencies, but both had lower within and between hemisphere alpha coherence values and longer P300 latencies than the "controls" with normal rCBF. There were no group differences in the flash VEP P2-pattern reversal P100 latency difference values.

Serial visual evoked potential recordings in geriatric psychiatry

Serial visual evoked potentials to flash and pattern reversal stimuli were recorded in elderly patients with senile dementia of the Alzheimer type (SDAT), multi-infarct dementia (MID) and functional psychiatric illness, and in a group of elderly control subjects. Recordings were made at 6 monthly intervals over a 2 year period. Latency and amplitude of the main components were measured and the flash P2-pattern reversal P100 latency difference value was calculated. In all groups significant changes over time did not occur for any parameters but in the SDAT group the regression coefficient for the latency of the flash P2 component and the flash P2-pattern reversal P100 latency difference was significant, reflecting a trend towards increasing flash P2 latency as time progressed. The flash P2-pattern reversal P100 latency difference was longer in the SDAT and MID groups than in the functional patients, confirming the findings of previous reports. The latency difference in the SDAT group only was significantly greater than that in the control group.

[Specificity of visual evoked potential alterations in Alzheimer's disease]

We have studied visual evoked potentials (VEP) in four groups: healthy young and aged subjects and aged patients suffering from depression or Alzheimer's disease (AD). In the flash modality, peak IV delay in AD patients as compared to aged controls corresponded to lengthened III-IV interlatency (IL). When AD and depressed patients were compared, peak IV delay in the former did not reach significance. Normal aging resulted in delayed peaks II and III, without IL modification. In the pattern reversal modality, no difference was observed between AD patients and aged, healthy or depressed controls. Aging delayed peaks P50 to P180. The abnormality exhibited by AD patients was specific to this group. However, the lack of significant difference between AD and depressed groups argues against the ability of VEP to differentiate those conditions.

Visual evoked potentials in Alzheimer's disease: correlations with age and severity

Flash and pattern reversal visually evoked potentials were recorded in 25 patients fulfilling NINCDS-ADRDA criteria for 'probable' Alzheimer's disease (AD). Results were compared with those obtained from groups of normal elderly subjects and patients with mild memory impairment not amounting to dementia. The P2 component of the flash VEP was significantly delayed in AD patients of 74 years or less and correlated with severity whereas the P100 component of the pattern reversal VEP remained relatively unchanged. The latency difference between the P2 and the P100 proved to be a valid discriminator between demented and non-demented subjects only in the younger age group. This limits its usefulness as a diagnostic test of dementia in patients over the age of 75.

Electroencephalography, visual evoked potentials, and cerebral CAT-scan as diagnostic tools in senile dementia of Alzheimer type

The usefulness of a cerebral computed tomogram (CAT-scan), an electro-encephalogram (EEG), and flash visual evoked responses (FVER) as diagnostic tools in dementia was studied in 36 mentally impaired and 32 unimpaired persons aged 75 yr and above, who were recruited from a random sample of elderly people living at home. The clinical diagnosis of dementia was made after a full psychogeriatric assessment supplemented by a follow-up 18 mo later. When the measures of cortical atrophy from a cerebral CAT-scan, the presence/absence of diffuse slow activity on a standard EEG, and FVER P200 and FVER P100 latencies were introduced in a logistic regression model, the clinical diagnoses being the dependent variable, an effective prediction of senile dementia of Alzheimer type (SDAT) was obtained (sensitivity 93%, specificity 86%, misclassification rate 12%). We conclude that the use of FVER, an EEG, and a cerebral CAT-scan may facilitate the diagnosis of senile dementia of Alzheimer type.