[Importance of the EEG in early and differential diagnosis of dementia of the Alzheimer type]

The role of the electroencephalogram in the diagnosis of dementia of the Alzheimer type: an attempt at technology assessment

In a first attempt at technology assessment of the electroencephalogram (EEG) in the diagnosis of patients with Alzheimer's disease (AD), three conclusions were reached: notwithstanding the well defined clinical criteria, there remains a need for a laboratory technique to confirm the diagnosis since a 100% accuracy cannot be obtained by clinical methods only; although the EEG has a high sensitivity in separating AD patients from normal controls, the sensitivity of the EEG is at present not satisfactory when studying populations with a low prevalence of AD patients; the sensitivity of the EEG is higher or equal to the best other laboratory techniques (magnetic resonance imaging [MRI], computerized tomography [CT], SPECT, PET) available at the moment. Since the EEG and MRI can be helpful in different aspects of the differential diagnosis it is argued that all AD patients should be studied at least once by EEG as well as by MRI.

EEG spectral analysis in vascular and Alzheimer dementia

The role of EEG spectral analysis in the diagnosis of syndromes of dementia is still disputed. Since there have been few studies dealing with the profile of power spectra, the present investigation has focused on this aspect, constructing power spectra taken from 16 derivations and calculated by averaging twenty 2 sec epochs, using a serial array of frequencies from 1 to 32 Hz. The spectral analysis of the EEG, recorded under awake resting eyes closed (REC) and open (REO) conditions, was performed in 50 patients with Alzheimer's disease (AD), 37 with vascular dementia (VaD) and 36 elderly controls. Three spectral profiles were found under REC: (i) type A, showing a dominant 6.5-12 Hz peak (44% AD, 97.3% VaD), although lower than in controls; (ii) type B, lacking a dominant peak in the 6.5-12 Hz band, but characterised by high power in 1-6.5 Hz band (44% AD, 2.7% VaD); (iii) type C, corresponding to a flat, low voltage, spectrum (12% AD). Unlike controls, demented patients showed an increased REO/REC power ratio in the 6.5-12 Hz band, especially in those with type B spectra. AD patients with type B spectra had an earlier age of disease onset.

Age-related changes of spontaneous EEG described by equivalent dipoles

One of the most commonly used methods for quantification of an EEG is Fast Fourier Transformation (FFT), which suffers from some serious disadvantages, for example: FFT-power data are highly dependent on the choice of reference and thus the topographical distribution of FFT-power data varies according to the used reference. Novel methods which partly resolve this problem have been developed. These methods provide unambiguous data in the frequency domain with regard to reference. In comparison to conventional FFT-power data this approach allows to a higher degree to draw topographical valid conclusions regarding brain function. The aim of the present study on brain electrical activity, using the method of FFT approximation, was to investigate age-related alterations of brain function in carefully screened healthy subjects. The major finding was that, except for a more superficially located beta-activity of higher strength with increasing, age no age-related changes in electrical brain activity were observed.