Multichannel EEG frequency analysis and somatosensory-evoked potentials in patients with different types of organic dementia.

Thirty-five patients with organic dementia were investigated with multichannel FFT analysis of EEG. In 21 of them, somatosensory-evoked potentials (SEPs) with stimulation of the median nerves were also recorded. Based on clinical and psychometric data and regional cerebral blood flow measurements, the patients were subdivided into Alzheimer-type dementia (DAT) of moderate (n = 10) and severe (n = 11) degree, multi-infarct dementia (MID) (n = 7), and frontotemporal degeneration (FTD) (n = 7). The FTD patients showed mild EEG abnormality and the MID patients showed increases of low frequency activity in combination with a well-preserved posterior dominant activity. The DAT patients showed the most pronounced abnormalities with deterioration of the posterior activity combined with a large increase of low frequency activity. The SEPs of the DAT group showed an amplitude enhancement of the parietal response components. The FTD group showed only a moderate delay of the precentral N30 component. The MID group showed individually varying abnormalities, including a delay of the primary cortical response. It is concluded that the different distributions of pathology in the different organic dementia disorders are reflected in the quantified EEG and SEPs as studied with multichannel technique.