[Electroencephalographic findings in dementia diseases].

Even if generally the EEG cannot yield specific pointers that are typical for a special pattern of dementia, it is nevertheless meaningful and helpful to perform routine EEG in demented patients. EEG is the functional additional examination that does not place any stress on the patient and is easy to perform at a low cost (1). As a functional diagram the EEG reflects the electrical processes taking place in the cerebral cortex, yielding an excellent image of the cerebral functional state. Assessment of the EEG is done in accordance with internationally standardised criteria. Particular attention is directed at a slowing-down of the background activity, the occurrence and extent of scattered theta and delta waves, their topographical distribution and the development of pathological EEG characteristics during recording (44). Update spectral analysis EEG procedures, i.g. the possibility to calculate power spectra for the individual EEG frequency bands and their topographic distribution, it may be possible in the near future to further improve differentiation between normal and pathological EEG findings. The functional dynamic aspect of the EEG is its particularly strong point in the differential diagnostic clarification of dementia patterns. By repeated EEG recordings, i.e. by close follow-up, and by relating the electrophysiological findings to the clinical pattern, reliable pointers are obtained for the extent of the activity of the process underlying the dementia pattern. EEG is predestined like no other method to enable early detection of rapid changes in cerebral function thanks to its easy operation and unlimited repeatability. The occurrence of parenrhythmic theta and delta waves in the EEG reflects in a special manner the acuity of an organic basic process. In this way EEG enables differentiation between acute and chronic processes of cerebral damage. Over and above this, correlation with the relevant clinical findings makes it possible to differentiate between reversible states of dementia and irreversible defect syndromes and hence also to point to the long-term outcome. Finally, the occurrence of certain patterns of findings or the identification of characteristic wave forms allows essential differential diagnostic pointers and definitions.