ELECTROENCEPHALOGRAPHY AS A DIAGNOSTIC-TOOL IN DEMENTIA

Clinical electroencephalography is a relatively simple and inexpensive diagnostic tool with a high sensitivity for diffuse organic encephalo pathy of various aetiologies but with a rather low specificity for the type of diagnosis. The highest sensitivity is shown in DAT and Parkin son dementia, and in these conditions the degree of EEG abnormality is correlated with the disease severity. Quantification of EEG makes the se correlations more reliable and provides a method for monitoring the rapeutic effects. Dementias with predominantly frontal pathology show much less EEG abnormality, and in these conditions the EEG is often no rmal despite obvious clinical dementia. Also, alcohol dementias often show normal EEG patterns. At an early stage of clinical evaluation, EE G may be useful in the discrimination of organic dementia from pseudod ementia, because EEG is usually normal in depression, confusion, agita tion and other psychiatric conditions. In pseudodementia due to intoxi cation with sedatives the EEG is usually dominated by diffuse beta act ivity. At the stage of differential diagnosis of an organic brain diso rder, EEG cannot reliably discriminate between encephalopathies second ary to hydrocephalus, AIDS, cerebrovascular disease, B-12 deficiency a nd primary degenerative diseases such as DAT. More specific EEG patter ns are seen in acute cerebrovascular lesions, metabolic encephalopathi es, i.e. of hepatic origin, Creutzfeldt-Jakob disease, herpes encephal itis, and nonconvulsive status epilepticus as possible causes of a rap idly deteriorating mental and neurological condition. Repeated EEG rec ordings over time would add significantly to the diagnostic informatio n. New techniques such as topographical brain mapping, analysis of the EEG during REM sleep, coherence analysis of the EEG activity, and the combination of quantified EEG techniques with evoked potentials and e vent-related potentials will presumably add to the sensitivity as well as the specificity of the electrophysiological methods in the diagnos is of dementia.