Serial quantitative electroencephalography.

Repeated EEG examinations are often used in diagnostically difficult cases to assess whether an EEG abnormality is progressive, regressive, or stationary. The conventional visual method is, however, poorly adapted to consider the variability when consecutive EEG recordings are compared. Using computer analysis of EEGs, the feature of the recordings as well as their variances can be measured, and the differences between the recordings can be tested statistically. The aim of the present study was to develop a practicable method for quantitative serial EEG examinations. Twenty EEGs from 5 volunteers were recorded to obtain reference data. The data acquisition was automated to obtain data without visual bias. The previously developed method using age ratios was employed for the primary analysis. The changes of the EEG activity during the observation period were evaluated statistically. Differences between consecutive EEGs could be observed even in normal subjects but the number of 'false positive' findings was reduced by the automatic data selection, by the choice of proper measures, and by adequate statistical treatment. The diagnostic value of the method was tested in 59 EEGs from 13 patients with well-defined brain disorders. Most EEG changes which could be attributed to the development of the disease were discovered and labelled as statistically significant.