Table 1.

EEG Changes in HE.

1. Normal or low frequency alpha rhythm (8.5 Hz) disturbed by random waves in the theta range (4–8 Hz) over both hemispheres. Theta waves are generally predominant in the temporal, parietal and occipital derivations, but can also be observed in the frontal derivations or be diffuse on the scalp. Eye opening reactivity can be reduced

2. Background activity in the theta range (4–8) diffused over both hemispheres. Random appearance of rare high voltage waves in the delta range (<4 Hz). Eye opening reactivity is usually reduced or absent. Bursts of intermittent rhythmic delta activity (IRDA) as well as triphasic waves can appear

3. Severe disorganization of EEG activity without any normal element. Asynchronous theta and delta waves diffuse over both hemispheres. Triphasic waves are usual

4. High voltage arrhythmic delta activity

5. Arrhythmic delta activity decreases both in frequency and amplitude

6. Flat EEG