EEG Findings in Encephalopathy

General EEG Patterns

Progressive slowing of the EEG is the hallmark finding, with the degree of slowing correlating with encephalopathy severity 1, 2
Initial EEG changes may include frontal predominance of alpha rhythm or an increase in beta waves, particularly in early stages 1
As encephalopathy worsens, there is typically an initial increase followed by a decrease in EEG amplitude 2
In severe cases, the EEG may progress to a discontinuous pattern and eventually an isoelectric EEG 1

Frontal predominance of alpha rhythm or increased beta activity is seen in mild encephalopathy 1
Subtle background slowing with minimal disruption of normal rhythms is characteristic of mild encephalopathy 3
P300 latency changes may be detected before overt EEG changes in mild encephalopathy 4
Dominant theta activity replacing normal alpha rhythm is seen in moderate encephalopathy 2
Appearance of triphasic waves, particularly in metabolic encephalopathies, is characteristic of moderate encephalopathy 1
Dominant delta activity is seen in severe encephalopathy 2
Decreased EEG amplitude is characteristic of severe encephalopathy 1
Discontinuous patterns are seen in very severe cases of encephalopathy 1

The absence of cortical responses in sensory evoked potentials indicates particularly severe neuronal dysfunction with generally poor prognosis 5

For diagnostic purposes, use the standard 19 electrodes of the 10-20 International System 5, 3
For monitoring purposes, four electrodes may be sufficient 5, 3
Recording duration should be 20-30 minutes to capture variations in vigilance levels 5, 3
Both eyes-closed and eyes-open recordings should be included when possible 5
Quantitative EEG analysis may improve reliability in assessing encephalopathy severity 6, 3

Failing to consider medication effects that can mimic encephalopathic patterns 3
Not recognizing that triphasic waves, while suggestive of hepatic encephalopathy, are not specific to it 1
Overlooking non-convulsive status epilepticus, which can occur in encephalopathic patients 5
Using EEG patterns alone for definitive diagnosis without considering clinical context 3
Misinterpreting normal variants or benign patterns as pathological 3