What are the typical EEG findings in encephalopathy?

Typical EEG Findings in Encephalopathy

The most characteristic EEG finding in encephalopathy is progressive slowing of background activity, which correlates with increasing severity of the condition, often accompanied by triphasic waves in moderate to severe cases. 1

General EEG Patterns in Encephalopathy

• Progressive slowing of the EEG is the hallmark finding, with the degree of slowing correlating with encephalopathy severity 1
• 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 1
• In severe cases, the EEG may progress to a discontinuous pattern and eventually an isoelectric EEG 1
• Triphasic waves are a remarkable finding, particularly common in hepatic encephalopathy but not specific to it 1, 2

Specific EEG Findings Based on Severity

Mild Encephalopathy

• Frontal predominance of alpha rhythm or increased beta activity 1
• Subtle background slowing with minimal disruption of normal rhythms 3
• P300 latency changes may be detected before overt EEG changes 1

Moderate Encephalopathy

• Dominant theta (4-7 Hz) activity replacing normal alpha rhythm 1, 4
• Appearance of triphasic waves, particularly in metabolic encephalopathies 1, 5
• Theta/delta mixtures with variable amplitudes 4

Severe Encephalopathy

• Dominant delta (<4 Hz) activity 1, 6
• Decreased EEG amplitude 1
• Discontinuous patterns in very severe cases 1
• Stupor often associated with triphasic waves; coma usually associated with delta waves 1

Specific Patterns and Their Clinical Correlations

• Triphasic waves are frequently seen in hepatic encephalopathy but also occur in other metabolic encephalopathies (uremic, hyponatremic) and drug intoxications (lithium, valproate, baclofen) 1, 5
• Theta activity is associated with brain atrophy 4
• Theta/delta patterns correlate with intracerebral hemorrhages and generally unfavorable outcomes 4
• Frontal intermittent delta activity (FIRDA) is associated with past cerebrovascular accidents 4
• Delta activity correlates with alcohol/drug abuse and HIV infection 4
• Low-voltage cerebral activity (LVCA) is associated with poor outcomes, particularly in hypoxic-ischemic encephalopathy 6

Prognostic Value of EEG Patterns

• EEG patterns generally correlate well with encephalopathy severity and can help predict outcomes 5, 6
• Triphasic waves are associated with higher mortality rates 4
• Generalized background slowing without other abnormalities tends to predict better outcomes than patterns with low voltage or epileptiform discharges 6
• The absence of cortical responses in sensory evoked potentials indicates particularly severe neuronal dysfunction with generally poor prognosis 1

Technical Considerations for EEG Recording

• For diagnostic purposes, use the standard 19 electrodes of the 10-20 International System 1, 3
• For monitoring purposes, four electrodes (e.g., P3, P4, F3, F4) may be sufficient 1, 3
• Recording duration should be 20-30 minutes to capture variations in vigilance levels 1, 3
• Both eyes-closed and eyes-open recordings should be included when possible 1
• Quantitative EEG analysis may improve reliability in assessing encephalopathy severity 1, 3

Common Pitfalls in EEG Interpretation for Encephalopathy

• 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, 5
• Overlooking non-convulsive status epilepticus, which can occur in encephalopathic patients 1
• Using EEG patterns alone for definitive diagnosis without considering clinical context 3
• Misinterpreting normal variants or benign patterns as pathological 3

EEG remains a valuable tool for assessing encephalopathy severity, monitoring disease progression, and providing prognostic information, though patterns should always be interpreted in the appropriate clinical context.