The Electroencephalogram in Hepatic Encephalopathy

Abstract

The electroencephalogram (EEG) corresponds to cortical postsynaptic activity that is modulated by both physiological and pathological diencephalic and brain-stem influences. It is extremely sensitive to metabolic and toxic influences; therefore, the EEG is a reliable tool to detect metabolic brain dysfunction. The EEG can have two diagnostic roles in cirrhotic patients with consciousness/cognitive alterations. The first one is the occasional possibility for the EEG to detect a cause of brain dysfunction different from hepatic encephalopathy. The second one is the possibility to obtain quantitative data on brain dysfunction that are independent of cultural influences and of patient cooperation. Therefore, the EEG monitoring of patients with HE can provide information useful for their follow up. The resting eye-closed EEG of patients with cirrhosis or non-cirrhotic portal hypertension and portal-systemic shunt can be classified by visual-pattern recognition; however, this approach is poorly reproducible. An improvement is provided by the visual reading of the frequency of the posterior background activity. Further improvement is obtainable by quantitative analysis that can be obtained by spectral analysis. Spectral analysis of the background activity of the EEG in patients with cirrhosis provides measures that have prognostic value both on the occurrence of bouts of overt HE and on survival. New quantitative techniques are developing: their real utility should be scrutinized.

The EEG recorded during cognitive tasks allows the extraction of the electric potentials evoked by the tasks themselves. These event-related potentials have more theoretical than practical utility, due to their poor reproducibility and inconstancy of appearance across various individuals.

In conclusion, the EEG provides functional data that are similar and complimentary to the behavioural ones, but more objective and quantifiable, that can improve the neuromonitoring of HE.