The diagnostic specificity of triphasic wave patterns.

A blind analysis of 56 EEGs with triphasic wave patterns was performed to determine the diagnostic specificity of individual electrographic features. EEG and clinical variables analyzed included longitudinal topography, phase lags, symmetry, background activity, reactivity, longitudinal bipolar phase reversal sites, responses to photic stimulation and mental status at the time of recording. The only statistically significant finding for any of the diagnostic groups tested was the presence of severe background slowing in cases of hepatic encephalopathy (P less than 0.001). We found no evidence to suggest that other features may contribute to a more highly characteristic pattern for hepatic encephalopathy. None of the features studied reliably distinguished hepatic encephalopathy from other forms of metabolic encephalopathy.