Visual evoked potential--a tool in the diagnosis of hepatic encephalopathy?

Visual evoked potentials (VEP) have been suggested to be of value in the diagnosis of subclinical and mild hepatic encephalopathy. In the present study, a comparison between VEP and four psychometric tests (number connection test A and B, digit symbol and word memory test) was performed in 42 cirrhotic patients, 17 of whom had clinical signs of encephalopathy. The results were compared to sex- and age-matched healthy controls. The VEP latencies for P2 (the second positive wave) and N3 (the third negative wave) were 11% and 26% longer (P less than 0.01-0.001) in the patients than in the controls. Moreover, the latencies for N2 (the second negative wave) and P2 were longer in the encephalopathic as compared to the non-encephalopathic patients (P less than 0.05). There was a significant correlation between the latencies for N2 and number connection tests A and B and digit symbol test. However, of the patients with clinical encephalopathy, less than half had VEP latencies longer than the mean +/- 2 S.D. above those for the controls. In contrast, none of the encephalopathic patients had normal results on the psychometric tests. This study demonstrates that although statistically significant differences exist between groups of cirrhotic patients and controls, VEP is not a reliable tool for the diagnosis of encephalopathy in the individual patient.