Somatosensory evoked potentials in hepatic encephalopathy.

Median nerve somatosensory evoked potentials were recorded from 33 patients with various degrees of hepatic failure and from 10 age-matched controls. Within 20 ms poststimulation, one negative peak (N13) could be recorded from the middle of the back of the patient's neck at the C2 vertebral level. Within 150 ms, three negative and three positive peaks, sequentially designated as N1, P1, N2, P2, N3, and P3, could be recorded from the scalp over the contralateral sensory cortex. There was a progressive prolongation of peaks and interpeak latencies correlating with the severity of hepatic encephalopathy. In 10 patients with hepatic failure but no clinical evidence of hepatic encephalopathy, latencies of peak N3 and P3 were delayed and N1-N3 interpeak latencies were prolonged. Thirteen patients with grade 1 or 2 hepatic encephalopathy showed further delayed latencies of peaks P2, N3, and P3, further prolonged N1-N3, N1-P2 interpeak latencies, and distortion of waveforms. Peaks N2, P2, N3, and P3 were further delayed, and even disappeared in 10 patients with grade 3 or 4 hepatic encephalopathy. However, central conduction time (N13-N1 interpeak latency) was not prolonged in all stages of hepatic failure. In addition, serial somatosensory evoked potential studies correlated well with the clinical course. The present data suggest that somatosensory evoked potential recording is a reliable objective method in the early assessment and monitoring of hepatic encephalopathy.