Evoked potentials in severe herpes simplex encephalitis

Diagnostic and prognostic value of evoked potentials (EP) were studied in 5 patients with severe herpes simplex encephalitis (HSE). Latency of the third negative cortical N70 peak, elicited by median nerve stimulation, was prolonged in 3 survivors with Glasgow coma score of less than or equal to 6 (115 vs 71 ms in controls, p less than 0.05), but normal after improvement of the acute disease. N70 right to left interhemisphere difference was increased initially in the 4 survivors (26 vs 3 ms in controls, p less than 0.05) indicating focal brain involvement, a crucial finding in HSE. The first cortical N20 peak was preserved in all survivors even during deep coma where evaluation of brain function is difficult. Auditory brainstem EP were normal in all patients and useful to exclude brainstem death. In severe HSE, somatosensory long-latency EP are an effective monitor of the level of impaired consciousness and can detect brain focal signs. Short-latency N20 components may be predictive of the outcome.