Persistent vegetative state. Review and report of electrodiagnostic studies in eight cases.

Of 81 comatose patients studied for two years, eight entered the persistent vegetative state (PVS), of whom four died and four survived. Clinically, all eight showed characteristic findings of wakefulness without cognitive function. Electrodiagnostic studies were characterized by (1) electroencephalograms that showed a range of patterns that were unchanged from the comatose through the vegetative state, (2) normal brainstem auditory evoked responses, (3) median somatosensory evoked responses that showed prolonged central conduction time, and (4) diminishing amplitude of the N20 response. These features may serve for identifying and monitoring patients in the PVS with a view to accurately predicting outcome.