Multimodality evoked potentials (auditory, somatosensory and motor) in coma.

Auditory brainstem responses (ABRs) have proved to be significantly related to outcome, both in severe head injury and brain hemorrhage. Nevertheless, the usefulness of ABR is limited by the anatomic extent of the investigated pathways. The combined use of ABRs and somatosensory evoked potentials (SEPs) improves the outcome prediction in comparison to the use of only one modality. It mainly decreases the rate of false negatives, since patients with severe hemispheric damage sparing the brain stem may have a poor outcome despite normal ABRs. The use of motor evoked potentials (MEPs) from magnetic transcranial stimulation is also significantly related to outcome: it appears to be far superior to the clinical evaluation of motor responses, while the combined use of MEPs and SEPs gives a new opportunity of checking sensorimotor dysfunction. ABRs and SEPs may also be useful tools in the confirmation of brain death, the kernel of which is the assessment of brainstem death: they allow to check lemniscal pathways, which cannot be properly evaluated by clinical examination, and provide an objective confirmation of absence of brain stem activity.