Far field correlates of thalamic activity in cortical and cervical somatosensory evoked potentials

Important abnormalities in recordings of somatosensory evoked potentials in coma

We have chosen six illustrations showing how much vital information can be obtained from median nerve SEPs during the first 24 hours in coma. With avulsion of brachial plexus roots there was loss of SEPs at the cervical cord and the scalp from the affected side. In a severe injury of the cervical cord there was preservation of brachial plexus potentials, while SEPs at the cervical cord were absent. After critical deterioration in a case of repeated subarachnoidal hemorrhage, scalp SEPs with very short latency occurred, which is a finding suggestive of destruction of cortical SEP generators heralding a fatal outcome. In a case of brain injury combined with central hyperthermia, there was initially a loss of scalp SEPs probably due to the combined effect of these factors. In a case of brain injury there were bifid peaks at the scalp level. It is important to assess central sensory conduction time only to the first scalp SEP, otherwise an erroneously abnormal state may be inferred. In a patient with clinical and EEG evidence of brain death there was a loss of far-field thalamic potentials at the neck. It is important to be aware of such presentations to be able to provide corroborative assurance for the assessment of prognosis.