Loss of evoked potentials during spinal surgery due to spinal cord hemorrhage.

The cortical somatosensory evoked potential (SEP) disappeared during corrective spinal surgery in a patient with muscular dystrophy. The patient died 18 hours after surgery. Autopsy revealed an intramedullary hemorrhage 4 mm in diameter in the posterior horn of the cervical spinal cord. Microscopically, hypoxic neurons were seen adjacent to the hemorrhagic area, implying that the lesion was at least 6 hours old. The hemorrhage corresponded to the loss of SEPs and confirms that spinal cord monitoring can detect such lesions.

Brainstem auditory evoked potential abnormalities in myelomeningocoele in the older child.

Brainstem auditory evoked potentials and clinical findings were examined in 18 children over the age of 5 years who were born with myelomeningocoele which was closed at birth, and whose hydrocephalus was managed by long term shunting in most of them. The potentials were compared with age and sex matched normal subjects and with four patients with hydrocephalus only. All but one had an abnormal brainstem auditory evoked potential with 72% showing a delay in the II-V and I-V interpeak latencies of more than three standard deviations. It is proposed that the abnormalities are a reflection of brainstem dysgenesis which is part of an associated Arnold-Chiari malformation, though the malformation was clinically asymptomatic in all. The usefulness of the brainstem auditory evoked potential for assessing the course of hydrocephalus and for predicting symptomatic Arnold-Chiari malformation is questioned.

Ambulatory monitoring of the electroencephalogram in high altitude mountaineers.

Twenty-nine 24 h ambulatory EEG recordings were obtained from 9 British Army mountaineers at heights ranging from 4115 to 6220 m during the period of acclimatization. Three individuals also had ambulatory sea-level EEGs. Sea-level clinical recordings were made on all the mountaineers. All the high altitude EEG recordings were readable and accurate sleep stage scoring was possible on 28 recordings. No paroxysmal activity, which had been reported previously, was noted in any of the high altitude EEGs. There was a marked reduction in stage 4 sleep compared to the amounts normally attained at sea-level, despite strenuous activity which might have been expected to increase slow wave sleep. There was a lesser reduction of REM sleep. These findings are consistent with complaints of poor quality sleep at high altitude, despite ample opportunity for sleep and the maintenance of health. The latter was attributed to careful acclimatization.

Evoked potentials and contingent negative variation during treatment of multiple sclerosis with spinal cord stimulation.

Cervical somatosensory evoked potentials, brainstem evoked potentials, visual evoked potentials, and the cerebral contingent negative variation were recorded in patients with definite multiple sclerosis before, during, and after spinal cord stimulation. Improvements were seen in the cervical somatosensory and brainstem evoked potentials but neither the visual evoked potential nor the contingent negative variation changed in association with spinal cord stimulation. The results indicate that spinal cord stimulation acts at spinal and brainstem levels and that the clinical improvements seen in patients are caused by an action at these levels rather than by any cerebral arousal or motivational effect. The evoked potentials were not useful in predicting which patients were likely to respond to stimulation.