Abstracts

Rationale: Intracarotid anaesthetic procedures (IAPs) result in temporary deficits, including contralateral hemiparesis and certain cognitive changes. This procedure provides a model to investigate the hemispheric differences in occurrence of anosognosia, or loss of awareness into symptoms. In various neurological disorders there is a robust association between nondominant hemisphere lesions and anosognosia. Consistent with this, the great majority of patients show no recall of hemiparesis following right hemisphere amobarbital injection. A smaller number of patients do not recall hemiparesis following left hemisphere injection and these patients usually have a seizure focus in their right hemisphere. However, anosognosia is not always a right hemisphere phenomenon. Loss of awareness sometimes occurs in aphasia. Whereas patients with Broca’s aphasia are usually aware of their naming deficit, patients with Wernicke’s aphasia appear unaware of their comprehension deficit. No previous research has focused on this distinction during the IAP. To date, most of the research on IAPs has been done with amobarbital as the anesthetic agent. We have recently introduced an alternative anesthetic agent, etomidate. It was the drug used in the current study. Our aims were to compare awareness for motor changes after left or right injections, to compare awareness in patients with left vs. right TLE, and to compare awareness for naming vs. comprehension deficits after left injections. Methods: Subjects were 35 unilateral TLE patients, all left hemisphere dominant for language. At the conclusion of etomidate speech and memory (eSAM) testing, patients were asked standard questions probing awareness into motor weakness, dysarthria, naming and comprehension. Their responses were coded as no awareness, partial awareness, or full awareness. Memory scores from the eSAM were also analyzed as related to the awareness scores. The data were analyzed using nonparametric statistics. Results: For motor symptoms, less awareness was seen following right hemisphere injections (56.8% no awareness vs. 43.2% following left hemisphere injections), and injections contralateral to the seizure focus resulted in the least awareness; this was not associated with memory scores. Following right hemisphere injection, awareness for dysarthria was also significantly reduced only when the seizure focus was contralateral to the injection. Following left hemisphere injection, the predicted dichotomy was evident, with 10% of patients not aware of naming deficits, whereas 73% were not aware of comprehension deficits. This result did not differ by side of seizure focus. Conclusions: This study confirmed the difference in awareness between left and right injections seen in earlier studies using amobarbital, but in contrast relatively more awareness overall was evident during the eSAM. In addition, this was the first study to show the striking difference in awareness between comprehension and naming deficits after injection into the dominant hemisphere. Funding: Canadian Institutes of Health Research