Abstracts

Controversy exists in what structures are inactivated in the intracarotid sodium amobarbital (ISA) test. Therefore, intracranial EEG patterns were correlated to electrode location in patients with bilateral depth electrodes. To determine the EEG change that occurs with successful ISA testing, clinical and EEG findings were analyzed. A previous study described primarily increases in [Delta] activity. 7 ISA injections were performed in 4 presurgical temporal lobe epilepsy patients with bilateral frontal and temporal depth electrodes. Each patient had angiography to determine crossfilling. An ISA bolus injection of 75 to 200 mg was given in the dose needed to achieve hemiplegia. Testing for language dominance and hemisphere memory support was then attempted. Digital EEG recorded was analyzed to determine duration, location, progression and type of change. In each case, the seizure focus showed EEG change. EEG baseline returned prior to contralateral testing. Clinical responses to ISA testing were correlated with EEG findings. The physician performing the ISA test and a physician blinded to the case reviewed each EEG. The most common pattern found was an increase in [Delta] activity with a striking superimposed [beta] and/or [theta] activity, 5/7 injections (71%). Increased [beta] activity was first seen in the frontal lobe followed by the temporal lobe. [beta] activity was more prominent in mesial temporal structures than [Delta] activity. Presence of bifrontal EEG changes in 4 of 7 injections correlated with crossfilling in 3 cases. With increased [Delta] and [beta] activity in the frontal and temporal lobe, clinical hemiplegia was achieved and patient attention was adequate for testing. EEG changes averaged 402.2[plusmn]53.87 seconds before return to baseline. In one injection, a unilateral burst suppression pattern of high amplitude [beta] and [theta] activity occurred. This patient[apos]s strength returned prematurely and EEG baseline returned significantly quicker than other injections, 260.5[plusmn]13.44 seconds (p=0.03). A generalized low amplitude fast [beta] activity not associated with crossfilling occurred in one injection. This was associated with somnolence and inability to complete any testing and the EEG returned to baseline in 653.5[plusmn]9.19 seconds, significantly slower than other injections (p=0.03). Duration of EEG changes correlated highly between readers (r=0.95, p=0.001). Increased [Delta] activity with a superimposed [beta] and/or [theta] activity in frontal and temporal depth electrodes is often found with ipsilateral functional inactivation and successful completion of the ISA test. Mesial temporal structures show more prominent [beta] activity than [Delta] activity suggesting direct inactivation of that area. Intracranial EEG may show low amplitude fast [beta] activity or a burst suppression pattern with suboptimal amobarbital doses.