Abstracts

Rationale: Only three prior studies have described iEEG changes during the Wada test, a procedure commonly employed to assess language dominance and to screen for global amnesia during the pre-surgical evaluation for medically intractable epilepsy patients. In addition, all previous studies used amobarbital sodium for the injections. We report iEEG findings in five patients with intracarotid injections of pentobarbital or methohexital during the Wada procedure. Methods: Clinical or electrographic seizures during Wada testing would invalidate the results, therefore, EEG data is routinely collected during the procedure. This study is a retrospective analysis of iEEG data that was obtained during Wada testing on five patients with implanted intracranial electrodes between 2010 and 2014 at Stanford Hospital. All patients had refractory epilepsy and suspected dominant hemisphere left temporal lobe onset seizures. Intracranial electrodes included depths or subdural strips and grids implanted into or covering the amydgala, anterior and posterior hippocampus, temporal pole, and lateral temporal regions. Concurrent scalp and iEEG recordings were collected and patients were injected with either 25 to 35 milligrams (mg) of pentobarbital or 3.3 to 9.9 mg methohexital. EEG data was visually analyzed by a fellowship trained epileptologist (SL). Results: A total of five cases were analyzed with a total of 7 intracarotid injections. On scalp EEG, all injections produced bilateral slowing on scalp EEG though slowing was asymmetric. On iEEG, all injections produced a combination of ipsilateral high amplitude rhythmic slowing, voltage attenuation and increased epileptiform spikes on iEEG for an average of 4 minutes 30 seconds (range = 2'57" to 7'10"). No clinical or electrographic seizures were recorded on iEEG, but there was an on average an 8.9 fold increase in spikes (average number spikes before = 18 versus after = 162) after injection compared to baseline recordings. Conclusions: Intracranial EEG data during Wada testing with these two medications have not been previously described. During Wada testing, both pentobarbital and methohexital produced characteristic changes in the iEEG including high amplitude rhythmic slowing, voltage attenuation and most notably increased spikes without seizures.