Clonidine- and methohexital-induced epileptiform discharges detected by magnetoencephalography (MEG) in patients with localization-related epilepsies

Purpose: During presurgical evaluation, 14 patients with medically intractable focal epilepsies underwent magnetoencephalographic (MEG) recordings to localize the epileptogenic focus. To increase the number of epileptiform discharges required for MEG analysis, methohexital a short-acting barbiturate that is known to activate epileptiform activity, was used. Additionally, we investigated the spike provoking properties of clonidine in comparison to methohexital. Methods: After oral premedication with clonidine, shortlasting anesthesia was provided by intravenously administered methohexital. The number and location of epileptiform MEG discharges were assessed after clonidine premedication and during methohexital anesthesia. Results were compared with baseline MEG recordings. Results: Methohexital increased the frequency of focal epileptiform discharges in eight of 13 patients (one of the 14 patients did not receive methohexital after premedication with clonidine). Additionally, premedication with clonidine was found to increase focal epileptiform discharges in nine of 14 patients. When compared with baseline MEG recordings, recordings after treatment with both clonidine premedication and methohexital anesthesia showed a significant increase in the total number of epileptiform signals and the number of spikes contributing to MEG source localizations. Conclusions: This study confirms the selective proconvulsant effects of methohexital on the epileptogenic focus as suggested previously by EEG and electrocorticogram (ECoG) investigations. Additionally, our data establish for the first time that clonidine increases epileptiform activity in patients with seizure disorders. These results indicate that clonidine is suited as an activating agent for the localization of epileptogenic foci by means of MEG. This effect of clonidine on specific epileptic activity also indicates that clonidine should be used with caution as an antihypertensive drug in patients with seizure disorders.