Abstracts

Rationale: In challenging patient population, for example, pediatric epilepsy patients or those with severe cognitive deficits, sedation or anesthesia is imperative for adequate MEG assessment. However, the question whether it is possible to localize functional auditory areas by eliciting auditory evoked fields (AEFs) during sedation/anesthesia in challenging patients still remains a matter of debate. Whereas the effect of anesthesia (e.g., propofol) on auditory evoked fields (AEFs) was studied to a certain degree (Simpson et al. 2002), there is no literature pertaining the effect of new and becoming increasingly popular sedative agent, such as alfa2 agonist dexmedetomidine (Precedex), on these responses. In our preliminary study, we aimed for the first time with MEG to evaluate whether AEFs responses can be reliably elicited during sedation with Precedex. Methods: We retrospectively reviewed the AEF data from two female patients with intractable epilepsy (4 and 14 yo), who underwent sedation with Precedex during MEG procedure for evaluation of epilepsy focus and localization of eloquent auditory cortex. These two patients were selected on the bases of their minimal epileptic discharges, affecting AEF responses. MEG recording was performed on 306-sensor MEG machine (Neuromag, Triux) at MEG Lab at Florida Hospital, Orlando. The novelty paradigm, intended to elicit AEFs, consisted from standard, (70%), frequency deviant (20%) and novel (unexpected) (10%) tones. AEFs were analyzed in two conditions: full sedation (100% dose) and decreased sedation (70% of initial dose). Equivalent current dipole (ECD) approach was used to localize AEFs on patient s own MEG-coregistered MRIs.Results: At the sensor level, AEFs waveforms were noticeable in all study participants under both levels of sedation (Fig. 1). The waveform distribution and amplitudes were strongly associated with seizure focus and patients head size, respectively. At the source level, we were able to identify all three expected components and localize them to the areas of expected generation (Fig. 1). It must be mentioned though, that the number of successfully localized AEF sources was not consistent throughout the subjects and within the same subject during different sedation levels.Conclusions: Our preliminary results indicate that AEF responses can be localized during conscious sedation with Precedex. It is possible to speculate that this type of sedation may provide with possibility of assessing cognitive and language function and identification of eloquent language cortex in epilepsy patients unable or unwilling to cooperate. Future studies addressing these specific questions are underway.