Abstracts

Rationale: In the case of pediatric patients who for reasons of age, developmental delay, and/or general anxiety may not be able to cooperate, localization of epileptiform activity using simultaneous scalp electroencephalography/magnetoencephalography (EEG/MEG) is typically performed under sedation. Given the variety of anesthetics by which this may be achieved, as well as their effects on cerebral metabolism, the ability to identify epileptiform discharges may in part be influenced by the choice of agent. To assess this possibility, we compared EEG/MEG interictal mapping results in a patient with symptomatic seizures under sedation using propofol induction/maintenance and, subsequently, using propofol induction and dexamedetomidine and low-dose propofol maintenance, during a follow-up assessment. Methods: A 3-1/2-year-old female with a diagnosis of intractable, symptomatic hemi-myoclonic-tonic seizures, and encephalopathy characterized by developmental delay with autism spectrum disorder secondary to left brain structural abnormality, was referred for detailed non-invasive Phase 1 evaluation. Initial EEG/MEG interictal mapping was performed under general anesthesia induced by propofol injection, and maintenance achieved by a propofol infusion rate of 166 ug/kg/min. At an 18 month follow-up, EEG/MEG interictal mapping was repeated in the same patient using a modified sedation protocol, entailing an initial bolus of propofol, followed by a 10 minute load of 1-1.5 ug/kg of dexamedetomidine, and low dose infusion of propofol (< 100/ug/kg/min). During both the initial and follow-up assessments, 30 minutes of baseline EEG/MEG recordings were obtained, in the absence of any stimulation. Epileptiform discharges were identified through visual inspection of the 30 minute simultaneous EEG/MEG trace, and active sources underlying each epileptiform event were modeled as a single equivalent current dipole localized on patient's anatomical MRI. Results: Visual inspection of the interictal EEG/MEG recording obtained under propofol induction and maintenance revealed a preponderance of high frequency artifacts, and limited visibility and localization accuracy of epileptiform discharges (Fig. 1A). On the other hand, a review of the EEG/MEG trace obtained at follow-up in the same patient using the modified sedation protocol was characterized by the absence of excess high frequency activity, and more prominent evidence of localizable epileptiform activity sources (Fig. 1B). Conclusions: Compared to traditional propofol induction and maintenance, we found that a modified sedation approach using propofol induction, and dexamedetomidine and low-dose propofol maintenance, improved detectability of interictal spiking activity and localization accuracy of MEG-derived sources. While preliminary, this observation highlights the influence of choice of sedatives on quality of EEG/MEG interictal recordings in patients with symptomatic epilepsy, while maintaining patient safety. Funding: Neuroscience Institute- Le Bonheur Children's Hospital