Abstracts

Rationale: High-frequency oscillations (HFOs) are a promising biomarker of epileptic tissue, but past work has focused on single channels evaluated outside of their clinical context. The common method of identifying a single seizure onset zone from short periods of EEG does not account for patients in which the location of active seizure focus changes over time.  Here, we evaluate the clinical consequences of determining HFO rates in patients with multiple seizure foci. Methods: 18 patients with intractable epilepsy were recorded with intracranial EEG for potential surgical resection.  All periods of slow wave sleep during the entire hospitalization were evaluated with an automated HFO detector.  A blind source separation algorithm then determined clusters of channels that tended to have high firing rates at similar times, which allowed visualization of the composition and temporal variability of each channel cluster over the entire recording.  After completing the analysis, we evaluated the clinical reports to compare resected volumes, seizure onset zone, and outcomes.  We compared the location of the seizure foci with the identified HFO clusters. Results: Five of the 18 patients had multiple, independent seizure foci.  In each of these 5 patients, the location of the seizure focus was not stable over the course of the hospitalization, and clinical decisions regarding resection margins were complex.  Comparison of those clinical data with the HFO clusters showed a wide range of results and correlation.  We could identify no algorithm to correlate HFOs directly with resection margins or seizure onset zone in these patients. Conclusions: HFOs are highly correlated with epileptic tissue; however, the timing and location of HFOs, like spikes and seizures, can be highly variable.  Just as clinical evaluation incorporates standard EEG as one part of a complex clinical decision, HFOs should be evaluated in their full clinical context as an additional biomarker, rather than in isolation from other clinical data. Funding: NIH K01-ES026839 (S.G.), NIH K08-NS069783, R01-NS094399, Doris Duke Foundation Clinical Scientist Development Award #2015096 (W.S.)