Abstracts

Rationale: Source localization can help to identify the seizure onset zone or propagation zone, but it is unclear how often dipole localization techniques influence surgical planning.

Methods: Patients who received a HD-EEG from 7/2014-7/2019 at Stanford were included if they met the following inclusion criteria: (1) seizure focus localization was not clear; (2) epileptiform discharges were recorded during HD-EEG for source localization analysis, (3) patients underwent surgical treatment after HD-EEG evaluation. Six board certified neurophysiologists independently reviewed each case through an HIPPA protected online survey. Their choices regarding surgical intervention were recorded anonymously. The same cases were then presented with additional data of HD-EEG findings, and the response about next step management for intracranial EEG and/or surgical intervention were recorded again. The feedback of whether HD-EEG findings having additional value for the decision-making were recorded. Dipole localization used the LORETTA method on age-matched MRIs.

Results: In 202 patients who received HD-EEG (total 1030 hours recording, among 83 total receiving epilepsy surgery), 50 met the inclusion criteria. Mean age was 40.1 ±11.3 years old. All patients had scalp EEG and a brain MRI, 88% had neuropsychological testing, 78% had either PET (n=37) or SPECT (n=12). HD-EEG was rated as helpful in 83.8% cases, not useful in 14.4% cases, and misleading or potentially harmful in 1.8% cases by raters. The HD-EEG changed their decision-making in the following ways: in 19.9% the plan was changed in a major way, e.g., a different procedure or avoidance of invasive recording or new depth electrode sites; in 22.6% HD-EEG changed the plan in a minor way, e.g., extra invasive electrodes near the previously planned sites; in 41.6% cases HD-EEG did not change their plan but provided confirmation or reassurance; in 15.9% cases technical problems precluded evaluation. Taking all surgical patients as the denominator, HD-EEG influenced the surgical planning in 34.9%.

Surgical procedures comprised anterior thalamic DBS in 3, RNS in 24, laser resection in 10, VNS in 8, open lobectomy in 5. Mean follow-up time after surgery was 24.1 ± 17.1 months. One patient was lost to follow-up. For patients receiving HD-EEG, Engel class I outcome was achieved in 34.7% and class II in 18.4%. Our Center’s average Class I outcome is 62.5%, reflecting the high complexity of patients selected to receive a HD-EEG. Among patients achieving Engel class I/II outcome, the concordance rate of HD-EEG and resection zone was 63.6% versus 36.4% with class III/IV (p=0.027).

Conclusions: HD-EEG assists presurgical planning for refractory epilepsy patients with unclear focus localization, altering the work-up in 41% of cases and in 34.9% of all surgical cases. Concordance of HD-EEG dipole analysis localization and resection site is a favorable outcome indicator.

Funding: Please list any funding that was received in support of this abstract.: None.