Predicting Outcomes with Stereotactic Laser Amygdalohippocampotomy for Mesial Temporal Lobe Epilepsy Using an Infradelta Biomarker

Introduction: Infradelta activity ( < 1Hz) is associated with primary inhibitory control of cortical mechanisms, with recent work showing infradelta power is decreased near the seizure onset zone during non-REM sleep. In this retrospective study, we assess the predictive value of a biomarker based on delta and infradelta frequencies recorded from intracranial electrodes for seizure-free outcome after SLAH.

Methods: Patients with medically intractable focal epilepsy who underwent sEEG-guided SLAH were selected. On post-op nights 1 and 2, 15-minute artifact free clips during NREM sleep were chosen from periods with high delta/beta power (marker of NREM sleep). Delta(1-4Hz), infradelta(0.3-1Hz) and beta(12-25Hz) band limited power was calculated after Butterworth bandpass filtering.
For every clip, infradelta power at each temporal lobe contact was calculated and normalized by delta power. The contact with the lowest power was found. Next, the brain MRI performed immediately after SLAH was co-registered to the head CT after SEEG implantation to determine if the lowest infradelta power contact was ablated.

Results: Of the 18 patients, 39% are seizure free at last follow up (minimum follow up 22 months). Using the first available night only, when the lowest infradelta contact was lesioned, 7/11(64%)were seizure free compared to 0/7(0%)(p=0.028,rank sum). 14 patients had clips from 2 nights, with the calculated contact being identical in half of patients. In the 7 patients where all calculated contacts were lesioned, 6(86%) were seizure free, compared to 1/3(33%) seizure free when 1 of 2 contacts were lesioned, and 0/4(0%) when none were lesioned(p=0.002, Spearman).

Conclusion : Infradelta/delta ratio proved to be strongly predictive of seizure-free outcome in a patient population that has proved to have generally poor outcomes after SLAH. This study provides proof of concept that the ratio is a reliable epileptic biomarker, and may also provide a route for selecting patients who are likely to benefit from SEEG-guided SLAH.