Assistant Professor University of Texas Southwestern Dallas, Texas
Rationale: Epilepsy patients with mesial temporal sclerosis (MTS) usually undergo epilepsy surgery without previous invasive evaluation. Unilateral MTS (UMTS) responds well to standard anterior temporal lobectomy (SATL) vs. selective amygdalohippocampotomy via laser interstitial thermal therapy. Bilateral hippocampal responsive neurostimulation (RNS) is an option for patients with bilateral MTS (BMTS) if bilateral temporal seizures were recorded with scalp EEG. Nevertheless, it is not clear how to identify patients in UMTS cohort who might not benefit from SATL, and in BMTS cohort who would not respond to RNS therapy of bilateral hippocampi. Methods: We included patients who had UMTS or BMTS on MRI, didn’t have previous SATL, and underwent stereo-EEG (SEEG) evaluation at our center. We analyzed SEEG localization results, epilepsy risk factors, seizure semiology and epilepsy surgery outcomes. Results: Among 179 adult SEEG implantations screened, 17 patients met selection criteria. In this patient cohort, 13 patients had UMTS and four BMTS. Ten out of 17 patients were selected for SEEG due to presence of the other brain lesion(s), 12/17 - discordant seizure semiology, 10/17 - discordant scalp EEG, and 12/17 had combination of these factors.
SEEG ictal onset was concordant with MTS localization (i.e., seizures started only from the hippocampus with MTS) in 5/13 patients with UMTS and in 3/4 patients with BMTS.
Only one out of ten patients with additional brain lesion(s) had SEEG ictal onset from such a lesion. Four out of 13 patients in UMTS group had positive family history of epilepsy (FHE). None of them had unilateral mesial temporal SEEG ictal onset.
Three out of 17 patients (one UMTS, two BMTS) had history of viral encephalitis, 3/3 had bilateral temporal SEEG ictal onsets, 2/3 - discordant with MTS location.
Eight out of 17 patients (seven UMTS, one BMTS) had non-mesial temporal auras, 6/8 had SEEG/MTS discordant ictal onset.
Five out of 13 patients with UMTS had frequent (more than one per year) generalized convulsions (fGTC), 4/5 had SEEG/MTS discordant ictal onset.
Ten out of 13 UMTS patients had resective surgery (mean followup 23 (3-51) months), 7/10 have Engel class I outcome, one - Engel class III, two - Engel class IV.
In Engel class I cohort, the ictal onset was concordant with MTS location in 4/7 patients, only 1/7 had fGTC, 1/7 - FHE, none - history of viral brain infection. Conclusions: Our study demonstrated that seizures may start outside of the hippocampus with MTS. Positive family history of epilepsy, history of viral brain infection, frequent generalized convulsions and non-mesial temporal auras could indicate ictal onset outside of the mesial temporal lobe. Patients with BMTS potentially could be poor responders to RNS therapy of bilateral hippocampi if seizures start outside of hippocampi. Larger studies are needed to replicate these findings and create guidelines for the role of genetics, neuroinflammation and invasive evaluation in epilepsy surgery candidates with UMTS and BMTS. Funding: Please list any funding that was received in support of this abstract.: None
