Is it necessary to define the ictal onset zone with EEG prior to performing resective epilepsy surgery?

Yield of video electro encephalography for phase 1 pre-surgical evaluation of drug resistant epilepsy in 1200 adults: retrospective study from a tertiary center situated in a lower-middle-income country

INTRODUCTION

Video Electroencephalography (VEEG) is crucial for presurgical evaluation of Drug Refractory Epilepsy (DRE). The yield of VEEG in large volume centers, particularly those situated in Low-and Middle-Income countries (LMIC) is not well studied.

METHODOLOGY

We studied 1200 adults with drug resistant focal epilepsy whose seizures were recorded during VEEG in the epilepsy monitoring unit. VEEG review and analysis was done independently by trained epileptologists. Video EEG and MRI data were examined for concordance in order to generate a hypothesis for the presumed epileptogenic zone.

RESULTS

Analysis of seizure semiology provided information on the symptomatogenic zone in most cases except for 33 (2.75%) patients. A total of 1050 (87.5%) patients showed interictal epileptiform discharges (IEDs) with most (58.3%) showing unilateral IEDs. Most patients (n = 1162, 96.83%) showed ictal EEG discharges of which 951(81.8%) had unilateral ictal onset. Abnormal MRI was seen in 978 (81.5%) patients. Concordance of electroclinical data obtained by analysis of VEEG with MRI abnormality could be established in most patients (63%). Concordance was higher for patients with ictal onset from temporal regions (83.71%) as compared to posterior cortex (55.4%) and frontal regions (43.5%.) CONCLUSION: This study highlights the high yield of VEEG in phase 1 presurgical evaluation in DRE. Systematic evaluation of data from VEEG provided lateralizing and localizing information in most cases. Concordance between VEEG and MRI findings was noted in most patients. These findings support steps to increase referral for pre-surgical evaluation in DRE.

Presurgical video-EEG monitoring with foramen ovale and epidural peg electrodes: a 25-year perspective

Background

Epilepsy surgery cases are becoming more complex and increasingly require invasive video-EEG monitoring (VEM) with intracranial subdural or intracerebral electrodes, exposing patients to substantial risks. We assessed the utility and safety of using foramen ovale (FO) and epidural peg electrodes (FOP) as a next step diagnostic approach following scalp VEM.

Methods

We analyzed clinical, electrophysiological, and imaging characteristics of 180 consecutive patients that underwent FOP VEM between 1996 and 2021. Multivariate logistic regression was used to assess predictors of clinical and electrophysiological outcomes.

Results

FOP VEM allowed for immediate resection recommendation in 36 patients (20.0%) and excluded this option in 85 (47.2%). Fifty-nine (32.8%) patients required additional invasive EEG investigations; however, only eight with bilateral recordings. FOP VEM identified the ictal onset in 137 patients, compared to 96 during prior scalp VEM, p = .004. Predictors for determination of ictal onset were temporal lobe epilepsy (OR 2.9, p = .03) and lesional imaging (OR 3.1, p = .01). Predictors for surgery recommendation were temporal lobe epilepsy (OR 6.8, p < .001), FO seizure onset (OR 6.1, p = .002), and unilateral interictal epileptic activity (OR 3.8, p = .02). One-year postsurgical seizure freedom (53.3% of patients) was predicted by FO ictal onset (OR 5.8, p = .01). Two patients experienced intracerebral bleeding without persisting neurologic sequelae.

Conclusion

FOP VEM adds clinically significant electrophysiological information leading to treatment decisions in two-thirds of cases with a good benefit–risk profile. Predictors identified for electrophysiological and clinical outcome can assist in optimally selecting patients for this safe diagnostic approach.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00415-022-11208-6.