Improving the Noninvasive Surgical Workup of Drug-Resistant Focal Epilepsy

Surgical intervention in epilepsy is underused.

The combination of electroencephalographic source localization (ESL) and magnetoencephalographic source localization (MSL) is superior to either ESL or MSL alone for surgical intervention in patients with drug-resistant focal epilepsy. This is according to a study published in a new issue of Brain.

A total of 13 patients with drug-resistant focal epilepsy (non-lesional, n=10; extensive-lesional, n=3) underwent synchronized high-density EEG (HDEEG) magnetoencephalography (MEG) with 72-94 channel EEG and 306-sensor MEG. The investigators applied source localization to mean interictal epileptiform discharges (IED) and ictal discharges during 3 phases.

The phases included an early phase (first latency 90% explained variance), mid-phase (first of 50% rising-phase, 50% mean global field power), and late-phase (negative peak). The first of the 3 early-phase solutions, including ESL, MSL, and combined ESL and MSL (EMSL), comprised the earliest-solution.

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The prospective follow-up periods were 3 to 21 months (median, 12 months) prior to surgery as well as 14 to 39 months (median, 21 months) following surgery. Researchers recorded IEDs in 1474 patients, which were observed in 42%, 16%, and 42% of HDEEG only, MEG only, and both, respectively.

Of the 33 seizures captured, 21% were observed with HDEEG, 3% were observed with MEG only, and 76% were observed with both. The odds ratios (ORs) of epileptogenic zones were higher for the earliest-solution compared with the early-phase IED-surgical resection as well as earliest-solution vs all mid-phase and late-phase solutions.

A superiority in performance was observed for ESL compared with EMSL for ictal-surgical resection (OR, 3.54; 95% CI, 1.09-11.55; P =.036). Additionally, MSL was associated with better performance than EMSL for IED-intracranial EEG (OR, 4.67; 95% CI, 1.19-18.34; P =.027), whereas ESL outperformed MSL for ictal-surgical resection (OR, 3.73; 95% CI, 1.16-12.03; P =.028).

Conversely, MSL outperformed ESL for IED-intracranial EEG (OR, 0.18; 95% CI, 0.05-0.73; P =.017).

According to the researchers, one limitation of the study was the small number of patients who had data available for follow-up assessment.

Findings from this study appear to “challenge current practice of source localization with its emphasis on mid-phase discharge analysis and its common inclusion of the late-peak phase of the discharge in the source solution,” the researchers concluded.


Plummer C, Vogrin SJ, Woods WP, Murphy MA, Cook MJ, Liley DT. Interictal and ictal source localization for epilepsy surgery using high-density EEG with MEG: a prospective long-term study [published online February 25, 2019]. Brain. doi:10.1093/brain/awz015