The technique at the center of the research is stereoencephalography-guided radiofrequency thermocoagulation, or SEEG-RFTC. In this procedure, depth electrodes implanted under robotic navigation serve double duty: they record seizures from inside the brain, and then they deliver focal radiofrequency energy through selected contacts, heating tissue to as much as 80 degrees Celsius and creating small thermal lesions roughly seven millimeters across. It converts a purely diagnostic implantation into a therapy without a single additional surgical trajectory — an appealing option for patients whose seizure networks overlap eloquent cortex or who decline open craniotomy.

But which patients actually benefit? The Nanjing team, led by Y.-q. Yang and colleagues, turned to the seizure-onset pattern — the specific electrographic sequence that appears at the very start of a seizure on SEEG. Among the patterns classified in prior work, one stands out: low-voltage fast activity, or LVFA, a burst of rapid, low-amplitude rhythms that many epileptologists regard as the fingerprint of the epileptogenic core itself. Pathophysiologically, LVFA is thought to reflect local inactivation of inhibitory interneurons and synchronized firing of pyramidal cells — a disinhibition mechanism that optogenetic experiments have directly implicated. Slow waves and electrodecremental patterns, by contrast, are widely considered propagation territories rather than the source.

The study’s design exploits a unique property of RFTC: because the thermal lesions are strictly confined to the electrode contacts that recorded the seizure onset, there is an intrinsic spatial co-localization between the recorded brain-wave pattern and the clinical response. Unlike open resection, where the extent of tissue removal confounds interpretation, RFTC provides a clean model to test whether LVFA carries independent prognostic significance. The researchers analyzed 25 patients who received SEEG-RFTC as their sole intervention between 2022 and 2024, all with at least 12 months of follow-up and a mean observation period of 31.6 months.

The results are remarkably clear-cut. Among the 13 patients whose seizures began with an LVFA-containing pattern, 12 — 92.3 percent — achieved complete seizure freedom, graded Engel class I. Among the 12 patients with LVFA-absent patterns, only 4 — 33.3 percent — did so, a difference the authors report as statistically significant. The stratification held even when the team separated patients by MRI status: in MRI-negative patients, LVFA-present cases achieved 100 percent seizure freedom versus 20 percent for LVFA-absent cases, while MRI-positive patients showed 85.7 versus 42.9 percent. Notably, MRI positivity alone did not predict outcome at all.

The MRI-negative finding may be the most clinically provocative. When no structural lesion is visible on 3-Tesla epilepsy-protocol MRI, LVFA frequently corresponds to occult focal cortical dysplasia — particularly bottom-of-sulcus dysplasia, a malformation tucked into sulcal depths that evades even modern imaging. The authors suggest that MRI-negative patients with LVFA onset, especially when PET hypometabolism concords with the SEEG-defined onset zone, may form an electro-metabolic double-positive subgroup with exceptionally favorable ablation outcomes. Such patients, they argue, should not be excluded from RFTC solely on the basis of MRI negativity.

Yet seizure freedom, as graded by the Engel classification, is an inherently subjective measure. It relies on patient-reported seizure counts and recall, which can be inaccurate for subtle or nocturnal events. More fundamentally, Engel class I does not guarantee that the epileptogenic network has been completely disintegrated — residual subclinical electrical activity may persist and later evolve into clinical seizures, particularly when medications are tapered. This uncertainty complicates decisions about antiseizure medication withdrawal and long-term prognosis, leaving patients and clinicians without an objective readout of whether the driver has been adequately destroyed.

Here the study introduces its second key contribution: postoperative scalp EEG as an objective, noninvasive, longitudinally trackable complement to Engel grading. At six months after RFTC, 20 of the 25 patients underwent 24-hour scalp EEG recordings using the international 10–20 system, independently reviewed by two clinical neurophysiologists blinded to the seizure-onset patterns and clinical outcomes. EEG normalization — the absence of interictal epileptiform discharges without focal slowing beyond the expected postoperative range — was significantly more frequent in LVFA-present patients, appearing in 7 of 8 normal-EEG cases versus 4 of 12 abnormal-EEG cases. Seven of the 8 patients with normalized EEG were seizure-free, a positive predictive value of 87.5 percent.

The dissociations the team observed are as informative as the concordances. One LVFA-absent patient with delta brush onset achieved EEG normalization yet remained Engel class III — proof that scalp EEG and seizure counts capture complementary dimensions of therapeutic success. Conversely, among seizure-free patients with persistent EEG abnormalities, only half belonged to the LVFA-present group, suggesting incomplete network disruption despite clinical remission. The authors propose that Engel class I with a normal EEG may represent a more complete therapeutic outcome than Engel class I with persistent discharges, and might guide safer medication withdrawal. Among non-LVFA patterns, delta activity, beta sharp activity, and electrodecrement yielded zero seizure freedom, consistent with their interpretation as propagation rather than core phenomena — though sharp activity, an exception, achieved 100 percent seizure freedom in three patients while still lacking EEG normalization, hinting at a potentially less durable mechanism.

The authors are careful to frame these conclusions as preliminary. The cohort is small, the design retrospective, five patients lacked postoperative EEG, and the 64 percent Engel I rate in the RFTC-only subgroup reflects natural selection — the 18 patients who proceeded to open resection did so precisely because RFTC failed, whereas some non-seizure-free patients declined further surgery or were satisfied with reduced seizure burden. Across all 43 patients who initially received RFTC, the overall seizure-free rate was 37.2 percent, consistent with the 23 to 50 percent reported in meta-analyses. Still, the proposed decision framework — favoring RFTC as potentially definitive therapy when SEEG reveals LVFA, and urging caution and early evaluation for second-stage resection when slow-wave or electrodecremental patterns dominate — offers a concrete, testable path forward. If larger prospective studies confirm that targeting LVFA reliably produces both seizure freedom and scalp EEG normalization, epilepsy surgery may gain something it has long lacked: an objective brain-wave readout of whether the seizure generator has truly been silenced.

Subject of Research: SEEG-guided radiofrequency thermocoagulation outcomes stratified by seizure-onset pattern, with postoperative scalp EEG as an objective complement to Engel classification

Article Title: Complementing Engel Classification: Postoperative Scalp EEG as an Objective Indicator in SEEG‐Guided Radiofrequency Thermocoagulation—A Seizure‐Onset Pattern‐Based Stratified Analysis—

Article References: Yang, Y.-Q., Zhang, R., Ma, H., Yang, L., Qu, X., Chen, Q., & Zhang, Y. (2026). Complementing Engel Classification: Postoperative Scalp EEG as an Objective Indicator in SEEG ‐Guided Radiofrequency Thermocoagulation—A Seizure‐Onset Pattern‐Based Stratified Analysis—. Annals of Clinical and Translational Neurology, Article acn3.70553. https://doi.org/10.1002/acn3.70553

Image Credits: AI Generated

DOI: 10.1002/acn3.70553

Keywords: epilepsy, SEEG, radiofrequency thermocoagulation, low-voltage fast activity, scalp EEG, Engel classification, seizure-onset pattern, drug-resistant epilepsy, focal cortical dysplasia, epilepsy surgery, Complementing, Engel