Interictal and seizure-onset scalp electroencephalographic patterns in malformations of cortical development

Malformations of cortical development (MCDs) are a frequent cause of drug-resistant epilepsy and a common indication for resective epilepsy surgery. As magnetic resonance imaging (MRI) lacks sensitivity for subtle MCDs, supplemental diagnostic tools are needed. This study aimed to characterize scalp electroencephalographic (EEG) patterns in MCDs and investigate their association with surgical outcomes.

This was a retrospective case-control study including patients who underwent inpatient video-EEG monitoring at two Australian hospitals. Cases were individuals with MCDs confirmed on MRI or histopathology; controls included patients with other focal epilepsies. Two epileptologists independently reviewed interictal and seizure-onset EEG patterns using a standardized classification framework. Patterns were compared between cases and controls and assessed with respect to postoperative seizure outcomes, adjusting for antiseizure medication reduction.

We included 38 cases with MCDs (52.6% females, median age = 34 years) and 114 controls (45.6% females, median age = 41 years). Among interictal patterns, repetitive epileptiform discharges type 1 and type 2 were more prevalent in patients with MCDs than controls (p = .002 and .005, respectively). Focal fast epileptiform discharges were also more frequent in MCD patients, after excluding nonlesional focal epilepsy controls (p = .038). Among seizure-onset patterns, paroxysmal fast activity was more prevalent in MCDs (p < .001). Among 38 patients who underwent surgery, 70.0% of MCDs and 75.0% of controls had favorable outcomes. No EEG pattern predicted postoperative seizure outcomes.

Distinct scalp EEG patterns may support differentiation of MCDs from other focal epilepsies. Larger prospective studies are needed to clarify their role in detecting MRI-negative MCD or guiding targeted imaging.