Scalp rhythmic epileptiform discharges in focal cortical dysplasia: A clinicopathological study

Rhythmic epileptiform discharges (REDs) are a prevalent interictal pattern on scalp electroencephalogram (EEG) in patients with focal cortical dysplasia (FCD). The study aims to assess the relationship between REDs and epileptogenicity by investigating their clinical and pathological correlations.

We retrospectively included patients who underwent resective surgeries with confirmed FCD. Presurgical scalp EEGs were evaluated regarding the presence or absence of REDs. Associations between REDs and clinical variables were analyzed. Furthermore, we investigated the pathological substrates of REDs in patients with FCD type 2 by comparing densities of abnormal chloride transporters and pathological cells in the patients with and without REDs.

Our results demonstrated that REDs were more common in patients with an earlier onset (P < 0.0001), FCD type 2 (P < 0.0001) and were more likely recorded in the extratemporal region (P < 0.0001). REDs predicted a favorable surgical outcome in FCD patients (Odds ratio = 4.35, P = 0.02). In patients with FCD type 2, presence of REDs was associated with increased cytoplasmic expressions of potassium-chloride-co-transporter 2 (P = 0.048).

REDs are associated with favorable surgical outcomes in patients with FCD. Abnormal expressions of the chloride transporters may underlie the RED generation.

Our results expand the clinical significance of REDs and provide further insights into its pathogenesis.