Repetitive clustered low‐voltage fast activity on intracranial electroencephalogram in mild malformation of cortical development with oligodendroglial hyperplasia and epilepsy: A candidate electroencephalographic biomarker study

OBJECTIVE: Mild malformation of cortical development with oligodendroglial hyperplasia and epilepsy (MOGHE) is a recently recognized cause of drug-resistant focal epilepsy. It is often magnetic resonance imaging-negative or radiologically resembles focal cortical dysplasias, which makes recognition difficult and limits presurgical counseling. We aimed to identify an intracranial electroencephalographic (iEEG) biomarker that distinguishes MOGHE from other developmental brain lesions encountered in epilepsy surgery. METHODS: We analyzed long-term stereo-EEG and subdural recordings in a retrospective multicenter test cohort (18 MOGHE, 20 non-MOGHE) to identify an iEEG pattern distinguishing MOGHE from other developmental brain lesions. We then evaluated its diagnostic performance by blinded visual assessment in an independent single-center validation cohort (11 MOGHE, 11 non-MOGHE). Firth-penalized multivariable logistic regression tested whether MOGHE histology independently predicted the presence of this pattern after adjustment for spasms, frontal localization, age at seizure onset, and age at implantation. Finally, within MOGHE, we assessed whether resection of the territory exhibiting this pattern was associated with postsurgical seizure freedom. RESULTS: We identified highly stereotyped clusters of very brief low-voltage fast activity (LVFA), recurring in statuslike episodes lasting several minutes and sometimes lacking clear clinical symptoms. LVFA clusters occurred in 16 of 18 MOGHE and in no non-MOGHE patients in the test cohort. In the validation cohort, visual identification of LVFA clusters correctly classified 10 of 11 MOGHE and 10 of 11 non-MOGHE cases (overall agreement = 90.9%, 95% Wilson confidence interval = 72.2%-97.5%). MOGHE histology was the dominant independent predictor of LVFA clusters. Within MOGHE, resection of LVFA cluster territory was associated with postsurgical seizure freedom (Mann-Whitney U-test, p = .0021). SIGNIFICANCE: Because LVFA clusters can be recognized visually on routine iEEG without specialized software, they may provide a clinically applicable candidate biomarker for presurgical identification of MOGHE and support surgical planning and outcome prediction. Prospective studies should validate their diagnostic and prognostic utility.