Epileptic Disorders


“Generalized-to-focal” epilepsy: stereotactic EEG and high-frequency oscillation patterns Volume 24, issue 6, December 2022


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1 Montreal Neurological Institute and Hospital, McGill University, Montréal, Quebec, Canada
2 Research Institute of the McGill University Medical Centre, Montreal, Quebec, Canada
3 Department of Neurology and Neurosurgery, Montreal Children’s Hospital, McGill University Health Centre, Montreal, Quebec, Canada
4 Division of Neurology, Department of Pediatrics, Université de Sherbrooke, Sherbrooke, Quebec, Canada
5 Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
6 Division of Neurology, Department of Pediatrics, Montreal Children’s Hospital, McGill University Health Centre, Montreal, Quebec, Canada
Kenneth Myers
Montreal Children’s Hospital, MUHC Glen Site, 1001 Décarie Blvd, Montreal, Quebec, H4A 3J1 Canada


We aimed to clarify the pathophysiology of epilepsy involving seizures with apparently generalized onset, progressing to focal ictal rhythm through stereotactic EEG (SEEG) implantation, recording, stimulation and highfrequency oscillation (HFO) analysis.


We identified two patients with seizures with bilateral electrographic onset evolving to focal ictal rhythm, who underwent SEEG implantation. Patients had pre-surgical epilepsy work-up, including prolonged video scalp EEG, brain MRI, PET, ictal/interictal SPECT, MEG, and EEG-fMRI prior to SEEG implantation.


Both patients had childhood-onset seizures involving behavioural arrest and left versive head and eye deviation, evolving to bilateral tonic-clonic convulsions. Seizures were electrographically preceded by diffuse, bilateral 3-Hz activity resembling absence seizures. Both had suspected focal lesions based on neuroimaging, including 3T MRI and voxel-based post-processing in one patient. Electrode stimulation did not elicit any habitual electroclinical seizures. HFO analysis showed bilateral focal regions with high fast-ripple rates.


“Generalized-to-focal” seizures may occur due to a diffuse, bilateral epileptic network, however, both patients showed ictal evolution from a generalized pattern to a single dominant focus which may explain why the focal aspect of their seizures had a consistent clinical semiology. Patients such as these may have a unique form of generalized epilepsy, but focal/multifocal cerebral abnormalities are also a possibility.