"Generalized-to-focal" epilepsy: stereotactic EEG and high-frequency oscillation patterns

Epileptic Disord. 2022 Dec 1;24(6):1-8. doi: 10.1684/epd.2022.1489.

Abstract

Objective: 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 high-frequency oscillation (HFO) analysis.

Methods: 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.

Results: 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.

Significance: “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.

Keywords: high-frequency oscillations; focal epilepsy; stereotactic EEG.

MeSH terms

  • Child
  • Electroencephalography / methods
  • Epilepsies, Partial* / diagnosis
  • Epilepsies, Partial* / surgery
  • Epilepsy, Absence*
  • Epilepsy, Generalized*
  • Humans
  • Seizures / diagnosis
  • Seizures / surgery