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

Area of Science:

• Neuroscience
• Epileptology
• Clinical Neurophysiology

Background:

• Epilepsy with apparently generalized onset evolving to focal ictal rhythm presents diagnostic challenges.
• Understanding the underlying pathophysiology is crucial for effective treatment strategies.
• Stereotactic EEG (SEEG) offers high-resolution intracranial recordings for complex epilepsy cases.

Purpose of the Study:

• To elucidate the pathophysiology of epilepsy characterized by generalized-onset seizures that progress to focal ictal rhythms.
• To analyze high-frequency oscillations (HFOs) in patients with this seizure type using SEEG.

Main Methods:

• Two patients with generalized-to-focal seizures underwent SEEG implantation.
• Comprehensive pre-surgical epilepsy work-up included prolonged video scalp EEG, MRI, PET, SPECT, MEG, and EEG-fMRI.
• Analysis of high-frequency oscillations (HFOs) and electrode stimulation were performed.

Main Results:

• Both patients exhibited seizures starting with diffuse, bilateral 3-Hz activity, evolving to focal ictal rhythm and clinical semiology.
• Neuroimaging suggested suspected focal lesions in both cases.
• HFO analysis revealed bilateral focal regions with high fast-ripple rates.

Conclusions:

• Generalized-to-focal seizures might originate from a diffuse epileptic network, with a dominant focus potentially driving consistent focal semiology.
• These cases may represent a unique form of generalized epilepsy or indicate underlying focal/multifocal cerebral abnormalities.
• SEEG and HFO analysis are valuable tools for investigating complex epilepsy pathophysiology.