An electro-encephalogram beta gap after induction with diazepam: a localization method in epileptogenic lesions

We clinically tested a quantitative EEG method to localize abnormal variations in benzodiazepine-induced fast rhythms to localize focal epileptogenic lesions, assuming altered quality/quantity of GABA receptors in the lesions.

During a 64-channel-EEG (sampled at 1 kHz) recording benzodiazepines were administered to five patients with localization related epilepsy associated with an MRI visible focal lesion. We determined the post-injection dominant spectral modulation using Gabor wavelets and analysed the symmetry of spatial distribution. This was compared to the localization of the lesion on the MRI scan.

The principal component was found in the beta/gamma band. In all patients one region of decreased change was associated with the lesional hemisphere, and overlapped with the site of the lesion in four. Three patients underwent surgery: interictal corticographic findings concurred with the area of decreased benzodiazepine response.

This simple method localized abnormal function associated with epileptogenic lesions. Further methodological validation is now justified. Final clinical validation must be done in MRI-negative cases as well.

This research may lead to techniques for non-invasive easy localization of epileptogenic tissue that is not visible on a structural MRI scan.