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

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