Abstracts

RATIONALE:_ In 25% of patients with epilepsy, seizures continue despite medication. In 20% of these potential surgical candidates, standard MRI does not identify the cause. GABA is the principal inhibitory neurotransmitter in the brain, and [11C]-Flumazenil (FMZ) PET images the central benzodiazepine-GABAA receptor complex. METHODS:_ We studied 18 patients with temporal lobe epilepsy (TLE) and 16 patients with unilateral frontal lobe epilepsy (FLE), all with normal high resolution MRI. Parametric images of FMZ-volume-of-distribution (FMZ-Vd) were calculated. Statistical Parametric Mapping (SPM99) was used for the comparison of individual patients and controls. RESULTS: Of the 18 TLE patients, 11 showed abnormal FMZ-Vd; three of these had single and eight multiple abnormalities. Two patients had increases of FMZ-Vd, seven had decreaes and two both increases and decreases. Findings were potentially surgically useful in 6/18: one localised neocortical decrease, one unilateral hippocampal decrease and four asymmetrical hippocampal decreases. Of the 16 FLE patients, 14 had abnormal FMZ-Vd; four had single and 10 multiple abnormalities. Ten had increases of FMZ binding, one had decreases, and three had both increases and decreases. In 10, abnormalities were found in the lobe of presumed seizure onset. CONCLUSIONS: Optimal FMZ-PET showed abnormalities in 11/18 TLE patients with normal high resolution MRI. In 6 of these, findings were concordant with EEG and clinical data, enabling further presurgical evaluation. Abnormalities in the FLE group consisted mainly of increases in FMZ-binding. These have not previously been seen in acquired lesions but only in malformations of cortical development (MCD), suggesting that occult MCD may be the underlying cause of epilepsy in some of our cases. [Supported by Action Research, the Medical Research Council and the Deutsche Forschungsgemeinschaft]