Interictal hippocampal benzodiazepine receptors in temporal lobe epilepsy:comparison with coregistered hippocampal metabolism and volumetry

The significance of benzodiazepine receptor (BZR) concentration in comparis on with hippocampal metabolism and volumetry was assessed in 14 patients di agnosed with temporal lobe epilepsy (TLE) without hippocampal signal change on T2-weighted magnetic resonance imaging (MRI) scans. Focus lateralizatio n was achieved by clinical, electroencephalographic and neuropsychological examinations. Three-dimensional positron emission tomography (PET) and MRI scans were coregistered for determination of hippocampal C-11-flumazenil (F MZ) binding, normalized to average cortical values for glucose metabolism ( rCMR(glc)) and volume. The hippocampi were individually outlined on T1-weig hted MRI. Volumes of interest (VOI) were used for calculation of asymmetrie s between clinically affected and unaffected sides. Eleven out of 14 TLE pa tients presented a significant reduction in hippocampal volume. In nine of these 11 patients hippocampal FMZ binding and in seven cases hippocampal CM Rglc was also reduced. In two patients without hippocampal volume asymmetry FMZ binding was markedly reduced in the mesial temporal lobe appropriately to the clinically diagnosed side. In our study volumetry is therefore the most sensitive tool for the detection of hippocampal abnormality in TLE. Ho wever, in cases without hippocampal atrophy the reduction of FMZ may indica te functional impairment of BZR before neuronal loss becomes evident. Our r esults emphasize the complementary nature of these tests in TLE patients.