Evidence for coupling between glucose metabolism and glutamate cycling using FDG PET and H-1 magnetic resonance spectroscopy in patients with epilepsy

The purpose of this study was to examine the relation between glucose metab olism and glutamate concentration in the human bl ain, in both the normal a nd diseased state. Regional values of glucose metabolism measured with 2-de oxy-2[F-18]fluoro-D-glucose positron emission tomography (FDG PET) studies and single-voxel proton magnetic resonance spectroscopy (H-1 MRS) measureme nts of the glutamate/ glutamine/gamma-aminobutyric acid (Glx) tissue concen tration were determined in multiple brain regions in 11 patients (5 girls a nd 6 boys, mean age 7.5 years) with medically intractable partial epilepsy. FDG PET and H-1 MRS studies were performed in the interictal state in seve n patients and in the ictal/periictal state in four patients. Regions of in terest were identified in epileptic cortex (determined by intracranial and/ or scalp electroencephalography) and in contralateral normal brain regions. Lower glucose metabolism and lower Glx concentrations were found in the ep ileptic focus than in the contralateral normal cortex in all seven patients examined in the interictal state, whereas higher glucose metabolism and hi gher Glx concentrations were observed in the epileptic focus in the four pa tients who had ictal/periictal studies. Significant correlations were found between the values of cerebral glucose utilization and Glx concentration i n epileptic brain region, in nonepileptic brain regions, and in epileptic a nd nonepileptic regions combined. These results demonstrate a significant r elation between glucose metabolism and glutamate/glutamine concentration in normal and epileptic cerebral cortex. This relation is maintained in both the interictal and ictal slates.