Double-blind stereo-EEG and FDG PET study in severe partial epilepsies: are the electric and metabolic findings related?

The aim of this study was to evaluate, in 16 patients with drug-resistant partial epilepsy who were waiting to undergo surgical treatment, the relation between positron emission tomography (PET) findings with fluorine-18 fluorodeoxyglucose ([18F]FDG) in the interictal state and the different stereo-electroencephalography (SEEG) patterns that characterize: (a) the epileptogenic zone (low-voltage fast-activity discharge before or concurrent with ictal clinical symptoms), (b) the irritative zone (spikes, spikes and waves, isolated or grouped in short bursts) and (c) the lesional zone (continuous, sometimes polyrhythmic slow waves or continuous delta waves or very important voltage depression). SEEG was performed following an individually defined electrode implantation strategy. Whereas at least one area of hypometabolism was detected by visual interpretation of PET/[18F]FDG images in all the subjects in the study, there was poor agreement between PET/[18F]FDG quantitative measures of regional metabolism and SEEG findings. Normal metabolic rates were found in up to 62% of the areas with abnormal SEEG activity, independent of the type of electrical activity, i.e. epileptogenic, irritative, or lesional, while abnormal metabolic rates were found in up to 23% of the areas with normal SEEG activity. In conclusion, whereas the visual interpretation of interictal studies of glucose utilization in our series of drug-resistant epileptic patients consistently allowed the localization of an area of temporal hypometabolism, the quantitative and regional metabolic analysis demonstrated that such a finding is not specifically related to any of the three very different SEEG patterns (epileptogenic, irritative, lesional) or combinations thereof. These results complement those of previous interictal and ictal single-photon emission tomographic studies and of receptor studies in epileptics, suggesting functional and biochemical heterogeneity within the interictal hypoperfused/hypometabolic area in epileptic patients, and contribute to the debate on the use and interpretation of interictal PET/[18F]FDG studies in patients with medically refractory partial seizures.