Dynamic [18F]fluorodeoxyglucose positron emission tomography and hypometabolic zones in seizures:: Reduced capillary influx

We performed dynamic [F-18]fluorodeoxyglucose ([F-18]FDG) positron emission tomographic (PET) analyses in 8 patients. Rate constants of influx (K-1*), efflux (k(2)*), phosphorylation (k(3)*), and dephosphorylation (k(4)*) were derived for the regions of interest (ROIs), which included (1) the hypometabolic epileptogenic regions and (2) the homologous regions in the contralateral hemispheres. In addition, the four constants were determined from at least one clearly defined (control) ROI from the same plane and its homologous contralateral ROI. Influx (K-1*) in the epileptogenic region was reduced in comparison with the contralateral ROI. Reductions in influx (K-1*), which averaged 18 +/- 13% (mean +/- SD), [F-18]FDG phosphorylation (k(3)*) (25 +/- 20%), and brain glucose utilization rates (26 +/- 10%) were observed in the epileptogenic region. Reductions in efflux were not statistically significant (k(2)* = 13 +/- 28%) but were comparable in magnitude to the average reduction in K-1*. No ipsilateral versus contralateral differences were seen for any rate constants measured outside the epileptogenic region, Influx correlated highly with phosphorylation in the epileptogenic region. Our data suggest that the hypometabolic epileptogenic focus seen in [F-18]FDG-PET studies is also a region of reduced blood-brain barrier glucose transporter activity and that reductions in phosphorylation are proportional to reductions in [(18)]FDG influx.