Temporal lobe epilepsy: Evidence for interictal uncoupling of blood flow and glucose metabolism in temporomesial structures

Measurements of regional cerebral glucose metabolism (rCMRGlc) and blood flow (rCBF) are widely considered exchangeable for the detection of dysfunctional zones in temporal lobe epilepsy (TLE). However, the underlying assumption of preserved coupling of rCBF and rCMRGlc is questionable and requires verification. Thirteen patients with unilateral mesiolimbic TLE underwent interictal positron emission tomography (PET) measurements of rCBF using [O-15]butanol and of rCMRGlc using (18)FDG. rCMRGlc, rCBF and glucose extraction fraction (rGEF) were obtained from temporomesial and temporolateral structures. When compared to the respective homotopic contralateral reference region, in temporomesial structures ipsilateral to the EEG-defined focus ('dysfunctional zone'), average rCMRGlc and rGEF were decreased while rCBF was unaffected. Analysis of (18)FDG kinetics revealed that (18)FDG transport was unaltered but the hexokinase reaction was specifically decreased. In the temporolateral structures, no such mismatch between metabolism and blood flow was observed. In mesiolimbic TLE, interictal rCMRGlc-PET is superior to rCBF-PET with respect to the sensitivity to detect regional functional abnormalities. This seems to be due to focal uncoupling of glucose metabolism and blood-brain barrier transport or blood flow. We hypothesize that the observed uncoupling of transport and metabolism may be characteristic of epileptogenic zones in TLE of typical etiology.