α-[ 11 C] methyl- L -tryptophan and glucose metabolism in patients with temporal lobe epilepsy

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Abstract
Objective: To determine whether metabolism in the brain serotonergic system, including the kynurenine pathway, is involved in temporal lobe epilepsy (TLE). Methods: The authors studied 14 patients with intractable TLE by PET using α-[11C] methyl-l-tryptophan (α-MTrp) and 2-[18F]-fluoro-deoxy-glucose (FDG) and compared results with 21 healthy control subjects who had α-MTrp PET studies. Seven patients had unilateral hippocampal atrophy (HA), and seven had normal hippocampal volumes (NV). The regional uptake constant (K*) for α-MTrp and regional FDG uptake were calculated in regions with high serotonergic innervation, including the hippocampus, amygdala, lateral temporal lobe, frontal lobe, thalamus, lenticular nucleus, and cingulate cortex. Results: A significant increase of α-MTrp uptake was observed in the hippocampus ipsilateral to the seizure focus in seven TLE patients with NV compared to seven patients with HA as well as to healthy controls. In patients with TLE, glucose utilization in the lateral temporal lobe ipsilateral to the seizure focus was correlated negatively with K* for α-MTrp in the ipsilateral hippocampus and positively with K* in the ipsilateral lenticular nucleus and cingulate cortex. Glucose utilization in the frontal lobe ipsilateral to the seizure shows a reduction in the glucose utilization which relates to the increase in the α-MTrp uptake in the ipsilateral lateral temporal lobe. Conclusion: This study demonstrates dysfunction of the serotonergic system, which could include metabolism through the kynurenine pathway in TLE patients with normal hippocampal volumes. α-MTrp PET studies might be useful for lateralizing the epileptic focus in TLE patients with normal hippocampal volumes.