Localizing value of alpha-methyl-L-tryptophan PET in intractable epilepsy of neocortical origin

Background: [C-11] alpha -methyl-L-tryptophan (alpha -MTrp) has been develo ped as a tracer for the study of the synthesis of serotonin in the brain wi th PET. However, it has been shown that in pathologic conditions the tracer may reflect the activation of kynurenine metabolism. Increased levels of s erotonin and quinolinic acid have been described in resected epileptogenic cortex, raising the possibility that alpha -MTrp can localize seizure foci in patients with intractable partial epilepsy. The authors assessed the upt ake of alpha -MTrp in 18 patients (11 men, mean +/- SD age 27.1 +/- 10.1 ye ars, range 13 to 54) with intractable partial epilepsy to correlate the PET findings with the epileptogenic area defined by electroclinical and neuroi maging data. Method: Seven patients with cortical dysplasia (CD) and 11 wit h partial epilepsy in which conventional MRI and fluorine-18-deoxyglucose ( (18)FDG)-PET studies failed to detect any abnormality were studied. All und erwent scalp EEG monitoring during the PET scan to exclude ictal events and estimate the interictal epileptic activity. Results: In seven patients (39 %; CD four and cryptogenic partial epilepsy three), PET showed focal increa sed uptake of alpha -MTrp corresponding to the epileptogenic area. alpha -M Trp uptake in the epileptic focus correlated with the frequency of interict al spikes (r = 0.7, p < 0.05). Conclusions: alpha -MTrp-PET may be of value in the localization of the epileptogenic area not only in patients with vi sible dysplastic lesions, but also in those with cryptogenic partial epilep sy.