Abstracts

Tuberous sclerosis complex (TSC) is often associated with medically intractable seizures. Surgical resection of epileptogenic tubers may result in seizure-freedom. However, scalp EEG is commonly poorly localizing and, without any other localizing information, such patients are often rejected from epilepsy surgery. Previous studies have demonstrated that alpha-[¹¹C]methyl-L-tryptophan (AMT) PET can show selectively increased uptake in epileptogenic tubers, and may be a useful imaging method to localize epileptogenic brain regions in children with TSC. In the present study, we evaluated the additive localizing value of AMT PET in TSC patients whose scalp EEGs did not provide sufficient information to proceed with surgery. From a sample of 51 children with TSC and intractable epilepsy who underwent AMT PET scanning in our center, 15 children with non-lateralizing (generalized seizure onset) and/or localizing (seizure onset lateralized but not localized) EEG were selected for this study. AMT uptake values were measured in all tubers visualized on MRI, and those patients with at least one tuber showing AMT uptake higher than the normal cortical uptake were selected and compared to scalp EEG, ictal intracranial EEG findings, as well as surgical outcome data. Eight of 15 children (53%) with poorly lateralizing/localizing scalp ictal EEG had at least one tuber with increased AMT uptake. In these 8 children, scalp ictal EEG was non-lateralizing in two, while it was lateralizing but showed extensive hemispheric seizure onset in the other 6 cases. In this subgroup, AMT PET showed increased uptake in a single tuber in 6 children, in 2 adjacent tubers in 1 child, and in 2 tubers in two opposite hemispheres in another patient. Intracranial EEG with subdural electrodes was performed in 5 cases, and demonstrated that tubers with increased AMT uptake were epileptogenic. Four of 6 children who underwent resective surgery (including the tuber with increased AMT uptake) became seizure-free; the remaining two showed [gt]75% improvement in seizure frequency. In one child who has not yet been operated, scalp ictal EEG showed bi-frontal onset, while increased AMT uptake was found at a right frontal tuber close to the mid-line. Seizure semiology was consistent with a right hemispheric focus. In TSC patients with intractable epilepsy but poorly lateralizing and/or localizing scalp EEG findings, AMT PET can identify epileptogenic tubers and can guide subdural grid placement to assist in the identification of epileptogenic brain regions to be resected. Thus, following AMT PET, some patients with TSC and intractable epilepsy, not otherwise considered for surgery, may indeed be suitable candidates. (Supported by NIH grant NS 38324 )