Abstracts

Rationale: Resection of the epileptogenic focus is an effective treatment option for patients with drug-resistant focal epilepsy. Surgery typically demands congruence of ictal/interictal EEG recording, structural imaging (high-resolution magnetic resonance imaging, MRI), and functional imaging (positron emission tomography, PET). Especially in extratemporal lobe epilepsy (XTLE), though, the localizing findings of EEG and PET may not be congruent with the localization of the MRI detectable lesion. We investigated whether the occurrence of interictal epileptiform discharges (IEDs) outside the lesional lobe in XTLE is associated with hypometa­bolisms in these respective lobes. Methods: In the database of our epilepsy monitoring unit 66 patients with XTLE, interictal and ictal EEG recording, as well as [¹⁸F] fluorodeoxyglucose PET (FDG-PET) examination were identified. EEGs were analyzed by two independent epileptologists and both agreed on extratemporal seizure onset as well as the interictal spike localization. FDG-PET data were analyzed with statistical parametric mapping and evaluated by two experienced nuclear medicine radiologists. Results: IEDs were recorded in 87.8% of the 66 patients with XTLE. In 33 patients (47.8%) IEDs were localized over the temporal lobe. In these patients, a temporal glucose hypometabolism on PET was found in 33.3% (11/33 patients). Temporal IEDs and temporal glucose hypometabolism were ipsilateral in 30.3% (10/33 patients). In one patient (3.0%) the temporal glucose hypometabolism was found contralateral to temporal IED. In XTLE without temporal IED, only 5 of 36 patients (13.9%, p<0.05) showed a temporal hypometabolism. In all 14 patients with temporal IEDs and extratemporal hypometabolism, the hypometabolism was localized ipsilateral to the temporal IEDs. Conclusions: Temporal IEDs are common in XTLE. In those patients with temporal IEDs, the rate of temporal hypometabolisms is also higher than in patients with no temporal IEDs. We suggest that this demonstrates that the temporal IEDs are not arbitrary, but rather the reflection of a widespread epileptogenic pathology that extends into the temporal lobe and is also reflected on PET studies of metabolism. Furthermore, these findings may help to interpret extralesional PET findings better when IEDs over these hypometabolic lobes are present as well.