Interictal estimation of intracranial seizure onset in temporal lobe epilepsy

To evaluate the lateralizing and localizing values of interictal focal slow activity (IFSA), single pulse electrical stimulation (SPES) and (18)FDG PET, in order to estimate their potential to complement ictal intracranial recordings and reduce prolonged monitoring in patients with temporal lobe epilepsy.

The study includes 30 consecutive patients with bilateral temporal subdural electrodes and focal seizure onset. IFSA, SPES and (18)FDG PET when available, were visually assessed and their combined lateralization was based on the majority of the individual lateralizing tests.

In the 18 patients who had all three tests, lateralization was congruent with seizure onset areas in 15 (83%). When lateralized (15 patients), (18)FDG PET was always congruent with intracranial seizure onset. In all 12 patients without (18)FDG PET, lateralization combining IFSA and SPES was congruent with seizure onset, including two with bilateral independent seizure onset on subdural monitoring. 22 out of the 23 patients who had surgery enjoyed favorable outcome (Engel I or II).

Intracranial IFSA and SPES can reliably predict the side and site (mesial versus lateral temporal) of seizure onset when they lateralize to the same side.

(18)FDG PET can be useful in planning electrode implantation. During intracranial recordings, IFSA and SPES have the potential to reduce telemetry time, risks and costs.