Etomidate: A Complementary Diagnostic Tool for Pre-Surgical Evaluation in Temporal Lobe Epilepsy

Temporal lobe epilepsy is the most frequent drug-resistant epilepsy. It has a high success rate in surgical treatment, provided that the epileptic zone (EZ) was accurately localized through a pre-surgical evaluation and removed. Pharmacological activation inducing interictal activity is tested as a complementary method in the pre-surgical diagnosis, although with nonspecific results and limited safety, due to poorly tolerated side effects. Etomidate is a well-tolerated, fast onset and rapid decline drug with a few side effects. Studies conducted to evaluate the safety and usefulness of etomidate to identify the EZ showed that etomidate activates irritative zone only in the areas where spikes previously appeared in basal conditions, besides having a high coefficient of lateralization for ictal onset zone (IOZ). Regarding the analysis of the topography of the voltage sources, it is shown that interictal, ictal and etomidate-induced activities greatly overlap, indicating that the biophysical mechanisms are similar, and the cortical areas where all types of activities appear are likely the same or closely related. In addition, from the point of view of complex networks, etomidate produces very similar changes in the limbic network to those occurring during temporal seizures i.e. an impaired connectivity in the ipsilateral side to the IOZ. All findings suggest that etomidate, in a specific manner, activates the neural and biophysical mechanisms of spontaneous epilepsy. This technique can be used as a diagnostic tool during the pre-surgical evaluation of patients with TLE to define the region resected during epilepsy surgery with confidence.