Subacute and chronic electrical stimulation of the hippocampus on intractable temporal lobe seizures: Preliminary report

Background. Recent animal experiments show that the application of an elect rical stimulus to the amygdala or hippocampus following the kindling stimul us produced a significant and long-lasting suppressive effect on this exper imental model of epilepsy, This is a preliminary report on the development of a surgical neuromodulatory procedure by chronic electrical stimulation o f the hippocampus (CHCS) for control of intractable temporal lobe seizures in patients in whom anterior temporal lobectomy is not advisable, i.e., pat ients with bilateral temporal foci or a unilateral focus spreading to surro unding cerebral regions of the dominant hemisphere. Methods. This work was divided in two main consecutive stages. In the first stage, we demonstrated that subacute hippocampal stimulation (SAHCS) block s intractable temporal lobe epileptogenesis with no additional damage to th e stimulated tissue, and in a second stage, we attempt to demonstrate that CHCS may produce a sustained, long-lasting antiepileptic condition without additional undesirable effects on language and memory, In addition, taking advantage of this unique and ethically permissible situation, we attempt to determine whether or not the antiepileptic effects of SAHCS and CHCS are d ue to inhibition of the stimulation of hippocampal tissue by means of a num ber of electrophysiological, single photon computed tomography (SPECT) perf usion, and autoradiographic techniques, Results, SAHCS during 3-4 weeks prior to anterior temporal lobectomy applie d to a critical area located either at the anterior Pea hippocampus close t o the amygdala or at the parahippocampal gyrus close to the entorhinal cort ex abolished clinical seizures and significantly decreased the number of in terictal spikes at focus after 5-6 days. Microscopy analysis of the stimula ted tissue showed no evident histopathological differences between stimulat ed vs. non-stimulated hippocampal tissues. Additionally, CHCS persistently blocked temporal lobe epileptogenesis for 3-4 months with no apparent addit ional undesirable effects on short memory. Also, inhibition of the stimulat ed hippocampus seems to be one of the possible mechanisms underlying the be neficial antiepileptic effects of SAHCS and CHCS. This was revealed by incr eased threshold and decreased duration of the afterdischarges induced by hi ppocampal stimulation, flattening of the hippocampal-evoked response recove ry cycles, SPECT hypoperfusion of the hippocampal region, and increased hip pocampal benzodiazepine receptor binding. Conclusions. Future studies increasing the number and time of follow-up of patients under hippocampal stimulation are necessary before considering CHC S a reliable procedure for controlling intractable temporal lobe seizures. (C) 2000 IMSS. Published by Elsevier Science Inc.