Abstracts

Rationale: Patients with TLE represent the most suitable candidates for epilepsy surgery. On the other hand, patients with TLE and normal MRI findings or with bilateral MTS represent a challenge for surgical treatment. Patients with normal MRI and dominant TLE are at high risk for cognitive decline after cortico-amygdalo-hippocampectomy. We present our experience Hip-DBS, a non-resective technique, in this patient population. Methods: Six patients with bilateral interictal temporal lobe spiking and non-lateralized ictal video-EEG recordings were studied. Three had normal MRI and 3 had bilateral MTS. All patients were submitted to pre- and post-operative standard neuropsychological testing. All patients were implanted bilaterally in the hippocampus using a Kinetra device. The electrodes were inserted along the axis of the hippocampus through a posterior approach; the most anterior contact was positioned in the head of the hippocampus. Pre-, intra- and post-stimulation scalp EEG recordings were obtained in all patients intra-operatively. Continuous stimulation was carried out using 300usec, 130Hz, 4-6V pulses. Results: In 4 patients, an increase in temporal lobe spiking was noticed unilaterally at the time of electrode insertion; no bilateral increase was noted. In all patients an ipsolateral temporal lobe recruiting response was noted during acute stimulation. In 5 patients, high frequency intraoperative hippocampal stimulation reduced or abolished interictal spiking. Four patients (2 with normal MRI; 2 with bilateral MTS) received unilateral and 2 bilateral stimulation (1 with normal MRI and 1 with bilateral MTS) so far. Two patients with unilateral stimulation are seizure free and the other two had at least 90% reduction in seizure frequency. One patient with bilateral hippocampal stimulation had 70% reduction and the other one got 80% reduction in seizure frequency. There was no memory decline in patients submitted to bilateral hippocampal stimulation. Mean follow-up time was 9 months. Conclusions: Hippocampal stimulation seems to be a very effective and safe non-resective technique in this patient population. Memory decline did not occur with bilateral hippocampal stimulation suggesting that Hip-DBS did not lead to complete inactivation of the mesial temporal lobe structures.