Neuromodulation of Bilateral Hippocampal Foci, an Alternative for Mesial Temporal Lobe Seizures in Patients with Non-Lesional MRI: Long-Term Follow-up

Background: Patients with bilateral independent hippocampal refractory seizures, who show no evidence of lesion in the MRI, constitute a challenge for their treatment. The risk of severe retrograde amnesia and/or residual seizures is high when bilateral temporal lobectomy is performed. Several groups have reported electrical neuromodulation of the hippocampus as a reversible surgical alternative for mesial temporal lobe epilepsy seizures that are refractory to medical treatment. Methods: In the Epilepsy Clinic of the General Hospital we have had three patients with bilateral independent foci and non-lesional MRI. The present publication shows their long-term seizure status and their neuropsychological outcome. Stimulation parameters were 3.0 V amplitude, high frequency (130 Hz), 450 μs pulse width, one minute ON and 4 min OFF cyclic stimulation. Follow-up extended over 9 years. Results: Patients showed dramatic seizure reduction. In two patients in whom stimulation was stopped (due to battery depletion or skin erosion), seizure reduction persisted for months after stimulation stopped, but eventually seizures reappeared slowly. One patient has had uninterrupted stimulation and has been seizure free for nine years. The neuropsychological tests showed no functional decrease at the selected modulation parameters. Conclusion: Bilateral hippocampal stimulation is effective in seizure control in patients in whom ablative surgery is not recommended.