Temporal Lobe Epilepsy and Hippocampal Stimulation

Abstract

Hippocampal stimulation in medically intractable mesial temporal lobe epilepsy may be effective in reducing seizure frequency in patients for a period of up to 18 months Clinical Scenario: A 55-year-old man has had temporal lobe epilepsy for 20 years and has failed treatment with multiple antiepileptic medications. He has on average 20 complex partial seizures per month. He does not have mesial temporal sclerosis on magnetic resonance imaging (MRI). He is not considering surgery. Video electroencephalogram (EEG) and electrode depth recording has confirmed a left mesial temporal lobe (MTL) focus.Clinical Question: What is the safety, efficacy, and long term seizure control in patients with MTL epilepsy treated with hippocampal stimulation? Search Strategy: Medline was used to search for articles by combining "epilepsy, Temporal lobe/th [therapy]" with hippocampal stimulation which mapped to "electric stimulation/ or hippocampus". This yielded 51 articles; when English language and humans were used as limits yielded 35 articles. Three articles were relevant. The first article by Boon et al (2007) was an open pilot study and two of the 12 consecutive patients with refractory MTL seizures underwent resective surgery. The other study by Tellez-Zenteno et al (2006) used an individual patient randomized-controlled trial design (N of 1), but only included 4 patients. It was felt that the study by Velasco et al (2007) was the best evidence having the largest published study using a doubleblinded protocol. Clinical Bottom Lines:1. A seizure reduction of 79% (p<0.0005) occurred in all patients with electrical stimulation of the hippocampus. In patients without mesial temporal sclerosis (MTS) compared to those with MTS, seizure reduction appeared earlier (at 1 mo vs. 8 mo) and to a greater extent (95%, p<0.0005 vs. 69%, p<0.05 at 18 months).2. There was a significant rate of complication consisting of skin erosion resulting in infection requiring removal of the stimulation device in three out of nine participants (33%).The evidence: Velasco et al (2007) evaluated the safety, efficacy of hippocampal electrical stimulation and long-term follow-up in nine non-consecutive patients with medically refractory mesial temporal lobe epilepsy. All patients had complex partial seizures with 7/9 also having secondary generalized tonic-clonic seizures. Patients were selected from a larger group of patients who underwent bilateral hippocampal electrode implantation for diagnostic purposes. The study group consisted of nine patients (six male, three female) between the ages of 14-43 years. Average number of seizures per month was 28 (15-70) measured within a three month period. Five had normal MRIs and the remaining four had mesial temporal sclerosis. Three patients had bilateral foci and six had a unilateral focus of MTL seizure activity. Patients were randomized to a double blind stimulation protocol: five of the patients had an initial one month "off" period and the remaining four initiated stimulation immediately after implantation. P...