The relationship between paired pulse magnetic MEP and surgical prognosis in patients with intractable epilepsy

PURPOSE To assess whether paired pulse magnetic motor evoked potential (MEP) can predict surgical prognosis in patients with intractable epilepsy. METHODS MEP of the unilateral hand muscles were recorded following paired pulse transcranial magnetic stimulation (TMS) of the motor cortex. The interstimulus intervals of paired stimulation were 1-16 ms with a conditioning stimulus that was 90% active motor threshold. Subjects were six patients with temporal lobe epilepsy (TLE) scheduled for anterior temporal lobectomy and three patients with myoclonic or head-drop seizures scheduled for anterior corpus callosotomy, resulting in the unilateralization of epileptic discharges. The hemisphere showing unilateral discharges was defined as the affected hemisphere. The intracortical inhibition and facilitation curve was drawn based on MEP before and after surgery and the relationship between MEP and surgical prognosis was investigated. RESULTS In five patients with TLE showing class I surgical results (Engel's classification), the affected hemisphere showing cortical hyperexcitability preoperatively was almost normalized after surgery. However, in a patient with class III, the unaffected hemisphere showed cortical hyperexcitability before and after surgery. In the callosotomy group, two patients with excellent outcomes showed the same results as TLE group with class I. CONCLUSIONS Paired pulse magnetic MEP may provide predictive value in terms of surgical outcome in those patients with intractable epilepsy.