[Less invasive treatment of intractable epilepsy--vagus nerve stimulation and stereotactic radiosurgery]

Vagus nerve stimulation (VNS) and stereotactic radiosurgery (SRS) represent novel and less invasive therapeutics for medically intractable epilepsy. VNS ushered in the recent advancement in clinical application of electrical stimulation therapy for epilepsy. Chronic stimulation of the left vagus nerve with implanted generator and electrodes inhibits seizure susceptibility of the cerebral cortices. Its efficacy and safety have been established by randomized clinical trials in 1990s in the Western countries and it has been widely accepted as a treatment option for patients with medically intractable epilepsy for whom brain surgery is not indicated or failed. Although the effect on seizures is not so dramatic, the less invasiveness and a wide range of indication have made VNS indispensable for comprehensive care of epilepsy. Since the devices are not approved for clinical use in Japan, there exist barriers to provide VNS to patients at present. Use of SRS for intractable epilepsy started in mid 90s as gamma knife surgery for mesial temporal lobe epilepsy. The marginal dose of 25 Gy to the medial temporal structures has been confirmed to be effective for seizure control, but there seems to be an unignorable risk of brain edema and radiation necrosis. It is still controversial whether the therapy is more effective and less invasive than brain surgery. A randomized clinical trial using the dose of 20 or 24 Gy is ongoing in the United States. SRS for intractable epilepsy associated with hypothalamic hamartoma has been advocated because of a high surgical morbidity, but further study is needed for standardization of the treatment. Substitute use of SRS for other surgical technique like callosotomy or disconnection of epileptic focus seems to be another direction worth pursuing.