2 The condition, current treatments and procedure
2.1 Epilepsy is a neurological condition characterised by episodes of abnormal electrical activity in the brain which cause recurrent seizures. The seizures can be focal or generalised.
2.2 The main treatment for epilepsy is anti-epileptic drugs taken to prevent or reduce the occurrence of seizures. However, many people have drug-resistant (refractory) epilepsy. They experience frequent seizures and are at risk of status epilepticus and sudden unexpected death in epilepsy.
2.3 Surgery may be considered for refractory epilepsy. Surgical options include open surgical resection (such as lesionectomy, anterior temporal lobectomy or hemispherectomy) or disconnection (such as multiple subpial transection or corpus callosotomy), neuroablation (using stereotactic radiosurgery, radiofrequency thermocoagulation or MRI-guided focused ultrasound) or neuromodulation (such as cranial nerve stimulation, deep brain stimulation or closed loop stimulation).
2.4 Deep brain stimulation involves implanting electrodes into specific target areas of the brain. Although the mechanisms of action are not fully understood, the aim of the procedure is to reduce or suppress seizure frequency. A potential advantage of the procedure is its reversibility. It is an option for some patients with medically refractory epilepsy when resective surgery is not indicated.
2.5 The procedure is done using general or local anaesthesia. A stereotactic frame may be used. Imaging (MRI or CT) is used to identify the target area of the brain (most commonly the anterior nucleus of the thalamus but may include the centromedian thalamic nucleus, hippocampus and nucleus accumbens). One or more small holes are drilled in the skull and electrodes are implanted into the target area.
2.6 A neurostimulator is surgically placed into a subcutaneous pocket below the clavicle. The electrodes are connected to the neurostimulator by leads that are tunnelled under the skin of the neck and scalp. Postoperative imaging is usually used to confirm the location of the electrodes. A handheld remote-control programming unit is used to turn the neurostimulator on or off, adjust stimulation parameters, and monitor activity.