2.2.1 Available Epilepsy Treatment
Pharmacologic treatment is the most common way used to suppress epileptic seizure. Due to the diversification of epilepsy, there are more than 20 types of medications, and each is developed for specific type of epileptic seizure. According to patients’ age, types of epilepsy, syndromes, and intensity of seizure, doctors will choose suitable medications (antiepileptic drugs or AED) for treatment. There are two types of AEDs which can be used: one is narrow spectrum AEDs, and the other is broad spectrum AEDs. While the narrow spectrum AEDs focus on small number of epileptic seizure, the broad spectrum AEDs work for a large group of seizure. However, epilepsy is a complicated disease. There is no standard recipe to decide which medication is the best for an epileptic patient. Besides the effectiveness, side effects are also the mainly consideration for a doctor to write out a prescription. Most of patients’ condition of seizure can be ameliorated by AEDs. However, every kind of medicines might sometimes lead to side effects including blurry vision, dizziness, headaches, and fatigue [15]. In addition, these medications might lead to allergic in roughly 10 % of people and can impair blood cell or liver. Unfortunately, there are still many patients who do not respond to AEDs, which is called medically refractory. For these patients, other treatments should be taken into consideration such as surgical treatment.
Surgical treatment is an alternative for those medically refractory patients whose epileptic seizure cannot be controlled by medications [16]. Before the surgery, a cautious evaluation of the patient is taken. Through the evaluation, the brain location that abnormally discharges is located. Besides the brain areas, the functions which may be affected are found out as well. The evaluation includes long-term EEG recording, neurological examination, MRI, and so on. What kind of surgery is applied depends on
different kind of seizure and the location of the brain. There are two basic brain surgeries for epilepsy: one is resection surgery, and the other is disconnection surgery.
In the resection surgery, the surgeon removes abnormal brain areas that initiate seizure.
The most common type of resection surgery is temporal lobectomy. In disconnection surgery, which is sometimes called functional disconnection, the surgeon interrupts the nerve directions that spread abnormal discharges. Surgical treatment is not a suitable option for every patient whose seizure cannot be ameliorated by medications. Because some sections of brain are too important to be removed by the surgery. It is a risky treatment because patients may loss some physical functions permanently after taking the surgery. In addition, there is no guarantee that epileptic seizure can be cured completely by surgery.
Expect for traditional treatments such as pharmacologic treatment and surgical treatment mentioned above, electrical stimulation is an innovative treatment for drug-resistant epilepsy [17]. It has been investigated and approved currently.
Advantages of electrical stimulation are flexible, recoverable, and non-destructive.
Vagus nerve stimulation (VNS), is one kind of electrical treatment [18], [19]. The vagus nerve is autonomic nervous system, which controls physical functions that are not under voluntary control. The vagus nerve is situated the neck and connects abdomen and the lower part of brain. Device of VNS consists of pulse generator, flexible wires, and electrodes as shown in Fig. 2.5. By sending regular pulses of electrical signal via vagus nerve, VNS system can suppresses epileptic seizure before seizure happens. Currently, VNS is approved by Food and Drug Administration (FDA). Other electrical treatments have also been researched such as deep brain stimulation (DBS) shown in Fig. 2.6 [20], [21].
Fig. 2.5. Vagus nerve stimulation [18].
Fig. 2.6. Deep brain stimulation [20].
2.2.2 Epileptic Seizure Detecting and Controlling System
In recent decades, as bioelectronics developed, epileptic seizure becomes predictable by detecting and analyzing EEG in time or frequency domains [22], [23], [24]. Several methods to predict epileptic seizure such as predictable features, prediction by classification, and entropy calculation have been researched [25]. It has also been demonstrated that the abnormal discharge signal that causes epileptic seizure can be suppressed by TES before seizure happens. A variety of epileptic seizure detecting and controlling systems has been studied and implemented. The systems for epileptic treatment can be mainly classified into open-loop systems and closed-loop systems [26].
Open-loop systems, which are also called blind systems, are not able to respond to physiological activities immediately. The neuroscientists intend to modulate seizure by activating and inactivating regions and set the required stimulus current for individual region. Open-loop systems regularly turn on and off at a fixed pattern which is determined by neuroscientists before the event. Almost all of the currently existing systems that have been approved by FDA adopt open-loop systems [19]. Closed-loop systems, which are also called intelligent systems, are more complicated because they are able to respond to physiological activities immediately. The systems are switched on only when the physiological signals of epileptic seizure are detected. To be compared with open-loop systems, closed-loop systems can stimulate the location of seizure only and hence minimize the effect to human body. Closed-loop systems are consisted of detector, signal analyzer, controller, and stimulus driver.
As current researches shown, the seizure of epilepsy can be traced back to tens of seconds before onset by the EEG, which means that when the seizure-like brainwave is detected, there is still up to 10 seconds remained before the epileptic seizure happens [27]. During this time, the use of closed-loop systems may be effective to deal with
epileptic seizure. Therefore, a number of algorithms have been proposed for rapidly detecting and classifying the sign of different kinds of epileptic seizure. These algorithms analyze the brain activities recorded from EEG or electrocorticogram (ECoG) and extract the features of seizure-like brainwave, and the outcome of analysis can be utilized to decide whether to provide TES or not. Due to the complexity of closed-loop systems, power consumption is also one of mainly considerations while being applied to implantable systems. Fig. 2.7 shows a closed-loop epileptic seizure monitor and controller presented in 2011 [28].
Fig. 2.7. The closed-loop epileptic seizure monitor and controller system consisted of (a) microcontroller board, (b) signal conditioning board, and (c) stimulator board [28].