Treating the Medically Intractable Patient
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Patients who continue to have seizures despite treatment with appropriate AEDs in monotherapy over six months should be referred to a neurologist. If seizures are not controlled within six months, then referral to a tertiary epilepsy center is indicated. If it is established that seizures are epileptic, then the patient will be a candidate for second line AEDs, for investigational AEDs, or for epilepsy surgery.

Epilepsy Surgery

Identification of Surgical Candidates
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Epilepsy surgery is an underutilized therapy that should be considered in patients with localization~related epilepsies that are medically intractable and clinically disabling (NIH Consensus Development Conference, 1990). Medical intractability is defined as failure to achieve seizure control without adverse drug effects on maximal monotherapy. Seizures must be frequent and disabling, ie, complex partial or secondarily generalized. However, disability may be defined differently for each individual. For instance, daytime seizures occurring one or more times a year will restrict driving privileges in most states and may limit employment. Nocturnal GTCS confer less potential for injury than daytime GTCS and even complex partial seizures. Other considerations in candidates for epilepsy surgery include the long-term effects of seizures and of AEDs on cognition, memory and learning. Data in humans is circumstantial but supports the concern that frequent epileptic events may lead to progressive cognitive impairment in some individuals. Children whose seizures begin earlier in life have a tendency to display lower I.Q. Cognitive side effects of AEDs in children are also of concern. Phenobarbital in particular has been associated with diminished cognitive function in the pediatric population.

Psychosocial disability must also be considered. The unpredictable, recurrent nature of seizures can lead to anxiety, depression and low self-esteem. A sense of diminished competence and independence can develop. Children with epilepsy often face parental over-protectiveness. The final consequence of uncontrolled seizures is limited social, educational and vocational potential.
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The Evaluation for Epilepsy Surgery

Data obtained from extracranial electrophysiological monitoring forms the basis of the noninvasive evaluation for epilepsy surgery. The goal of the evaluation is to record several of the patient’s typical behavioral seizures. By identifying the precise anatomic region of seizure onset, the epileptogenic region may be defined.
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Successful localization of the epileptogenic region is further confirmed by tests of brain structure (MRI) and function, including neuropsychological testing, the intracarotid amytal test, single photon emission computed tomography (SPECT) and positron emission tomography (PET). Neuropsychological testing evaluates I.Q., memory, visual-spatial and language function in order to identify deficiencies in a restricted brain region that might correspond to areas believed to represent the epileptogenic region. This testing also allows comparison of pre and post-operative cognitive function. The intracarotid amytal test (Wada test) assesses hemispheric lateralization of language and memory after intracarotid injection of amytal, a short-acting anesthetic. This procedure establishes the safety of surgery in terms of preservation of language and memory and is used to confirm localization of a temporal lobe epileptogenic region by detecting asymmetries in memory function.

SPECT measures regional cerebral blood flow, an indicator of local cerebral metabolic rate. The sensitivity and specificity of interictal SPECT scans is not sufficiently high to be an accurate tool for localization of the epileptogenic region. However, at the time of a seizure, the SPECT scan shows extensive hyperperfusion of the region from which the seizures arise, particularly with seizures arising from the temporal lobe.

PET provides another means to obtain functional brain images. A variety of tracers are available and can be selected to portray blood flow, blood volume, tissue pH, oxygen metabolism or neurotransmitter metabolism. The radioisotope most commonly used is 18F-flurodeoxyglucose (FDG) which reflects glucose metabolism. PET scanning is a valuable tool in identifying the region from which seizures arise. 70% of patients with partial seizures demonstrate an area of hypometabolism interictally, which correlates .highly with the epileptogenic region. PET can identify the epileptogenic region in some very young children with intractable seizures, such as infantile spasms.

While each center has its own protocol, in general, a minimum number of tests must localize the epileptogenic region concordantly. Most centers have developed testing protocols that allow some patients to go directly to surgery after the initial noninvasive evaluation, bypassing implantation with intracranial electrodes.
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If the epileptogenic region can not be adequately localized during the noninvasive evaluation, or if the epileptogenic region involves essential cortex, then the patient may require evaluation with intracranial electrodes. There are a variety of electrode types which can be placed in the epidural or subdural space, or stereotaxically within the brain parenchyma. In most centers, different types of electrode may be combined within an individual patient. All intracranial electrodes can be used acutely (in the operating room) or chronically, for periods up to 4 to 6 weeks. The electrodes are used for electrographic monitoring as well as mapping of brain function. Intracranial electrodes are not subject to many of the artifacts that confound recordings with scalp electrodes, such as muscle and movement, and are in close proximity to neural generators of the EEG signal. However, intracranial electrodes sample from a restricted area of cortex (6 mm2), are costly, and carry a small (<3%) risk of infection, hemorrhage and injury to brain structures.