SURGICAL TREATMENT OPTIONS FOR INTRACTABLE EPILEPSY

This section of the chapter will be devoted to nonmedical options for the management of intractable epilepsy. Intractable epilepsy goes by many terms including medically refractory treatment resistant, and drug resistant epilepsy. Although there tends to be a general consensus regarding what constitutes intractable epilepsy, there is not a universally accepted definition clinically or in research. Epilepsy that fails to respond to the first two to three antiepileptics with at least one seizure every month for 2 years is considered intractable (138). One caveat to the definition is that trials of antiepileptics need to be appropriately tailored based on the seizure syndrome and type (138). Therefore, drug resistant epilepsy is defined by failure to control despite adequate trials of two appropriate and well-tolerated antiepileptic medications (139). Surgical intervention for intractable epilepsy may be curative or palliative (140).

EPIDEMIOLOGY

Seizure disorders occur in 1% of children and adolescents (141). Disability associated with seizures has declined in the past decade (142), but for some children seizures are debilitating and difficult to control. Seizures are intractable in less than one-third of children with epilepsy (140,143,144). Some genetic conditions such as TS are associated with a strong predisposition toward developing intractable epilepsy (145). A vast majority of children with TS will develop seizures that are frequently medically refractory (145,146). Focal seizures in TS may precede or evolve into infantile spasms, or may coexist.

First-line treatment for infantile spasms in babies with TS is vigabatrin (147). Nearly all young children with TS who present with focal seizures or infantile spasms develop other seizure types as they age that are challenging to treat medically.

For children with hemimegalencephaly and hemispheric cortical dysplasia (rare congenital brain malformations characterized by early intractable epilepsy, intellectual impairment, and contralateral hemianopsia and hemiplegia), anatomic or functional hemispherectomy is usually indicated (148). Children with acquired conditions such as brain tumors and traumatic or otherwise acquired brain injuries are also at risk for intractable epilepsy. For example, for children with Rasmussen's encephalitis surgery is curative by hemidisconnection in which the affected hemisphere is disconnected by either hemispherectomy or functional hemispherectomy (94).

DIAGNOSIS OF INTRACTABLE EPILEPSY AND PRESURGICAL WORKUP

Before proceeding with surgical evaluation, medical management should be optimized. Antiepileptic medication management should be determined first by the seizure syndrome, if one can be identified, and then the seizure type. Monotherapy is ideal and when a second agent is added because of inadequate response, removal of the first agent should be considered (substitution monotherapy) (138). Some antiepileptics are synergistic and are therefore given together as rational polytherapy (138). Table 19.17 is adapted from McTague and details commonly occurring issues to consider when making a diagnosis of intractable epilepsy (138).

TABLE 19.17 COMMON ISSUES FACED WHEN MAKING THE DIAGNOSIS OF INTRACTABLE EPILEPSY

Children with medically refractory epilepsy should be referred early for surgical evaluation. Outcomes are improved at high volume centers (149), so if possible a referral should be made to a highly experienced center. Occasionally, children without refractory epilepsy should be referred for operative evaluation. Potential reasons for referral include significant toxicity of antiepileptics, desire for pathologic diagnosis, notable growth and mass effect, and risk of rupture from arteriovenous malformation (150).

The presurgical workup should include EEG, neuroimaging, neuropsychological testing, a complete neurologic and functional examination, and additional corroboration if needed (138). Neuroimaging maps to the interictal and ictal EEG findings (147,151). When the seizure focus is not lesional, perictal single-photon emission computed tomography and/or a subtraction image coregistered to the MRI may help localize the onset location (151). Magnetoencephalography is also a helpful tool in localizing seizure foci and may be more accurate than EEG (145,147,151). Intracranial EEG is often used to localize or refine localization, which can help minimize the size of the resection (145). See Figure 19.6 for a plain film x-ray of a child status post grid placement for EEG monitoring and mapping.

Neuropsychological testing should evaluate intelligence, memory, executive functioning, attention, and behavior (151). Focused speech and language assessments should also be performed as well as assessments of motor and sensory functions. Language and memory lateralization may be determined by functional MRI or Wada testing (amobarbital sodium is injected into the carotid to inactivate the ipsilateral cerebral hemisphere to allow for testing of the contralateral hemisphere temporarily) (151). Many centers exclusively use functional MRI due to the invasive nature of the Wada test.

Cortical resection can include functional (eloquent) cortex that is associated with predictable neurological deficit such as hemiplegia and homonymous hemianopsia (94). Understanding the consequences of sacrificing eloquent cortex is important as patients and families decide to pursue surgical management (140). The risks and benefits need to be thoroughly discussed (138). When deciding to pursue seizure surgery, it is important to look beyond the likelihood of seizure freedom and also consider the potential impacts on function, quality of life, and other outcome domains (152).