Medical / Surgery

Surgical intervention for adults with intractable, drug-resistant epilepsy

Remember the first time a patient had a seizure on your shift? Chances are, it took you by surprise and gave you a good scare. Over time, you’ve probably grown more adept at handling these events.

But how would you cope with seizures if you had them yourself every day—if they were part of your day-to-day routine? For adults with intractable epilepsy, seizures are a daily reality. Despite medications, many still experience breakthrough seizures. Intractable epilepsy increases the risk of morbidity, depression, physical trauma, cognitive disorders, and sudden unexpected death. (See the box below.)

Defining epilepsy and related terms

Epilepsy: brain disorder characterized by recurrent seizures

Intractable epilepsy: persistent seizure activity despite maximal medical treatment, debilitating enough to warrant surgery. Seizures occur despite use of at least two different antiepileptic drugs at maximum dosages. At least 20% of patients with epilepsy don’t respond to drug therapy; removal of the focal abnormality may achieve a cure.

Seizure: temporary disturbance of neurologic function caused by abnormal and excessive electrical discharges in the brain. Seizures are categorized as focal or generalized.
Focal seizures are marked by abnormal electrical activity in only a portion of the brain. They usually affect just one side of the body or one side of the face. When a focal seizure impairs consciousness, it’s called a complex partial seizure. When it doesn’t, it’s called a simple partial seizure.
Generalized seizures are marked by abnormal electrical activity throughout the brain, with loss of consciousness and violent muscle contractions. They last from seconds to minutes.

Epilepsy is the fourth most common neurologic condition in the United States. About 1% of U.S. adults have been diagnosed with it; 1 in 26 will be diagnosed with it at some point in their lives. Children and older adults are the fastest growing epilepsy population.

While children typically have the support systems of parents and other family members, adults with intractable epilepsy face challenges that can impede their livelihood, their lives, and the lives of loved ones. Intractable epilepsy reduces quality of life by affecting work, family and social life, and independence. This article focuses on surgical treatment of intractable epilepsy in adults.


Pathophysiology of epilepsy

In epilepsy, the brain’s electrical or chemical activity is disturbed by an imbalance of cerebral excitation and inhibition. Neurons in the focus area (epileptogenic focus) are hypersensitive and easily triggered by hyperthermia, hyperglycemia, hypoxic states, sodium disorders, repeated sensory stimulation, or certain sleep phases. As a result, they fire more often and with greater amplitude. When the seizure threshold (balance between excitatory and inhibitory forces) is reached, excitatory transmissions spread.

During a seizure, the brain consumes roughly 60% more oxygen than normal. While blood flow increases, oxygen depletes more rapidly, along with glucose and lactate. Lactate builds up in the cerebral tissues. As the seizure continues, more oxygen, glucose, and lactate are used, possibly setting the stage for severe brain damage and irreversible injury. If the seizure persists, serious brain-tissue deficits can occur, possibly resulting in physical and cognitive impairments.

What causes epilepsy

Causes of epilepsy include:

  • autoimmune or inflammatory disorders (such as Rasmussen encephalitis).
  • brain trauma
  • congenital malformations, such as focal cortical dysplasia, lissencephaly, and tuberous sclerosis complex
  • genetic abnormalities, such as Dravet syndrome and glutamine deficiency
  • infections
  • metabolic defects
  • perinatal injury
  • structural brain disorders, such as tumors, abscess, or mesial temporal sclerosis
  • vascular disease.

Sometimes, the cause of epilepsy remains unknown.

Diagnosis

Early recognition of and intervention for epilepsy are crucial. The longer a seizure lasts, the greater the risk of cognitive decline from ongoing damage to brain tissue. With advancing age, the brain’s plasticity (ability to change) declines. The brain of a younger person can compensate when neuronal areas are interrupted or damaged by ongoing seizures; in an older person, compensation declines. Unless diagnosed and treated early in life, adults with epilepsy have compromised cognitive function. Seizures may cause continuing deterioration of neurologic status and lead to depression and other psychiatric conditions.

In some children, epilepsy goes undiagnosed during childhood or young adulthood and continues into later adulthood. Parents may not recognize epilepsy because seizures can occur in many different types and may be misdiagnosed as odd behavior or habits. Even if parents recognize a seizure in their child, their physician may not refer the child to a comprehensive epilepsy center with expert diagnosticians. In some cases, economic factors and lack of a nearby comprehensive epilepsy center may hinder timely diagnosis. Without accurate diagnosis, a child with intractable epilepsy matures into an adult who can’t work, be self-supporting, or become a productive member of society.

Referral to a comprehensive epilepsy center can mean the difference between existing with intractable epilepsy and proper treatment—or even a cure. Extensive testing at these centers includes bloodwork, genetic tests, advanced radiographic imaging, and dietary review. The multidisciplinary team consists of specially trained epileptologists, neurosurgeons, neuroradiologists, neuropsychologists, pathologists, pharmacists, advanced practice nurses, social workers, and speech/occupational and physical therapists.

Surgical treatment

When management with antiepileptic drugs (AEDs) fails in an adult with intractable epilepsy, the patient may be referred for surgical intervention. The objectives of surgery are to:

  • achieve freedom from seizures without causing additional deficits
  • prevent progressive cognitive or psychological dysfunction
  • improve overall quality of life.

In potential candidates for surgery, radiographic images must identify a localized area causing the seizures that can be removed surgically without compromising functional status. Removing the focal deficit may bring a cure. Also, extensive testing must rule out nonepileptic seizure disorders, paroxysmal movement disorders, generalized epilepsy, and treatable disorders, such as vitamin B6-dependent epilepsy, glucose transporter epilepsy, immune-mediated epilepsy, and progressive neurologic disorders.

Surgery for epilepsy involves a two-phase approach.

Phase 1: Presurgical evaluation

The patient is evaluated thoroughly at a comprehensive center where clinicians are experienced in diagnosing and treating intractable epilepsy. Multiple radiographic tests are done to yield information that helps determine the type of surgery required. In the epilepsy monitoring unit (EMU), electrodes are placed on the patient’s scalp for continuous electroencephalographic (EEG) video monitoring to capture epileptic events. This monitoring usually is completed over the course of about 1 week.

Other phase-1 studies include:

3 Tesla (3T) magnetic resonance imaging (MRI). This technique offers increased sensitivity to better define neurologic structures not shown by the less sensitive 1.5 MRI technique.
Single-photon emission computed tomography (SPECT). The patient is injected with a radioisotope within 30 seconds of an habitual seizure. During the seizure, blood flow in the focal area of the brain increases. This test involves both an ictal scan (done during a seizure) and an interictal scan (done between seizures as a baseline).
Neuropsychological development tests. These tests investigate the patient’s cognitive and problem-solving abilities, measure the intelligence quotient, examine the patient’s memory, and identify visual-spatial, motor, and behavioral functioning. Results help pinpoint the brain areas involved in seizures that may be affected by surgery.
Positron-emission tomography (PET). The PET scan detects where the glucose uptake is low; that often is the seizure site. Functional deoxygenase (FDG) positron emission tomography is a study used with PET to visualize areas of decreased metabolism; the area of suspected hypometabolism may be larger than the epileptogenic zone.

Presurgical functional mapping
Candidates for surgical resection are those with a localized lesion found on MRI that may represent a pathologic process. Surgeons must try to avoid injury to so-called eloquent brain areas—the parts of the brain that control speech, motor, and sensory functions.

Presurgical functional mapping evaluation may involve the following studies:

Ictal SPECT and SISCOM (subtraction ictal SPECT co-registered to MRI). These techniques combine MRI images with nuclear SPECT images to highlight areas of abnormal perfusion during a seizure, which helps localize the focus area.
Magneto-encephalography (MEG). This test measures smaller magnetic fields produced by smaller electrical currents inside brain cells, which can be affected by the skull and overlying brain tissue.

After these tests are done, the clinical team develops an individualized surgical plan to help achieve the best outcome. In some cases, the patient undergoes the phase-2 tests described below to further determine eligibility for surgery.

Phase 2: Surgical intervention
The patient enters the hospital for operative placement of subdural grids. Intracranial EEG electrodes are placed in the subdural space directly on the brain surface to allow more precise mapping of the seizure focus. Usually, these electrodes stay in place for 1 week so the epileptologist can review at least three seizure episodes.

A functional MRI (fMRI) tests language and memory during the MRI scan, helping to determine if brain tissue in the focus area can be removed safely without affecting functional ability. The Wada test is done to identify memory and language areas of the patient’s brain and determine the brain’s language dominance. For this test, amobarbital is given by intracarotid injection.

Cortical stimulation mapping also is done. Clinicians strategically place intracranial electrodes during surgery to detect seizures. This final test further determines key motor, speech, and sensory areas.

Removing the seizure focus
Surgical removal of the seizure focus is the final process in phase 2. Brain tissue containing the focus is removed while eloquent brain tissue is protected. Common surgical procedures to remove the seizure focus are described below; they may be used in combination.
Amygdalo-hippocampectomy: removal of medial brain structures, usually in a temporal lobectomy procedure. These areas are responsible for memory in general as well as memory of emotion.
Lesionectomy: removal of an anatomic abnormality or a benign brain tumor in a noneloquent region.
Standard lobectomy: removal of a whole or partial section of the brain, usually in a nondominant hemisphere
• Corpus callosotomy: surgical disconnection of the binding fibers between the brain hemispheres, most often done for a nonlocalizing seizure focus
Functional hemispherectomy: removal of the parts of one hemisphere that are causing seizures, in conjunction with cutting of the corpus callosum, to end communication between the hemispheres and prevent seizures from spreading to the other side of the brain. This procedure is done for epilepsy in which seizures affect an entire hemisphere, secondary to a congenital stroke or diffuse cortical dysplagia.

Surgery may last 4 to 8 hours; afterwards, the patient recovers in a neurologic intensive care unit with specially trained nurses. Unless complications occur, the patient may be discharged within a few days and followed on an outpatient basis.

Case study

Roberta T, age 49, had her first seizure as a 19-month-old toddler. Her seizures were well-managed until age 23. Since then, she has had recurrent seizures marked by staring, left-hand posturing, and lip smacking. She also has had two episodes of generalized tonic-clonic seizures. Recently, she has been having three seizures daily and is unable to work or drive. She has failed multiple AED trials and currently takes lamotrigine. Her neurologic exam results are normal.

Her physician refers her to a comprehensive epilepsy center to determine if she is a candidate for surgery. She is admitted to the EMU for phase-1 evaluation and undergoes MRI, SPECT, neuropsychological examination, PET, and MEG testing. After 5 days, she is discharged.

At a multidisciplinary meeting, clinicians determine Roberta has mesial temporal sclerosis and develop a surgical plan of care. She is brought back for electrode grid placement and cortical mapping. Tests reveal a seizure focus in the right temporal area. She is scheduled for a right anterior temporal lobectomy and an amygdalo-hippocampectomy.

She recovers from surgery without complications and is discharged after 5 days. In the year since surgery, she has been seizure free. She’s now applying for a job and learning to drive.

Selected references

Boss B. Alterations in cognitive systems, cerebral hemodynamics, and motor function. In: Huether SE, McCance KL. Understanding Pathophysiology. 5th ed. St. Louis: Mosby; 2011: 364-5.

Cascino GD. Surgical treatment of epilepsy in adults. Literature review current through November 2014. Topic last updated October 9, 2014. https:/uptodate.com/contents/surgical epilepsy

Institute of Medicine. Committee on the Public Health Dimensions of the Epilepsies. England MJ, Liverman CT, Schultz AM, et al, eds. Washington, DC: National Academies Press; 2012.

Kwan P, Arzimanoglou A, Berg AT, et al. Definition of drug resistant epilepsy: consensus proposal by the ad hoc Task Force of the ILAE Commission on Therapeutic Strategies. Epilepsia.2010;51(6):1069-77.

Morbidity and Mortality Weekly Report. Epilepsy in adults and access to care—United States, 2010. November 16, 2012; 61(45):909-13.

Uijl SG, Leijten F, Moons KG, et al. Epilepsy surgery can help many more adult patients with intractable seizures. Epilepsy Res. 2012;101(3):210-6.

Misti Tuppeny is a clinical nurse specialist for Neuroscience, Behavioral Health, & Rehab in Florida Hospital, Orlando.

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