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Epilepsy monitoring
Epilepsy surgery
Epilepsy monitoring is performed at the Regional Epilepsy Center at Aurora St. Luke's Medical Center in Milwaukee.
Epilepsy monitoring is the use of simultaneous video-electroencephalography (EEG). Performed on an inpatient basis, video-EEG provides brainwave recordings simultaneous with videotaping of the patient. This technique has been called long-term monitoring. Epilepsy monitoring takes many forms including: prolonged standard EEG, ambulatory EEG monitoring and simultaneous video-EEG monitoring.
Long-term monitoring has several potential uses:
- It can establish the diagnosis of epilepsy, separating it from other intermittent non-epileptic events that mimic epilepsy. In most epilepsy centers, about 1 in 4 patients recorded with seizure-like events that are unresponsive to medication do not have epilepsy.
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- It can be used in differentiation of seizure types. Seizures may not respond to medication for primary generalized epilepsy if these seizures are actually secondarily generalized seizures. This problem arises typically in childhood where complex partial seizures and absence may be mistaken. For more information, click on
Epilepsy or
common types of Epilepsy.
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- Long-term monitoring localizes the brain region of seizure onset. The area of seizure origin must be defined to provide a surgical treatment for epilepsy. The correlation of the video appearance with the EEG provides part of that definition.
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- Video-EEG monitoring quantifies seizure frequency. Routinely in epilepsy care, determining an absolute seizure frequency is unnecessary. Video-EEG monitoring can be used to count seizures when such accuracy is demanded. The use of new anti-epileptic medications may involve administering doses on an inpatient basis with seizures verified by video-EEG to show the effectiveness of the drug.
Why are both the video and EEG monitoring needed?
The simultaneous use of video and EEG is needed to verify when seizures begin and what they look like. Ambulatory monitoring provides a recording of EEG that is focused at the time patients report in a seizure diary. An event marker pushed after the fact makes the correlation between the patient's event and the EEG. This correlation is loose enough that a random EEG discharge could be misinterpreted as part of a seizure depending on when an event was signaled. The patient who may be unaware of the nature of the event also makes the report of the event. When possible, it is desirable to record and treat the seizures disabling the patient.
Patients with multiple seizure types may find it impossible to record which type occurred. The video recording eliminates classification difficulties by allowing videotape review by patient family members familiar with the patient's seizure types.
The patient is admitted to the Regional Epilepsy Center on a Monday
morning. Electrode sensors are attached to the patient's scalp. The
patient is then escorted to the 6th Floor to a designated monitoring
room and connected to the monitoring equipment. The equipment receives
the EEG and incorporates digitalized EEG with the video image.
An online computer constantly monitors EEG changes. When a seizure has occurred, the computer records the time and a brief EEG sample of that event.
Patient medication is tapered by approximately 33% each day and therefore shortens the monitoring time.
Prior to admission,
neuropsychological tests
are given to the patient and scored. In addition, computed tomography (CT) and
magnetic resonance imaging (MRI) are ordered or reviewed prior to admission. Once the evaluation is complete, a neurosurgical consultation is obtained. The neuropsychologist, neurologist, and neurosurgeon review the patient's tests to decide if there is an isolated seizure focus to indicate if surgery or more testing is necessary. The patient is informed of the results either at discharge or in a subsequent appointment following discharge. Contact is maintained with the referring physician during and following the hospitalization.
Epilepsy surgery is performed at the Regional Epilepsy Center at
Aurora St. Luke's Medical Center
in Milwaukee. For more information, see other treatments for epilepsy in
Continuing Seizures.
Seizures beginning in the area of motor, sensory or language function are clinically mapped using stimulation mapping. Mapping is performed by stimulating the brain at low electrical current and mapping the appearance of a localized muscle jerk or loss of higher cortical function. This mapping can be performed intraoperatively (during surgery) with an awake patient or extraoperatively with sheets of grid electrodes. The seizure may begin in a crucial area of brain function and surgery may not be recommended. Fortunately, this is not a common occurrence.
Neuropsychology can localize an area of functional loss in the brain. This area of dysfunction is strongly correlated in epilepsy with the area of seizure onset. Functions such as memory have verbal and nonverbal components that can be separated out along language-dominant and non-dominant hemispheres of the brain.
The protocol used for confirmation of seizure onset incorporates neuropsychological results. Most epilepsy centers have found that with testing they can also predict memory difficulties before surgery on the temporal lobe and therefore modify the surgical procedure to prevent amnesia. Selection of appropriate tests in the neuropsychological test battery is crucial for its success. The interpretation is very dependent on familiarity with prior results in epilepsy patients.
What makes uncontrolled epilepsy severe enough to consider a surgical
treatment?
Alternative therapy, including
vagus nerve stimulation
and
epilepsy surgery, should be reserved for those patients continuing to have seizures despite the use of standard medications. If medications work, then invasive procedures are not an appropriate treatment.
Persistent, continuing seizures may be perceived as non-threatening to
the patient, but seizures do restrict patient freedom and increase risk
of injury. Alternative treatment, like surgery, may not be an option if
the severity of the patient's limitations are too difficult to
appreciate. Seizures should not be allowed to restrict a patient's life
when he or she might be seizure-free with a surgical treatment.
The concept of the epilepsy scar or gliosis is a reasonable way to explain the cause of epilepsy to a patient, but gliosis
does not produce seizures. Damaged neurons produce seizures. These
epileptic cells form the epileptic focus that may or may not be
structurally different from surrounding tissue.
The process of surgical incision is a different process. When the cortex of the brain is divided by incision, the line of injury is well demarcated and neurons are either transected or unaffected. Little damage occurs in the controlled environment of epilepsy surgery to produce new, injured neurons. Hence, the cause of epilepsy is removed without producing a new cause. A surgical treatment of epilepsy works very well.
Routine electroencephalography (EEG) can be a useful tool in
classifying a patient's seizure syndrome. Some seizure manifestations
are typical for seizure onset in the temporal, frontal, parietal or
occipital cortex. Specific electrical discharges from these areas can
help determine where seizures originate.
Unfortunately, EEG is limited by the amount of time that can be sampled. The prevalence of any specific abnormal discharge is difficult to estimate from standard EEG. Prolonged recordings can estimate the ratios of certain discharges and predominance to help localize seizure onset when accompanied by video-EEG monitoring. Patients who have abnormalities on both sides of the brain, according to the EEG, may still be candidates for surgery. Video-EEG monitoring can record all the patient's typical seizure manifestations. If the recordings all have unilateral onset, then surgery may be successful.
Many patients have been personally touched or are familiar with someone
who has had a craniotomy and believe that paralysis or speech difficulty
are the only outcomes from craniotomy. They are frequently unaware or
don't realize that an initial, life-threatening cause, such as a
cancerous tumor or collection of blood between the layers of membranes
covering the brain, leads to that craniotomy.
Surgery as a treatment of epilepsy is not usually viewed as
life-saving. This fact places the responsibility on the evaluators to
avoid high-risk surgeries that could cause unwanted damage to the brain.
The morbidity of these surgeries is about 5%. The evaluation process
helps define and explain to the patient the risks involved.
Neuropsychological tests help predict patients at risk for amnesia.
The
Wada test (unilateral intracarotid sodium amobarbital test), produces temporary hemispheric anesthesia and allows testing of memory in the opposite hemisphere. Functional brain mapping can also assist in preventing deficits following surgery.
Not all patients whose seizures are resistant to medical therapy can be helped by surgery. The involvement of functionally important brain areas or the bilateral condition of seizure onset often precludes a surgical treatment. It should be reiterated that these decisions are not often discernible before monitoring, and many initial assumptions concerning the suitability of a patient for surgery may be erroneous. Trials of newer anti-epileptic medications are available to patients where surgery is unavailable. Four such clinical trials are ongoing under the direction of the Regional Epilepsy Center.
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