Epilepsy
Introduction

(Note: Some terms used in this article may be new to the lay person. A "(G)" after a term will indicate that an explanation of the term can be found in the Glossary)

This article is intended to give the reader an idea of the scope of surgery in the treatment of epilepsy. For the man in the street, epilepsy is often still steeped in mystery that goes back to Biblical times and beyond; and the thought of operating on a person who suffers from epilepsy must be just as strange and mystical as the condition itself. I hope to bring a little more understanding of the condition and its treatment as there must be many patients and families suffering unnecessary hardship due to the ignorance that surrounds this affliction. Medical science does not yet have all the answers, but it has come a very long way in understanding epilepsy and that knowledge can be put to good use in improving the quality of life of many who suffer from the condition.

Epilepsy is not a disease and it does not signify a mental illness. Medical science can very often offer people who suffer from epilepsy freedom from the seizures, but true freedom will only come through a better public understanding of the condition. There is still a great deal of public ignorance concerning all aspects of epilepsy.

DEFINITION

Epilepsy is any of a group of conditions that are characterized by a sudden transient disturbance in brain function. This disturbance in function may manifest in a number of ways such as episodic impairment or loss of consciousness, abnormal movements or disturbances in sensation. Other, less easily described disturbances such as psychic phenomena and autonomic disturbances may occur. A single epileptic episode is known as a seizure. (The term epilepsy is derived from the Greek epilepsia, meaning seizure) The condition is due to sudden abnormal disturbances in the electrical activity of the brain. There are many different types of epilepsy and these are classified according to the description of the seizural event.

INCIDENCE

Roughly two out of every one hundred people will suffer from epilepsy at some time
during their lives. Of these patients about a third will develop recurrent seizures and again about a third to a quarter of these will suffer from epilepsy that is not controlled by antiepileptic medication. It has been estimated that in a country with a population of 45 million people, there will be about 30,000 people who suffer from uncontrolled epilepsy. Many of these patients can be cured by surgical treatment.

UNCONTROLLED OR INTRACTABLE EPILEPSY

The great majority of patients who develop epilepsy will respond to medication and many will find that after a while the seizures regress and then long term treatment is no longer necessary. There is a small group, about 25% of all patients, who find that the medication they are given to bring the seizures under control does not have the desired effect. The seizures persist despite the best efforts of the neurologist who directs the treatment programme. In some instances the medication itself has unwanted side effects. Antiepileptic drugs often have a sedative effect and some patients find themselves overcome by drowsiness and spend many hours sleeping and even when they are awake their minds are dulled by the medication to the extent that they are unable to function at their full potential. When the patient's seizures are not fully controlled or if the price that must be paid by the patient is too high in respect of the undesirable side effects, it must be conceded that the patient has uncontrolled epilepsy. Some patients may have many seizures in a week or even a day, while others may have one or two a year. The frequency of the seizures and the side effects of the anti-epileptic medication must be considered in the special context of the particular patient. If the seizures and or medication cause the patient to experience a significant disruption to the quality of life one must look upon the patient as suffering from intractable epilepsy. Intractability is different to differing individuals. A few examples will be of value in bringing the idea of intractability to mind.

1. A person working with the public, a policeman for instance, develops epilepsy and he has a seizure every few months. He is unable to continue with his normal duties and thus may be regarded as suffering from intractable epilepsy.

2. A mentally retarded person who is cared for in an institution may suffer from many seizures during a week has uncontrolled epilepsy but the circumstances are such that the condition need not necessarily be regarded as being intractable, as the quality of life for the patient is not affected only by the epilepsy.

3. The bus driver who has his epilepsy fully controlled at the expense of uncontrollable drowsiness must surely be regarded as suffering from intractable epilepsy, as he is not able to continue with his chosen career.

4. The young man who experiences his seizures only at night and wishes to have total control of the epilepsy, only so that he can enter a recreational scuba diving course does not suffer from intractable epilepsy, although one would accept that his epilepsy is not controlled.

There are many individuals who suffer from intractable epilepsy who are potential candidates for epilepsy surgery. Epilepsy surgery may offer the patient complete freedom from the scourge of epilepsy and freedom from the need to take anti-epileptic medication. If one looks back at the incidence of epilepsy, it will be seen that epilepsy units have an enormous task, if the investigation of uncontrolled epilepsy is to be properly attended to.

INVESTIGATION OF INTRACTABLE EPILEPSY FOR SURGERY

If a patient has suffered from intractable Epilepsy for two years and has been given a thorough trial of available anti-epileptic medication, that person should be given the opportunity to be assessed by a neurologist that fully understands the benefits of the surgical treatment of epilepsy. This presupposes that the neurologist will be working in close cooperation with a neurosurgeon who has taken an interest in this form of neurosurgery. The surgery for epilepsy is very much a team effort and involves the neurologist, neuroradiologist, EEG technician, psychologist and neurosurgeon.

INITIAL CLINICAL ASSESSMENT

The Neurologist, when assessing a patient with epilepsy will obtain a detailed account of the seizure pattern from the patient and close relatives. This description of the seizures (known as the semiology (G) of the epilepsy) is the first step in understanding the nature of the condition and makes it possible for the neurologist to work out exactly what type of epilepsy it is that the patient suffers from. This classification is a very important first step in understanding the condition and deciding on further steps to be taken in the investigation of the patient.

Brain MRI (G)
An MRI of the brain is an essential early step in the investigation of intractable epilepsy. This is a specialized MRI and is best performed by a Neuroradiologist (G) who has a special interest in he investigation of epilepsy and one who works closely with an epilepsy team. It is not unusual for epilepsy specialists to find that a standard MRI performed by a general radiologist, not associated with an epilepsy team, does not provide the special detail that is required by the expert neurology / neurosurgery team. The test may need to be repeated at unnecessary expense.

Scalp EEG Monitoring (G)
Most patients who suffer from intractable epilepsy will no doubt have had many standard EEG tests in the course of their previous management. These tests generally do not give the detailed information about the epilepsy that is required to decide upon whether surgical treatment is possible.

The epilepsy surgery team needs to know if the seizures originate at one particular point in the brain or whether they originate from many different areas. In order to make this decision the team needs to "capture" a number of seizures using a continuous monitoring technique. The patient is admitted to a monitoring unit where he or she can be connected to a continuously recording EEG system. The long wait for a seizure then begins! Sometimes the epilepsy team and the patient must wait for many days before there is enough information on the EEG recordings to make a proper decision about the nature of the epilepsy. The monitoring unit will often include a video facility for the simultaneous recording of the patient having a seizure on a videotape. This can then be studied in conjunction with the EEG recordings.

NEUROPHYSIOLOGICAL TESTING

Psychologists are able to add to an understanding of the nature of the patient's epilepsy by performing various "IQ" tests that indicate strengths and weaknesses in the patient's thought processes. Patterns of altered function in the patient with uncontrolled epilepsy may be so subtle that they can not be noticed without these specialized tests. Just as the EEG provides important clues to brain function and the nature of the epilepsy, so the neuropsychological tests are able to add to the understanding of the particular patient's brain function.

SPECT Scanning (G)
During the 1980's it was noticed that a SPECT scan performed soon after a seizure can show an alteration in blood flow in the brain in the region of the epileptic focus. The isotope used in the test must be injected into the patient at the time of a seizure for the test to be of any value. This test may be helpful to the epilepsy team in making a decision about the origin of the epilepsy, but does not always form an essential part of the investigation.

PET Scanning (G)
PET scanning is a very expensive addition to the tools that are available to the epilepsy team. The test is hardly out of the realms of medical research and is only available in a few epilepsy centers and is not yet available as a cost-effective routine investigation.

By the time that the patient has been through the clinical assessment, the specialized MRI, the Neuropsychology Tests and the EEG / Video Monitoring the epilepsy team can make a fairly reasonable decision on the likelihood of surgical treatment being able to help the patient. If surgery is considered as a possibility for the patient, additional tests may be performed. These tests are not always required and are avoided unless it is felt that they are essential for the process of deciding on the treatment of the patient. These are known as invasive tests as they involve operative procedures, they are the Wada Test and Subdural Electrode Monitoring.

Wada Test
The Wada (G) Test involves injecting a short acting anaesthetic agent into one of the arteries that supply one half of the brain. The anaesthetic agent is carried into the brain and rapidly anaesthetizes that portion of the brain that has been targeted. This is either the left or the right cerebral hemisphere. The effect of the anaesthetic lasts long enough for the examining neurologist or psychologist to put the patient through a few tests of language or memory function. In this way, it is possible to decide which cerebral hemisphere is most important in determining speech and memory function. This test is not always required in the evaluation of the patient. The Wada Test is an "invasive investigation" as it does entail injecting substances into arteries that supply the brain and so there is a small risk of causing the patient an injury.

Subdural Electrode EEG Monitoring
On some occasions the EEG Monitoring of the patient does not give the neurologist all the information that he needs when deciding whether the patient is a candidate for surgical treatment. In order to obtain more accurate information it may be necessary to place recording electrodes over the surface of the brain. The dura is a firm membrane that lies just under the skull that covers the brain. The delicate electrodes, held within a sheet of thin silastic are placed over the surface of the brain at positions that are chosen by the neurologist. Fine electrical leads are then brought to the surface through the scalp and connected to the EEG Monitoring system. The electrodes are positioned over the brain during a routine operation. Depending upon the specific circumstances, the electrodes may be placed in the subdural space through a small hole that has been drilled into the skull (a burr hole). Sometimes the neurosurgeon may need to make a window (we call that a craniotomy) in the skull in order to place the electrodes over the surface of the brain.


Glossary of Terms

EEG (Electroencephalogram). This is a test performed under the guidance of a neurologist. Brain function depends upon countless millions of electrical impulses passing along millions of nerve fibres within the brain. These impulses set up a pattern of electrical waves that can be recorded over the surface of the brain in the form of an electroencephalogram. The neurologist studies the brain wave patterns and can make decisions about the nature of the patient's brain function.

MRI (Magnetic Resonance Image). This is a test performed by the neuroradiologist that creates an image of the brain that looks rather like a series of photographs of slices through the brain. It is thus possible to recognise abnormalities of brain structure.

Neuroradiologist. A specialist doctor who is an expert in the imaging of the brain and spinal cord. His most useful tool is the MRI scanner.

PET Scan (Positron Emission Tomography). Isotope labelled substances that are used in the metabolism of the brain (such as glucose) are used to demonstrate changes chemical activity of the brain.

(Semiology). A detailed description of a patient's epilepsy that helps the neurologist decide on the type of epilepsy that the patient has.

SPECT (ScanSingle Photon Computed Tomography). A radioisotope such as 99m technetium is injected intravenously and the area of interest (such as the brain) is then studied under a modified geigercounter, which produces images that indicate areas where the isotope has accumulated in the body. The test has many useful applications in medicine.

Wada. The Clinical Psychologist who devised the test and first published its use in the investigation of epilepsy patients gave the test his name