A seizure is a paroxysmal self limited event caused by an excessive electrical discharge of the central nervous system. Epilepsy is a disorder characterized by recurrent seizures (Hauser & Kurland 1975). All of us have a lifetime risk of having a single seizure of approximately 8.8%. The prevalence of epilepsy is however approximately 0.65%.

A seizure is a frightening event for families and friends, but for patients it may engender a certain degree of confusion and reluctance to seek attention. They are often amnestic for the event, and the consequences of a diagnosis of "epilepsy" are serious. In one's approach to diagnosis and management one must not only draw upon our collective knowledge of the pathophysiology of seizures but upon our abilities to humanely guide and counsel anxious patients. The consequences of a diagnosis and treatment must be weighted against the risks of recurrent seizures.

This review will cover the following areas
Definitions, and prevalence
Risk of recurrence
Predictors of recurrence
Patient evaluation
Long term monitoring
Definitions and Prevalence

Seizures are a symptom of a disturbance of cerebral gray matter. Only neurons can generate enough electrical activity to produce the clinical symptoms of epilepsy. Seizures may be triggered or initiated by external forces: cardiac arrhythmias, hypotension, hypoglycemia, trauma, infection, fever, toxic exposure. When they are recurrent and secondary to intrinsic cerebral cortical activity it is called epilepsy.

There are several classifications based on the epilepsy syndrome or the clinical semiology of the individual seizure. A functional and therefore practical classification is based on the area of brain in which the seizure starts. There are two major seizure types partial and generalized.

Partial seizures start in one area or "part" of the brain. If consciousness is maintained it is a simple partial seizure. If consciousness is impaired it is a complex partial seizure. Partial seizures may spread to involve the contralateral hemisphere becoming secondarily generalized.

Generalized seizures may be convulsive (tonic, clonic, tonic clonic, atonic, myoclonic), or non convulsive staring called absence. These seizures are thought to arise simultaneously and bilaterally from large areas of cortex. Consciousness is always lost.

Partial Seizures

Simple partial seizures may be characterized by involuntary movements of onelimb or sensory disturbances of one part of the body all the while the patient is aware of what is occurring. We categorize the types of simple partial seizures by their manifestations and can thus infer their cerebral origin.

Simple partial seizures may evolve into a complex partial seizure in which the patient’s consciousness is impaired. The forms vary widely depending on which region of the brain is involved but commonly involve staring, repetitive semi-purposeful movements and tonic posturing. The eyes are commonly deviated and the patient is unresponsive to verbal commands and resistant to physical manipulation.

• Such seizures frequently are heralded by a subjective warning or aura. Auras generally take the forms described in simple partial seizures. They are generally very brief lasting seconds. They can be isolated but usually evolve into a complex partial seizure.
• The aura is followed by the externally recognizable seizure activity or ictus, which as it resolves leaves the patient in an abnormal state of fatigue or confusion called the post ictal period.
• The ictus typically involves an alteration of consciousness in which though posture is maintained there is usually a cessation of motor activity. The patient then usually demonstrates automatisms involuntary, repetitive and semi-purposeful activity. There are several "classic" forms.
• Oral-facial-lingual movements such as lip smacking, repetitive swallowing, usually seen in mesial temporal lobe origin seizures.
• Repetitive limb movements, fiddling, rubbing, rearranging or ordering objects, even undressing.
• Ambulatory or walking and circling movements.
• Vocalizations such as tuneless humming, grunting or whistling.

Partial seizures may progress and become secondarily generalized with bilateral tonic clonic rhythmic jerking movements of the limbs, unresponsiveness, tongue or cheek biting, occasional incontinence. When this occurs rapidly it is often difficult to differentiate from a primarily generalized seizure.

Generalized Seizures

Generalized tonic clonic

Primarily generalized seizures may be convulsive or non-convulsive. Convulsive seizures are what most people think of when they think of epilepsy. They usually involve bilateral and symmetrical rhythmic movements in an unconscious patient. The patient may be generally stiff or tonic. With this stiffening there may be a forced exhalation and a vocalization. The patient will fall if standing. There may be a brief period of tonic flexion followed by axial rigidity and extension of the torso with adducted arms and clenched jaw and fists. They may tremble or seem to vibrate. This stiffening generally gives way after 10 to 30 seconds to rhythmic, clonic, bilateral body movements. Patients often flex violently (clonic), or jerk rhythmically tonic clonic (grand mal),. During this phase they are unresponsive, and their tidal volume is modest. Cyanosis may be seen peri-orally. They are unable to swallow thus oral secretions pool. Saliva may be blood tinged due to biting of the tongue or cheek. Bowel or bladder incontinence may occur. The clonic jerking tends to decrease in frequency and increase in amplitude. This activity seldom lasts more than a minute or two and is followed by relaxation, continued unresponsiveness and an apparent deep sleep. This phase usually lasts from 2 to 30 minutes. When patients awaken they are universally confused. The confusion usually lasts longer than the convulsive phase but is quite variable lasting from minutes to hours. The patient often falls into a deep sleep awakening in minutes to hours often tired and generally feeling sore and stiff. Patients are often amnestic for the event only recognizing the seizure afterwards but the way they feel.

The EEG demonstrates suppression during the tonic phase followed by low voltage fast activity then slower higher amplitude waves of increasing amplitude and decreasing frequency. During the clonic phase there may be bursts of fast activity associated with the clonic jerks. These become less frequent as the seizure abates. Post ictally the EEG is generally slow. Muscle artifact often obscures the recording.

Typical Absence

Generalized seizures may also be non-convulsive. In typical absence seizures patients will suddenly stop participating in their activities, stare blankly as if frozen. Tone is preserved and the person does not fall. Occasionally there is a fine flutter of the eyelids or lips. The event lasts seconds, 80% of the time less than 10, and the patient generally resumes their previous activity and is amnestic for the event. They may occur many times per day. Often occurring in clusters when awakening or falling asleep. Fatigue, photic stimulation or hyperventilation are common precipitants. Typical absence develop in childhood and may or may not be the only seizure type in an individual. These events are accompanied by 3 per second spike and wave abnormalities on EEG are what is classically referred to as "Petit Mal" epilepsy. This term is unfortunately commonly used by non neurologists to refer to all seizures that are not convulsive.

Atypical Absence

These seizures differ from the typical absence in that the onset and cessation are less abrupt, and the duration is longer. There may be loss of or changes in tone tonic or clonic movements and the EEG is irregular and abnormal both intericatally and ictally with slow or faster spike wave complexes than the typical 3 per second seen in typical absence.

Myoclonic Seizures

These are characterized by brief shock like contractions of a muscle group resulting in a twitch or jerk in which the patient my drop an object or stumble and fall. The ictal EEG demonstrates generalized or poly-spike and wave discharge. Myoclonic seizures may be induced by various environmental activities or may be a component of a variety of seizure disorders such as Lennox-Gastaut syndrome and progressive myoclonic epilepsies.

Clonic Seizures

These seizures are characterized by jerking usually irregular and asymmetrical. The ictal EEG is fast, mixed with large amplitude slow waves. They are most often seen in neonates, infants or young children.

Tonic Seizures

These seizures are characterized by a tonic (stiffening) muscle contraction with an alteration of consciousness. There is no clonic or rhythmic jerking phase. Classically the patient’s neck is extended and the facial muscles contract so that the eyes are open though the orbits roll upwards (Bell’s phenomenon). The chest muscle contract and a gasp or cry is often heard followed by apnea as there is no relaxation or intake of air until the seizure is over. The proximal arm muscles contract and the arms are abducted, semi-flexed and rise above the level of the shoulders. The legs may be extended or flexed. There may be some brief partial relaxation and the patient may have some fluctuation of the spasm with a kind of nodding and change in rigidity of the limbs. Such seizures usually last less than 60 seconds.

The ictal EEG may demonstrate an initial flattening followed by rapid activity (epileptiform fast) which increases in amplitude as the seizure progresses. The significant amount of muscle activity often makes EEG interpretation difficult.

Persons with such seizures rarely if ever have only one seizure type. These events tend to occur in settings of diffuse cerebral damage with associated learning difficulties.

Atonic Seizures

These seizures are characterized by a sudden loss of postural tone and the patient falls to the ground like a sack of potatoes. At times the event is less pronounced with only a brief buckling of the knees or forced nodding of the head. The duration is very brief and recovery immediate. They may occur in clusters and aqre usually seen in persons with significant and diffuse cerebral damage.

The EEG demonstartes irregular spike and wave and polyspike discharges sometimes mixed with slow or low amplitude fast activity.

Unclassifiable Seizures

Despite these efforts of classification many seizures are unclassifiable.

Nonepileptic events or NEE

Nonepileptic seizures should always be considered in the differential diagnosis. The prevalence is unclear, but 25-33% of patients referred for EEG telemetry obtain this diagnosis. While a large number of such patients are conversion reactions there are a number of other etiologies. Vasovagal attacks, cardiac arrhythmia’s, sleep disorders, and intoxications can present as a seizure and need to be ruled out. Having said this the preponderance of non-epileptic events seen in a long term monitoring unit are conversion reactions. These are more commonly seen in women than men. Frequently but not always, such patients have had a significant emotional trauma such as rape. Unlike a post traumatic stress disorder in which the event is replayed, in a NEE the event may be suppressed and the stress of such suppression manifests itself as a "seizure". If diagnosing an NEE one must be prepared to assist the patient in dealing with the seizures in a positive manner and never accuse them of malingering.

Persons with NEE may also have genuine epilepsy. They co-exist in 5 to 40% of cases. Persons with mental retardation have higher than expected rates of co-morbidity with NEE. Persons with NEE may present with "seizure" associated injuries, tongue biting or incontinence. A substantial proportion will have an abnormal neurologic examination, EEG or MRI.

Classification of the Epilepsies and Epilepsy Syndromes

To make matters more confusing an attempt has been made to use a broader range of features (not just clinical appearance and EEG) to more precisely classify seizure types. An epilepsy syndrome is "an epileptic disorder characterized by a cluster of signs and symptoms customarily occurring together." (International League Against Epilepsy, ILAE 1989).

Idiopathic generalized epilepsies are also called primarily generalized epilepsies. They are considered genetic conditions in which epilepsy is the major clinical feature.

Cryptogenic or symptomatic generalized epilepsies are epilepsies existing within a diffuse encephalopathic condition.

Idiopathic localization related epilepsies are focal seizure disorders with no known cause. There are three syndomes identified to date: benign childhood epilepsy with centro temporal spikes (Rolandic epilepsy), childhood epilepsy with occipital paroxysms, primary reading epilepsy.

Symptomatic localization related epilepsies are those caused by specific cerebral lesions such as trauma, stroke, or tumor.

Cryptogenic localization related epilepsies are considered focal epilepsies in which the etiology is unknown.

ILAE - Classification of Epilepsies and Epilepsy Syndromes

I - Generalized

• Idiopathic generalized with age related onset, in order of age.
• Benign neonatal familial convulsions
• Benign neonatal convulsions
• Benign myoclonic epilepsy in infancy
• Childhood absence
• Juvenile absence
• Juvenile myoclonic
• Epilepsy with GTC seizures on awakening
• Other not defined
• Activation related epilepsies
• Cryptogenic or symptomatic generalized epilepsies
• West syndrome
• Lennox-Gastaut syndrome
• Epilepsy with myoclonic-astatic seizures
• Epilepsy with myoclonic absences
• Symptomatic generalized epilepsies
• Non-specific etiology
• Early myoclonic encephalopathies
• Early infantile encephalopathy with burst suppression
• Other symptomatic
• Epilepsies in other disease states

II - Localization — Related

III - Epilepsies and syndromes undetermined as to whether focal or
Generalized

• With both generalized and focal seizures
• Neonatal seizures
• Severe myoclonic epilepsy in infancy
• Electrical status epilepticus in slow wave sleep
• Acquired epileptic aphasia

IV - Special syndromes

• Febrile convulsions
• Isolated seizures or isolated status epilepticus
• Seizures occurring only when there is an acute metabolic or toxicevent caused by factors such as alcohol, drugs, eclampsia,non-ketotic hyperglycemia

RISK of RECURRENCE

Not all seizures recur. In fact a substantial proportion of persons with an initial seizure will never have another. To understand the risk of recurrence the most important factor is whether the event was provoked. The concept of provoked (a seizure secondary to a neurological or physiological insult) vs. unprovoked (no clear precipitating insult) seizure has been developed by Dr. Allen Hauser. Prior to this concept the literature on risk of recurrence varied widely and hence was not as helpful. There was a greater risk seen in retrospective studies and for studies of first generalized tonic clonic seizure. Many persons with partial seizures are unrecognized until they have a generalized convulsive episode thus their recurrence rates appeared very high. We now recognize certain features which are predictors of recurrence and which must be searched for in the evaluation of patients presenting with this disorder.

?A substantial proportion of persons with an initial seizure will never have another. Treatment of a person with a single seizure is generally not recommended. Exceptions are circumstances in which recurrence risk is high: symptomatic seizure secondary to brain infection or injury, persons with pre-existing neurological deficit, persons with juvenile myoclonic epilepsy. Evidence of injury to cortical gray matter appears to be the best general predictor of risk, but there are exceptions.

There are some persons presenting with multiple seizures who one would not treat. Children with Benign Rolandic Epilepsy probably do not need pharmacologic treatment. Persons whose seizures are the result of alcohol or drug withdrawal are generally not treated. Their risk of recurrence is a function of their risk for recidivism. It is possible however for persons with substance abuse to also have an underlying epilepsy. The rare woman whose seizures only occur during pregnancy gestational epilepsy, probably does not need treatment when no longer pregnant.

The natural history of untreated epilepsy is essentially unknown. Gowers writing in 1881 reported that in 1/3 of patients with an initial seizure a second one occurred within one month. A retrospective study by Elwes et al. (1988), found that in 32% of persons with a first seizure a second attack followed in one month. In 51% it followed in 3 months and by one year 87% of persons developing epilepsy had had their second seizure. It is for this reason that clinically we seldom have to deal with the question of recurrence. following an initial seizure.

Predictors of Recurrence

History of previous neurologic insult

A person presenting with a history of a previous neurologic insult (severe head injury, stroke, CNS infection, or intracranial lesion) have a 2 to 3 fold risk of recurrence compared to persons without such as history (Hauser, Annegers and Kurland 1991). For those persons with congenital neurological abnormalities who have mental retardation or cerbral palsy prior to the development of their first seizure, the risk of recurrence is virtually 100%.

Abnormal neurologic examination

When a person has a remote neurological insult and presents with an initial seizure the presence of abnormalities on a neurologic examination is a predictor of future recurrence. If no such etiologic event has occurred an abnormal neurologic examination appears to have little predictive value (Hauser 1995).

Electroencephalogram

Following a first unprovoked seizure an abnormal EEG has excellent predictive value. An EEG with epileptiform abnormalities has an 60 - 80% risk of recurrence. If the abnormalities are simply slowing and not epileptiform, the risk of recurrence drops to 30-40%. Persons with a normal EEG have a risk of 10-25% (Von Donselaar et al. 1992).

Seizure type

The evaluation of the predictive value of seizure type is complicated by the difficulty in accurately determining whether the onset is partial or generalized. In children partial onset seizures appear to increase the risk of recurrence. In adults this is not the case (Shinnar et al. 1990, Hirtz et al. 1984, Camfield et al. 1985). Juvenile Myoclonic Epilepsy of Janz or the more modern term, myoclonic epilepsy of adolesence is an unusual disorder occurring in 3 - 4% of persons with epilepsy (Janz & Christian 1957). Characterized by myoclonus upon awakening approximately 85% of patients also have generalized tonic clonic seizures. Affected persons appear to never enter remmission. A history of myoclonus upon awakening and the typical EEG with polyspike and slow wave complexes in a patient presenting with a generalized seizure secures the diagnosis.

Family history

Most of the studies evaluating the impact of family history on recurrence have been performed in children. Only one has found an association and that for children in whom a sibling had epilepsy (Hauser et al. 1990).

History of Acute Symptomatic (Provoked) Seizures

By symptomatic seizure one refers to a patient with a previous history of a seizure following a neurological insult such as a head injury, stroke, or CNS infection. Such persons by definition have not had a diagnosis of epilepsy until their recurrence. A history of a seizure following a previous neurological insult increases the risk of recurrence by a factor of 4 (Hauser et al. 1990, Annegers et al 1980, Annegers et al 1988, So et al 1993).

Febrile Convulsions

The seizures are by definition convulsions occurring during a febrile illness in a child between the age of 6 months to 3 years. Their prevalence is 3% in the general population but higher 14% in siblings of children with febrile convulsions and slightly higher in children of parents with epilepsy, 5%. Persons with febrile convulsions are at increased risk for the development of epilepsy, 7% by the age of 26 years. This risk appears to be associated with recurrent febrile convulsions within the same illness, those which last more than 15 minutes, and those with lateralizing features (Wallace 1988). In a study of adults presenting with their first seizure a history of febrile convulsions was associated with a 50% chance of recurrence within 5 years ( Hauser et al. 1990).

Circadian Timing

The time of day of the appearance of a seizure is a predictor of recurrence. Nocturnal seizures have a greater likelihood for recurrence than those occurring while awake (Shinnar et al. 1991).

In practical terms the risk of recurrence is seldom an issue. Most persons will have had multiple seizures by the time they present for medical attention.

DIAGNOSING EPILEPSY

Seizure Recognition

As one can see with such a variety of seizure types, recognition can be difficult. The sine qua non is the matching of the clinical description with concurrent EEG. Generally one makes the diagnosis of epilepsy clinically, that is based on the combined evidence of an historical description of the seizure, the presence of risk factors, the consistency of attacks, and an abnormal interictal EEG. Most of the time epilepsy can be accurately diagnosed in an outpatient setting on the basis of a good history, examination and EEG. There are times however when this cannot be done. Sometimes the history is lacking. Persons with epilepsy are often anmestic for the events and cannot give a description. In such cases an observer is important to provide the description. This may fail either because there has been no observer or the observer was so unnerved by the seizure that they were unable to report accurately.

The EEG while the primary tool of epileptologists has limitations. Between seizures the EEG may be normal. Abnormalities are sometimes non specific. Long term monitoring (LTM) also called EEG telemtry, is a method of recording EEG abnormalities in an attempt to improve diagnostic accuracy. In involves either outpatient (ambulatory) or inpatient recording of EEG over several days. Out patient monitoring is similar to Holter monitoring of EKG. The patient has electrodes glued to the scalp and wears a recorder in a fanny pack and goes about their normal activities. It can be convenient for the patient, but there is seldom a good clinical description of the seizure and electrodes may loosen and fail to record all of the EEG. Inpatient monitoring is more expensive and confines the patient to a hospital room but it is usually more accurate. In inpatient LTM closed circuit video is combined with EEG to collect both clinical description and EEG changes, thus providing the most accurate manner of collecting information about the epilepsy.

ELECTROENCEPHALOGRAM (EEG)

The EEG is a collection of amplifiers that records the electrical activity of the brain. It consists of electrodes, small metal disks glued to the scalp, wires connecting these discs to an amplifier, and a method of visualizing the electrical activity. We formerly used a collection of ink pens over a traveling roll of paper. Modern machines use a video screen to visualize the activity.

The primary brain cell or neuron differs from other cells in that it is electrically excitable using its ability to develop electrical potentials to communicate with adjacent cells. Changes in the "normal" electrical excitability can result in a seizure. Electrodes placed outside of the brain cells, such as those glued to the scalp in an EEG, can record the collective or synchronized activity of a collection of neurons as field potentials. These electrical signals are on the order of hundreds of milliseconds to seconds and appear as transient electrical signals or spikes. By arranging the location of the electrodes on the scalp in certain patterns or montages we can determine the relative location of any abnormal electrical activity.

The electrical activity of each active electrode on the scalp is compared to that of a distant inactive or reference electrode in a "mono polar" recording or to an adjacent active electrode in a bipolar recording.

The electrical activity recorded at the scalp represents an area of underlying brain tissue. The strength of the signal is diminished by the underlying tissues, dura, cerebral spinal fluid, bone, fat muscle and skin. Thus the amplitude of the EEG at the surface is smaller (micrvolts), than the amplitude in a single neuron (millivolts).

The surface EEG shows typical patterns that can be correlated with the various stages of sleep or wakefulness. And with a pathological process such as a seizure. We rely on two measures of EEG, the frequency and amplitude of the signal. Normally the EEG frequency is 1-30Hz with amplitudes varying from 20-100uV. Frequencies are divided into groups alpha (8-13Hz), beta (13-30Hz), delta (0.5-4Hz), theta (4-7Hz). Alpha activity is generally seen in relaxed awake states and most prominent over parietal and occipital regions. Beta is generally seen over the frontal regions and during intense mental activity. Alerting a relaxed person will desynchronize the EEG with reduction of alpha and increase in beta activity. Theta and delta waves are normally seen in drowsiness and early sleep.

The abnormal neurons responsible for seizures tend become synchronized and their currents summate resulting in abrupt changes from the baseline recorded as spike or sharp waves. As long as the abnormal activity is restricted to approximately 1000 neurons there is no clinical manifestation though an EEG may detect spike waves. The propagation of the seizure is inhibited by afterhyperpolarization of the abnormal cells, and the tendency of GABAergic inhibitory interneurons which produce an effect called inhibitory surround. When a seizure develops the inhibitory surround is overcome. The afterhyperpolarization disappears and additional neurons are recruited. Membrane repolarization fails and continuous high frequency action potentials are generated resulting in continuous spike waves on EEG. If the activity in the seizure focus of abnormal neurons is sufficiently intense it may spread to other areas of brain even the contralateral hemisphere resulting in a secondarily generalized seizure.

GOALS of LONG TERM MONITORING

One uses LTM when: the diagnosis is uncertain, or in cases where despite aggressive attempts with multiple medications the patient has failed to respond and continues to have seizures. The primary goal is to determine whether the patient’s symptoms are epilepsy and if so what type. Based on the type one can then determine whether the patient is best served by medical therapy, surgical therapy or an alternative therapy such as vagal nerve stimulation.

TECHNIQUE of LONG TERM MONITORING

Long Term Monitoring refers to the technique of performing continuous 24 hour EEG with simultaneous closed circuit television (CCTV). The data is collected on a computer and reviewed to establish the clinical and electroencephalographic signature of the seizure. Because the data is collected 24 hours a day it is not possible to review every minute of the recorded information. One must review those parts of the recording most likely to yield information. The epochs of interest are identified in three ways.

As the information is collected by computer the EEG technologist will regularly review the recorded information for evidence of seizures. A subset of the previous 24 hours of recording is edited and read daily by a neurologist. Additional information on the clinical nature of the seizure is provided by the observations of the nursing staff.

When a seizure occurs the nurse’s first obligation is to protect the patient from potential injury. After determining that they cannot injure themselves the nurse notes the time and systematically records information on the patient’s movements, alertness, ability to comprehend, speak and remember. The nurse must do this all the while avoiding blocking the view of the patient on camera. A check list of observations by the nursing staff is as follows:

Check list for clinical evaluation of seizures:

Patient:
Date:

Time            Onset            Cessation

Response to verbal stim.

• Appropriate
• Inappropriate
• None

Orientation

Person

Place

Time

Able to recall a phrase:

• Yes
• No

Response to physical stimuli:

• Correctly followed commands
• Incorrectly followed commands
• Did not follow commands

Facial movements:

• rhythmic
• arrhythmic

Eye position/movements:

• rhythmic
• arrhythmic

Head position/movements:

• rhythmic
• arrhythmic

Limb position/movements:

• rhythmic
• arrhythmic

This information both the EEG and the clinical observations are used to determine whether the events of interest are epilepsy or not. At times it is necessary to "encourage" the seizures because one cannot continue to monitor a patient for weeks. Sleep deprivation is a common technique for inducing seizure activity. The number of seizures necessary to make a diagnosis differs depending how clear to EEG and clinical information is. Loose electrodes, muscle artifact, patients off camera or blocked from the video camera by personnel are all common problems which interfere with good data collection. Long term monitoring is an elective procedure. Patients are generally scheduled for admission on Mondays. If they are taking antiepilepsy medication (AED) they start to reduce the dose over the previous weekend. On or prior to admission they will have an MRI brain scan often with and without contrast and multiple slices through particvular regions of interest. When admitted the patient has a standard EEG as a basis for comparison and is then hooked up to the head set in their hospital room. The head set is hard wired to the computer. A CCTV is present in the room allowed simultaneous viewing of the patient and their EEG. Both the EEG technician and the nursing staff can monitor the patient using remote TV monitors placed at the nursing station and in the EEG work room. The nurses and EEG staff can remotely move the camera to better view the patient. An IV access is usually secured. Most patients will not require IV fluids but if seizures do not stop quickly or come in clusters with no recovery between events, the nursing staff will need to have rapid IV access to administer medication. Patient rooms are otherwise quite standard having oxygen and suction available.

Once enough seizures have been recorded to make a diagnosis the EEG recording can stop. If the diagnosis is not epilepsy AED are generally no longer prescribed and appropriate consultation with other specialties are arranged. If the seizures appear to be best managed medically AED will be started before hospital discharge. If it appears as though the patient can best be managed surgically additional information is then required.

Potential for Surgical Therapy

Epilepsy surgery is actually an ancient concept. Many cultures used trephination, drilling small holes in the skull to release "evil spirits". It was practiced by natives of Meso-America and ancient Egypt. In he late 19^th century surgeons began to remove traumatically injured brain tissue and with better knowledge of localization remove functionally abnormal cortex in treat epilepsy. Odd though it may seem at first the area of brain involved in generating a seizure is "non-functional". These neurons are no longer contributing in a positive way to the patient’s function. If one can identify the area in which the cells are located, and if this area is not involved with mobility or speech it can usually be removed with little in the way of adverse consequences to the patient.

Candidates for epilepsy surgery are persons with localization related or partial epilepsy. They must have tried and failed to respond to several AED. Ideally they should be free of serious psychological difficulties (psychosis or suicidal ideation). Age and mental abilities are not contraindications.

Persons fitting these characteristics who would be willing to consider surgery if a surgical focus can be found can then undergo a presurgical evaluation. This includes LTM similar to that described above. At times additional electrodes may be used to better identify the seizure focus. In addition to the EEG data which will "prove" that there is an epileptic focus, one also examines the focus with neuroimaging (MRI, PET, SPECT), Language lateralization and neuropsychometric testing.

-

One must not only prove that the epilepsy is localized in onset but that removal of this area will not result in a serious neurological deficit for the patient. One needs to know what hemisphere is dominant for language. Conventually a Wada test using amytal to transiently put half of the brain to sleep while asking the patient to recall and identify verbally a series of objects or words. Newer techniques called functional MRI may soon replace this technique.

MRI, PET or SPECT scanning is used to identify a lesion scar or tumor in brain.

A neuropsychologist will perform a series of tests to determine whether there is evidence of damage in one area of brain.

When all of the data is convergent the EEG, neuroimaging and neuropsychological testing all point to abnormality in the same area of brain the likelihood of surgery resulting in a successful outcome.

The best results occur in persons with temporal lobe epilepsy (TLE). Persons undergoing surgery for this disorder have an 85% chance of improvement. There are subtypes of TLE. The largest subgroup is mesial temporal epilepsy due to hippocampal sclerosis. Persons with this epilepsy type have a classical syndrome. A history of febrile seizures in childhood, followed by a seizure free interval, followed by development of partial seizures with an aura (frequently a rising epigastric sensation) usually in adolescence. The EEG reveals ictal temporal lobe abnormalities. The MRI atrophy of the ipsilateral temporal lobe. Neuropsychological testing reveals memory deficits and on pathology one finds cell loss in the hippocampal region of the temporal lobe.

Surgery for extratemporal epilepsy has not been as successful as for TLE. Extra temporal epilepsies can occur in any region of brain. The abnormalities can be classified as: tumor, malformation, ischemic, traumatic or infectious. With most of these abnormalities it is not the injured tissue but the excitability of surrounding cortex that is responsible for the seizures, hence the difficulty in obtaining control by simply removing the lesion

Bibliography

Hauser WA, Kurland LT. The epidemiology of epilepsy in Rochester Minnesota, 1935 through 1967. Epilepsia 1975;6:1-66.

Hauser WA, Hesdorffer DC. Incidence and Prevalence. In: Hauser WA, Hesdorffer DC. Epilepsy: Frequency, Causes and Consequences. New York: Demos Publications, 1990:2.

Hauser WA, Rich SS, Jacobs MP, Anderson VE. Patterns seizure occurrence and recurrence risks in patients with newly diagnosed epilepsy. Epilepsia 1983;24:516-517.

Shinnar S, Berg AT, Moshe SL, et al. The risk of recurrence following a first unprovoked seiure in childhood: a prospective study. Pediatrics 1990;85:1076-1085.

Hopkins A, Garman A, Clarke C. The first seizure in adult life: value of clinical features electroencephalography and computerized tomographic scanniung in prediction of seizure recurrence. Lanceet 1988; 1:721-726.

Hauser WA, Annegers JF, Kurland LT. Prevalence of epilepsy in Rochester Minnesota. 1940 - 1980. Epilepsia 1991; 31:429-445.

Hauser WA. Prognosis of people with unprovoked seizures and epilepsy: when to start and stop antiseizure medication. American Academy of Neurology Annual Meeting Seattle, Washington May 1995.

Van Donselaar CA, Schimsheimer RJ, Geerts AT, Declerck AC, Value of the Electroencephalogram in Adult Patients with Intreated First Idiopathic First Seizures. Arch Neurol 1992;49:231-237.

Hirtz DG, Ellenberg JH, Ne3lson KB. The risk of recurrence of nonfebrile seizures in children. Neurology 1991;41:965-972.

Camfield PR, Camfield CS, Doolet JM, Tiblles JAR, Fung T, Garner B. Epilepsy after a first unprovoked seizure in childhood. Neurology 1985;35:1657-1660.

Janz D, Christian W. Impulsive petit mal. Deutsche Zeitschrift Nervenheilk. 1957;176:346-386.

Hauser WA, Rich SS, Annegers JF, Anderson VE. Seizures recurrence after a 1st unprovoked seizure: an extended follow-up. Neurology 1990;40:1163-1170.

Annegers JF, Grabow JD, Groover RV, Laws ER, Elveback LR, Kurland LT. Seizures after head trauma: A population study. Neurology 1980;30:683-689.

Annegers JF, Hauser WA, Beghi E, Kurland LT. The risk of unprovoked seizures after encephalitis and meningitis. Neurology 1988;38:1407-1410.

So EL, Annegers JF, Hauser WA, Whisnant JP, O’Brien PC> Risk of epilepstic seizures after cerebral infarction: A population based study. Epilepsia 1993;34 Suppl 6:29.

Wallace SJ. The child with febrile seizures. Wright, London 1988.

Shinnar S, Berg AT, Pr=tachewich Y, Alemany M. Sleep state and the risk of seizure recurrence following a first unprovoked seizure in childhood. Neurology 1991;41:971-972.

Gowers WR. Epilepsy and other chronic convulsive diseases. Churchill, London 1881.

Elwes RDC, Johnson AL, Reynolds EH. The course of untreated epilepsy. Br. Med. J. 1988;297:948-950.

Brorson LO, Wranne L. Long term prognosis in childhood epilepsy: survival and seizure prognosis. Epilepsia 1987;28:324-330.

Klenerman P, Sander JWAS, Shorvan SD. Mortality of epilepsy: a study of patients in long term care. J. Neurol. Neurosurg. and Psychiatr. 1993;56:149-152.

Leetsma JE, Walczak T, Hughes JR. A prospective study of sudden death in epilepsy. Ann. Neurol. 1989;26:195-203.

Elwes RDC, Johnson AL, Shovron SD. The prognosis for seizure control in newly diagnosed epilepsy. N. Eng. J. Med. 1984;311:944-947.

Beghi E, Tognoni G. Prognosis of epilepsy in newly referred patients; a multicenter prospective study. Epilepsia 1988;29:236-249.