Methods of examination

A full description of the symptoms as experienced by the patient is always very important, no matter what neurological illness is in question. It can help the doctor make the right diagnosis.

All people with seizures are given a full neurological examination to find out if there are any signs of brain disease which could be causing the seizures. If the neurological examination does not reveal any abnormalities, the patient's epilepsy may be of the idiopathic type, where the cause is not known. During the neurological examination, which causes no discomfort, the patient's nervous system is checked. The nerves which control the various senses, sight, hearing, touch and smell, the so-called cranial nerves, and the nerves which lead to other parts of the body, the chest, arms, legs, etc. are examined. The sense of touch is tested, as well as muscle tension (tonus), muscle power, reflexes and coordination.

The person's memory and concentration are evaluated, as well as his actual physical condition. If abnormalities are found during the neurological examination, the cause of the epilepsy can in some cases be established straight away. In other cases it may be necessary to undertake more tests to find the cause (see below). When the cause of seizures can be found the epilepsy is said to be symptomatic. When brain disease is suspected it is important to make comprehensive tests. This is in order to be able to treat the underlying brain disease, and not just the seizures. Antiepileptic drugs control only the symptoms (the seizures). They do not remove the cause of the epilepsy. The fact that many forms of epilepsy tend to disappear with time is not due to the drug treatment, but to the "natural history" of epilepsy.

The following examinations may be undertaken:

The activity of the innumerable nerve cells of the brain causes constant emission of a weak electrical current. In the normal brain this takes place in a regular, orderly pattern which enables normal functions to be carried out, for example, talking. Even in sleep the nerve cells are working and sending out impulses.

This electrical activity can be recorded by placing electrodes on the scalp and amplifying the resulting signal about 1 million times.

Recording the EEG

About 16-20 electrodes are usually used, placed in a pre-determined pattern on the scalp. The electrodes can either be small metal plates which are stuck to the scalp by means of a sticky paste, or they can consist of small needles which are inserted in just under the surface of the skin. Needles are usually chosen, as they give the best results.

During the actual recording the person lies and relaxes, with eyes closed, in a dark room for about 20 minutes. The reason for having closed eyes is that eye movements and visual stimulation can alter the curve of the recording. It is important that the EEG should be taken under similar and standardized conditions.

The normal EEG

EEG in epilepsy

Epileptic seizures are caused by a simultaneous, synchronized discharge of impulses from a smaller or larger group of nerve cells. These are visible on EEG as paroxystic abnormalities or "spikes". Another abnormality seen in connection with epilepsy is so-called low frequency activity where the number of waves is less than 8-12 per second. This may be seen just after an epileptic seizure. It can also be constantly present on the EEG and be a sign of an underlying brain disease as the cause of the epilepsy.

In persons with generalized seizures all EEG waves will be abnormal during the seizures, which involve the whole brain. In a partial seizure only the waves which come from the area which triggers the seizure, the so-called epileptic focus, will be abnormal.

EEG changes with age, in that a certain "maturing" of the brain takes place. The wave patterns from children and adults are not at all alike. Changes which are quite clearly abnormal in an adult can be found in a child's EEG without giving any suspicion of abnormality.

Interpretation of EEG

EEG is a very approximate investigation. There is a sliding scale of what is looked upon as normal and abnormal. About 10% of the population has an "abnormal" EEG, without having any neurological defect. EEG findings should therefore be considered together with a person’s clinical condition.

The diagnosis epilepsy is made by combining the clinical symptoms (seizures) with characteristic EEG abnormalities. "Healthy" relatives of a person with hereditary epilepsy may show changes typical of epilepsy in their EEG, without actually having seizures. They do not have epilepsy.

EEG and control of treatment

EEG recording plays a large roll in diagnosing epilepsy. Whenever epilepsy is suspected an EEG will be taken. On the other hand EEG cannot be used to control the effect of the antiepileptic treatment. The treatment can be completely successful and give freedom from seizures, without the EEG being more "normal" than it was before drug treatment started. Conversely, it can also be seen that an EEG has normalized despite frequent seizures. EEG is therefore of no use in the control of treatment. The only exception to this rule is children with absences. In that case there is a close connection between how abnormal the EEG is and how many absences the child has at a particular time.

As an EEG investigation only takes about 20 minutes, it is very rare seizures occur during an EEG recording. Fortunately persons with epilepsy frequently show abnormalities in their EEG between seizures. If epilepsy is suspected and this cannot be confirmed by EEG, there is every reason to repeat the investigation.

Provocations

Another possibility is to take an EEG with some sort of provocation. In people with epilepsy this tends to bring out epileptic abnormalities in the EEG recording.

Hyperventilation, rapid breathing for a few minutes, is a form of provocation which often causes abnormalities, particularly in children with absences. One can sometimes provoke absences by this method. If a child is referred to the clinic on suspicion of having absences, the diagnosis can be made in many cases without using EEG, if hyperventilation is sufficient to trigger absences. Breathing in and out fast for some minutes provokes seizures because expiration of carbon dioxide alters the body's balance from acid to alkaline. This is of no importance in a healthy person, but in a person with epilepsy it is common knowledge that acidity in the body limits seizures occurring. In contrast, a change to the alkaline side will often provoke seizures in a person with epilepsy.

Photic stimulation can also induce EEG abnormalities in a person with epilepsy. During the EEG recording, a light flashes into the person's eyes at different frequencies, from a few flashes per second to up to 60 times. Some people with epilepsy are sensitive to this kind of provocation. This causes abnormalities to appear on the EEG, which can be accompanied by a feeling of discomfort and in rare cases even give rise to a seizure. It is nearly always persons with generalized epilepsy who are sensitive to this form of provocation. It is called photosensitive epilepsy.

When partial epilepsy is suspected, it may be an advantage to record an EEG when the person is asleep. Sleep has a tendency to provoke localized (focal) abnormalities in the EEG.

The patient is asked to go to bed late the night before, so that he will find it easier to fall asleep during the EEG recording. A mild sleeping tablet may also be given to be sure the person falls asleep. The patient should not drive home himself after the test because of having had the sleeping medicine. Sleep EEG after sleep deprivation for a whole night is also suitable to use where seizures occur on waking (primary generalized epilepsy).

This investigation has many names. Oxford refers to the brand name of the technical equipment often used.

The person is equipped with a small battery-driven tape recorder which can be taken home, and a number of electrodes fixed to the scalp. The tape records the EEG at a very slow speed. The person can meanwhile move about freely. The recorder has a button which can be pushed if the person feels a seizure coming on during the recording. Playback takes place at high speed, on a television screen, and where one can review a 24 hour recording in the course of about an hour and find possible abnormalities.

Video-EEG combines a video recording of the person with a simultaneous recording of EEG. This method of investigation gives the possibility of seeing the seizures.

A video camera films the person, while EEG is recorded and stored electronically. A normal TV screen can be used for viewing, both during the recording and afterwards. The picture of the patient fills half the screen, the EEG recording the other half.

It is an investigation that calls for a little higher level of technical resources, because it calls for the constant presence of staff to watch the person being investigated. The person being investigated has fewer possibilities of moving around. To keep within the video camera's range, he has to stay in one room. It is possible to record in the dark with the help of infra-red lighting, which does not disturb the subject.

Video-EEG has played a large part in our understanding of what the individual seizures look like. It has given doctors the possibly of "witnessing" many seizures. Before these techniques were developed most seizures went by unobserved. Only a minority of doctors ever saw an epileptic seizure. Video-EEG has therefore been of great importance in the development of the classification of seizure types. It can also be used in teaching, as particular seizures can be repeated as many times as required.

In the everyday situation, the investigation plays an important role in the making of a correct diagnosis in cases with seizures of uncertain type.

Video-EEG is quite crucial in the localizing the seizure's starting point (focus) in persons on whom surgical epilepsy treatment is being planned. A precondition for taking video-EEG is a certain frequency of seizures, otherwise it could be a very time consuming investigation!

X -ray examinations of the cranium, as used in the past, have now been entirely replaced by CT-scanning (computer assisted tomography). In this examination slice-shaped, cross-sectional X-ray pictures of the brain are produced. This is possible in that the x-ray pictures are sampled by a computer.

The CT-scanning apparatus looks like a large washing machine. The person lies on a moveable couch, with his head inside the apparatus. During the examination the apparatus moves slowly round the head. It uses only a few seconds to take each cross-section. It is very important that the head is kept quite still during these "takes". Semi-conscious or restless unconscious patients in some cases would need to be anesthetized to make sure that they lie still. The same applies to small children. 4 to 5 series are taken from different positions.

If there is a suspicion that the patient has a tumor, a malformation of the blood vessels, or an accumulation of blood in the head, the procedure will be repeated after a contrasting medium has been injected into a vein in the arm. By comparing the pictures with and without the contrast medium, a very exact diagnosis can frequently be made. Brain tumors, malformations of blood vessels, cerebral thrombosis, and many other conditions can clearly be made out on the pictures. X-ray radiation from CT -scanning is very low, much lower than in the case of a normal head X-ray. The examination lasts about 20 minutes in all, and is completely safe and without discomfort. If one is very nervous prior to the examination, a little diazepam can be given as an injection in the rectum.

MRI (magnetic resonance imaging)-scanning also produces cross-sections of the brain, The apparatus looks very like a CT-scanner. The difference is that it is not X-rays which are used, but a powerful magnetic field, with a strength many times in excess of that of the earth's magnetic field. This examination also calls for the person to lie still while it is being carried out. It takes about one hour in all. There is no discomfort, apart from the fact that people with claustrophobia might find it unpleasant to lie in the scanner which is deeper than the CT-scanner. The whole body, apart from the feet, is rolled into the machine on a couch. Loud knocking sounds occur during the examination. A person who has had metal operated into his body cannot be MR-scanned. This is because the powerful magnetic field can "tear" the metal parts out of the body. All watches, glasses and other metal objects should be removed beforehand. On arriving for the test, one goes through a metal detector, just like at an airport.

The advantage of MRI-scanning is that it can show up smaller changes in the brain than a CT-scanning can. Small malformations, or quite small tumors can best be seen on a MRI-scanning. MRI-scanning is therefore always used as part of the preliminary investigative program before a planned operation for epilepsy. MRI has almost replaced CT in the investigations of persons with epilepsy.

In a SPECT-scanning (Single photon emissions computed tomography) the blood-flow through the brain is examined. The examination is carried out by injecting a very small amount of radio-active tracer into one of the blood vessels of the arm. From here it is transported to the brain, where it is "bound". How much of it is "bound" depends on the speed of the blood flow in each area. Pictures of the brain (cross sections) are then taken by an apparatus that resembles a CT-scanner. The pictures of the brain develop different colors in the different areas, depending on how much different radio-active matter was present.

The examination can be carried out both during a seizure and at other times. The radio-active material is immediately "bound" in the brain and stays there for a few hours. Therefore it is possible to give an injection during a seizure and later transport the person to the scanner and record the pictures. The investigation is without any form of discomfort.

SPECT-scanning is carried out nearly exclusively on people who are being considered for epilepsy surgery. It can help in localizing the part of the brain (the focus) which triggers the seizures.

It is now known that an epileptic focus "rests" between seizures. This means that between seizures, interictally, a reduced blood flow is seen in the area. On the other hand, when the nerve cells trigger a seizure, they need to increase their metabolism considerably, and need a lot more blood. Therefore during the seizure, in the ictal period, an increased blood flow can be seen. In this way the investigation can help to localize the area in the brain which is responsible for starting epileptic seizures.

Location of the speech center

If one is right-handed, the speech center will normally be in the left hemisphere . Most left-handed people also have the speech center on the left side, but in a minority of cases it may be on the right. Lastly, there are people who have their speech center in both hemispheres. It is therefore necessary to find out where the speech center is located before an operation for epilepsy.

A little plastic tube (catheter) is fed into an artery, after being inserted in the groin. It is pushed in so far that it can be placed alternatively in each of the two large arteries in the neck which supply the two hemispheres of the brain with blood. Then a anaesthetic drug, which lasts for only a short time, is injected through it. In this way each hemisphere is paralyzed in turn for 5 to 10 minutes. This leads to a one-sided paralysis of arm and leg. When the hemisphere where the speech center is located is affected, the person will be unable to talk for a short time. This is shown by the person not being able to put names to pictures or objects shown to him while the anaesthetic is working.

Application

Neuropsychological tests can be used in many ways. If brain damage has occurred, they can show to what extent. In the case of a localized brain disease, they may help to localize the lesion.

The investigation of dementia is important to find out if the person is capable of carrying out a job, if there is potential for rehabilitation, or if an disable pension should be recommended. As the tests give an indication of the person's abilities in many different areas, they can be of importance in choosing a future job.

The psychologist can also help in solving problems which may arise at home or at work. Good results can be arrived at where there is close contact between patient, psychologist, social worker and doctor.

Finally, psychological tests are carried out on all persons who are thought to be likely candidates for epilepsy surgery. If an operation is being considered in one temporal lobe, it is important to discover if the other temporal lobe is functioning normally. This is a precondition for surgery. People can manage perfectly with one temporal lobe. Without both temporal lobes, memory is completely lost. If one temporal lobe is operated on and the other does not function normally, serious problems will occur. It is therefore a prerequisite that the temporal on the opposite side to that which is to operated on, functions normally.