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EEG (Electroencephalogram)

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The factual information on this page has been approved by the EEG department of a UK hospital.

 

Introduction

EEG is short for electroencephalogram. It is the name of a commonly performed and important investigation that most people suspected of having epilepsy will have. This test is only one part of the investigation into diagnosing epilepsy. Further information on how epilepsy is diagnosed can be obtained through Epilepsy Action.

The EEG test

Generally, an EEG is carried out at an outpatients appointment at the hospital. The EEG records brainwave patterns from the continuous tiny electrical signals coming from the brain. The EEG machine then magnifies the size of these signals, without affecting the brain, so that the information can be recorded on paper or computer. This can then be interpreted by the EEG consultant (neurophysiologist).

During the Test

The EEG, which usually lasts around one hour, is painless, with the minimum of discomfort. You will be asked to sit or lie down on a couch and to relax. It is important to keep still during the EEG as body movement can be recorded, making it difficult for the specialist to interpret the results of the test. Electrodes are placed on the scalp by way of a cap or a special glue or paste and connected by wires to the EEG machine.

During the session you may be asked to open and close your eyes. You may also be asked to breathe deeply for some minutes, because this could reveal or increase abnormal brainwave patterns. You may also be asked to look at a flashing light to show if this triggers epileptic activity. If the flashing light produces an abnormal pattern during the EEG, the light is immediately switched off by the staff, so there is little risk of further epileptic activity developing.

Medication

There is generally no need to stop your anti-epileptic drugs before having an EEG, unless your doctor advises you to do so. Never stop your medication except under medical supervision, as this could trigger uncontrolled seizures.

Interpretation of the EEG

The EEG gives information about how the brain works, but not about its structure. A normal EEG does not exclude epilepsy because between seizures the brainwave patterns could be normal. An abnormal EEG does not necessarily indicate that someone has epilepsy, because abnormal patterns can occur for other reasons.

During an outpatient's standard EEG there may be no abnormal activity occurring in the brain, so several EEGs may be needed. Sometimes it can be helpful to record the EEG at times when seizures are more likely (such as, in some women, before the menstrual cycle).

If you have generalised seizures (absences, primary tonic-clonic seizures, myoclonic jerks), EEG abnormality is usually seen on both sides of the brain.

If you have partial (focal) epilepsy, abnormality may be seen in one or more specific areas of the brain and there may also be some abnormality of the background rhythms.

Some people have epileptic activity in their brain that does not show itself as a seizure but which may be picked up on an EEG. In this case, it may be necessary to repeat EEGs from time to time, so that doctors can see what progress is being made and decide on treatment.

Children and the EEG

The interpretation of a child's EEG recording is more difficult than an adult's, because the EEG changes during the childhood years. An adult pattern is usually developed by the age of 15 years. As the EEG pattern in infants and children can vary considerably, an abnormal EEG can be over-reported by those unfamiliar with the EEG patterns of children. The phrase ‘compatible with epilepsy' (similar EEG patterns to those seen in epileptic seizures) is often used. However, it is said by some professionals that this is meaningless, as any finding could be ‘compatible with epilepsy'. This highlights the need for a professional interpretation from a neurophysiologist, experienced in interpreting EEGs in children.

 

Other ways in which the EEG is used to detect epileptic activity

Sleep EEG

If an EEG recorded during waking has not shown any epileptic activity, an EEG during sleep may be recommended. This is because everyone's brainwave patterns change dramatically during sleep. Sleep can also make the brainwave patterns between seizures more obvious. This extra information can help with diagnosis.

A sleep EEG is also usually recommended when someone has seizures during sleep only. It may be carried out in hospital, or at home using an ambulatory EEG (see below).

Sleep Deprived EEG

Depriving someone of sleep can cause changes in the electrical activity of the brain. Recording these changes on an EEG can provide the doctors with important information. Sleep-deprived EEGs are often used when a routine EEG has failed to show anything useful.

The ambulatory EEG

The diagnosis of epilepsy is made from an account of the seizures given to the doctor personally and/or by someone who has actually seen the seizures. The results of any tests are also taken into account. Where there is doubt about the nature of the seizures it is possible to record the EEG over a period of one or more days, using a small portable EEG recorder which is worn on a waist belt. Recording can thereby be made during normal daytime activities, and during sleep.

When you have a seizure the EEG recorder will record the event which can be viewed later on a special machine in the EEG laboratory. You will be asked to keep an account of daily activities, so that they can be related to the EEG recording made at the time. This investigation is called ambulatory EEG monitoring.

Video-telemetry

Where there is doubt about a diagnosis of epilepsy, or where the type of seizures someone experiences is unclear, video-telemetry can be helpful. This is a test that uses a video camera linked to an EEG machine. The camera will visually record your movements and at the same time the EEG machine will record your brainwave pattern. Both the video and EEG are stored onto a computer that can be reviewed once the test is finished. The consultant will be able to see any episodes/seizures that you may have had, as well as any changes in your EEG at that time. The test is often carried out over a number of days in order to increase the chances of recording one of your seizures.

Conclusion

While the EEG cannot, in itself, diagnose epilepsy, it is a useful tool in helping with the diagnosis and treatment of epilepsy.

See also:

 

Further information about the EEG is available from Epilepsy Action by using the Email Helpline or if you live in the UK, by phoning the Freephone Helpline on 0808 800 5050.


We can provide references and information on the source material we use to write our epilepsy advice and information pages. Please contact our Epilepsy Helpline by email at helpline@epilepsy.org.uk.
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Comments

I have recently had an EEG and my GP tells me it is abnormal. I then attended a physician who says while it is abnormal he does not feel it is anything to worry about. As a followup I was sent for an MRI, the results of this have not come back yet. The physician says that he is 99% certain that this test will be normal. I am still worried as to why the EEG read abnormal in the first place.

Can anyone give me advice on this?

Submitted by Anne Murray on 20 December, 2008 - 23:10.

Some people can have an abnormal EEG. This does not necessarily mean someone has epilepsy, because abnormal patterns can occur for other reasons. However, it might be epilepsy. You could discuss this with your doctor, but they may not be able to give you any information until your investigations are complete.

Mark @ Epilepsy Action

Submitted by Mark@Epilepsy Action on 23 December, 2008 - 15:40.

We are taking our 24 yr old daughter down to Kings to discuss the possiblilty of telemetry leads being inserted in to her brain. She has had eegs performed numerous tiems. Has anyone any information about this to guide our questioning or any experiences, good or bad for when we go down for the outpatient appointment?

Submitted by karen radley on 16 January, 2009 - 14:49.

My child is 8 and had a unprovoked seizure lasting a couple of minutes a few days ago. It was treated by paramedics and then emergency room Doctor. They all took it pretty lightly and said it was most likely onset by video game playing since he had been playing games on the computer just before he seized. We scheduled MRI and a EEG a couple days later as the ER was very busy that day and said it would be better to do those on our own. They took some blood as well. It looked as though they were right about it being video game related because all tests were comming back normal until the last one which is the EEG. It came back abnormal and I have no Idea how serious that is. My Dr. didn't tell me, the nurse did, and they said they would get back to me when the nuerologist appt. would be and I didn't hear back today. Now I have to hope they can get him in right away tomarrow? some one on some site said they had to wait four months. Thats crazy what if it is a brain infection, shouldn't it be caught right away. Is there anything that can give a false abnormal. If it truely is abnormal will they know why by the current test or will they have to do more tests?

Submitted by Melissa Haworth on 23 January, 2009 - 06:21.

I have done EEG yesterday and told me that is not yet the time to stop the medication I am using tegretol 200 in the morning and 400 evening ! It has been five years since my last attack yeton medication just am taking now diazepam to 6mg a day can someone tells me why EEG is not right ?! if i havent got attack for 5 years ?!

Submitted by Angel on 30 January, 2009 - 17:28.

I recently had an eeg due to four instances of aura-like symptoms (deja vu), feeling faint, then altered state of consciousness for about 15 minutes, and the eeg was negative so the neurologist thinks it may be caused by low blood pressure and referred me back to a cardiologist.

I looked up causes of deja vu, and can find NOwhere a link between heart and that symptom. So, the eeg may not pick up if I am having seizures??? How effective has it been in diagnosing you or a family member?

Submitted by Carla on 4 February, 2009 - 23:40.

The doctor is concerned that you may have neurocardiogenic syncope. That is why he is referring you to a cardiologist. This condition is low blood pressure and causes you to have seizure like episodes that mimic epilepsy.

Submitted by Rebecca on 12 February, 2009 - 00:07.

I had an EEG earlier this year and it was abnormal. Specifically, slow activity in the right posterior quadrant with sharp waves. I have no idea what this means and only know that I have been having seizures since last November. The neurologist has said that this makes it seem more likely that the attacks are epileptic in nature, but I had a normal MRI. Does this mean that I do have epilepsy? The neurologists mentiones commencing an anti-epileptic medication but I feel like I'm in limbo at the moment...I can't place myself under any standardised definitions that I've seen here and I'm desparately frustrated that I have no answers that will allow me to start getting on with my life again. Any advice would be appreciated.

Submitted by Nina on 9 March, 2009 - 16:01.

I have had an EEG and MRI test. My EEG has come back with 'some features of epilepsy' and I have not yet had the results of my MRI scan. My new neurologist now wants me to have a sleep deprived EEG scan. I am so glad that after 17 years of having seizures and days at a time not having the strength to even clench my fist so that I can hold a pen, my symptons are now being taken seriously. Having said this I am really worried that I won't be allowed to sleep in the position I can only sleep in. I sleep with all my weight on my left hand side (my fits occur on the left hand side of my body) so that if anything happens in my sleep my weight hopefully stops it. Can anyone tell me will I be allowed to sleep on my side? During my EEG and my MRI My left arm, hand and leg were jerking and the feeling was scarey, and I like to be in control of that jerking all the time hence my sleep position.

Thanks for any replies
Kate

Submitted by Kate on 27 March, 2009 - 20:31.

My son had his first seizure at 14. He had a few during the night and then one during an EEG. (Although he said he had twitching in his arms throughout the day for several months. His neurologist diagnosed it as a complex partial seizure and started him on trileptal. He was seizure free for 2 years and taken off meds. 6 months later he had another seizure and then another 4 nights later. He's back on trileptal. His seizures start in his right arm and then generalize to a tonic (freeze and lose breath and consciousness but no shaking) seizure. He had a normal EEG while sleeping this last time. I'm reading about seizure types and it appears to me he has juvenile myoclonic seizures but he wasn't diagnosed with that and it didn't show up on his EEG. Can he have Juvenile Myoclonic seizures and have a normal EEG? Also, if he has seizures at night will they most likely always occur at night?

Submitted by Tess Lorraine Smith on 2 April, 2009 - 04:11.

I am now 47 and have lived my life with epilepsy

i started with epilepsy when i was about 11 and was given medication from that time on. The start of the epilepsy corresponded with the fact my periods started and i set a chip pan on fire and the hospital blamed the epilepsy on the accident saying it was delayed shock. Over the years i coped with the medication carbamazapinem, epilem phenytoin epineuten getting various side effects such as headaches and sleeping on my school desk. I met my man got married the thought of having a baby gave me mixed thoughts would i cope? can i have a baby.? The seisures continued but we asked the doctors. They decided to take me off my medication and i fell pregnant. Throughout my pregnancy i had no attacks again changes in the body hormones. Nine months later i had a ceseran as the hospital decided the birth would be too risky. As soon as i had my son my fits started again. i was again giving medication and went on bringing my son up, me having fits.. About 5 years ago my fits became less and eventually stopped my consultant took me off my medication. I have had a couple of occasions where i have felt "out of sorts" Not knowing i had done something or a bit forgetful my monthly cycle is less timed and i am waking up in bed at night sweating again a change in my hormones. Is it time to say women with epilepsy can be linked with their hormones etc. I have been driving and feel on top of the world to be independant passing my test and advanced test waiting 45 years to do it. I feel fine except for this feeling of loss can medication help i dont want to go back to been labelled an epileptic every one panics i think they need the medication to cope not me

Submitted by mandi on 15 April, 2009 - 23:07.

Dear everyone,
I am desperately seeking assistance. My Nuerologist specialist has done a recent sleep-deprived E.E.G. study on me. During the flashing lights I was uncomfortable but she continued throughout the whole process. I didnt have any trouble breathing deeply. The results were abnormal. My doctor told me all that the results meant is my brainwaves are slow during drowsy periods. I was wondering if any one had any information on this. I am trying to get a normal eeg reading for the military. I do not have seizures.

Submitted by Kyle on 2 May, 2009 - 00:49.

I have a 6 year and 3 months old boy.He was a premature baby(20 days) and weighed app 1.8 kgs at birth.He had a seizure 2 years back due to high temperature.An EEG taken at that time revealed NORMAL.Again few days back from now,he had another seizure again due to high temperature.Doctors say that Seizure during high temperature is common for children below the age of 5 and since the boy is 6 years old,another EEG was advised.I hope that the second EEG will reveal normal.Kindly guide whether I should do further diagonise on him and if so what Should I Do.

Submitted by Balaji.K. on 11 May, 2009 - 13:01.

Hiya everyone!.
I just wondered if anyone could give me any advice on my experience...Here's my story..
Im 22 years old and got a pretty stressfull job at times of working with children with autism. One morning a couple of months ago when i was sleeping my partner woke up to the sound of me taking a deep breath and saw that i was half in and out of bed with my body jerking this lasted arouind 40 secs..after the seizure he tried talking to me and i was mumbling back i eventually came around fully a few minutes later with no recollection of what had happend...i'd bit my tongue on both sides cut my foot and bruised my legs..i also had red spots just under my eyes and on my neck. I was then taken to casualty as that was the advice they gave from NHS direct, i had bloods taken and was given oxygen, they said they wouldnt put me on meds as it was my first ever seizure and arranged for an ECG, MRI and EEG tests to be done...My ECG and MRI came back clear but my EEG (the breathing test) came back abnormal when i spoke to the consultant he said this could be why i had a seizure and increases my chance of further ones..problems iv got now..is not being able to drive for a year which really upset me but iv got over that now and Iv not being allowed back to work since as because i work with children, my work wanted to know that i was safe to and got in touch with my doctor with a list of questions which included if i was able to work alone with children (in this job it means a lot of the time) and the doctor said he could see no reason why i couldnt work but that i shouldnt be on my own and should be with other staff...this at the moment is not possible..so im worried as i carnt go back until i can work soley with the children..
I was very stressed and upset the week leading up to having the seizure and im just wondering whether is all connected in some way with my breathing..?
I would just like to know if anyone else has been in my position of if anyone can offer advice thankyou
Rachel

Submitted by Rachel on 19 June, 2009 - 16:40.

i have a scheduled eeg the 23rd of this month .i been having problems with periods of lower levels of conciousness ,a feeling of getting dizzy but nothing actually spinning but i lose control of my whole body i meen i dont start to shake or nothin but i lose all motor function..i cant walk i sound drunk i cant talk right my whole family is concerned...they just put me on topamax because they thought it was a type of migraine but the nero says it can be aura or possible seizures ...does anyone here possibly have the same problem and could it be epilepsy????thanks hope to get lots of replies

Submitted by eric on 19 June, 2009 - 22:56.

Hi Eric

I have been backward and forward the Hospital for over a year and half now, my gp thought that i had, had a stroke and was refered to the stroke clinic, it wasnt long before they realised that I had not had a stroke and that there must be some other problem. My symtom started with numbness down one side I would speak as if I had been drinking all day, total lack of coordination. When I have funny turns as I call them I collapse my hole body feels as if someone has put a lead wait on me and I cannot move this can go on for sometime and has happend offten when I have been on my own, I can now feel the funny turns coming on and I try to fight them but I always loose, after these events I cannot speak I can hear everything people are saying I just cant respond, my husband has called the ambulance a few times but they just treat me like im mental. I dont know if you become very dixlexic after a funny turn as I call them? I know I do. I also find that my reactions are very slow also. I am due to have a electronenecphalogram this week. wish me luck. I hope everything works out for you and it is good that you have the support of your family.

PS: Sorry for any spelling mistakes this is yet another symtom, its not that im stupid

Submitted by Sarah on 6 July, 2009 - 18:31.

hi, i'm going into kings soon for an intracranial mat and was wondering if anyone could share their experience with me as i'm not going to see the surgeon until november, it's driving me mad not knowing what to expect.

Submitted by janine gammond on 2 September, 2009 - 16:53.

I was looking for some information.

My sister (32 yrs old) was on holidays in Cyprus recently and whilst out having dinner felt a bit unwell and light headed. Her friends took her outside and she collapsed backwards hitting her head off the ground. She came round and then passed out again. She started feeling sick so they called an ambulane. After having a scan at the hospital she was told that she had fractured her skull in three places and had a brain haomerage (can't spell it!). After a further scan she was told that she didn't faint she had an epileptic episode which brought on the seizure. She has been in hospital for 10 days and is now allowed to fly home. She has been told to have an MRI and EEG test done when she gets home. Does this mean she has epilepsy? We have heard of another person who has been diagnosed with epilepsy after having one seizure whilst on holidays (this happened on two separate holidays although he has never had a seizure at home)- is this more common than we think. I'd be glad to hear your views.

Submitted by S Kelly on 23 September, 2009 - 19:53.

I had an MRI scan, an EEG which was normal, followed by a sleep deprived EEG which was also normal. After having the tests done I got a letter back from the doctor saying both were normal. I then went for a five day long EEG and an ECG. This time they are sending a letter back saying no major abnormailities, not that the test result is nomral, and that they will review me at their out patient clinic in due course.

I do not know if this means that the test is normal, or simply that there is a small abnormaility.

Can anyone let me know?

Submitted by M McFadyen on 29 September, 2009 - 20:21.

Genetically linked seizure: You're not getting any seizures because of the medication. If you were to stop the medications you may get the seizures back. The thing with seizures is that they cause more seizures to occur in the future, so stopping all seizures from occurring is the best way to treat them. Furthermore, just because you haven't gotten one in 5 years doesn't mean you're cured.

Trauma linked seizure: There's no data for anyone to be on anti-epileptics for more than 7 days. I would taper the dose down and then stop the drugs.

Submitted by Bill on 1 October, 2009 - 03:57.

2 mths ago i collapsed blacked out its never happened before i was taken to a&e were i was addmited to hospital the same evening in hospital i had taken 3 seizures, i was given a vitamin drip and kept in for observation for 3 days .
I still havnt heard anything from the seizure clinic and im at the end of my terrior .

Submitted by diane on 28 October, 2009 - 09:28.

hi i have a eeg scan aboot my fits..can u tell me if i will be forced to take a fit wen i am havein the scan please...

Submitted by SAMUEL JOHNSTON on 3 November, 2009 - 17:23.

Hi Rachel,

Just came over your comment.
I am a Primary School Teacher and have also been signed off work due to recurrent seizures.

Unfortunately,my episodes have been ongoing for 7 years, but it is only these last few months that I have needed time off work as it is starting to impact on my job. As I am sure is the case with yourself, I absolutely love my job and not being able to work is having a huge effect on me.
I have mostly dealt with the cardiologists who up until now felt my collapses were due to 1. Low heart rate ( pacemaker was inserted for this) 2. Vaso vagally sensitve ( put on Beta Blockers) 3. Hypotensive ( felt I was collapsing due to drops in my blood pressure - even though there was no evidence to support this) 4. Hyperventilation - panic attacks ( was sent for a test to the respiratory clinic where it was confirmed that I was not prone to hyperventilation). I never felt any of these suggestions were correct, but I am not a doctor and I am being guded by them.

It was only after a 'seizure' at my doctors surgery, have I now been taken down the Neurology route. I had an EEG which came back normal, but only last week my husband filmed one of the seizures and we managed to take this into the neurologist. Whilst he feels there are some elements which suggest epilepsy there are other features which he'd expect to see that are not there. The good news, is they are now saying it is a seizure and not just a 'faint' which has been suggested in the past.

I am waiting for a referral for Video-Telemetry and a prolonged EEG which will hopefully shed more light on the situation. I also hope to be referred to an epilepsy Specialist.
I totally understand your situation and really hope you can get things sorted out. Why don't you go back to your GP and suggest going to a Respiratory Function Service where they could carry out a hyperventilation assessment? By having all the tests done, you can find out one way or another.

My advice to anyone is not to give up. Whilst I do not claim to be medical expert , I do know my own body and can tell when something is not right. We are all entitled to get the treatment we deserve.
All the best
Lisa

Submitted by Lisa on 24 November, 2009 - 10:42.

Hi,

I'm wondering if anybody can help? In June 2009 after a night out and feeling abit worse for wear the next morning I had my first fit. Needless to say I gave my partner and the rest of my family a fright! Im 28 and this is the first time anything like this has happened.
For about a year before this I had problems with my hearing. My hearing would change and suddenly everything around me went really loud! It was magnifyed and I felt like people were shouting. This happened daily or some times only once a week. Of course I went to the doctors and got my ear cleared as they thought it was just wax ha ha. After looking at various website I hadnt heard of anybody having the same as me! Somebody said it might have been an aura. Has anyone had this problem? or anything simular? Neurologist said he had never heard of this in his life!
Anyway when my first fit happened I was taken to hospital, bloods taken etc and everything was fine & I was told it was prob due to blood sugar levels being low but my blood came back fine! Following this I had 3 more fits (4 in 7weeks).
Got an MRI scan, clear. Then an eeg and this was fine too, everything was normal. I have since been put on lamacital 225mg in the morning and 250mg at night but OMG the side effect were terrible, insomnia, headaches, spots, sore bones etc the list could go on. Finally the effects have gone and I dont notice being on tablest anymore.
After all my fits, tests and being on medication the neurologist said he wouldnt commit in saying it was epilepsy! Is anybody else in the same position or had hearing problems like me??
At the end of the road, hate being left alone, work no that confident with me incase I have another and the big think is no license for a year.

thank

barry

Submitted by Barry Leishman on 15 January, 2010 - 13:48.