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How is an electroencephalogram (EEG) used in epilepsy? What is the difference between ambulatory, Video-EEG and routine EEGs? Dr. Christos Lambrakis

In this issue we sat down with Dr. Christos Lambrakis, epileptologist and Associate Director of the Northeast Regional Epilepsy Group in New York.  He treats patients with epilepsy and seizures at several of our New York hospital units.  We asked him all about Electroencephalograms (EEGs) and how they are used for epilepsy diagnosis.

Dr. Lambrakis was born and raised in New York State. He completed his Bachelor of Science in Biomedical Engineering at Rensaeler Polyteclinic Institute and his Doctorate of Medicine at New York Medical College in Valhalla, New York.  He completed his Residency in Neurology and Epilepsy Fellowship at Westchester County Medical Center, Valhalla, NY. He is Board Certified in Psychiatry and Neurology and in Clinical Neurophysiology.  His research interests include the Vagus Nerve Stimulator (VNS), Deep Brain Stimulation (DBS), and epileptic seizure detection devices.  We asked Dr. Lambrakis to talk to us about a very important tool epilepsy specialists use: the electroencephalograph (EEG).  All patients with epilepsy have had some sort of contact with an EEG so it is important to understand the different kinds of EEG studies there are and what their uses are.

1.  When was the EEG invented and how did it change things for epilepsy patients and epilepsy doctors?

The brain contains billions of cells called neurons that communicate with each other by sending and receiving electrical signals.  In 1924, Hans Berger, a German neurologist, was the first to record these electrical signals and is credited as the inventor of electroencephalogram (EEG).  It took years of further research to understand what these electrical signals meant.  Ultimately, they proved helpful in helping physicians diagnose various seizure disorders.

Many patients with seizures will have regions of their brain that are electrically excitable. With the help of EEG monitoring, physicians are able to detect these areas; this enables accurate characterization of the seizure type.  Determining a patient’s seizure type is of vital importance in helping decide the most appropriate treatment plan.  Thankfully, we have many treatment options these days including anti-seizure medicines, implantable neural stimulators, epilepsy surgery and dietary modifications.  

2.  How does the EEG work?

The EEG records the brain’s electrical activity.  This is accomplished by the placement of electrodes which are small metal discs attached to the surface of the scalp and held in place by a paste.  Electrodes and wires are further secured with gauze and tape wrapped around the head.  These electrodes are very sensitive and are able to detect the small electrical discharges from the brain under the scalp and skull.  This information is transferred to the EEG machine, which is a sophisticated computer that amplifies and modifies the electrical signals.  The information is then displayed on the TV monitor where the doctor interprets the data.  Each line of the data that you see on the EEG screen represents the electrical activity coming from a specific region of the brain.  

3.  When the EEG technologist places the electrodes on the scalp, is she or he following a certain pattern and what is it?

Yes, the EEG technologist is a specially trained professional with expertise in electrode application and maintaining the sophisticated computer systems involved in recording a patient’s brain activity.

The application of the electrodes is a painless process that typically takes between 30 to 60 minutes to perform.  Accurate placement of the electrodes is crucial.  The exact positioning of the electrode is standardized.  The electrodes are placed over the head at specific landmarks and spaced out in such a way that ensures the highest yield in recording the brain’s electrical activity.  This standardization of electrode placement allows physicians across the world to understand results from testing.  

4.  How is an EEG performed in the office different from the EEG testing performed in the hospital?  Why may a neurologist need to request the EEG in the hospital?

A routine EEG performed in the office is typically of shorter duration than an inpatient Video-EEG monitoring (VEEG).  The office EEG typically lasts between 30 to 60 minutes.  The inpatient Video-EEG monitoring can take several days depending on the specific information the physician is attempting to obtain.  

The office routine EEG is a quick screening tool, however, it can often miss abnormalities due to its short duration. The longer the EEG is recorded the greater the likelihood of detecting an abnormality.  Because of this, inpatient Video-EEG monitoring is often the preferred test in the assessment of patient’s with seizure disorders and is the reason a neurologist would request the EEG be performed in the hospital. .  

5.  Why does the epilepsy doctor need to film the patient with the camera while EEG testing is done in the hospital?

By reviewing the video obtained during a seizure the physician is able to see exactly what is happening to the patient during the seizure event.  For example, a patient that has a generalized clonic seizure (often referred to as a grand mal seizure), the shaking of the limbs is obvious, but the physician upon review of the video during the seizure will look for other less subtle clues.  For example, head turning to one side, arm posturing, or preferential jerking of certain muscle group or one side of the body will help the physician better understand the seizure type and where within the brain it is originating from.  Ultimately, this information allows for accurate seizure classification and provides the physician the information necessary to recommend the best treatment options.

Also, seizures might be detected on the EEG that were unrecognized.  On review of the video, the doctor may be able to detect not so obvious phenomenon such as confusion, pauses in movements or brief periods of staring.  

6.  There is another long term type of EEG that can be done at home called the Ambulatory EEG (AEEG).  Share with us what an AEEG is. 

In certain situations, thanks to rapid advances in technology, EEG monitoring can be conducted at home.  The name of this procedure is called Ambulatory-EEG monitoring (AEEG).  This test allows for long-term monitoring of the patient’s brain electrical activity outside of a hospital setting.  

Patients are connected to standard EEG electrodes in the office which then communicate wirelessly to a small laptop computer which they bring home.  Typical recording time is 3 to 4 days during which the patient can move around freely and even leave the house.  Newer AEEG machines even come with video recording capability so that in the event of an episode the physician will be able to see it upon review.

7 When might the doctor ask for EEG testing in the hospital rather than the 3-day EEG testing done at home?

The decision as to what test, either home Ambulatory-EEG or inpatient Video-EEG monitoring would be preferable is really a highly individualized decision made by the physician.

The quality of the inpatient Video-EEG monitoring is generally better as the patient is moving around less and the EEG technicians are closely watching and fixing the electrodes that may come loose.  For the AEEG, the electrodes are carefully placed by the technician in the office, but once the patient leaves and goes home, there is a potential for some loss of recording quality.  This being said, the AEEG more often than not provides excellent quality recordings and the information can be extremely valuable to the physician. Obviously, the AEEG is less of a hardship for the patient as they can move around as they please at home.

Lastly, Inpatient Video-EEG monitoring is preferred in situations where patients are being evaluated for possible epilepsy surgery as recording an actual seizure is crucial for accurate diagnosis.  For some patients due to the relatively infrequent nature of the seizures and the limited time available to record their EEG, the physician may elect to taper their antiepileptic medication in an attempt to provoke a seizure.  This would only be done in the supervised hospital setting of inpatient Video-EEG monitoring .

8.  Do epilepsy doctors receive specialized training in EEG reading and how long does that training take?

Yes. typically, an epileptologist is a neurologist who has undergone additional training specifically in the field of epilepsy. The duration of this training varies but is typically between one to two years beyond the regular training of a neurologist.  The physician can also take a board certification exam in clinical neurophysiology/EEG to further demonstrate their knowledge. Many epileptologists hold dual board certifications in both neurology as well as clinical neurophysiology/EEG.

9.  Can an EEG be useful in diagnosing other conditions or is it only used for epilepsy?

The primary focus of the EEG is to provide important information pertaining to seizures. It can help in distinguishing between events that are epileptic from those that are not.  Not everything that looks like a seizure is a seizure.  Many other medical conditions stemming from cardiac, metabolic, endocrinological and psychiatric conditions can result in episodes that could mimic seizures, but are completely non-epileptic.

As the brain is a busy organ, with many responsibilities, the pattern of electrical activity obtained with the EEG can also provide insight into overall brain function. For example, the information obtained on an EEG could be helpful in the evaluation of patients with various cognitive issues or in children with developmental delays.

Thank you, Dr. Lambrakis for this very clear and useful explanation of all the different types of EEGs that a patient might encounter when being tested for epilepsy.  


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