EEG is the single most useful ancillary test to support the clinical diagnosis of epilepsy, but if used incorrectly it can lead to misdiagnosis and long-term mental and physical health sequelae. Its application requires proper understanding of its limitations and variability of testing results.

In this episode, Katie Grouse, MD, FAAN, speaks with Daniel Weber, DO, author of the article “EEG in Epilepsy,” in the Continuum® February 2025 Epilepsy issue.

Dr. Grouse is a Continuum® Audio interviewer and a clinical assistant professor at the University of California San Francisco in San Francisco, California.

Dr. Weber is the director of adult epilepsy and vice chair of clinical affairs at the St. Louis University in St. Louis, Missouri.

Additional Resources

Read the article: EEG in Epilepsy

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Guest: @drdanielweber

Full episode transcript available here

Dr Jones: This is Dr Lyell Jones, Editor-in-Chief of Continuum, the premier topic-based neurology clinical review and CME journal from the American Academy of Neurology. Thank you for joining us on Continuum Audio, which features conversations with Continuum's guest editors and authors who are the leading experts in their fields. Subscribers to the Continuum journal can read the full article or listen to verbatim recordings of the article and have access to exclusive interviews not featured on the podcast. Please visit the link in the episode notes for more information on the article, subscribing to the journal, and how to get CME.

Dr Grouse: This is Dr Katie Grouse. Today, I'm interviewing Dr Daniel Weber about his article on EEG and epilepsy, which appears in the February 2025 Continuum issue on epilepsy. Welcome to the podcast and please introduce yourself to our audience.

Dr Weber: Hi, thanks for having me. My name is Dan Weber and I'm an epileptologist at Saint Louis University. I direct the adult epilepsy program here and also serve as the vice chair for Clinical Affairs. Been my pleasure to work on this article.

Dr Grouse: I'm so happy to have you today. I read your article. I found it to be incredibly useful as someone who often orders EEG in the general neurology clinic. So, I wanted to start with asking, what is the most clinically relevant message or takeaway from your article that you'd really like neurologists to know? 

Dr Weber: Yes, when I was asked to write this article, I looked back at the previous Continuum on epilepsy and just the general literature. And there's a lot of good articles and books out there on EEG and epilepsy and sort of giving you a primer on what you might see and how to interpret it. So, we wanted to try to go a slightly different direction. This article gives you some of that gives you the background of EEG and some of the basic things that you may see, but the real thrust of it is more about the limitations of EEG in the clinical picture of epilepsy and common things you might avoid. There are some things that we get hammered into our brains in training that aren't always true and there's plenty of examples in the literature to review, and this article sort of tries to encapsulate as many of those as possible in a digestible format. The main takeaway would be that EEG is an extremely helpful tool in the diagnosis of epilepsy, is the best tool we have to help supplement your clinical acumen. But it does not make the diagnosis of epilepsy. And there are certain circumstances when it may not be as helpful as you may have been led to believe in residency.

Dr Grouse: Maybe not the most comforting of messages, but certainly an important one, very important to learn more about this. So, we appreciate that. Can you tell us your decision-making process when deciding whether to order a routine EEG, an extended EEG, prolonged ambulatory EEG, or inpatient video EEG?

Dr Weber: Sure. So, it's a multi-part question because each one, I think, has a different clinical scenario. In the current state, our best data for estimating risk of recurrence after an initial seizure comes with routine EEG abnormalities. So, often I will order routine EEGs in those scenarios. So new patient presentation, new patients coming in with an initial seizure who want to know what's their risk of recurrence. So, risk stratification, I use a lot of routine EEG for, often sleep deprived if possible to increase the sensitivity. If you'd like, the extended EEG does offer higher sensitivity, or you can repeat the routine EEG if the first routine EEG is nonconclusive.

For generally extended EEGs, I tend to order them in my practice if patients have come to see me with a suspected diagnosis of epilepsy but haven't yet had any electrographic confirmation.

Maybe they've already had routine EEGs done in the past, so we'll try to obtain just a little more data. The longer-term EEGs I tend to use in different clinical scenarios, in patients usually who already have established diagnosis or people who have become refractory and we haven't yet confirmed their diagnosis. I tend to do inpatient EEGs in those situations. Ambulatory EEGs I do more when there are certain characteristics of the patient or the patient 's presentation that may not fit well on the inpatient side. Patients who are reliant on substances who can't use while they're inpatient and may have withdrawal effects complicating the stay. Or people who have a strong activation component to their epilepsy where activity really draws it out, certain activities that they do at home that they might not do during the inpatient stay. Those are the sorts of people I'll do ambulatory EEGs on. There are a couple other scenarios as well that come up less commonly, but everything has its own little niche.

Dr Grouse: That's a really helpful review as we sort of think about which way we want to go as we're working up our patients in the inventory setting. Can you tell me a little more about the difference between sensitivity of, for instance, doing maybe two routine EEGS versus prolonged ambulatory EEG?

Dr Weber: Generally speaking, the longer you're recording someone's brain waves, the higher the sensitivity is going to be. So routine EEG is twenty to forty minutes at most places. One of those gives you a certain sensitivity. More of them will give you more sensitivity. And there was a recent study highlighted in the article that compared routine EEGs to initial multi-day ambulatory EEG, and the ambulatory EEG obviously, as would be expected, has a higher sensitivity than either of the routines. So, there may be some cases with that initial evaluation where an ambulatory EEG may be held and we get into that in more detail in the article. But with the caveat, a lot of this article is about limitations, and the data that we have to talk about increased risk of recurrence was based off seeing epileptic form discharges on routine EEG. So you could hypothesize that if you only have one epileptic form discharge in three days on an ambulatory EEG, that may not carry the same recurrent significance as catching one on a twenty minute EEG. But we don't have that knowledge.

Dr Grouse: Getting a little bit more into what you mentioned about the limitations, when is the scalp EEG less useful or limited in the evaluation of epilepsy?

Dr Weber: So, one thing I see a lot in my residence at here and other places where I've worked is, I get them very excited about EEG and they may order it a bit too much. So, if patients have a known, established diagnosis of epilepsy, electrographically confirmed, and they come in with a breakthrough seizure and they're back to their baseline, there's really not a strong reason to get an EEG. We often seem to in the emergency department as part of our evaluation, but we already know what happened to the patient. The patient's not doing poorly right now, so the EEG is not going to give you any additional information. Just like really any test, you should think, what are the possible outcomes of this test and how would those outcomes alter the care of this patient? And if no outcome is going to affect the care of the patient or give you any additional diagnostic information, then probably don't need to be doing that test.

Dr Grouse: This is probably a good segue into asking, what is an area of confusion or common pitfalls that you've seen in the clinical application of EEG and epilepsy?

Dr Weber: So, a lot of times on the inpatient service, we'll get longer-term EEGs for patients who are having spells that are occurrent while they're in the ICU or other places or altered in some way, encephalopathic. And these patients will have their spell, and in my report, I'll say that there is not any electrographic correlate. So, there's no EEG finding that goes along with the movement that they're doing that's concerning for a seizure. And that doesn't always mean that it's not an epileptic seizure. An EEG is not a one-hundred-percent tool. Epilepsy and seizures are a clinical diagnosis. The EEG is a helpful tool to guide that diagnosis, but it is not foolproof, so you need to take the whole clinical picture into account. Particularly focal seizures without impaired awareness often can be electrographically silent on surface EEG. If you see something that looks clinically like a seizure but doesn't show up on the EEG, there are circumstances that they get to in the paper a little bit where that can still be an epileptic seizure. And you just have to be aware of the limitations of the tests that you're ordering and always fall back on the clinical skills that you've learned.

Dr Grouse: Are there any tips or tricks you can suggest to improve the clinical utility of EEG for diagnosis of epilepsy? And also thinking about the example you just gave, but maybe other cases as well?

Dr Weber: Again, definitely need to incorporate EEG as part of a larger picture. The video component of EEG is incredibly helpful. You can't interpret EEG in isolation. Regardless of what the EEG shows, you can't make a diagnosis of epilepsy, but you certainly can be very suspicious of one. So, in those cases where you have a high suspicion for an epileptic seizure and the EEG has not given you any confirmatory evidence, it's really helpful to rely on any clinical expertise that you have access to. So, people who have seen lots of seizures may be helpful in that situation. Getting good recordings, good data to prove yourself one way or the other is helpful and continuing to evaluate. So usually, as I said, focal seizures that don't show up well on the EEG. People who have focal seizures will often have larger seizures if left untreated. So, you can try to admit them to an epilepsy monitoring unit where we try to provoke seizures and try to provoke a larger seizure to help confirm that diagnosis.

Dr Grouse: This kind of gets into what we've already reviewed to some degree, but what is the easiest mistake to make (and hopefully avoid) when using EEG to diagnose epilepsy or make other treatment decisions?

Dr Weber: I think the easiest, most common mistake I see is overreliance on the test. There's a lot of subjectivity to the interpretation of this test. There are a lot of studies out there on interrater reliability for epilepsy and intrarater reliability for epilepsy. We continue to try to make the findings more objective and get more quantified. The articles talk about our six criteria for epileptiform discharges and have reference to where that came from and the sorts of specificity that each of those criteria lead to. Just because an EEG report has said something, that does not diagnose or negate a clinical diagnosis of epilepsy. It is common for folks with non-epileptic seizures to have a history of reported epileptic form discharges on their EEG. Again, because there is some subjectivity to the test, some abnormal-looking normal variants will pop up and get interpreted as epileptiform discharges. It's important to review the whole patient, as much of the data as you can, and make the best clinical judgment you can of the overall case.

Dr Grouse: What is quantitative EEG and how can it be clinically useful?

Dr Weber: Now that most EEG is obtained digitally through the use of computer software, we have been able to employ computers to do a lot of the work for us. There are many different ways of looking at the EEG data, but it's all frequency bands over time. The quantitative EEG goal is really to simplify and condense what you're seeing on your normal EEG page into a more digestible format. Lets you look at a larger amount of data faster, which becomes more and more important as we're doing more of these long-term recordings, particularly in the intensive care unit. Quantitative EEG can help you assess a lot of data at a snapshot and get a general sense of what's going on with the patient over the past several hours. It does require some extra training to become familiar with it, but it's training that can be done at all levels. Again, it can help you see more, faster. Obviously, like everything, it has its own limitations. Sometimes the sensitivity and specificity may be a little off from the raw data review, and you should always go back to the raw data anytime there are questions. But it can be helpful to make things faster.

Dr Grouse: Do you think you could give me a hypothetical example of a case where this would be something really nice to have? 

Dr Weber: The most common example is folks with repetitive seizures in the ICU. If you're just looking at the raw data, you will get a sense of how often the seizures are happening. But if you look at the quantitative data, it sort of compresses that all down to a much smaller snapshot. So you can see much more readily, yes, these are how many seizures were happening. And here's where we gave our intervention; and look, there are fewer seizures after that intervention. So, it can help you assess response to treatment, help you assess just overall volume of seizures in a much more condensed fashion, and you can get through it much faster with the appropriate training.

Dr Grouse: Can you tell us about any new developments in EEG that are on the horizon we should be aware of? 

Dr Weber: Yeah. So, I think my two favorites, which I highlight in the article, are longer-term recordings---so, there's some companies that are working on subcutaneous EEG. So, implanted EEG electrodes that can stay in your body for the short, long term on the order of year or years and constantly send some EEG data. Obviously, it's not a full montage in most of those cases, but some EEG data that can help you assess long-term trends in epilepsy and long-term response to therapies. I think that's going to be really cool. I think it's very exciting and I think it'll change how we do clinical trials in the future. I think we'll be able to rely less on seizure diaries from folks and more on objective seizure data for patients who have these implanted. But with that will come an ever-increasing amount of data to be reviewed, which leads into the other exciting future trend is AI in the use of interpretations. AI is becoming more and more advanced and there are very exciting articles out on how good AI is getting at interpreting our EEGs. I think soon, in the very near future, the AI platforms will be able to dramatically reduce the amount of time it takes the experts to review an EEG. They'll be able to do a lot of the screening for us and then we can go back, just like I was talking about the quantitative EEG, go back and review segments of the raw data rather than having to review every page of every file, which is quite time consuming.

Dr Grouse: Wow, that's really exciting. It certainly does seem like AI is making breakthroughs in just about every area of how we touch the practice of medicine. Exciting to hear that EEG is no exception.

Dr Weber: Yeah, I'm fully excited. I think it's going to revolutionize what we're doing and also just greatly expand people's ability to access that level of expertise that the AI will offer.

Dr Grouse: I wanted to transition to talking a little bit more about you and your career in neurology. How did you become interested in this area of neurology to begin with?

Dr Weber: Yeah, it's sort of a roundabout fashion. So, I started out planning to be a neurointerventionalist, and then I realized that I didn't want that sort of call. For a hot minute in my PGI 3 year. I was planning to be a neuro-ICU doctor. I think that's largely because medicine is all I had been exposed to at that point and the ICU seemed like a very comfortable place. Then as I transitioned into PGI 3 we started doing more electives and outpatient rotations in my residency. And then I was planning on being a movement disorder specialist or an epileptologist, couldn't make up my mind for the longest time. And then I started to like EEG more than I liked watching videos. So, tilted myself towards epilepsy and haven’t looked back. 

Dr Grouse: Well, I really appreciated you coming to talk with us today about your article. I can't recommend it enough to anyone out there, whoever treats patients with epilepsy or orders the EEGs, I just think it was just incredibly useful. And it was such a pleasure to have you.

Dr Weber: Thank you very much for having me, Katie. 

Dr Grouse: Again, today I've been interviewing Dr Daniel Weber about his article on EEG and epilepsy, which appears in the most recent issue of Continuum on Epilepsy. Be sure to check out Continuum Audio episodes from this and other issues. And thank you to our listeners for joining today.

Dr Monteith: This is Dr Teshamae Monteith, Associate Editor of Continuum Audio. If you've enjoyed this episode, you'll love the journal, which is full of in-depth and clinically relevant information important for neurology practitioners. Use this link in the episode notes to learn more and subscribe. AAN members, you can get CME for listening to this interview by completing the evaluation at continpub.com/audioCME. Thank you for listening to Continuum Audio.