What type of EEG (or EEG-video) does your patient need?

Abstract

For many years, EEG has been synonymous with ‘routine’ EEG, a short recording without video. With digital technology, there are now many ways to perform EEG recordings. Variable attributes of EEG recordings include: inpatient versus outpatient, prolonged versus short, with video versus without, and with provocation/activation versus without. Each method has advantages and disadvantages, and, in particular, inpatient versus outpatient studies have major cost differences. In some situations EEG-video monitoring can be performed in the ambulatory/home rather than the inpatient setting.

Keywords:

• EEG
• EEG monitoring
• EEG-video
• epilepsy monitoring
• long-term monitoring

Despite major advances in neuroimaging in the last two decades, EEG remains critical in the evaluation of patients with seizures. For many years, EEG meant ‘routine’ EEG, a brief (20–30 min) recording without video. Over the last 20 years, with technological (digital) progress, EEG has evolved in two major ways: the ability to record simultaneous video, and the ability to record for prolonged periods of time. Thus, somewhat ironically, while the utility of routine EEG has decreased, the utility of prolonged EEG and EEG-video has increased and its use expanded rather dramatically [1]. Over the years, terminology has also evolved and many terms are used inter-changeably: EEG, long-term monitoring, EEG-video, prolonged EEG, continuous EEG, bedside EEG, ambulatory EEG, and so on. There are many types of EEGs and many terms to refer to them.

Let us begin with some clarification of the terminology

• Routine EEG: 20–30 min, usually without video (but can easily be added). Often this is performed with standard ‘activation procedures’ that increase the yield for capturing interictal epileptiform discharges or even seizures. The most commonly used activation procedures are photic stimulation, hyperventilation and sleep deprivation (staying up late the night before);

• Prolonged EEG (1–2 h): again with or without video;

• Ambulatory EEG: outpatient recording, usually for 1–3 days but duration varies, with or without video;

• EEG-video monitoring: this is usually assumed to be inpatient and prolonged, but really does not have to be either;

• Long-term monitoring: this term is confusing because it only refers to duration. It does not necessarily include video, and there is no definition of how many hours constitute ‘long term.’ It is usually associated with video recording even though it is not in its name;

• Epilepsy monitoring and EEG monitoring are general terms that specify neither what is monitored (video or not) nor for how long, and probably should not be used;

• The terms ‘prolonged’ and ‘long-term’ have no strict definition, so it is probably best to specify duration, that is, 2 h, 6 h, 24 h, 3 days, and so on. Obviously, the longer the better as it increases sample time, but there are practical limitations.

With all these options and various combinations of duration and video or not, it is probably best to use specific descriptive term. Monitoring of a type or another is arguably the main activity of referral epilepsy centers, be it for children or adults, and is now also performed in smaller hospitals and in the ambulatory setting.

So in summary, the variables in EEG are: inpatient versus outpatient, prolonged versus short, with video versus without, and with provocation/activation versus without. Those are of course independent attributes, which do not necessarily have to go together. Consequently, there are many (2⁴ = 16) combinations possible and many types of studies, some more realistic than others, and we will review their pros and cons.

Different types of EEG recordings

Outpatient short EEG (no video)

This is usually referred to as ‘routine EEG.’ It is the oldest, cheapest, and the ‘default’ way to obtain an EEG. The limitations of routine EEG are well known and obvious, and have to do with low sensitivity (due to a short-time sample). For the diagnosis of seizures, the yield of a single routine EEG is between 30 and 50%, and increases with repeated EEGs, possibly up to 90% by the fourth EEG [2]. Certainly, some patients with epilepsy will lack interictal epileptiform discharges despite repeated EEGs [2]. Specificity of routine EEG (for epilepsy) is very high in theory, but is low in practice because of the (under-reported) problem of over-reading [3–5]. Nonetheless, despite obvious limitations, routine EEG is inexpensive and simple, and can be sufficient, even if normal, in most clinical situations, that is, when patients respond to treatment.

Outpatient short EEG with video

Virtually, all EEG machines nowadays have a (digital) video recorder, so video should probably be added to any routine EEG, in case a clinical event is captured. If the purpose is mainly to capture the event in question for diagnosis, EEG-video can be short-term and have a high diagnostic yield. Appropriate to such situations would be, for example, patients with generalized epilepsies of the Lennox–Gastaut type with multiple daily seizures, and other patients with daily events that are strongly suspected to be psychogenic, especially when combined with activation procedures [6].

Outpatient prolonged EEG without video

This is commonly referred to as ‘ambulatory EEG.’ Because it is cheaper than inpatient EEG monitoring, ambulatory EEG can and has been used not with the intent of capturing an episode, but as an extension of routine EEG to increase the yield of capturing interictal discharges. That longer recordings increase the yield would seem logical, since we know that repeated routine EEGs certainly do [2], but this has not specifically been studied;

One situation where there may be no need for video is when episodic (seizure-like) symptoms are purely subjective, that is, there would be nothing visible on video.

Inpatient prolonged EEG without video

This was once performed commonly in intensive care unit (ICU) settings, but is now understandably rare since there is little justification for not adding a video, other than possibly cost.

The gold standard: prolonged EEG-video monitoring

For the epilepsy specialist, this is the gold standard and the starting point to care for patients whose seizures do not respond to basic treatment [7–9]. Because it is both prolonged and with video, this combines an increase in yield of capturing interictal discharges and, even more important, the ability to record the episodes in question. In most cases [7,8], EEG-video monitoring will allow us to answer the following questions:

• Are the events epileptic or not?

• If not epileptic, what are they?

• If epilepsy, what type?

• If focal, where is the likely focus?

Does prolonged EEG-video monitoring need to be performed in the inpatient setting?

Until recently, it has been assumed that prolonged EEG-video monitoring had to be performed in the inpatient setting, and has in fact implied hospital admission. Similarly, until recently the term ambulatory EEG has meant EEG monitoring without video [10–13]. However, with the improvement in computer, storage, processing, and remote access, most functions of EEG-video can now be obtained in an ambulatory or home setting. So long as the video and EEG data are acquired, stored and displayed with good quality, where the data are acquired has become largely irrelevant.

Since the cost of outpatient prolonged EEG-video monitoring is significantly lower than inpatient, it is worth comparing the two in terms of advantages and disadvantages.

Inpatient setting

Advantages

• Probably the single most compelling justification for the inpatient setting is the ability to reduce medications safely (to obtain a seizure) since patients have an intravenous line. Most patients who need EEG-video monitoring are on antiepileptic drugs. If antiepileptic drugs are to be reduced in order to record an event, this must be done in the inpatient setting, and preferably while the patient has intravenous access;

• The second major advantage of the inpatient setting is that it is a relatively controlled environment. While this is not guaranteed and sometimes fails, the likelihood that the patient will be on camera at the time of the event/seizure is much higher than in the ambulatory setting;

• Similarly, the likelihood of the patient or family pressing the alarm is likely higher in the inpatient setting;

• The ability to address technical problems with technologists during recording is better, since technologists are on site;

• Activation procedures, such as hyperventilation, photic stimulation, sleep deprivation, and suggestion, are easily performed;

• An indirect but important advantage of the inpatient setting is that the interpretation will be performed by specialists who are credentialed by the hospital, which usually requires some board certification in clinical neurophysiology.

Disadvantage

• The hospital is an artificial environment with little stress or activity, which is not the same as daily life, and occasionally patients will not have their events or seizures in this setting;

• An admission to the hospital may be inconvenient or not feasible due to home or family obligations, distance, time off work or having an accompanying person in the hospital;

• The availability in epilepsy monitoring units is sometimes limited, and the wait time is often significant;

• The cost is artificially high for services that are either not medically necessary (e.g., 24-h nursing, vital signs every shift) or needs that are just as well available at home (e.g., bed, meals and medications).

Ambulatory setting

Advantages

• The ambulatory setting provides a regular environment and stress in which the episodes in question normally occur;

• Patients and families can enjoy the comfort of their home;

• The cost is significantly lower;

• The availability is only limited by equipment, with no need for a hospital bed, and less wait time. For example, patients who cluster may not be able to wait days or weeks to undergo monitoring.

Disadvantages

• Probably the main limitation of ambulatory EEG-video, and the main reason it has not surpassed inpatient EEG-video, is the frequency with which patients are not on camera during the events in question. Although this has not been studied, high proportion of such studies end up being inconclusive and eventually require an inpatient study. Situations that are appropriate for home EEG-video, with a high likelihood of patient being on camera, include nocturnal events and homebound non-ambulatory patients (home or facilities). The challenge of being on camera is, of course, critical when the symptoms in question would be visible on video (e.g., motor manifestations), but may be not as important when the symptom events are purely subjective, that is, potential auras (i.e., there would be nothing to see on video);

• A related issue is the patient and family’s cooperation in identifying the events and pressing the alarm, which is probably more than that in hospital monitoring;

• Another important limitation is that medications cannot be safely decreased. This does not apply when events are frequent enough on medications so that no reduction is needed;

• The ability to fix technical problems during recording is improving, as this can now be monitored remotely, but is still not as good as in the hospital setting;

• With outpatient studies, there is a potential danger of EEG-video studies being interpreted by untrained neurologists (as is currently happening for routine EEGs);

• In the vast majority of ambulatory studies with no recorded event, there is a potential for over-billing. When the video is recorded but no event is recorded, the current procedural terminology for the professional component should probably be coded without video.

EEG-video monitoring in the ICU setting

The use of prolonged EEG-video recordings in the ICU setting has markedly expanded, mostly for the diagnosis and management of status epilepticus, especially non-convulsive or non-obvious status epilepticus. As is true in non-ICU setting, the longer the better, with reasonable limits. The general consensus is that 24–48 h of monitoring has the best yield [14], though in some situations shorter recordings can be sufficient [15].

Conclusions

EEG-video monitoring is an essential tool to manage patients with difficult seizures. In general, the hospital setting has definite advantages, but, with major advances in technology, the need for the inpatient status should be reassessed. The inpatient setting may no longer be justified in a significant proportion of cases.

Financial & competing interests disclosure

The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.