Electroencephalography in Outpatient, Epilepsy Monitoring Unit, and Intensive Care Unit Settings

Clinical Application and Value

The main indication for performing EEG is clinical suspicion of epilepsy. In addition to helping with epilepsy diagnosis, EEG may be used to monitor the therapeutic effects of antiseizure medications (ASMs) in patients with epilepsy. In infants, EEG is useful in assessing the extent of brain maturation.

Bedside continuous electroencephalography (cEEG) and quantitative electroencephalography (qEEG) in the intensive care unit (ICU) setting are used primarily to increase the detection of nonconvulsive seizures (NCSs) and nonconvulsive status epilepticus (NCSE) in critically ill patients, including those with acute or chronic encephalopathies and those with focal brain lesions. qEEG allows for a compressed view of several hours of EEG monitoring and may be used to enhance the clinical diagnosis and treatment planning.

Intracranial EEG is used in patients with medically intractable focal epilepsies who are potential candidates for surgical intervention as a means of localizing the epileptic focus and its relationship to eloquent cortex. In the course of such presurgical evaluations, intracranial EEG can also help to detect and localize seizures that are not detected or not well localized with scalp electrodes (scalp EEG–negative seizures) or to demonstrate the presence of pathologic high-frequency oscillations in the 100 to 600 Hz frequency range, which may aid in definition of the epileptogenic zone.

Historical Development

Human EEG was recorded for the first time by Hans Berger (1873–1941), a professor of psychiatry in Jena, Germany, in 1924. He devised the word electroencephalography, and he was the first person to illustrate the alpha frequency (posterior dominant) background rhythm on a single channel EEG recording.

Over time, EEG recording techniques became more refined with the addition of more channels and protocols of acquisition. Current guidelines require that electrodes be placed in accordance with the international 10–20 system, to adequately sample the areas producing most of the normal and abnormal EEG patterns. ^, Progress in video technology now allows for the patient’s peri-ictal state to be recorded on video time-locked with EEG. Advances in epilepsy surgery led to development and systematic application of intracranial long-term video EEG in selected patients with medically intractable focal epilepsies.

Routine Electroencephalography

Standard routine EEG (rEEG) should include at least 20 minutes of technically satisfactory EEG recording. rEEG may yield interictal epileptiform abnormalities in 30% to 50% of patients with epilepsy but can be normal in the rest. ^, Serially repeating rEEG or prolonged EEG with activation maneuvers can increase the yield to 60% to 90%. Yield plateaus around 92% after the fourth rEEG in the same patient. In up to 10% to 19% of patients with epilepsy, interictal abnormalities may not be detected despite repeat EEG examinations and various EEG modalities. ^,

EEG is essential in the diagnosis and management of new-onset epilepsy. rEEG should be performed as soon as possible, ideally within 24 hours after the seizure to increase the test sensitivity.

Long-Term Multihour and Ambulatory Electroencephalography

Long-term EEG is cEEG recording for at least 1 hour. It can vary anywhere from 1 to 24 hours or several days, usually with video recording. Multihour EEG in adults usually ranges from 1 to 3 hours and is preferably performed following sleep deprivation (sleep-deprived electroencephalography [sdEEG]).

Long-term EEG is commonly used when standard rEEG is normal and epileptic seizures are suspected. It increases detection of interictal abnormalities and helps with classification of epileptic syndromes. .

Ambulatory EEG (aEEG) is defined as EEG recording during which patients are sent home connected to EEG, typically for a minimum of 24 hours with the usual duration ranging from 24 to 72 hours. Although it is considered more valuable than rEEG and can contribute to diagnostic validation in up to 72% of patients, the quality of aEEG can be limited by various electrode and movement artifacts outside the EEG laboratory.

aEEG allows for clinical diagnosis and quantification of events and seizures. Patients maintain autonomy and are able to carry out activities of daily living. aEEG allows for recording of patients in their living environment, triggering of seizures by the patients’ everyday triggers, and recording of patients’ natural sleep-wake cycle. It has lower cost compared with inpatient admission.

Main disadvantages include difficulty in interpretation in the setting of movement artifact, inability for the patient to be assessed by physicians during ictal events, and inconsistency of video coverage, although advances in technology and widespread use of video cameras now allow for acquisition of ambulatory video-EEG data in the home environment. To ensure patient safety at home, patients are typically not weaned off ASMs during aEEG recordings. These restrictions limit the data that can be obtained via aEEG.

Indications for long-term EEG in the outpatient setting and the epilepsy monitoring unit (EMU) are summarized in Table 82.1.

Clarification of Diagnosis and Event Characterization

EMU admission is indicated for diagnosis and event characterization in order to determine whether typical clinical events are epileptic or not. Approximately one-third of patients undergoing EMU evaluation are found to have nonepileptic events. Notably, around 10% of patients with nonepileptic events also have epileptic seizures (epilepsy with coexistent nonepileptic events). To avoid unnecessary treatment with ASMs, EMU evaluation is the best way to diagnose patients with nonepileptic events (which are often confused with epileptic seizures) and separate the features and relative proportions of epileptic versus nonepileptic events.

Common differential diagnosis of epileptic seizures versus other paroxysmal nonepileptic events includes vasovagal syncope, cardiogenic syncope, paroxysmal movement disorders, sleep-related spells, migrainous phenomena, and psychogenic nonepileptic events (PNEE) and seizures (PNES).

Once identified, these conditions can be treated accordingly and guide appropriate referrals (to cardiologists or other specialists). PNES and paroxysmal psychiatric manifestations (such as anxiety attacks) are best treated with psychotherapy, and use of psychotropics when appropriate under the care of experienced psychologists and psychiatrists. Epileptic seizures are treated with ASMs. Neurostimulation and epilepsy surgery may be considered in patients whose seizures are not adequately controlled with medications.

Clinical Assessment of Seizures and Spells

A major component of the EMU admission is ictal and postictal assessment of the patient combined with the ongoing video-EEG recording. Every EMU needs to have a protocol for testing people systematically that includes ensuring that the camera is focused on the patient; that bedside safety concerns are addressed first; and that responsiveness, speech comprehension, ictal and postictal palsy, verbal function, verbal memory, orientation, visual memory, anomia, and other cognitive functions are tested appropriately during the ictal and postictal phase ( Fig. 82.1 ). Nurses should be able to document semiologic details accurately. Assessment protocols should be printed and readily available in the EMU.

Seizure/Syndrome Classification

The purpose of some EMU admissions is to distinguish between different types of seizures and to clarify the diagnosis of various seizure types (and make a precise diagnosis of the epilepsy syndromes in some patients) in order to optimize treatment and guide further management. Different seizure types or syndromes may respond well to different ASMs. Some ASMs may worsen certain seizure types. Medications that work best for focal epilepsies may not provide optimal control for patients with generalized epilepsies.

Seizure Quantification and Burden Assessment

Precise quantification of seizure frequency is crucial for appropriate epilepsy management. In infants, young children, and patients with intellectual disabilities who are unable to express themselves verbally, confirming seizures or quantifying seizures on the basis of history may become challenging.

A negative report of seizures (by the patient or family member) does not necessarily mean that the patient is in fact seizure free. Seizures may be subclinical or have subtle clinical features. Some individuals are unaware (amnestic) of their seizures even if seizures have overt clinical signs, and an accurate count may not be available. Among 91 adult inpatients with focal epilepsy undergoing video-EEG monitoring, patients failed to report 55% of all recorded seizures, including 85% of all seizures that occurred during sleep.

Repeat video EEG may be required to assess response to treatment in certain individuals. Overnight video-EEG monitoring may be required in conditions or seizures that manifest only during sleep—for example, electrical status epilepticus during sleep (ESES).

In all such cases, video-EEG monitoring serves as a valuable confirmatory tool for precise seizure quantification.

Medication Adjustment

Patients with medication side effects, those with an increase in seizure severity or frequency despite outpatient increase in or adjustment of medications, or patients with uncontrolled seizure clusters and recurrent status epilepticus (SE) may require an EMU admission for ASM adjustment. When an ASM needs to be discontinued or switched to another ASM because of side effects or for medical reasons, patients at high risk for seizure worsening during this transition period may be best served by a supervised medication switch following admission to the EMU. Video-EEG admission may also be necessary to evaluate clinical and EEG response to therapy.

Differentiation Between Seizures and Side Effects

Sometimes ASM side effects can be mistaken for worsening seizures or new seizure types. Making the distinction between side effects and worsening seizures is vital because increasing ASMs may exacerbate side effects if side effects are the cause of symptoms, and reducing ASMs may worsen seizures if breakthrough seizures are the reason for symptoms. An EMU admission can help in making this distinction.

Presurgical Evaluation

An EMU admission for presurgical evaluation is needed to reaffirm the diagnosis of epilepsy, document existing seizure types, systematically review the localizing value of seizure semiology, and regionalize interictal and ictal patterns. EMU admission is required in order to record seizures for presurgical evaluation. For presurgical evaluation, at least three to five seizures should be recorded in most patients, to confirm the stereotyped nature of clinical and EEG features and to ensure that seizures are not arising from more than one focus. For difficult-to-localize seizures and/or multifocal epilepsy, nine or more seizures may be required depending on the individual clinical scenario. EMU admission for around 5 to 7 days or longer may be required in some cases. Patients with complex intractable epilepsies who are evaluated for epilepsy surgery may be admitted to the EMU for ictal single-photon emission computed tomography (SPECT) injection and scanning, in addition to the recording of stereotyped seizures as a part of presurgical evaluation.

Anticipated Course of Treatment for Medical and Presurgical Evaluation

There is no set recommended duration of EMU stay. Duration varies based on the indication for the admission and the time required to record typical events. Seizures are episodic events that occur at irregular intervals. Seizures are more likely to be recorded in the EMU if the typical frequency is one or more per week or if they are likely to occur with medication reduction or discontinuation. Patients are assessed daily to determine if further medication reduction or withdrawal is needed to record typical events. After recording events, the treating team is able to make a full assessment and develop an appropriate management plan.

Tapering and Withdrawing Antiseizure Medications

ASM withdrawal to elicit seizures is the most common method used for increasing the yield of an EMU evaluation. Supervised ASM tapering in the EMU setting is generally considered safe, with <1% risk for major complications. Withdrawal seizures must be considered when withdrawing barbiturates or benzodiazepines, even in patients with no history of epilepsy. ^, ASM reduction or discontinuation should occur only in the EMU setting under supervision and monitoring by trained health care professionals who follow established safety protocols to diminish any potential patient risks. ^{, ,} The EMU team should be prepared with protocols in place to deal with any medical emergencies including respiratory or cardiac arrest and other complications that may accompany the occurrence of one or more seizures. ^,

Sleep Deprivation

Sleep deprivation has been reported as a seizure precipitant by 10% to 30% of patients with epilepsy. ^, Some seizure types and syndromes are more likely to be precipitated in the setting of sleep deprivation, as is the case in some patients with genetic generalized epilepsy (GGE).

The International League Against Epilepsy (ILAE) recommends that adult patients be sleep deprived the night prior to outpatient EEG. Full or partial (30%–50% of the patient’s usual sleeping time, or 4 hours of sleep) sleep deprivation may be recommended for the night prior to recording. However, both have been shown to yield similar efficacy. Therefore sleep deprivation is part of seizure-provoking protocols in many EMUs.

Studies have shown that slow-wave sleep deprivation triggers focal epileptiform discharges, whereas rapid eye movement (REM) sleep deprivation is likely to activate both generalized and focal epileptiform abnormalities.

Exercise

Physical activity can trigger seizures and may be considered (when feasible) in the course of EMU admission. ^, However, the risk of falls must be kept in mind, and appropriate safety measures must always be in place.