EEG

Question 1

What is the text book finding in hepatic encephalopathy on EEG?

Answer 1

Liver failure / encephalopathy often shows triphasic waves “In hepatic coma, the EEG often shows a triphasic wave pattern consisting of medium to high-voltage broad triphasic waves that occur rhythmically and bilaterally synchronous and symmetrical fashion over the two hemispheres. They have a fronto-occipital or occipitofrontal time lag. The triphasic waves usually have a frontal predominance.Š”

Question 2

What is the text book finding in CJD on EEG?

Answer 2

CJD often shows periodic complexes

Question 3

What is the text book finding in HSV encephalitis on EEG?

Answer 3

HSV encephalitis often shows periodic sharp waves

Question 4

What is this EEG? (triphasic waves)

Answer 4

Liver failure / encephalopathy often shows triphasic waves “In hepatic coma, the EEG often shows a triphasic wave pattern consisting of medium to high-voltage broad triphasic waves that occur rhythmically and bilaterally synchronous and symmetrical fashion over the two hemispheres. They have a fronto-occipital or occipitofrontal time lag. The triphasic waves usually have a frontal predominance.Š”

Question 5

How is the EEG record generated? what is the convention for negative and positive deflections?

Answer 5

“The EEG record is generated by recording electrical potential differences between pairs of electrodes. The universal convention is that negative potential differences are represented by a deflection above the baseline, ie,up.”

Question 6

What do the EEG electrical fields represent clinically?

Answer 6

the electrical fields that generate EEG signals are the results of inhibitory and excititory postsynaptic potentials (IPSPs and EPSPs) on the apical dendrites of cortical neurons. Pyramidal neurons contribute the plurality of the signal

Question 7

What are normal variants during drowsiness and sleep?

Answer 7

normal variants during drowsiness and sleep include 14Hz and 6Hz positive waves, small sharp spikes, wicket spikes, 6Hz spike and wave, rhythmic temporal theta. Occipital sharp transients.

Question 8

What is subclinical rhythmic electrographic discharges?

Answer 8

Subclinical rhythmic electrographic discharges of adults is a normal variant during wakefulness.

Question 9

What is the definition of electrocerebral inactivity?

Answer 9

Electrocerebral inactivity is defined as no EEG activity over 2 microvolts.

Question 10

What is the aetiology of frontal intermittent rhythmic delta activity?

Answer 10

“Frontal intermittent rhythmic delta activity can be seen with a variety of lesions including posterior fossa lesions, encephalopathy, intracranial lesions, increased intraventricular pressure.

Question 11

What is REM sleep associated with?

Answer 11

REM sleep is associated with a low-voltage desynchronized EEG.”

Question 12

What does this EEG show? (generalised polyspike and spike wave discharges)

Answer 12

this EEG shows generalized polyspikes and spike-wave discharges, the EEG correlate of primary generalized epilepsy syndromes, which are variously characterised by generalized tonic-clonic seizures, generalized myoclonic seizures or absence seizures.

Question 13

What is subacute sclerosing panencephalitis associated with?

Answer 13

“Subacute sclerosing panencephalitis is associated with periodic long-interval diffuse discharges in the EEG that recur every 4 to 15 seconds.”

Question 14

What does this EEG show (drowsiness)?

Answer 14

The EEG shows positive sharp waves in occipital leads.

Question 15

What is the significance of 3Hz spike and waves?

Answer 15

3-Hz spike and wave is characteristic for absence epilepsy. Absence epilepsy has a peak age around 6 years and more often affects girls (70%). These patients are generally normal neurologically. Absence epilepsy is characterized by multiple daily spells lasting a few seconds. They begin and end abruptly and interrupt whatever activity is being carried out. During a seizure, there will often be a blank stare; automatisms such as lip smacking, nose rubbing, and picking at clothes may also be present, especially with longer episodes. These seizures are classically provoked by hypoglycemia and hyperventilation. Mild ictal jerks of eyelids, eyes, and eyebrows may occur at the onset of the seizure. The thalamus is implicated in the generation and sustainment of absence epilepsy with the low- threshold (T-type) calcium channels of thalamic neurons playing a central role in thalamocortical interactions. First-line treatment includes ethosuximide (which acts via T-type calcium channel inhibition). Valproic acid, lamotrigine, topiramate, and zonisamide are also used.

Question 16

What is the normal adult pattern of dominant rhythm and when is it seen in children?

Answer 16

The adult pattern of normal posterior dominant α-rhythm in older children and adults is usually seen by the age of 8 to 10 years.

Question 17

What type of EEG finding would you expect in a patient with HSV encephalitis?

Answer 17

Periodic lateralized epileptiform discharges (PLEDs) would be expected Periodic lateralized epileptiform discharges consist of unilateral or bilateral, independent, high-amplitude, sharp, and slow-wave complexes at 0.5 to 3 Hz. Any destructive process such as anoxia, HSV encephalitis, stroke, and tumor can cause PLEDs.

Question 18

What are wicket spikes?

Answer 18

Wicket spikes belong to the benign normal variants

Question 19

What does this show?

Answer 19

his EEG reveals a run of 3-Hz spike and wave discharges typically seen with absence seizures in childhood absence epilepsy. A paroxysmal 3-Hz spike and wave pattern emerges abruptly out of a normal background and suddenly ceases after a few seconds.

Question 20

What does this show?

Answer 20

The EEG in Figure 5.2 reveals polyspikes in a patient with juvenile myoclonic epilepsy (JME),

he EEG reveals generalized 4- to 6-Hz polyspike and wave discharges interictally. Ictally, trains of spikes are seen, which are commonly triggered by photic stimulation (during EEG recordings).

Question 21

What does this show? What is its significance in children?

Answer 21

The EEG is suggestive of benign childhood epilepsy with centrotemporal spikes (benign rolandic epilepsy of childhood). The EEG classically reveals bilateral independent centrotemporal spikes on a normal background. The discharges on the two sides can either be independent or synchronized. They may extend beyond the centrotemporal regions. Although the spikes on the EEG appear in the centrotemporal area, the temporal lobe is not the generator of these spikes. Rather, they are felt to be generated in the base of the rolandic fissure.

Question 22

What does this show?

Answer 22

The EEG shows PLEDs. Periodic lateralized epileptiform discharges occur in acute lateralized pathology, such as a stroke, HSV encephalitis, rapidly expanding tumor, or any other destructive process to the brain parenchyma.

Question 23

What does this show? What is it characteristic of?

Answer 23

The EEG shows Hypasrrhythmia. Hypsarrhythmia is characterized by abnormal interictal high- amplitude slow waves on a background of irregular multifocal spikes. These waves and spikes have no consistent pattern or rhythm and vary in duration and size, resulting in a chaotic- appearing EEG record. Hypsarrhythmia disappears ictally during a cluster of spasms and/or REM sleep. It is the most common interictal EEG correlate of infantile spasms.

Question 24

What does this EEG show?

Answer 24

Normal eye opening with attenuation of background alpha.

Question 25

What are the EEG frequencies?

Answer 25

α-frequency is between 8 and 13 Hz and is usually present in normal people when they are awake, more prominent with eye closure, and attenuating with eye opening. Failure of attenuation with eye opening and reactivity with eye closure may be a sign of abnormality. Usually, an α-frequency of 8 Hz is seen by 3 years of age in normal children, and this frequency increases with age.

β-frequencies are those greater than 13 Hz, are normal, but may be enhanced by benzodiazepines or barbiturates, and may increase with drowsiness and light sleep.

θ-frequencies are those between 4 and 7 Hz and are present in

the frontal and frontocentral regions of one-third of young adults. These frequencies are enhanced with focused concentration, during mental tasks, by hyperventilation, drowsiness, and sleep.

δ-frequencies are those lesser than 4 Hz and can be seen in normal infants, in sleep, and sometimes in the elderly. Generalized δ frequencies may indicate nonspecific encephalopathy and if focal, may indicate a structural lesion.

Question 26

What can be done to increase EEG diagnostic yield?

Answer 26

Hyperventilation, photic stimulation, prolonged recording, drowsiness and sleep recordings.

Hyperventilation may produce generalized slowing or no effect in normal subjects; however, in certain epilepsies, such as absence epilepsy, hyperventilation may activate epileptiform discharges and even seizures. Photic stimulation is performed with various frequencies and may be helpful to induce epileptiform activity and seizures, most commonly myoclonic seizures, in individuals with photosensitive epilepsies. Sleep deprivation may also enhance epileptogenic activity. Furthermore, seizures may occur predominantly (or exclusively) during sleep in certain epilepsy syndromes, and EEG abnormalities may not be seen in the awake patient. The

Question 27

What does this EEG show?

Answer 27

The EEG in Figure 5.8 shows diffuse slowing and triphasic waves, suggesting a metabolic encephalopathy. Triphasic waves represent a special type of continuous generalized slow activity, with characteristic slow waves that consist of three phases, beginning with a small negative (upward) wave, followed by a prominent positive (downward) wave, and ending in a negative (upward) wave. These waveforms typically occur in a bilaterally symmetric, bisynchronous fashion with an anterior-to-posterior lag. They are seen in various types of toxic and/or metabolic encephalopathies that involve altered states of consciousness, most commonly in hepatic encephalopathy. Other common causes include uremia, hypoglycemia, and electrolyte disturbances, such as hyponatremia or hypercalcemia.

Question 28

What does this EEG show?

Answer 28

This EEG shows burst suppression, characterized by bursts of electrical activity at regular intervals separated by intervals of no electrical activity represented by the flat EEG line. Burst suppression signifies severe bilateral cerebral dysfunction. The etiology of burst suppression is nonspecific. This pattern may be iatrogenic, such as in general anesthesia or in barbiturate coma (as treatment for status epilepticus), among others. It may have a good prognosis in intoxications but typically signifies a poor prognosis when seen in patients with a hypoxic–ischemic insult. Patients with burst suppression are comatose and usually show no reactivity to activation procedures. Patients in status epilepticus intractable to antiepileptic agents may need to be treated with pharmacologically induced coma, in which case the therapy is initially targeted to burst suppression.

Question 29

WHat does this EEG show?

Answer 29

This patient has periodic lateralized epileptiform discharges (PLEDs) in the right hemisphere. Periodic lateralized epileptiform discharges are sharply contoured waveforms with various morphologies that appear at regular periodic intervals every 1 or 2 seconds and are lateralized to one hemisphere only or to a single region in one hemisphere. These are seen in structural brain lesions (usually in the acute or subacute setting), such as in a stroke, hemorrhage, infection (importantly, HSV encephalitis), brain abscess, or tumor, and are usually transient, disappearing with time as the patient recovers from the acute event. Typically, patients with PLEDs are encephalopathic with a diffusely slow EEG background. Usually, PLEDs are not thought to represent ongoing ictal activity and are considered among the interictal phenomena/patterns. It is important to remember, however, that seizures may be seen in a significant number of patients who are found to have PLEDs on EEG.

Question 30

What does this EEG show?

Answer 30

The EEG shown in Figure 5.11 demonstrates widespread high amplitude fast beta activity. This pattern is often seen in the presence of benzodiazepine use but can also be seen with barbiturate use. However, it is not unique to only these scenarios. It is typically maximal in the frontal and central regions. Since the EEG shows findings consistent with benzodiazepine activity, consistent with his known history of diazepam use, the initial treatment of choice would be IV flumazenil to empirically try to reverse a potential overdose. An initial dose of 0.2 mg is given, and if there is no response within 30 seconds, a 0.3-mg dose is given. If there is still no response after another 30 seconds, 0.5 mg is given every minute up to six times for a maximum total dose of 5 mg.

Question 31

WHat stage of sleep is this?

Answer 31

Figure 5.12 shows a K-complex and sleep spindle, which are features of stage N2 sleep, as discussed further below.

Question 32

What are the four stages of sleep? What do you expect to find on EEG for each?

Answer 32

leep stages are separated into four stages: stage NREM1 (N1), stage NREM 2 (N2), stage NREM 3 (N3), and rapid eye movement (REM) sleep. Stages 3 and 4 sleep, previously considered separate stages, are now combined together and called slow-wave sleep. Normal sleep consists of 4 to 6 cycles/night of non-REM (NREM) sleep, with each cycle followed by a period of REM sleep. The first REM period normally occurs around 90 minutes after sleep onset.

The sleep stages are defined electrographically by certain criteria as specified by the American Academy of Sleep Medicine scoring manual. Some characteristics of the different sleep stages are as follows:

Stage N1: This stage normally occupies approximately 5% of total sleep time. It is marked polysomnographically by slow rolling eye movements, a reduction in muscle artifact, attenuation of the occipital dominant α-rhythm, and increasing slower frequencies. Diphasic sharp waves maximal at the vertex (vertex sharp waves) and positive occipital sharp transients of sleep (POSTS) are other features.

Stage N2: Typically accounts for approximately 45% of sleep time. This stage is characterized on polysomnogram by the presence of K complexes, such as the one depicted in Figure 5.12. A K-complex is a diphasic wave (with an initial upward and then a downward deflection) that is maximal over frontocentral regions. The other main feature of stage N2 is the sleep spindle, also seen in Figure 5.12 (red arrow), following the K complex (yellow arrow). K-complexes typically appear around 5 months of age. A sleep spindle is relatively high frequency (12 to 14 Hz), brief (<2 seconds) activity that is maximal over central regions. Delta activity may be present but occupies less than 20% of this stage of sleep. Developmentally, sleep spindles first appear around 2 months of life but do not reach adult appearance until 2 years.

Stage N3, or slow wave sleep, was previously separated into stages 3 and 4. It typically accounts for 20% to 25% of sleep time but decreases with increasing age. In N3, delta activity accounts for more than 20% of visually detectable frequencies.

REM sleep accounts for 20% to 25% of sleep time. Alpha activity, reminiscent of that seen during wakefulness, may be seen in occipital leads. Obviously, this stage is characterized by the

presence of rapid eye movements, as is seen in Figure 5.14A (yellow arrows). Other features include sawtooth waves in central regions. Normally during REM sleep, most muscles are atonic (aside from the diaphragm and extraocular muscles). REM sleep atonia is seen on polysomnography as minimal activity in surface EMG leads placed on the chin, as seen in Figure 5.14A (green arrows; discussed further in questions 92 and 93). REM sleep accounts for up to 50% of sleep time in neonates, and the percentage of sleep spent in REM sleep then decreases with increasing age. Selective serotonin reuptake inhibitors reduce the length of time spent in REM sleep and increase REM sleep latency.

The amount of sleep required is greatest in the neonatal period and decreases across the life span. While in the average adult population, sleep requirements are typically in the range of 7 to 8 hours, this is highly variable and long sleep requirements (>10 hours per night) and short sleep requirements (<6 hours a night) may both occur.

Question 33

Answer 33

4. wakefulnessDiscussion:

Anterior eye blinks (first second of the page), facial muscle EMG artifact (throughout the page), and an occipital dominant alpha
rhythm (throughout the page) are characteristic of wakefulness.

Question 34

Answer 34

2. Light sleep

Discussion:

Fourteen and 6 positive spikes are sharply contoured and occur in the posterior head regions during light sleep. They are best demonstrated on referential EEG montages and are most common in adolescent patients.

Question 35

Answer 35

Lateral Eye Movements

Discussion:

Lateral eye movements are seen on the bipolar montages which are out-of- phase in derivations involving F7 and F8 electrodes as an increase in positivity at one is associated with a decrease in positivity in the other. Muscle activity produces very brief potentials. Movement of the tongue, whose tip is electrically negative with respect to its base, may produce widely distributed, low frequency intermittent potentials that may resemble “projected rhythms”. A burst of muscle potentials may precede such low frequency waves, serving to differentiate glossokinetic potentials from “projected” activity. Rhythmic delta activity confined to a single electrode position likely represents pulse artifact. Sequential eye blink artifacts are identifiable by their location at Fp1, Fp2, their considerably lower amplitude at F3, F4 and their response to eye opening. Eye movement is the most common cause of physiological artifact in EEG recordings.

Question 36

Answer 36

1.Infantile Spasms

●

Discussion:

Multifocal high-amplitude slow waves with irregular spikes and variable rhythm are called hypsarrhythmia and are associated
with infantile spasms. This rhythm is rarely seen beyond the age of 24 months.

●

Question 37

Answer 37

Stage 2

Discussion:

The illustration shows sleep spindles which are thought to be generated by the reticular thalamic nucleus.

Question 38

Answer 38

PLEDS

Discussion:

Periodic lateralized discharges (PLDs - formerly periodic lateralized epileptiform discharges, PLEDs) are often seen with acute or subacute cerebral dysfunction as produced by herpes simplex encephalitis, vascular insults like stroke, abscess, or subdural hematoma. Small sharp spikes are a benign variant seen in adults, usually during drowsiness and light sleep. Triphasic waves are generally seen in metabolic encephalopathies. A 3 Hz spike-and-wave pattern is seen in children between 5 and 15 years of age suffering from absence seizures. Positive occipital sharp transients of sleep (POSTS) are transient sharp waves seen in the occipital region spontaneously during sleep. While the sharp waves seem to be occurring at about the same frequency of the EKG there is not significant artifact and the sharp transients and EKG do not consistently line up.

Question 39

Answer 39

3. Observation

Discussion:

After a single nocturnal generalized tonic-clonic seizure in a patient with an EEG indicating centrotemporal spikes, the most appropriate management would be further observation without anticonvulsant therapy.

Question 40

Answer 40

CJD

Discussion:

Bilaterally synchronous spikes and spike-waves are seen with disorganized backround. These spikes repeat at a fairly regular rate. A subacute dementia with abnormal startle response and the above EEG pattern are suggestive of Jakob-Creutzfeldt disease.

Question 41

Answer 41

3. Left subdural haematoma

The major finding in the EEG is hemispheric asymmetry. In the absence of a skull defect, the side of the lower alpha activity is usually the abnormal one. In this case the left hemispheric attenuation is due to a large left hemispheric subdural hematoma. Alpha coma and hepatic encephalopathy both produce bilateral EEG abnormalities. Right-sided MCA stroke might be expected to produce focal slowing in the affected distribution. There is no evidence of ongoing epileptiform activity to support a diagnosis

of status epilepticus. Finally, the clinical history of trauma makes subdural hematoma the most probable cause of the EEG asymmetry.

Question 42

Answer 42

Lennox-Gastaut syndrome is characterized by multiple seizure types that are often intractable with mental retardation, and interictal EEG shows a slow spike-and-wave pattern

Question 43

Answer 43

Hypsarrhythmia (interictal high amplitude, arrhythmic delta activities with independent multifocal spike discharges) characterizes infantile West syndrome. Landau-Kleffner syndrome occurs in children with language regression and sleepactivated spikes. Lennox-Gastaut syndrome is marked by background activities of wakefulness that are too slow for state with interictal rhythmic 2 Hz spike wave discharges. Pyknolepsy in children occurs with generalized 3Hz spike-wave discharges

Question 44

Answer 44

Posterior occipital sharp transients of sleep (POSTS) are sharp contoured surface positive transients that occur singly or in clusters in the occipital region. They are usually bilaterally synchronous and are seen during light to moderate levels of sleep

Question 45

Answer 45

Triphasic waves with a anterior-posterior lag are signs of metabolic encephalopathies, most classically associated with hepatic stupor. Strokes and HSV infections are associated with PLEDS on EEG. Prion disease, specifically Jakob-Creutzfeldt disease, presents with generalized periodic epileptiform discharges

Question 46

Answer 46

Epileptiform abnormalities in expressive aphasias are usually sleep-activated. Landau-Kleffner syndrome consists of language regression, seizures, and the aforementioned sleep-activated spikes discharges

Question 47

Answer 47

Rasmussen disease is characterized by progressive focal seizures that increase in duration and severity. It is associated with changes in the white matter with hyperintensity and then atrophy. The EEG pattern is characterized by focal and multifocal epileptiform discharges and slowing

Question 48

Answer 48

14- and 6-per-second positive spikes are a benign phenomenon in the EEG and are seen over posterior and temporal head regions during drowsiness and light sleep

Question 49

Answer 49

Juvenile myoclonic epilepsy is characterized by generalized polyspike wave discharges that often are provoked by photic stimulation. Of the medications commonly available for treatment of JME, VPA is no longer preferred for chronic therapy for JME in childbearing women because of high risk of fetal abnormalities. Birth registry studies have shown that lamotrigine does not have similar risks (although soft palate abnormalities have been reported)

Question 50

Answer 50

Breach rhythm is seen on EEG with a skull defect. It appears as accentuation or increased amplitude of rhythms, especially theta, alpha, and beta, underlying the breach in the skull