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Absolute Epilepsy and EEG Rotation Review pp 141–148 Cite as

Benign or Normal EEG Variants

  • Mona Sazgar 3 &
  • Michael G. Young 4  
  • First Online: 02 March 2019

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Some EEG patterns look spiky and rhythmic and are commonly interpreted as abnormal findings. Incorrect interpretation may result in patient anxiety, over treatment or mistreatment. Before learning abnormal EEG patterns, it is absolutely important to master the normal EEG range and normal variants for specific age groups. As a rule, most of the normal variants occur during drowsiness and light sleep and disappear during deeper stages of sleep. In this chapter we discuss spiky normal variants including breach rhythm, benign epileptiform transients of sleep (BETS), 14 & 6 positive spikes, 6 Hz (phantom) spike and wave, wicket spikes, and rhythmic normal variants including rhythmic temporal theta of drowsiness (RTTD) and subclinical rhythmic electrographic discharge of adults (SREDA).

  • Normal variant
  • 14 & 6 positive spikes
  • Phantom spike and wave
  • 6 Hz spike and wave

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Gibbs EL, Gibbs FA. Electroencephalographic evidence of thalamic and hypothalamic epilepsy. Neurology. 1951;1(2):136–44.

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Hughes JR, Schlagenhauff RE, Magoss M. Electro-clinical correlations in the six per second spike and wave complex. Electroencephalogr Clin Neurophysiol. 1965;18:71–7.

Cobb WA, Guiloff RJ, Cast J. Breach rhythm: the EEG related to skull defects. Electroencephalogr Clin Neurophysiol. 1979;47(3):251–71.

Gibbs FA, Rich CL, Gibbs EL. Psychomotor variant type of seizure discharge. Neurology. 1963;13:991–8.

Westmoreland BF, Klass DW. A distinctive rhythmic EEG discharge of adults. Electroencephalogr Clin Neurophysiol. 1981;51(2):186–91.

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Mona Sazgar

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Sazgar, M., Young, M.G. (2019). Benign or Normal EEG Variants. In: Absolute Epilepsy and EEG Rotation Review. Springer, Cham. https://doi.org/10.1007/978-3-030-03511-2_7

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Normal variants and artifacts: Importance in EEG interpretation

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Research output : Contribution to journal › Article › peer-review

Overinterpretation of EEG is an important contributor to the misdiagnosis of epilepsy. For the EEG to have a high diagnostic value and high specificity, it is critical to recognize waveforms that can be mistaken for abnormal patterns. This article describes artifacts, normal rhythms, and normal patterns that are prone to being misinterpreted as abnormal. Artifacts are potentials generated outside the brain. They are divided into physiologic and extraphysiologic. Physiologic artifacts arise from the body and include EMG, eyes, various movements, EKG, pulse, and sweat. Some physiologic artifacts can be useful for interpretation such as EMG and eye movements. Extraphysiologic artifacts arise from outside the body, and in turn can be divided into the environments (electrodes, equipment, and cellphones) and devices within the body (pacemakers and neurostimulators). Normal rhythms can be divided into awake patterns (alpha rhythm and its variants, mu rhythm, lambda waves, posterior slow waves of youth, HV-induced slowing, photic driving, and photomyogenic response) and sleep patterns (POSTS, vertex waves, spindles, K complexes, sleep-related hypersynchrony, and frontal arousal rhythm). Breach can affect both awake and sleep rhythms. Normal variants or variants of uncertain clinical significance include variants that may have been considered abnormal in the early days of EEG but are now considered normal. These include wicket spikes and wicket rhythms (the most common normal pattern overread as epileptiform), small sharp spikes (aka benign epileptiform transients of sleep), rhythmic midtemporal theta of drowsiness (aka psychomotor variant), Cigánek rhythm (aka midline theta), 6 Hz phantom spike–wave, 14 and 6 Hz positive spikes, subclinical rhythmic epileptiform discharges of adults (SREDA), slow-fused transients, occipital spikes of blindness, and temporal slowing of the elderly. Correctly identifying artifacts and normal patterns can help avoid overinterpretation and misdiagnosis. This is an educational review paper addressing a learning objective of the International League Against Epilepsy (ILAE) curriculum.

  • EEG artifacts
  • normal EEG rhythms
  • variants of uncertain clinical significance

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  • 10.1002/epd2.20040

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  • Artifacts Medicine & Life Sciences 100%
  • Electroencephalography Medicine & Life Sciences 87%
  • Sleep Medicine & Life Sciences 53%
  • Eye Movements Medicine & Life Sciences 35%
  • Diagnostic Errors Medicine & Life Sciences 33%
  • Epilepsy Medicine & Life Sciences 29%
  • Alpha Rhythm Medicine & Life Sciences 25%
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T1 - Normal variants and artifacts

T2 - Importance in EEG interpretation

AU - Amin, Ushtar

AU - Nascimento, Fábio A.

AU - Karakis, Ioannis

AU - Schomer, Donald

AU - Benbadis, Selim R.

N1 - Publisher Copyright: © 2023 The Authors. Epileptic Disorders published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.

PY - 2023/10

Y1 - 2023/10

N2 - Overinterpretation of EEG is an important contributor to the misdiagnosis of epilepsy. For the EEG to have a high diagnostic value and high specificity, it is critical to recognize waveforms that can be mistaken for abnormal patterns. This article describes artifacts, normal rhythms, and normal patterns that are prone to being misinterpreted as abnormal. Artifacts are potentials generated outside the brain. They are divided into physiologic and extraphysiologic. Physiologic artifacts arise from the body and include EMG, eyes, various movements, EKG, pulse, and sweat. Some physiologic artifacts can be useful for interpretation such as EMG and eye movements. Extraphysiologic artifacts arise from outside the body, and in turn can be divided into the environments (electrodes, equipment, and cellphones) and devices within the body (pacemakers and neurostimulators). Normal rhythms can be divided into awake patterns (alpha rhythm and its variants, mu rhythm, lambda waves, posterior slow waves of youth, HV-induced slowing, photic driving, and photomyogenic response) and sleep patterns (POSTS, vertex waves, spindles, K complexes, sleep-related hypersynchrony, and frontal arousal rhythm). Breach can affect both awake and sleep rhythms. Normal variants or variants of uncertain clinical significance include variants that may have been considered abnormal in the early days of EEG but are now considered normal. These include wicket spikes and wicket rhythms (the most common normal pattern overread as epileptiform), small sharp spikes (aka benign epileptiform transients of sleep), rhythmic midtemporal theta of drowsiness (aka psychomotor variant), Cigánek rhythm (aka midline theta), 6 Hz phantom spike–wave, 14 and 6 Hz positive spikes, subclinical rhythmic epileptiform discharges of adults (SREDA), slow-fused transients, occipital spikes of blindness, and temporal slowing of the elderly. Correctly identifying artifacts and normal patterns can help avoid overinterpretation and misdiagnosis. This is an educational review paper addressing a learning objective of the International League Against Epilepsy (ILAE) curriculum.

AB - Overinterpretation of EEG is an important contributor to the misdiagnosis of epilepsy. For the EEG to have a high diagnostic value and high specificity, it is critical to recognize waveforms that can be mistaken for abnormal patterns. This article describes artifacts, normal rhythms, and normal patterns that are prone to being misinterpreted as abnormal. Artifacts are potentials generated outside the brain. They are divided into physiologic and extraphysiologic. Physiologic artifacts arise from the body and include EMG, eyes, various movements, EKG, pulse, and sweat. Some physiologic artifacts can be useful for interpretation such as EMG and eye movements. Extraphysiologic artifacts arise from outside the body, and in turn can be divided into the environments (electrodes, equipment, and cellphones) and devices within the body (pacemakers and neurostimulators). Normal rhythms can be divided into awake patterns (alpha rhythm and its variants, mu rhythm, lambda waves, posterior slow waves of youth, HV-induced slowing, photic driving, and photomyogenic response) and sleep patterns (POSTS, vertex waves, spindles, K complexes, sleep-related hypersynchrony, and frontal arousal rhythm). Breach can affect both awake and sleep rhythms. Normal variants or variants of uncertain clinical significance include variants that may have been considered abnormal in the early days of EEG but are now considered normal. These include wicket spikes and wicket rhythms (the most common normal pattern overread as epileptiform), small sharp spikes (aka benign epileptiform transients of sleep), rhythmic midtemporal theta of drowsiness (aka psychomotor variant), Cigánek rhythm (aka midline theta), 6 Hz phantom spike–wave, 14 and 6 Hz positive spikes, subclinical rhythmic epileptiform discharges of adults (SREDA), slow-fused transients, occipital spikes of blindness, and temporal slowing of the elderly. Correctly identifying artifacts and normal patterns can help avoid overinterpretation and misdiagnosis. This is an educational review paper addressing a learning objective of the International League Against Epilepsy (ILAE) curriculum.

KW - EEG artifacts

KW - normal EEG rhythms

KW - variants of uncertain clinical significance

UR - http://www.scopus.com/inward/record.url?scp=85160778565&partnerID=8YFLogxK

U2 - 10.1002/epd2.20040

DO - 10.1002/epd2.20040

M3 - Article

C2 - 36938895

AN - SCOPUS:85160778565

SN - 1294-9361

JO - Epileptic Disorders

JF - Epileptic Disorders

Phantom spike-and-wave bursts during REM-sleep

Affiliation.

  • 1 Epilepsy Unit, hôpital Gui-de-Chauliac, Montpellier, France.
  • PMID: 18662622
  • DOI: 10.1016/j.neucli.2008.04.002

Phantom spike-and-wave bursts or 6Hz spike-and-wave bursts consist of brief bursts of spikes of very low amplitude with a repetition range of 5 to 7Hz. This pattern usually occurs bilaterally and synchronously during relaxed wakefulness, drowsiness or light sleep. Bursts disappear during deeper levels of sleep. We present the case of a patient in whom this pattern reappeared in REM-sleep. This observation confirms that the stage of REM-sleep is close to wakefulness or drowsiness and may contain EEG patterns that are seen in these stages.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't
  • Consciousness / physiology
  • Electroencephalography*
  • Electrophysiology
  • Functional Laterality / physiology
  • Sleep Stages / physiology
  • Sleep, REM / physiology*
  • Wakefulness / physiology

LEARNING EEG

Normal variants, don't overcall normal variants.

Aside from the usual background findings and artifacts, EEGs will often have normal variant patterns that, to an untrained eye, may appear to be epileptiform or otherwise pathological and thus are at risk of being overcalled and leading to unnecessary tests or treatments. Technically these findings could be included in the normal awake and asleep sections, but they are not always seen and thus are not requisites for describing the background.

The Mu rhythm is the idling activity of the sensorimotor cortex, similar to how the PDR is the idling rhythm of the occipital regions. However, Mu goes away with both thoughts of and actual motor activity, and so is often not present (ex. if you think of moving the right arm, the left Mu will recede). As such, its not a required part of the background to comment on, but if you see it you should mention it. Mu appears as arch-like alpha activity (usually 7-11 Hz) over the parasagittal regions ; it can be bilateral but is often predominant on one side or the other. Particularly in cases of breach rhythm, it can appear rather high amplitude and sharp, but should not be mistaken for epileptiform activity.

phantom spike wave eeg

There are two prominent findings on this page; where is the abnormal finding, and where is the normal variant?

phantom spike wave eeg

Right Mu rhythm, and left hemispheric slowing with breach

This page shows prominent high amplitude, sharply contoured delta slowing throughout the left hemisphere, more prominent in the parasagittal than temporal chain. This is consistent with an underlying focal dysfunction of that region and breach artifact. There is mu rhythm seen in the right parasagittal region, marked by arch-like alpha activity that's often sharply contoured.

phantom spike wave eeg

Wicket waves

Wicket waves are so named because they are similar in appearance to the wickets (a set of three connected poles in the ground used in cricket). Somewhat simlar to the mu waves, wickets are arch-like, alpha range (again, usually 7-11 Hz) waveforms; unlike mu, however, wickets are seen in the temporal chains . Don't confuse wickets for epileptiform discharges (even when some wickets may be larger in amplitude than others) as wickets have no aftergoing slow wave, do not disturb the background, and are nonevolving even though they may come in runs.

phantom spike wave eeg

Is the discharge marked below a wicket or an epileptiform discharge?

phantom spike wave eeg

Epileptiform Discharge

This discharge is in the left temporal region, where wickets are expected to be seen. However, this particular discharge does not have the classic arch-like morphology of a wicket, instead showing a spike and slow wave appearance that is more in line with an epileptiform discharge. Furthermore, it has a field into the left parasagittal chain that would not be present with wickets.

phantom spike wave eeg

Rhythmic mid-temporal theta of drowsiness (RMTD)

Another example of EEG having very aptly named findings, rhythmic mid-temporal theta of drowsiness (RMT) is seen as sharply contoured, rhythmic theta activity restricted to the temporal regions; it is usually quite short, only a second or so. RMTD is usually most prominent in the mid-temporal region, and can be bilateral or independently unilateral. Note that RMTD does not evolve and thus should not be confused for a temporal seizure or brief ictal rhythmic discharge (BIRD).

phantom spike wave eeg

Are the marked waveforms below wickets or epileptiform discharges?

phantom spike wave eeg

These waveforms are sharply contoured, somewhat arcuate in appearance, come in bursts of about a second, and they do not have an aftergoing slow wave. All of these characteristics are consistent with wicket waves. Note that these wickets are coming both bilaterally and unilaterally, which is expected.

lambda waves

Lambda waves arise in the awake state when the patient is visually scanning something, such as with reading. Lambda waves are bilateral, symmetric sharply contoured positive occipital waves with a sail-like appearance, very similar to POSTS; unlike POSTS, however, lambdas come with other evidence of wakefulness, such as eye blinks, myogenic artifact and more, rather than early sleep.

phantom spike wave eeg

Are the waveforms marked below lambda waves or epileptiform discharges?

phantom spike wave eeg

Bioccipital epileptiform spike and waves

The marked waveforms, while relatively symmetric as you'd expect with lambda waves, are otherwise wholly different. First off, they have a negative polarity while lambdas are positive. Second, the marked waves have the classic epileptiform morphology of a spike and slow wave, although some show this more clearly than others. Don't let them fool you just because there are a series of them; epileptiform discharges can come in nonevolving runs as you see here.

phantom spike wave eeg

Benign epileptiform transients of sleep

Benign epileptiform transients of sleep (BETS) are also called small sharp spikes (SSS). While BETS have a slightly oxymoronic name, they are in fact a normal, benign finding that you can see in the drowsy and asleep states. In morphology they are very similar to epileptiform spikes, including having a field, but by definition BETS are low amplitude (technically less than 50µV) and short duration. They can be seen most often in the temporal chains. Differentiating BETS from real epileptiform discharges can be hard when you're starting to learn EEG; a good rule of thumb is that if the discharge is very low amplitude and seen only once or a few times, and only during sleep, its probably a BET but you should make note of it and keep a look out for anything more suspicious.

phantom spike wave eeg

Are the marked waveforms BETs or epileptiform discharges?

phantom spike wave eeg

Epileptiform Discharges

This is actually an easy question, as you can see a clear PDR of 9-10 throughout this page. Therefore, the marked discharges cannot be BETS, as BETS are only present in sleep by definition. In looking at the marked waveforms, however, they are also too high amplitude and last a little too long to be BETS, which should be very small (<50µV) and short.

phantom spike wave eeg

14 and 6 positive spikes

Taking the crown for perhaps the most uninspired name of EEG findings, 14 and 6 positive spikes describe 1-2 second bursts of sharply contoured positive waveforms that come in frequencies of either 14 Hz (13-17 Hz) or 6 Hz (5-7 Hz), or an admixture of both. They should be bilateral and synchronous, and are more common in the posterior quadrants when drowsy. They are most often seen in young adults and adolescents, and are not associated with increased epilepsy risk. In this first example below, you can see a one second run of diffuse ~14 Hz activity, consistent with 14 Hz positive spikes.

phantom spike wave eeg

In this second example, you can see a one second run of diffuse ~5-6 Hz activity, consistent with 6 Hz positive spikes. Note that 6 Hz positive spikes have two subtypes described as WHAM (waking, high amplitude, anterior, male) or FOLD (female, occipital, low amplitude, drowsy). These subtypes describe themselves, really, and the important thing to remember is that WHAM are associated with epilepsy while FOLD are not.

phantom spike wave eeg

Which normal variant is shown below?

phantom spike wave eeg

This page has intermittent periods of bilateral sharply contoured, arch-like alpha activity over the parasagittal regions without associated disturbance of the background. This is consistent with mu rhythm, the idling activity of the sensorimotor cortex that goes away when you think about movement or actually move an extremity.

phantom spike wave eeg

This tracing shows multiple intervals of brief bitemporal or unitemporal sharply contoured nonevolving activity with an arch-like morphology, consistent with wickets. Note that epileptiform activity tends to disturb the backgroud more, often including a field centrally that is not present here.

phantom spike wave eeg

Abnormal ; this is left frontal paroxysmal fast activity , an epileptiform finding

Far from a normal variant, this is a highly abnormal tracing from a patient with Lennox Gastaut Syndrome. Don't mistake the marked box for 14 and 6 positive spikes; even though they are indeed about 14 Hz, they are in the wrong area (14 & 6 spikes tend to be posterior) and come with too many other surrounding abnormalities including a highly disorganized background with multifocal phase reversing epileptiform discharges.

phantom spike wave eeg

Lambda Waves

This tracing shows symmetric occipital, sharply contoured positive waves that look very similar to POSTS that you'd expect in sleep. However, due to the presence of an eye blink in the middle of the page, along with a lot of frontal myogenic activity, you know this patient is awake. Therefore, these POST-like waves are in fact lambda waves; this patient was reading for several hours, during which time she had nearly continuous lambda wave activity because lambdas arise from visual scanning.

phantom spike wave eeg

This page has periods of both bilateral and independent unilateral parasagittal arch-like, sharply contoured alpha activity maximal over the centroparietal region. This is consistent with mu rhythm, the idling activity of the sensorimotor cortex. Note that while some periods of mu are better formed than others, the activity never evolves or really changes in appearance.

phantom spike wave eeg

Abnormal; this is a portion of a right temporal seizure

While this activity might look kind of similar to mu, it is off in the wrong distribution--this is in the right temporal region--and has too broad a field, moving into the right parasagittal chain. Mu does not do either. You may also consider wickets, but this morphology does not have the arch-like activity of wickets, and is too prolonged; also, again, it has a disruptive field into the parasagittal chain that wickets typically don't. We'll look at this full seizure, focusing on its evolution in time and location, in the seizures section.

phantom spike wave eeg

Mu rhythm is the resting activity of the sensorimotor cortex. It appears as arch-like, sharply contoured alpha activity in the bilateral or unilateral parasagittal regions, maximal over the centroparietal leads.

Mu will recede with thoughts of movement or actual movement, and can be unilateral, bilateral or a blend of both.

phantom spike wave eeg

Don't mistake mu for wickets, even though both have an arciform morphology. Mu is over the parasagittal chains, while wickets are a temporal phenomenon and typically come in shorter intervals.

phantom spike wave eeg

Wicket waves are sharp, temporal alpha frequency waves that can rhythmic in appearance and supposedly look like the wicket posts used in cricket. Each wicket should be the same duration.

phantom spike wave eeg

wicket waves

Wickets are a normal finding and can be symmetric or unilateral, and more commonly seen in drowsy states. Note that wickets are temporal, and mu (which can look similar) is more central.

phantom spike wave eeg

The field of wickets can mimic epileptiform activity, with their negative phase reversal, but wickets do not have any aftergoing slow wave as you'd expect with an epileptiform discharge.

phantom spike wave eeg

Lambda waves

Lambda waves are sharply contoured bilateral, symmetric positive occipital waveforms that arise with visual scanning such as reading.

Lambda waves look almost identical to POSTS (a hallmark of stage I sleep) , but lambdas come with other evidence of wakefulness such as eye blinks.

phantom spike wave eeg

Lambda Waves (circumferential)

Here we see lambda waves in a circumferential montage, driving home the point that they are very occipitally focused.

phantom spike wave eeg

rhythmic mid-temporal theta of drowsiness I

Rhythmic mid-temporal theta of drowsiness (RMTD) is a normal and very descriptive finding, being 1) rhythmic theta and 2) more common in the temporal regions (bilaterally or unilaterally) when drowsy.

phantom spike wave eeg

rhythmic mid-temporal theta of drowsiness II

RMTD is most often found in the mid-temporal region, and usually lasts less than 10 seconds. Unlike a seizure, there is no evolution, and there's not a spike wave morphology like you'd expect with a run of interictals.

phantom spike wave eeg

benign epileptiform transients of sleep (BETS)

BETS look very similar to epileptiform discharges, even having a field as such, but only arise during sleep (more often temporally) and are very small (<50uV) and short compared to real discharges.

phantom spike wave eeg

right temporal bet

BETS can be difficult to differentiate from epileptiform discharges early on--a good rule of thumb is that if you only see it once or twice, and it is less than 50uV, make note of it but don't call it epileptiform just yet.

phantom spike wave eeg

14 Hz positive spikes

14 and 6 positive spikes describe 1-2 second bursts of bisynchronous activity of 14 Hz or 6 Hz, often with an anterior or posterior predominance. It is more common in drowsy younger patients.

phantom spike wave eeg

6 Hz Positive Spikes

Among 14 & 6 positive spikes, 6 Hz positive spikes have two variants: WHAM (waking, high amplitude, anterior, male), which is associated with epilepsy, and FOLD (female, occipital, low amplitude, drowsy), which is not.

Learning eeg

This site is meant for neurology residents, epilepsy or clinical neurophysiology fellows, and EEG technicians. Please reach out with questions, concerns or suggestions; we're always working to improve our content.

useful links

Other resources.

phantom spike wave eeg

  • Neurology Reviews
  • Inflammatory and Demyelinating Diseases
  • Seizures & Epilepsy
  • Neurotrauma

Benign EEG Variants

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There are many variants on EEG that are considered normal and yet might be confused with epileptiform activity. These benign EEG variants are often found in only certain subpopulations: either young or old patients or patients with specific pathologies that are not epileptogenic. This makes it important to gather at least a basic history of the patient for the proper interpretation of the EEG.

This article adopts the classification of benign EEG (normal) variants as spelled out by Dr Barbara Westmoreland in her chapter entitled “Benign electroencephalographic variants and patterns of uncertain clinical significance” in the classic EEG text edited by Dr. John Ebersole and Dr. Timothy Pedley “Current practice of clinical electroencephalography.”

Each benign EEG variant will be characterized by the population in which it is found, the location at which it is most prominent, the appearance or frequency of events, and the sleep or wake state in which it is found.

Rhythmic, non-epileptiform, benign EEG variants

Rhythmic temporal theta bursts of drowsiness – the most commonly mistaken benign eeg pattern.

Also called rhythmic midtemporal theta discharges (RMTTD) or psychomotor variant, this bursting pattern occurs during the relaxed awake state or stage I sleep typically in adolescents and young adults. As the name implies, these are runs of sharp, sometimes notched spikes most positive over midtemporal regions. There can sometimes be a waxing-waning pattern to the train of spikes. The trains consist of 5-7 spikes per second and can last for several seconds.

Alpha variants

Alpha activity can present at sub-harmonic frequencies (4-5 Hz, “slow alpha”) or higher harmonics (16-20 Hz, “fast alpha”) of normal alpha activity. Slow alpha is similar to RMTD in spike shape, but are lower in frequency. Both slow and fast alpha are found in occipital or parietal leads since they predominate over the posterior aspect of the head, and both are found in awake adults.

The “alpha squeak” is a high frequency alpha burst (over occipital leads) for 1-2 seconds after an eye blink. Background frequency should not be calculated immediately after a blink due to the alpha squeak.

The mu rhythm is simply alpha-range activity produced by motor and somatosensory cortex that is maximal over central leads. While occipital alpha activity is suppressed by eye-opening, mu activity is suppressed by touch, movement, or movement planning.

SREDA – Subclinical Rhythmic Electrographic (theta) Discharge in Adults

Found in patients over 50, SREDA consists of a train of spiking activity that increases in frequency from 1-2 isolated spikes to 5-7 Hz activity lasting from tens of seconds to minutes. Unlikely epileptogenic activity, SREDA characteristically has an abrupt onset and abrupt offset. This activity can be either unilateral or bilateral, and is typically maximal in the temporo-parietal areas. The proposed etiology is possible subclinical ischemia in watershed zones since the rhythm is found in older patients and the localization correlates with watershed zones.

Midline Theta Rhythm

Midline theta rhythm is a theta-band spike train usually maximal over Cz that is found in both children and adults in the resting awake or stage I sleep states.

Frontal Arousal Rhythm

Frontal Arousal Rhythm (or FAR) is a pattern seen in frontal leads in children soon after awakening or sometimes during light sleep. The frequency of the arousal rhythm is variable, ranging from 7 to 20 Hz. This rhythm dissipates as the child fully wakens.

Paroxysmal hypnogogic hypersynchrony

This is a high amplitude, generalized slowing that presents as 2-3 Hz delta-activity across most or all leads. It is a benign EEG pattern often found in children as they are falling asleep.

Epileptiform but benign EEG variants

Fourteen- and six-hertz positive bursts.

More frequently found in children than adults, these are trains of narrow, positive spikes at either 6-Hz or 14-Hz (14-Hz is more common). They occur during stage I sleep and can be either unilateral or bilateral, most commonly over posterior temporal regions.

Benign EEG pattern 14-and-6 Hz positive bursts

Small Sharp Spikes

Small sharp spikes, sometimes called benign epileptiform transients of sleep or BETS, are found during sleep in adults. The morphology is consistent with their name: small (less than 50 microVolts), brief (less than 50 ms), unilateral, mono- or di-phasic spikes usually in the temporal area. They can have a slow-wave that follows the spike, but the slow wave is not typically as large as that of an interictal spike.

SSS 50/50 rule: less than 50 microVolts in amplitude, shorter than 50 ms in duration.

SSS can be differentiated from interictal spikes or epileptogenic discharges because 1) they are isolated, not in trains, 2) they get smaller in slow-wave sleep, 3) they do not have associated slow-wave rhythmic activity, and 4) they are not large enough to distort the background activity. Additional details about their polarity and more subtle morphology can be found in Westmoreland’s chapter (see reference).

Recent studies, however, suggest that some small sharp spikes could in fact be associated with hippocampal epileptiform discharges .

Phantom Spike and Wave (Six-Hertz Spike and Wave Bursts)

This variant appears as a waxing-waning burst of ~6 Hz sinusoidal activity, with a duration of 1-4 seconds. Each sinusoid is the slow-wave component (50-100 microVolts in amplitude) and is preceded by a small, sometimes imperceptable, spike (less than 25 microVolts) – hence the “phantom spike” nomenclature. The activity can be diffuse, found bilaterally and in both anterior and posterior leads. It is found in adolescent and adult patients typically during relaxed wakefulness and stage I sleep.

Wicket Spikes

Apparently first described by an Englishman who knows what a wicket is, these are sharp, tall (60-200 microVolts) spikes that can be found singly or in trains (6-11 Hz) in the temporal areas. The spikes are monophasic (not crossing baseline) with symmetric upsloping and downsloping sides. They are not followed by a wave which helps distinguish them from epileptogenic spikes. Wickets can be found in about 1% of normal patients older than 30.

Breach Rhythm

A breach rhythm is found in patients with a skull defect. Because the skull is missing, normal activity has a larger amplitude in leads over the defect. In addition, waveforms appear sharper despite having a predominant frequency in the theta to alpha range.

B Westmoreland (2003) Benign electroencephalographic variants and patterns of uncertain clinical significance in  Current practice of clinical electroencephalography  edited by Dr. John Ebersole and Dr. Timothy Pedley.

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About the Author: Naoum P. Issa MD PhD

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EEG normal variants: A prospective study using the SCORE system

Stephan wüstenhagen.

a Department of Clinical Neurophysiology, Danish Epilepsy Centre, Dianalund, Denmark

Daniella Terney

Elena gardella.

b University of Southern Denmark, Denmark

Pirgit Meritam Larsen

Connie rømer, harald aurlien.

c Department of Clinical Neurophysiology, Haukeland University Hospital and Holberg EEG AS, Bergen, Norway

Sándor Beniczky

d Department of Clinical Neurophysiology, Aarhus University Hospital, and Department of Clinical Medicine, Aarhus University, Aarhus, Denmark

  • • We analyzed the number of normal variants in a SCORE database of 3050 EEG recordings.
  • • The most common normal variant was sharp transients.
  • • We present typical examples and detailed characterization of the normal variants.

To determine the prevalence and characteristics of normal variants in EEG recordings in a large cohort, and provide readers with typical examples of all normal variants for educational purposes.

Using the SCORE EEG system (Standardized Computer-Based Organized Reporting of EEG), we prospectively extracted EEG features in consecutive patients. In this dataset, we analyzed 3050 recordings from 2319 patients (mean age 38.5 years; range: 1–89 years).

The distribution of the normal variants was as follows: sharp transients 19.21% (including wicket spikes), rhythmic temporal theta of drowsiness 6.03%, temporal slowing of the old 2.89%, slow fused transients 2.59%, 14-and 6-Hz bursts 1.83%, breach rhythm 1.25%, small sharp spikes 1.05%, 6-Hz spike and slow wave 0.69% and SREDA 0.03%.

Conclusions

The most prevalent normal variants are the sharp transients, which must not be over-read as epileptiform discharges.

Significance

EEG readers must be familiar with the normal variants to avoid misdiagnosis and misclassification of patients referred to clinical EEG recordings.

1. Introduction

“Primum non nocere – First, do no harm” is part of the original Hippocratic oath. This is also important for clinical EEG reading, as over-diagnosing patients can do great harm. In addition to the considerable economic burden, over-diagnosing epilepsy has detrimental consequence for the patients, such as exposure to the unnecessary side effects of a futile treatment and limiting the patients’ mobility and career choices ( Juarez-Garcia et al., 2006 , Nowack, 1997 ).

When reading EEG, it is important to distinguish normal from abnormal patterns, and to avoid over-reading of normal patterns that share features resembling the abnormal patterns. This is crucial as the same patterns can be seen in healthy individuals too. These benign (normal) variants can resemble both epileptiform waveforms and rhythmic patterns ( Tatum et al., 2006 ). With untrained EEGers, these patterns may lead to misdiagnosis, as they are often over-interpreted by readers lacking proper training ( Benbadis and Tatum, 2003 ). Rathore et al. looked at 282 EEG studies in which none of these normal variants were even mentioned and were probably misdiagnosed as epileptiform ( Rathore et al., 2021 ). Over-diagnosis of epilepsy is a common problem and often caused by unreliable history and misinterpretation of EEG. Approximately 25–30% of the patients with diagnosed epilepsy, who did not respond to initial antiepileptic drug treatment, were, in fact, incorrectly diagnosed with epilepsy. When first diagnosed with epilepsy, it is quite difficult to reverse the diagnosis even though several follow up EEGs are completely normal ( Amin and Benbadis, 2019 ).

SCORE is a standardized EEG terminology, developed by a working group of the International Federation of Clinical Neurophysiology (IFCN) and the International League Against Epilepsy (ILAE) terms ( Beniczky et al., 2013 , Beniczky et al., 2017 ). Using the SCORE EEG system (Holberg EEG AS, Norway), patterns identified in the EEG are annotated with the predefined, standardized terms, clinical reports are generated and the extracted features are stored in the SCORE database. The standardized feature extraction of SCORE EEG seems to be an ideal tool to evaluate the occurrence and types of normal variants. Here we report the normal findings identified using the SCORE EEG system. There is considerable heterogeneity in the literature concerning what is considered a physiologic pattern, and what is normal variant (aka. pattern of uncertain significance). We chose the list of normal variants as listed in the SCORE standard, as patterns of uncertain significance. In addition to detailed description of these phenomena, we provide screenshot examples of the identified typical normal variants in order to convey an educational value to the paper.

EEGs were recorded as part of the diagnostic workup of consecutive patients in the Danish Epilepsy Center (Dianalund, Denmark) and the EEG laboratory in Nuuk (Greenland) between May 1, 2019 and February 8, 2021.The EEGs were recorded with the NicoletOne EEG system (Natus Neuro, USA), using the IFCN electrode array ( Seeck et al., 2017 ). All recordings were carried out by certified EEG technicians or by EEG technicians in training under supervision of certified technicians. The duration of the recordings was 30 min for the routine EEG recordings, one hour for the sleep-EEG recordings, and up to 4 h for the short-term video EEG recordings. The recordings included different provocation techniques, such as intermittent photic stimulation, hyperventilation, sleep and specific provocation protocols (patient-tailored for reflex epilepsy and reflex epileptic traits).

Recordings were first evaluated by the clinical neurophysiology technicians and then by physicians with board-certification in clinical neurophysiology. Observed EEG features were annotated and logged in the database using the SCORE EEG system ( Beniczky et al., 2013 , Beniczky et al., 2017 ). SCORE (Standardized Computer-based Organized reporting of EEG) uses pre-defined terms to document the EEG-features annotated in the recording. The data for this study were prospectively recorded, with special emphasis on the presence of any normal variant or pattern of uncertain significance ( Beniczky et al., 2013 , Beniczky et al., 2017 , Klass and Westmoreland, 1985 ). In addition to the EEG features, we also extracted demographic data (age and sex), diagnosis, and type of benign variants. All recordings were evaluated by at least two experts. However, determining inter-rater agreement in this large prospective dataset was beyond the scope and limitations of this study. For each recording, the diagnostic gold standard was derived from the EEG in combination with all available clinical and para-clinical data. This was coded in the SCORE system as the entry “diagnostic significance”.

We analyzed 3050 consecutive EEG recordings from 2319 patients (1196 female, 1092 male, and 31 recordings where the sex was not available in the system). The mean age at time of the recording was 38 years (range from 6 months to 89 years). Fig. 1 , Fig. 2 , Fig. 3 , Fig. 4 , Fig. 5 , Fig. 6 , Fig. 7 , Fig. 8 , Fig. 9 , Fig. 10 , Fig. 11 show typical examples of the normal variants, along with a description of their characteristics. Fig. 12 shows the histograms of the age distribution of the normal variants.

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Sharp transients: fluctuations of the background activity which do not fulfill the operational criteria for epileptic discharges defined by the IFCN. Amplitude is usually higher than the rest of the background activity and they have a pointed peak. This normal variant is often misinterpreted as an epileptiform discharge. Observe the sharp transient at electrodes P10, P8, O2, at the time-point indicated by the black vertical arrow (A: Common Average montage; B: Longitudinal Bipolar montage).

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Wicket spikes / rhythm: subtype of sharp transients, with arciform waveforms, which are simple monophasic with surface negativity. They can be observed as single discharges or runs. Observe the wicket spike at electrode T8, at the time-point indicated by the black vertical arrow (A: Common Average montage; B: Longitudinal Bipolar montage).

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Rhythmic Temporal Theta of Drowsiness (RTTD): trains of theta activity, usually in the mid-temporal region, during drowsiness. It can be observed independently over one side or bilaterally. The typical configuration is arch-shaped and often notched. Observe the RTTD in the left temporal area, at the time-point indicated by the black vertical arrow (A: Common Average montage; B: Longitudinal Bipolar montage).

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Temporal slowing of the old: short runs of theta activity or delta potentials, mixed with the background activity of the same area, in age groups ≥ 50 years, without clinical abnormalities. Observe the delta potential in the left temporal area, at the time-point indicated by the black vertical arrow (A: Common Average montage; B: Longitudinal Bipolar montage).

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Slow-fused transients: by coincidence, a non-epileptiform sharp transient precedes a posterior slow-wave of youth or a temporal slowing of the old, giving the false impression of a spike-wave. Browsing the entire recording the two phenomena (sharp transients and slow-wave) are usually observed several times, dissociated from each other. Observe the slow-fused transient in the left temporal area, at the time-point indicated by the black vertical arrow. In addition, wicket rhythm is seen in the left frontal leads, in the 4th second. (A: Common Average montage; B: Longitudinal Bipolar montage).

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14-and 6-Hz positive bursts: 0.5–1 s bursts of arciform, 14 or 6 Hz activity with pointed positive peaks, recorded during light sleep and drowsiness, with shifting side-predominance and maximum amplitude mostly over the posterior temporal regions. Observe 14 Hz positive bursts in the left temporal area, at the time-point indicated by the black vertical arrow. In addition, vertex sharp wave is seen in the 14th second (A: Common Average montage; B: Longitudinal Bipolar montage).

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Breach rhythm: which consists of Focal / asymmetric high amplitude beta activity, due to an underlying skull defect. Observe the breach rhythm at F8 electrode. In addition, vertex sharp wave is seen in the 3rd second (A: Common Average montage; B: Longitudinal Bipolar montage).

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Small sharp spikes are a mono- or diphasic sharp transients with a short duration (usually < 50 ms) and low amplitude (usually < 50 µV), recorded in drowsiness/light sleep (N1, N2). Observe the small sharp spike in the temporal areas at the time-point indicated by the black vertical arrow. Other graphoelements in this figure correspond to N2 sleep: spindles, K complex and positive occipital sharp transients of sleep (A: Common Average montage; B: Longitudinal Bipolar montage).

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6-Hz spike and slow wave (aka phantom spike-waves) are short bursts of spike-and-waves of 5–7 Hz, of brief duration (<30 ms). The amplitude is mostly higher over the fronto-central regions – WHAM (Wake, High amplitude > 45 µV, Anterior, Male). Observe the bi-frontal, 6 Hz phantom spike-waves at the time-point indicated by the black vertical arrow (A: Common Average montage; B: Longitudinal Bipolar montage).

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6-Hz spike and slow wave (aka phantom spike-waves) are short bursts of spike-and-waves of 5–7 Hz, with low-voltage-spikes (<25 µV) of brief duration (<30 ms). It is seen in the occipital derivations and the amplitude is low – FOLD (Female, Occipital, Low amplitude < 25 µV, most often during Drowsiness). Observe the bi-occipital, 6 Hz phantom spike-waves at the time-point indicated by the black vertical arrow (A: Common Average montage; B: Longitudinal Bipolar montage).

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Subclinical rhythmic electrographic discharges in adults (SREDA): sharply contoured rhythm with theta frequency, usually bilateral, with shifting side-preponderance, in the temporal and parietal regions, with duration from 15 s to several minutes. Observe SREDA in the left temporal areas, starting at the time-point indicated by the black vertical arrow, and continuing throughout the page. Muscle artifacts in the 2nd and 3rd second (A: Common Average montage; B: Longitudinal Bipolar montage).

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Histograms of the age distribution of the normal variants evaluated in this study.

Fig. 13 shows the distribution of the clinical context of the EEG recordings, separately for each normal variant, according to the categories of diagnostic significance, as listed in the SCORE standard. 858 individual recordings showed 1085 normal variants, 143 (16.67%) of these examinations were normal recordings, 320 (37.30%) did not have definite abnormal findings, and 395 (46.03%) had clearly abnormal findings. When recordings were considered abnormal, this was not related the observed normal variants, and it was based on other, unequivocal EEG abnormalities, along with the clinical context.

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Distribution of the clinical context of the EEG recordings, separately for each normal variant, according to the categories of diagnostic significance, as listed in the SCORE standard.

Table 1 shows the distribution of the normal variants in our cohort. The most frequent normal variants were the sharp transients (including wicket spikes), 19.21%, followed by the rhythmic temporal theta of drowsiness (RTTD) 6.03%. In our prospective dataset of 3050 routine EEGs, we only found one patient with rudimentary spike-wave complex (male, 19 years old), four patients with Ciganek rhythm (2 female, 2 male, age: 1–13 years) and none with needle-like occipital spikes of the blind.

Overview of normal variants.

4. Discussion

Misinterpretation of normal patterns resembling abnormal EEG findings leads to erroneous diagnosis in normal patients and may lead to erroneous classification in patients with epilepsy. Therefore, it is essential that experts reading clinical EEG are familiar with the characteristics of the various normal variants. In this large prospectively recorded dataset, we extracted normal variants using the SCORE EEG system. Here, we describe them in order of their prevalence in our cohort.

4.1. Sharp transients

Sharp transients ( Fig. 1 ) are sharp EEG changes/fluctuations of the background activity which do not fulfill the operational criteria for epileptic discharges defined by the IFCN ( Kane et al., 2017 , Kural et al., 2020 ). These fluctuations in the EEG background activity have a sharp morphology and a higher amplitude and can easily be misinterpreted as epileptic discharges ( Benbadis, 2007 , Benbadis and Lin, 2008 , Benbadis and Tatum, 2003 ). In this study, sharp transients were the most often described normal variant with 19.25%. To our knowledge, there is no study describing the prevalence of sharp transients. However, several studies point out that these spiky fluctuations of the background activity are the most common cause of misinterpreting (over-reading) EEGs ( Benbadis, 2007 , Benbadis and Lin, 2008 , Benbadis and Tatum, 2003 ).

Wicket spikes ( Fig. 2 ) are a special subtype of the sharp transients, with arciform waveforms, which are simple monophasic with surface negativity. They can be seen in awake and sleep stages ( Reiher and Lebel, 1977 ) and can be best recognized during the initial sleep stages but also be seen in REM sleep ( Gélisse et al., 2003 , Reiher and Lebel, 1977 , Serafini et al., 2014 ). These waves can be observed as single discharges or runs. When seen in runs, the frequency is usually 7–11 Hz. The amplitude can range between 60 and 210 µV and their maximum is located over the temporal regions ( Klass and Westmoreland, 1985 , Reiher and Lebel, 1977 , Tatum et al., 2006 ). Their appearance can shift from side to side, but mostly one side is dominant. Some studies suggest that wicket spikes are more often lateralized to the left side ( Reiher and Lebel, 1977 ). The incidence ranges from 0.037 to 0.96% overall and in adults over 30 years up 2.9% ( Monin et al., 2018 , Radhakrishnan et al., 1999 , Reiher and Lebel, 1977 , Santoshkumar et al., 2009 ), while one of the newer studies describes it in 6.8% ( Rathore et al., 2021 ) and up to 15% ( Macorig et al., 2021 ). More specifically Santoshkumar et al. (2009) described them in 0.037%, mean age 55.36 (range 32–76), 38.46% male, followed by the numbers of Radhakrishnan et al. (1999) 0.96%, mean age 34.82 (range 20–52), 70.59% male and 6.80%, mean age 34.1 (range 7–75), 57% male, 72.4% normal EEG and 29% non-epilepsy ( Rathore et al., 2021 ).

In our dataset, sharp transients including wicket spikes occurred in 19.21% of all cases, with a median age 28 (1–89), 39.77% male, 9.39% normal, and 42.15% without definite abnormality. The combined numbers of prevalence of sharp transients and wicket spikes in our study are quite consistent with the prevalence in the literature especially regarding the studies of Beun et al. (1998) , who observed only sleep and Macorig et al. (2021) , who observed their participants with long term EEG.

4.2. Rhythmic temporal theta of drowsiness (RTTD)

RTTD ( Fig. 3 ) formerly known as psychomotor variant, is mostly seen during drowsiness and light sleep, even though it can be occasionally seen in awake patients as well. The maximum of the 5–7 Hz trains is usually mid-temporal but may sometimes spread to the parasagittal or occipito-temporal regions. RTTD can be observed independently over one side or bilaterally. The typical configuration is arch-shaped and often notched. Therefore, it can sometimes be misinterpreted as sharp waves. Sometimes, these arches are flat topped ( Chatrian et al., 1974 , Gibbs and Gibbs, 1941 , Lipman and Hughes, 1969 ). The runs of theta activity can last from mere seconds to several minutes ( Beiske et al., 2016 ). As other normal rhythms, this one is also clearly monomorphic, monorhythmic, and there is no evolution ( da Silva, 2018 ).

In the literature, the incidence has been reported in 0.4% in patients between the age of 15–19 years ( Gibbs and Gibbs, 1964 ) overall between 0.1 and 2.1% ( Gibbs et al., 1963 , Macorig et al., 2021 , Maulsby, 1979 , Radhakrishnan et al., 1999 , Rathore et al., 2021 , Santoshkumar et al., 2009 ), and in up to 10% in adults over 60 years old ( Kang and Krauss, 2019 ). More specifically, Santoshkumar et al. (2009) have seen RTTD in 0.12% of their cases, mean age 27.5 (range 9–80), 44% male, while Rathore et al. (2021) have described it in 0.4% of their recordings with a mean age of 21.8 (range 11–52), 57% male, 43% with normal EEG and 42.8% non-epilepsy. Even a higher number of 0.79% was described with mean age 31.36 (range 6–58), 71.43 male ( Radhakrishnan et al., 1999 ).

In our dataset, this normal variant was seen in 6.03% with a median of age of 30 (range 3–80), 42.39% male, while 47.83% of the recordings were normal, or, in 22.83% of all cases with no definite abnormality. This means that our prevalence is higher than most of the overall numbers of the studies, but still in the range of all reported numbers with a rising prevalence with age. In accordance with previous studies, we have also observed a little predominance of females.

4.3. Temporal slowing of the old

Temporal slowing of the old ( Fig. 4 ) is a mostly unilateral normal variant (mainly on the left or both sides) showing short runs of theta or delta activity mixed with the background activity of the same area. It is normal in age groups ≥ 50 years, without clinical abnormalities. Furthermore, it can be accentuated during hyperventilation or drowsiness ( Kane et al., 2019 ).

In our cohort, this normal variant was seen in 2.89%, median age 68 (range 49–86), 48.86% male, while 23.86% were described as normal and 62.50% with definite abnormality. To our knowledge, this variant has not previously been described in larger studies. This pattern may have been included into RTTD in previous studies, since both phenomena include theta activity in the temporal areas ( Kang and Krauss, 2019 ).

4.4. Slow fused transients

In patients with posterior slow waves of the youth ( Fig. 5 ), or in a patient with temporal slowing of the old, a sharp transient can precede a slow wave. This can give the false impression of a spike and slow wave ( Kane et al., 2019 ). To the best of our knowledge, there are no specific numbers in the literature for this phenomenon. It was seen in our study in 2.59% of all cases, with a median age of 16 (range 1–37). 29.11% of the recordings were normal and 37.97% were without any definite abnormality.

4.5. 14-and 6-Hz positive bursts

The typical bursts last between 0.5 and 1 s ( Fig. 6 ). They occur during light sleep and drowsiness; however, there are reported cases during REM sleep. These bursts can be seen unilaterally or bilaterally, but mainly with shifting predominance in the same patient. The laterality can shift but the maximum amplitude is mostly over the posterior temporal regions ( Ebersole and Pedley, 2003 , Klass and Westmoreland, 1985 , Tatum et al., 2006 ).

The numbers in the literature range from about 16% at the age of five to nine; 20% between the age of ten to 14; 8–10% between the age of 20 and 24; 1–2% between 25 and 29 years of age ( Eeg-Olofsson et al., 1971 , Gibbs and Gibbs, 1964 ). Another study described this normal variant in 58% in boys of the age between 13 and 15 years of age ( Lombroso et al., 1966 ). The incidence is falling with increasing age ( Klass and Westmoreland, 1985 ).

More recent studies have described 14-and 6-Hz positive bursts in 0.53% ( Santoshkumar et al., 2009 ), 0.6% ( Rathore et al., 2021 ) and to 5,68% ( Radhakrishnan et al., 1999 ) and 8.3% ( Macorig et al., 2021 ) of their EEGs looking at a wide age range of prevalence.

When having a closer look at the numbers, 0.53% was the lowest prevalence where extended data was available mean age 23.23 (range 4–67), 44.32% male ( Santoshkumar et al., 2009 ). A little higher prevalence was described with 0.6%, mean age 28.1 (range 11–50), 36% male, 90% normal EEG and 45.5% non-epileptic. While it was seen in 5.68%, mean age 14.72 (range 6.5–31.0), 49.50% male by Rathore et al. (2021) . In our study it was seen in 1.83% of all cases, 53.57% male, the median age was 13, 30.36% were normal and 19.64% without definite abnormality. These numbers are quite consistent with the detailed numbers in the literature.

4.6. Breach rhythm

A skull defect can lead to a breach rhythm, which consists of focal, asymmetric high amplitude beta activity ( Fig. 7 ). This is described as normal as long as it is not associated with spikes or focal slowing ( Tatum et al., 2006 ).

To the best of our knowledge, there are no specific reports about the incidence in a standard population. This is probably due to the fact that this normal variant appears only symptomatically if caused by a lesion of the skull. The numbers can vary depending on the examined population and can be influenced by a selection bias of patients after neurosurgery. Already in 1979, this was described in 21 cases of 33 patients (63.64%) with iatrogenic skull defect ( Cobb et al., 1979 ), which is a high number in patients with skull defect. In our study, this normal variant was seen in 1.25% of all studies, which includes several patients with follow-up after epilepsy surgery. The median age was 40, while the range was 2–82 years. Of these cases, 7.89% were classified as normal and 13.16% without any definite abnormality, while the rest of the recordings were abnormal. Since we do not have any information in this study about skull defects, we cannot perform a more detailed subgroup analysis.

4.7. Small sharp spikes (a.k.a. benign epileptiform transients of sleep)

Small sharp spikes ( Fig. 8 ) are sharp transients with a short duration (usually < 50 ms) and low amplitude (usually < 50 µV). Their simple shape consists of a mono- or diphasic spike with a steep descending arm. If present, the following slow wave is not prominent and of low amplitude. The background is not disturbed and they can be seen in drowsiness/light sleep (N1, N2) ( Ebersole and Pedley, 2003 , Klass and Westmoreland, 1985 , Olson and Hughes, 1970 , Tatum et al., 2006 ). Small spikes in patients with temporal lobe epilepsy may resemble small sharp spikes. To avoid over-reading (which is potentially more harmful than under-reading) it is advisable to opt for a conservative interpretation in these cases.

The incidence is described in up to 25% of the normal population ( Tatum et al., 2006 , White et al., 1977 ), but the numbers in the literature range from 1.85% ( Santoshkumar et al., 2009 )¸ through 3.3% ( Macorig et al., 2021 ), 3.7% ( Rathore et al., 2021 ) and, in more recent studies, to up to 8.16% ( Radhakrishnan et al., 1999 ). Small sharp spikes are almost never seen in children younger than 10 years ( Koshino and Niedermeyer, 1975 ). When having a closer look at the data (where available) Santoshkumar et al. (2009) described the lowest prevalence with 1.85%, mean age 39.75 (range 4–94), 52.91% male. This number is followed by 3.7% ( Rathore et al., 2021 ), mean age 27.6 (range 3–60), 72% male, 65.2% normal, 21% non-epileptic. While Radhakrishna et al. have seen in 9.16% of their recordings, mean age 33.83 (range 18–58), 72.41% male ( Radhakrishnan et al., 1999 ). In our study it was seen in 1.05%, 56.25% were male, the median age was 38 (range 10–80), 25% normal, 25% no definite abnormality.

The prevalence in our dataset is lower than previously reported, which is probably due to the fact that our staff is trained to spot sharp elements and then distinguish between epileptic or non-epileptic discharges. When this decision is made, most of the non-epileptic phenomes are often described as sharp transients. That may explain why by far the most normal variant in our data set is sharp transients incl. wicket spikes. Regarding the gender difference, we also see a little predominance in male patients, and our results are quite close the previous described age distribution.

4.8. 6-Hz spike and slow wave

6-Hz spike and slow wave ( Fig. 9 , Fig. 10 ) is also called phantom spike-and-wave. These are bursts of spike-and-wave of 5 to 7 Hz (typically duration of 1–2 s) with low-voltage-spikes (<25 µV) of brief duration (<30 ms). The amplitude is mostly higher over the fronto-central regions. Even though the bursts are usually diffuse, they can have anterior or posterior predominance. They can be seen during wakefulness but mostly occur during drowsiness and light sleep ( Marshall, 1955 , Tharp, 1966 , Tharp, 1967 ).

The incidence is described between from 0.1% ( Macorig et al., 2021 ) over 0.9% to 2.76% ( Hughes, 1980 , Marshall, 1955 , Olson and Hughes, 1970 , Radhakrishnan et al., 1999 , Rathore et al., 2021 , Santoshkumar et al., 2009 , Tharp, 1966 ). One of the lowest numbers with detailed data is 0.9%, mean age 25.5 (range 15–60), 56% male, 75% normal, 22.5% non-epilepsy ( Rathore et al., 2021 ). This is followed by 1.02%, mean age 23.23 (range 4–67), 44.32 male ( Santoshkumar et al., 2009 ) and 2.76%, mean age 20.84 (range 6–31), 48.98% male ( Radhakrishnan et al., 1999 ).

In our population the results showed a prevalence of 0.69%, median age 16 (range 1–66), 33.33% male, 9.52% normal and 66.67% without definite abnormality. Both prevalence and age are close to the numbers in the literature. We have seen it in less males, which deviates from the gender distribution in the literature where sex is described quite even.

4.9. Subclinical rhythmic electrographic discharges in adults (SREDA)

SREDA ( Fig. 11 ) can be seen mostly in relaxed awake patients or during drowsy states but also in sleep ( Fleming et al., 2004 , Westmoreland and Klass, 1981 ). The phenomenon is described as diffuse, sharply contoured rhythm with theta frequency. This pattern is usually bilateral in the temporal and parietal regions (it may be asymmetric). It can run from 15 s to a minute and even more ( Westmoreland and Klass, 1981 ).

The incidence ranges from none ( Macorig et al., 2021 , Radhakrishnan et al., 1999 ), through 0.07% ( Santoshkumar et al., 2009 ) to 0.2% ( Rathore et al., 2021 ). Santoshkumar et al. described SREDA in their study with af prevalence of 0.07% with a mean age of 52.1 (range 9–80), male 34.62% ( Santoshkumar et al., 2009 ), Rathore et al. (2021) found this variant in 0.2% patients with mean age of 58.7 (range 41–72), 67% male, 67% with a normal EEG and 67% with non-epilepsy.

In our dataset, we have only one documented case (0.03%) age 39, male, no definite abnormality. This is consistent with the other studies and its rarity. Comparing our data set with gender distribution and the age is therefore difficult. Nonetheless, it is important to be aware of SREDA and not to confuse it with an epileptic (electrographical) seizure.

5. Conclusion

Our prospective study of a large number of EEGs gives an overview of the various normal variants in EEG, sharp transients being the most often identified pattern (19.21%). This emphasizes the importance of the knowledge of this normal variant and the criteria for distinguishing it from epileptiform discharges ( Kural et al., 2020 , Kural et al., 2021 ). The numbers in our large prospective dataset were consistent with previous studies, for most types of normal variants. In our population, only the incidence of small sharp spikes and 6-Hz spike and slow wave were somewhat lower than previously reported.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of Competing Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Harald Aurlien is Chief Medical Officer and minority shareholder in Holberg EEG AS. The remaining authors do not have conflicts of interest related to this work.

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IMAGES

  1. Phantom Spike and Wave

    phantom spike wave eeg

  2. EEG Benign Variants Article

    phantom spike wave eeg

  3. phantom spike and wave

    phantom spike wave eeg

  4. 6-Hz spike and slow wave (aka phantom spike-waves) are short bursts of

    phantom spike wave eeg

  5. Six-Hertz Spike and Wave Epilepsy

    phantom spike wave eeg

  6. Awake EEG. Bilateral and asynchronous spike and spike-and-wave

    phantom spike wave eeg

VIDEO

  1. Top 10 Wonders of Siargao: An Island Paradise

  2. Persona 5: Introducing Morgana [DE]

  3. Mission: Phantom Liberty

  4. Defeating a Phantom

  5. Phantom Four Films/Marvel/Spike Original/New Line Television

  6. Phantom Wave predrop (Impossible Level)

COMMENTS

  1. EEG Benign Variants

    It is also called "phantom" spike-wave since it has a relatively low amplitude (less than 40 mV), fast spike (less than 30 ms) followed by a 5 to 7 Hz wave of equal or greater amplitude (figure 3). 6 Hz spike and wave discharges occur in young adult bilaterally, synchronously and predominantly during relaxed wakefulness, drowsiness or light slee...

  2. Benign Variants in the EEG

    The 6-Hz phantom spike and wave pattern may be observed in both adolescents and adults and is another pattern seen predominantly during drowsiness and light NREM sleep, vanishing in N3 and REM. The 6-Hz phantom spike and wave are diffuse or, alternatively, anteriorly or posteriorly predominant bursts.

  3. EEG Normal Waveforms

    EEG Abnormal Waveforms. HHS Vulnerability Disclosure EEG activity reflects the temporal summation of the synchronous activity of millions of cortical neurons that are spatially aligned. Analyzing and interpreting the EEG is both an art and science. The normal EEG is extremely diverse and has a broad range of physiological variability.

  4. Normal EEG Variants: Overview, Odd-Looking Waveforms, Artifacts

    The phrases "electroencephalogram (EEG) variant waves" or "normal EEG variants" refer to waves that are rare or unusual but not generally abnormal. They may be unusual in shape or in...

  5. EEG 6 Hz spike and wave

    Six-Hz spike-and-wave bursts ("Phantom spike and wave"; see arrows): three 1 second bursts from one routine EEG recording. (A) This pattern is accentuated in an average referential montage, sensitivity 5 uV/mm. Note the low amplitude, occipitally predominant "phantom" spikes (arrows), and the frequency of approximately 6 per second (B) in a longitudinal bipolar montage (7 uv/mm), this pattern ...

  6. Epileptiform Normal Variants on EEG

    This article reviews the following such patterns: small sharp spikes (SSSs), wicket spikes, 14- and 6-Hz positive spikes, phantom spike and waves, psychomotor variant, subclinical...

  7. Epileptiform Electroencephalographic Patterns

    —The 6-Hz spike and wave (also known as the "phantom spike and wave") is a generalized spike discharge with a repetitive rate of 6 Hz (range, 5 to 7 Hz). 34. ... The 6-Hz spike-and-wave EEG pattern occurs in adolescents and adults. Rhythmic Temporal Theta Bursts of Drowsiness.

  8. Normal variants and artifacts: Importance in EEG interpretation

    Six hertz spike-and-slow-wave was first described in 1950 as "wave and spike phantom", 130, 133 also known as rudimentary spike-wave complex or phantom spike-and-wave. "Phantom" refers to the low-amplitude spikes, which may be difficult to appreciate by visual analysis, followed by more prominent, higher amplitude slow wave component.

  9. Spike-and-Wave

    The hallmark EEG finding of CSWS is spike wave activity occurring during 85% of slow wave sleep. The etiology is poorly understood with a minority of patients having identifiable structural abnormalities such as cortical dysplasia, polymicrogyria, and thalamic lesions in the neonatal period.

  10. Normal EEG variants

    The 6-Hz spike-and-wave (phantom spike-and-wave) is a benign EEG variant initially described in 1950 (Walter, 1950). "Phantom" is derived from the low-amplitude spike within a burst of spike-and-slow wave activity (Fig. 9.9).

  11. Mimickers of generalized spike and wave discharges

    PMID: 25080775 Overinterpretation of benign EEG variants is a common problem that can lead to the misdiagnosis of epilepsy. We review four normal patterns that mimic generalized spike and wave discharges: phantom spike-and-wave, hyperventilation hypersynchrony, hypnagogic/ hypnopompic hypersynchrony, and mitten patterns. MeSH terms

  12. Normal Variants and Unusual EEG Patterns

    Phantom spike and wave discharges can appear in both adolescents and adults and usually have a diffuse, bilateral, synchronous distribution. This type of rhythm is called "phantom" due to its short duration and the fleeting quality of the spike, that is, smaller in amplitude and shorter than the slow wave component of the pattern [ 1 ].

  13. Normal EEG Variants and Artifacts

    Also known as phantom spike-and-wave. Consist of 5-7 Hz brief bursts of a subtle low-amplitude spikes followed by a more prominent slow wave. Occurs during relaxed wakefulness and drowsiness disappearing with deep sleep (unlike spike-and-wave discharges which persist during sleep). Usually occurs bilaterally and synchronously.

  14. Figure 52. [Example of 6-Hz "phantom" spike

    [Example of 6-Hz "phantom" spike...]. - Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants - NCBI Bookshelf Example of 6-Hz "phantom" spike and wave in an adolescent patient.

  15. Mystery Case: EEG FOLDer

    The pattern of 6/second phantom spike-and-waves observed in this young woman is termed FOLD (female, occipital, low-amplitude spike, and drowsy). 1 This rare and benign EEG finding should not be mistaken for epileptiform discharges. 1 The other variant, WHAM (waking, high-amplitude spike, anterior, male), might transiently impair cognition and h...

  16. Benign or Normal EEG Variants

    In this chapter we discuss spiky normal variants including breach rhythm, benign epileptiform transients of sleep (BETS), 14 & 6 positive spikes, 6 Hz (phantom) spike and wave, wicket spikes, and rhythmic normal variants including rhythmic temporal theta of drowsiness (RTTD) and subclinical rhythmic electrographic discharge of adults (SREDA).

  17. The electroencephalogram of idiopathic generalized epilepsy

    The interictal EEG shows brief 4-7 Hz spike-wave and polyspike-wave discharges, usually asymmetrical, as well as focal discharges (Panayiotopoulos, 2005a,b). IGE with phantom absences was proposed as a distinct syndrome by Panayiotopoulos to identify a group of IGE patients presenting with the first GTCS in adulthood and prior absences which ...

  18. Normal variants and artifacts: Importance in EEG interpretation

    Overinterpretation of EEG is an important contributor to the misdiagnosis of epilepsy. For the EEG to have a high diagnostic value and high specificity, it is critical to recognize waveforms that can be mistaken for abnormal patterns. ... Cigánek rhythm (aka midline theta), 6 Hz phantom spike-wave, 14 and 6 Hz positive spikes, subclinical ...

  19. Normal EEG variants

    The 6-Hz spike-and-wave (phantom spike-and-wave) is a benign EEG variant initially described in 1950 (Walter, 1950). "Phantom" is derived from the low-amplitude spike within a burst of spike-and-slow wave activity (Fig. 9.9). The amplitudes of the discharge are low with the spike component usually < 40 μV, and the aftergoing slow wave < 50 ...

  20. Phantom spike-and-wave bursts during REM-sleep

    Phantom spike-and-wave bursts or 6Hz spike-and-wave bursts consist of brief bursts of spikes of very low amplitude with a repetition range of 5 to 7Hz. This pattern usually occurs bilaterally and synchronously during relaxed wakefulness, drowsiness or light sleep. Bursts disappear during deeper levels of sleep.

  21. Normal Variants

    Taking the crown for perhaps the most uninspired name of EEG findings, 14 and 6 positive spikes describe 1-2 second bursts of sharply contoured positive waveforms that come in frequencies of either 14 Hz (13-17 Hz) or 6 Hz (5-7 Hz), or an admixture of both. ... mid-temporal region, and usually lasts less than 10 seconds. Unlike a seizure, there ...

  22. Benign EEG Variants

    These benign EEG variants are often found in only certain subpopulations: either young or old patients or patients with specific pathologies that are not epileptogenic. ... Phantom Spike and Wave (Six-Hertz Spike and Wave Bursts) This variant appears as a waxing-waning burst of ~6 Hz sinusoidal activity, with a duration of 1-4 seconds. Each ...

  23. EEG normal variants: A prospective study using the SCORE system

    Results The distribution of the normal variants was as follows: sharp transients 19.21% (including wicket spikes), rhythmic temporal theta of drowsiness 6.03%, temporal slowing of the old 2.89%, slow fused transients 2.59%, 14-and 6-Hz bursts 1.83%, breach rhythm 1.25%, small sharp spikes 1.05%, 6-Hz spike and slow wave 0.69% and SREDA 0.03%.