Adult EEG

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Adult EEG

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Alpha rhythm

• The normal alpha rhythm has the following
  characteristics
• Frequency of 8-12 Hz - Lower limit of normal
  generally accepted in adults and children older
  than 8 years is 8 Hz
• Location - Posterior dominant occasionally, the
  maximum may be a little more anterior, and it may
  be more widespread
• Morphology - Rhythmic, regular, and waxing and
  waning
• Amplitude - Generally 20-100 mV
• Reactivity - Best seen with eyes closed
  attenuates with eye opening

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alpha rhythm
Occasionally the alpha rhythm is of very low
amplitude or even not identifiable. This is not
abnormal. In addition to amplitude, other
characteristics can vary somewhat without being
abnormal, including morphology (eg, spiky),
distribution (eg, widespread), and harmonic
frequency (eg, slow or fast alpha variant).
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Beta activity

• Normal beta activity has the following
  characteristics
• Frequency (by definition) greater than 13 Hz -
  Common 18-25 Hz, less common 14-16 Hz, and rare
  35-40 Hz
• Location - Mostly frontocentral but somewhat
  variable some describe various types according
  to location and reactivity generalized,
  precentral, and posterior
• Morphology - Usually rhythmic, waxing and waning,
  and symmetric
• Amplitude - Usually range of 5-20 mV
• Reactivity - Most common 18- to 25-Hz beta
  activity enhanced during stages I and II sleep
  and tends to decrease during deeper sleep stages
  central beta activity may be reactive
  (attenuates) to voluntary movements and
  proprioceptive stimuli in infants older than 6
  months, onset of sleep marked by increased beta
  activity in central and postcentral regions

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Beta activity
In healthy individuals, beta activity commonly
can be mildly different (lt35) in amplitude
between the 2 hemispheres, which may be caused by
differences in skull thickness. Definite focal,
regional, or hemispheric difference (at least
50) in amplitude may be significant and may
suggest either skull defect (side with higher
amplitude) or a structural lesion (side with
lower amplitude). The amount and voltage of beta
activity is enhanced by commonly used sedative
medications (benzodiazepines, barbiturates).
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Mu rhythm

• Characteristics of the mu rhythms are as follows
  
• Frequency of 7-11 Hz - Generally in alpha
  frequency band (8-12 Hz)
• Location - Centroparietal area
• Morphology - Archlike shape or like an "m" most
  often asymmetric and asynchronous between the 2
  sides and may be unilateral
• Amplitude - Generally low to medium and
  comparable to that of the alpha rhythm
• Reactivity - Most characteristic feature defining
  the mu rhythm mu rhythm attenuates with
  contralateral extremity movement, the thought of
  a movement, or tactile stimulation contrary to
  the alpha rhythm, does not react to eye opening
  and closing

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Mu rhythm
Asymmetry, unilaterality, or asynchrony of the mu
rhythm is generally not abnormal unless
associated with other abnormalities.
Very-high-voltage mu activity may be recorded in
the central regions over skull defects and may
become sharp in configuration, and thus can be
mistaken for epileptiform discharges. When mu
rhythm is detected in an EEG, it should be
verified by testing its reactivity.
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Loomis provided the earliest detailed description
of various stages of sleep in the mid-1930s, and
in the early 1950s Aserinsky and Kleitman
identified rapid eye movement (REM) sleep.
Sleep generally is divided in 2 broad types
nonrapid eye movement sleep (NREM) and REM sleep.
NREM is divided further into 4 stages (stage
I, stage II, stage III, stage IV). NREM and REM
occur in alternating cycles, each lasting
approximately 90-100 minutes, with a total of 4-6
cycles. In general, in the healthy young adult
NREM sleep accounts for 75-90 of sleep time
(3-5 stage I, 50-60 stage II, and 10-20 stages
III and IV). REM sleep accounts for 10-25 of
sleep time.
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Normal Sleep EEG - Rapid Eye Movement Sleep
REM sleep normally is not seen on routine EEGs,
because the normal latency to REM sleep (100 min)
is well beyond the duration of routine EEG
recordings (approximately 20-30 min). The
appearance of REM sleep during a routine EEG is
referred to as sleep-onset REM period (SOREMP)
and is considered an abnormality. While not
observed on routine EEG, REM sleep commonly is
seen during prolonged (gt24 h) EEG monitoring
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REM sleep
By strict sleep staging criteria on
polysomnography, REM sleep is defined by (1)
rapid eye movements (2) muscle atonia (3) EEG
desynchronization (compared to slow wave
sleep). . muscle activity and eye movements
can be evaluated on EEG, thus REM sleep is
usually not difficult to identify. In addition
to the 3 features already named, saw tooth
waves also are seen in REM sleep.
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REM sleep

• EEG desynchronization The EEG background
  activity changes from that seen in slow wave
  sleep (stage III or IV) to faster and lower
  voltage activity (theta and beta), resembling
  wakefulness. Saw tooth waves are a special type
  of central theta activity that has a notched
  morphology resembling the blade of a saw and
  usually occurs close to rapid eye movements (ie,
  phasic REM). They are only rarely clearly
  identifiable.
• Rapid eye movements These are saccadic,
  predominantly horizontal, and occur in repetitive
  bursts.

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Stage I sleep also is referred to as drowsiness
or presleep and is the first or earliest stage of
sleep.

• The features of drowsiness are as follows
• Slow rolling eye movements (SREMs)
• Attenuation (drop out) of the alpha rhythm
• Central or frontocentral theta activity
• Enhanced beta activity
• Positive occipital sharp transients of sleep
  (POSTS)
• Vertex sharp transients
• Hypnagogic hypersynchrony

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Slow rolling eye movements
SREMs are usually the first evidence of
drowsiness seen on the EEG. SREMs of drowsiness
most often are horizontal but can be vertical or
oblique, and their distribution is similar to eye
movements in general . However, they are slow
(ie, typically 0.25-0.5 Hz). SREMs disappear in
stage II and deeper sleep stages.
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Alpha dropout
Drop out of alpha activity typically occurs
together with or nearby SREM. The alpha rhythm
gradually becomes slower, less prominent, and
fragmented.
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Positive occipital sharp transients of sleep
POSTS start to occur in healthy people at age 4
years, become fairly common by age 15 years,
remain common through age 35 years, and start to
disappear by age 50 years. POSTS are seen very
commonly on EEG and have been said to be more
common during daytime naps than during nocturnal
sleep. Most characteristics of POSTS are
contained in their name. They have a positive
maximum at the occiput, are contoured sharply,
and occur in early sleep (stages I and II). Their
morphology classically is described as "reverse
check mark," and their amplitude is 50-100 mV.
They typically occur in runs of 4-5 Hz and are
bisynchronous, although they may be asymmetric.
They persist in stage II sleep but usually
disappear in subsequent stag
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Vertex sharp transients
Also called vertex waves or V waves, these
transients are almost universal. Although they
often are grouped together with K complexes,
strictly speaking, vertex sharp transients are
distinct from K complexes. Like K complexes,
vertex waves are maximum at the vertex (central
midline placement of electrodes Cz), so that,
depending on the montage, they may be seen on
both sides, usually symmetrically. Their
amplitude is 50-150 mV. They can be contoured
sharply and occur in repetitive runs, especially
in children. They persist in stage II sleep but
usually disappear in subsequent stages. Unlike K
complexes, vertex waves are narrower and more
focal and by themselves do not define stage II.
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Hypnagogic hypersynchrony
Hypnagogic hypersynchrony (first described by
Gibbs and Gibbs, 1950) is a well-recognized
normal variant of drowsiness in children aged 3
months to 13 years. This is described as
paroxysmal bursts (3-5 Hz) of high-voltage (as
high as 350 mV) sinusoidal waves, maximally
expressed in the prefrontal-central areas, that
brake after the cerebral activity amplitude drops
during drowsiness.
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Stage II is the predominant sleep stage during a
normal night's sleep
.The distinct and principal EEG criterion to
establish stage II sleep is the appearance of
sleep spindles or K complexes. The presence of
sleep spindles is necessary and sufficient to
define stage II sleep. Another characteristic
finding of stage II sleep is the appearance of K
complexes, but since K complexes typically are
associated with a spindle, spindles are the
defining features of stage II sleep. Except for
slow rolling eye movements, all patterns
described under stage I persist in stage II sleep

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Sleep spindles
normally first appear in infants aged 6-8 weeks
and are bilaterally asynchronous. These become
well-formed spindles and bilaterally synchronous
by the time the individual is aged 2
years. Sleep spindles have a frequency of 12-16
Hz (typically 14 Hz) and are maximal in the
central region (vertex), although they
occasionally predominate in the frontal regions.
They occur in short bursts of waxing and waning
spindlelike (fusiform) rhythmic activity.
Amplitude is usually 20-100 mV. Extreme spindles
(described by Gibbs and Gibbs) are unusually
high-voltage (100-400 mV) and prolonged (gt20 s)
spindles located over the frontal regions.
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K complexes (initially described by Loomis) are
high amplitude (gt100 mV), broad (gt200 ms),
diphasic, and transient and often are associated
with sleep spindles. Location is frontocentral,
with a typical maximum at the midline (central
midline placement of electrodes Cz or frontal
midline placement of electrodes Fz). They
occur spontaneously and are elicited as an
arousal response. They may have an association
with blood pressure fluctuation during sleep
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Total sleep time in the healthy young adult
approximates 7.5-8 hours. In the full-term
newborn, sleep cycles last approximately 60
minutes (50 NREM, 50 REM, alternating through a
3-4 h interfeeding period). The newborn sleeps
approximately 16-20 hours per day these numbers
decline to a mean of 10 hours during childhood
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slow wave sleep
Stages III and IV usually are grouped together as
slow wave sleep or delta sleep. Slow wave
sleep (SWS) usually is not seen during routine
EEG, which is too brief a recording. However, it
is seen during prolonged (gt24 h) EEG monitoring.
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slow wave sleep
Men aged 20-29 years spend about 21 of their
total sleep in SWS, those aged 40-49 years
spend about 8 in SWS, those aged 60-69 spend
about 2 in SWS (Williams et al, 1974). Notably,
elderly people's sleep comprises only a small
amount of deep sleep (virtually no stage IV sleep
and scant stage III sleep). Their total sleep
time approximates 6.5 hours. SWS is
characterized by relative body immobility,
although body movement artifacts may be
registered on electromyogram (EMG) toward the end
of SWS
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slow wave sleep
SWS, or delta sleep, is characterized, as the
name implies, by delta activity. This typically
is generalized and polymorphic or semirhythmic.
By strict sleep staging criteria on
polysomnography, SWS is defined by the presence
of such delta activity for more than 20 of the
time, and an amplitude criterion of at least 75
mV often is applied. The distinction between
stages III and IV is only a quantitative one that
has to do with the amount of delta activity.
Stage III is defined by delta activity that
occupies 20-50 of the time, whereas in stage IV
delta activity represents greater than 50 of the
time. Sleep spindles and K complexes may
persist in stage III and even to some degree in
stage IV, but they are not prominent.
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As mentioned above, SWS usually is not seen
during routine EEG, which is too brief a
recording. However, it is seen during prolonged
EEG monitoring. One important clinical aspect
of SWS is that certain parasomnias occur
specifically out of this stage and must be
differentiated from seizures. These slow wave
sleep parasomnias include confusional arousals,
night terrors (pavor nocturnus), and sleep
walking (somnambulism).
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Epileptiform Normal Variants

• benign epileptiform transients of sleep,
• midline theta,
• phantom spikes and waves,
• psychomotor variants,
• small sharp spikes,
• subclinical rhythmic EEG discharges of adults,
• wicket spikes,
• 14- and 6-Hz positive spikes

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Most of these patterns initially were described
in the 1950s. Gibbs and Gibbs described small
sharp spikes in 1952, and 14- and 6-Hz positive
spikes were described at approximately the same
time (Gibbs and Gibbs, 1951 Grossman, 1954
Kellaway et al, 1959 Nidermeyer and Croft,
1961). The 6-Hz phantom spike-wave was described
by Walter (1950), and the psychomotor variant was
described by Gibbs and Gibbs (1952). Wickets were
described in 1977 (Reiher and Lebel).
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Small sharp spikes
Also known as benign epileptiform transients of
sleep (BETS), SSSs occur in light sleep (stages I
and II of nonrapid eye movement NREM sleep),
usually sporadically. Location is temporal,
either unilateral or bilaterally independent, and
with a broad field of distribution. Morphology is
typically monophasic, occasionally diphasic, and
the decline after the first negative peak is very
steep. SSSs rarely may have a single aftergoing
slow-wave component but generally are not
disturbing the background. The main features of
SSSs are in their name duration is short,
amplitude is small, and an easy guideline states
that SSSs generally should be less than 50 mV and
less than 50 milliseconds.
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Wicket spikes
Wicket spikes occur in both awake state and
light sleep. Frequency is 6-11 Hz, usually in
short runs (wicket rhythm) but also as single
sharp transients. Location is temporal, usually
bilateral and independent. Morphology is archlike
or mu-like, sharp, monophasic, and not followed
by an aftergoing slow wave. Amplitude may be
high, but the transient arises out of an ongoing
rhythm and does not "stand out."
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14-Hz and 6-Hz positive spikes
This pattern is observed at any age, but it is
expressed maximally in adolescents, especially
those aged 13-14 years (Klass and Westmoreland,
1985). The 6-Hz positive spikes predominate in
children younger than 1 year and in adults older
than 40 years, and the 14-Hz positive spikes
predominate or combine with 6-Hz spikes in the
other age groups (Gibbs et al, 1963). Both 14-
and 6-Hz positive spikes are observed
predominantly during light sleep. These spikes
usually appear in short runs lasting less than 2
seconds, and their frequencies, as the name
implies, are 14 Hz and 6 Hz. Location is mostly
posterior temporal, unilaterally or bilaterally.
Morphology is a sharply contoured positive spike
alternating with rounded negative component.
Amplitude is medium, around 20-60 mV.
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Phantom spike and wave (6 Hz)
The 6-Hz spike and wave pattern may be observed
in both adolescents and adults. It generally
occurs during relaxed wakefulness and stage I
sleep and disappears during deeper levels of
sleep. Frequency is 6 Hz, and the bursts last 1-2
seconds. Location is usually diffuse,
bisynchronous, and relatively symmetric. This
pattern may predominate in the anterior and
posterior head regions. Morphology is a typically
small (lt30 mV and lt30 ms), evanescent diphasic
spike followed by a higher (50-100 mV) slow wave
component. Thus, the spike component may be
difficult to see.
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Psychomotor variant
A more useful and descriptive term is rhythmic
midtemporal theta of drowsiness (RMTD). Frequency
is theta (4-7 Hz). Location is maximum
midtemporal, unilateral or bilaterally
independent or bisynchronous. Morphology
typically is notched, flat topped, or sharply
contoured. Bursts may last 1-10 seconds or longer
and thus resemble temporal lobe seizures.
Amplitude is medium to high.
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Subclinical rhythmic EEG discharges of adults
SREDA is an uncommon pattern observed mainly in
older persons (gt50 y). It may occur at rest or
during drowsiness. SREDA superficially resembles
an EEG seizure pattern. Frequency is typically
5-6 Hz. Location is widespread or bilateral with
a posterior maximum. Morphology is seizurelike
(ie, rhythmic sharply contoured theta). Abrupt
onset and termination may help distinguish SREDA
from an EEG seizure. Duration ranges from 20
seconds to minutes (average 40-80 s).
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Midline theta rhythm
(ie, Ciganek rhythm) Midline theta rhythm may be
observed during wakefulness or drowsiness. As
indicated by the name, frequency is 4-7 Hz, and
the location is midline (ie, vertex). Morphology
is rhythmic, smooth, sinusoidal, arciform, spiky,
or mu-like.
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Localization-related Epilepsies
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waveform
Spikes and sharp waves are sharp transients that
have a strong association with epilepsy. The two
are distinguished only by their duration (spikes
lt70 ms, sharp waves 70-200 ms), but they have no
differences in terms of clinical significance.
Several characteristics distinguish these from
benign epileptiform variants including high
amplitudes, which make them stand out from
ongoing background activity, and aftergoing slow
waves, which give the appearance of their
disrupting background activity
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waveform
Polyspikes are rarely focal, although focal
spikes can at times have a multiphasic
polyspike-like morphology
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waveform
Electrographic seizures Focal seizures are
discharges characterized by rhythmicity and
evolution (build-up) in frequency and
amplitude. The discharge can consist of rhythmic
theta or delta activity, or repetitive spikes or
sharp waves, but the most characteristic features
of electrographic focal seizures are rhythmicity
and evolution
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Idiopathic localization-related epilepsies
Benign focal epilepsy of childhood is the main
localization-related epilepsy that is idiopathic.
Two varieties have been well described and are in
the 1989 ILAE classification centrotemporal
occipital. A third type has been described
more recently autosomal dominant nocturnal
frontal lobe epilepsy (ADNFLE).
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Benign childhood epilepsy with centrotemporal
spikes (BECTS)
by far the more common. Age of onset is between
4 and 12 years (peak age 8-9 years). Seizures are
simple partial with motor symptoms involving the
face, and they tend to occur during sleep or on
awakening. Though these focal seizures are the
most characteristic seizure types in BECTS, they
can be quite subtle and are missed easily, so
that the most common mode of presentation is a
(secondary) generalized tonic-clonic seizure. As
with all idiopathic epilepsy syndromes,
neurologic examination findings are normal..
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Benign childhood epilepsy with centrotemporal
spikes (BECTS)
EEG findings are characteristic, with
stereotyped centrotemporal sharp waves that have
a characteristic morphology. They are activated
markedly by nonrapid eye movement (NREM) sleep,
often occur in repetitive bursts, and can be
bilateral and independent. Notably, the
interictal sharp waves of BECTS often occur in
asymptomatic children. In fact, only a minority
of children with these discharges may have
seizures
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Childhood epilepsy with occipital paroxysms
is less common and less consistently benign. It
shares all the characteristics of an idiopathic
syndrome (ie, normal findings on examination,
intelligence quotient IQ testing, and
neuroimaging studies). Age of onset is 4-8 years.
Seizures are rare and primarily nocturnal, and
often involve visual symptoms. Sharp waves have a
maximum occipital negativity, often occur in long
bursts of spike-wave complexes, and are activated
markedly by eye closure
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ADNFLE
is a recently described genetic
localization-related epilepsy. Several
mutations of the neuronal nicotinic acetylcholine
receptor alpha4 subunit have been identified in
association with this epilepsy. It has the
expected features of idiopathic (ie, genetic)
epilepsies, including onset early in life and
normal imaging findings. Seizures are nocturnal
and occur in clusters, mimicking parasomnias.
They are mostly brief tonic seizures and rare
(secondarily) generalized tonic-clonic
convulsions, often preceded by a nonspecific
aura.
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ADNFLE
Interictal EEG may show epileptiform discharges
with a frontal predominance, often seen only in
sleep. Ictal EEG does not always show definite
ictal discharges. Thus the electroclinical
features of ADNFLE are not different from those
of symptomatic or cryptogenic frontal lobe
epilepsy. Since the genetic findings are variable
(ie, locus heterogeneity), its definite diagnosis
is largely one of exclusion
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Cryptogenic focal epilepsies
This is by far the most common type of
adult-onset epilepsy. By definition, seizures
arise from a localized region of the brain. If
the cause is found, they are said to be
symptomatic. If imaging study findings are
normal, the cause remains presumptive and they
are said to be cryptogenic. As stated already,
the boundary between the two is largely dependent
on our diagnostic and imaging techniques, and
etiologies such as low-grade tumors, hippocampal
sclerosis, and subtle cortical dysplasias
Clinically, seizures may be simple partial or
complex partial, with or without secondary
generalization. Interictal EEG shows focal spikes
or sharp waves, and ictal EEG shows a focal or
regional discharge at onset. The main clinical
entities are mesiotemporal lobe epilepsy,
neocortical focal epilepsies, and hemispheric
syndromes.
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Generalized epilepsies -waveform
48

• Spike-wave complexes (SWC) are the repetitive
  occurrence of a spike followed by a slow wave.

• 3-Hz SWC This pattern is characterized by a
  frequency of 2.5-4 Hz and a very monomorphic
  (perfectly regular) morphology . It occurs in
  very discrete bursts, and between bursts the EEG
  is normal.
• Slow SWC This pattern is not only slower (lt2.5
  Hz) but also more irregular (less monomorphic)
  than the 3-Hz SWC. Bursts are less discrete than
  the 3-Hz SWC, and between bursts other
  abnormalities are seen in symptomatic/cryptogenic
  epilepsies of the Lennox-Gastaut type

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Polyspikes are multiple repetitive spikes
occurring at about 20 Hz Generalized
epileptiform discharges (ie, spikes, sharp waves,
SWCs) are usually maximal in the frontal regions,
with typical phase reversals at the F3 and F4
electrodes Hypsarrhythmia is defined as
continuous (during wakefulness), high-amplitude
(gt200 Hz), generalized polymorphic slowing with
no organized background and multifocal spikes
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Electrographic seizures

• Electrodecrement consists of abrupt attenuation
  (flattening) of background activity, often
  preceded by a high-amplitude transient. This
  typically is associated with infantile spasms or
  atonic seizures.
• Generalized paroxysmal fast activity (GPFA)
  consists of bursts of fast (10 Hz) activity and
  typically is associated with tonic seizures.

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Idiopathic generalized epilepsies
These syndromes, formerly called primary
generalized epilepsies, are the best known group
of idiopathic epilepsies. They epitomize the
meaning of the term idiopathic genetic basis,
normal neurologic examination findings, and
normal intelligence. EEG shows generalized
epileptiform discharges and may show
photosensitivity. Seizure types include
generalized tonic-clonic (GTC), absence, and
myoclonic. Accordingly, EEG typically shows
generalized spikes or sharp waves, 3-Hz or faster
SWCs (clinically associated with absence
seizures), and polyspikes (clinically associated
with myoclonic seizures). The EEG is normal
(ie, no abnormal slowing) except for the
epileptiform abnormalities.