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Which Electroencephalogram Patterns Are Commonly Misread as Epileptiform?
lobe spikes, 75% with frontal lobe spikes, 54% with central spikes, 38%
Figure 5: Hypnagogic Hypersynchrony in a Three-year-old Child
with occipital spikes, and 76% with multifocal spikes have clinical
seizures.
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At least 50% of children demonstrated to have focal spikes
will have disappearance of the foci two years after they were first seen.
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Nevertheless, there are focal patterns that are commonly misread in
children, and we will review the lobar spike mimics first and finish with
those patterns that mimic generalized discharges.
Temporal
In children, the source of confusion is often temporal theta from drowsiness,
which is most often bilateral but can be more prominent on one side. These
can be of high voltage. They are often present in EEG recordings of children,
because children often have EEGs performed when in a drowsy state. The
high voltage is particularly confusing to those who predominantly read adult
studies where such high-voltage activity is less likely to be seen. As noted in
the adult section, 6 and 14Hz positive spikes are most likely to be seen in the
adolescent EEG and present in the posterior temporal area.
Frontal and Central
Unilateral or bilateral sharp activity seen only in drowsiness can often be
confusing in EEGs of children. Children often have rapid transitions into
and out of sleep. Sleep phenomena such as the central diphasic wave of positive occipital sharp transients of sleep, these are positive over the
arousal or the initial vertex waves and k complexes are often more occipital leads and should not be confused with pathological activity.
sharply contoured and of much higher amplitude than in adult patients. They are maximal between two and 15 years of age and may occur
Particularly in the first years of life, these can be asymmetrical and of asymmetrically. An astute EEG technician can be valuable in noting
high voltage, causing confusion with pathological waves. The central scanning movements when these are present, asking the patient to close
diphasic wave that can mark the onset of true sleep becomes most his or her eyes, which causes them to disappear.
pronounced at three years of age and can be of high amplitude and
sharply peaked and be a possible source of misinterpretation.
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Posterior Slow Waves of Sleep
Recognizing that these occur only during drowsiness and sleep should These are predominantly found in children and disappear by early
help to differentiate them. adulthood. They are often found embedded in the alpha activity and when
superimposed on the sharply contoured alpha activity of many children can
Occipital resemble spike and wave foci. They can be repetitive at times and in
Occipital sharp activity has a much lower correlation with seizures than prolonged runs. Recognizing the presence of this elsewhere in the study and
temporal sharp activity (38 versus 91%). In particular, the two- to three-year- the underlying alpha rhythm should help to differentiate this normal variant
old child will often have the equivalent of benign focal epileptiform discharges from pathological activity.
(rolandic spikes) seen in this area, which can correlate with epilepsy
(Panayicytopulos syndrome) but at a low rate, and visually impaired children Generalized Activity
will have occipital needle spikes, which do not correlate with epilepsy.
Hyperventilation
Positive occipital sharp transients can mimic occipital spikes. These are most Children are hyperventilated both by activation procedures and by
highly present in the adolescent EEG. They have a characteristic checkmark crying. Recognizing the effect of hyperventilation during these times is
appearance with an initial positive deflection in the occipital leads followed by helpful in avoiding misreading. Hyperventilation is quite helpful in
a rapid surface negative deflection. They are seen in all stages of non-rapid bringing out the typical 3Hz spike and wave seen in absence epilepsy,
eye movement sleep but most commonly in stage two and three. They can so it is a common procedure in pediatric EEGs. Hyperventilation in
occur singly or repetitively in rates up to 5Hz (see Figure 4). Their duration normal young children can exceed 100 microvolts (see Figure 5).
ranges from 80 to 200 milliseconds and their amplitude can exceed 100 Although not well quantified by voltage, an early study showed 97% of
microvolts, but is usually 20–75 microvolts.
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They can be quite prominent and children aged three to five having a big build-up. The percentage of
can occur in prolonged runs superficially simulating an electrographic seizure. patients with this big build-up drops progressively as the age of the
They can be differentiated by their positivity (pathological spikes are rarely patient increases, until adulthood, where fewer than 10% have a big
positive on surface EEG), monomorpic appearance, lack of evolution in build-up.
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These high-voltage waves associated with hyperventilation
frequency, and their appearance only in sleep. response are often notched and should not be confused with
pathological spike and wave activity in which the spikes are quite
Lambda Waves dramatic. There is a wide range of normal hyperventilation response and
These are positive waves during wakefulness that occur during scanning the electroencephalographer should be cautious in calling anything but
activity, such as looking at patterns on the ceiling during an EEG. As with the clear 3Hz spike and wave response.
US NEUROLOGY 65
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