spikes or slow waves. Spikes are narrow-based waves that have a
relatively high amplitude, giving them a narrow and high form and a sharp
top. A sharp wave is slightly broader than a spike, but has the same
significance - it is the common hallmark of seizure activity and implies
multiple synchronous firing or activity(of dendrites). Sharp waves are
thought to represent the discharge as seen from some distance away
while spikes are recorded from close to the focus.
Wave patterns that have some specificity because of their morphology include:
Amongst other less common forms
Spike and wave format is seen at all ages but most often in children.
It consists of a spike, which is probable generated in the cortex, and
a large amplitude slow wave(usually delta), thought to originate from
thalamic structures, occuring recurrently. They may occur synchronously
and symmetrically in the generalized epilepsies or focally in the partial
ones. In the generalized types of spike and wave, true absense(petit mal)
is characterized by 3 Hz spike-wave, while slow spike-wave occurs more
usually with brain injury and the Lennox-Gastaut syndrome.
Faster than 3 Hz spike and wave will be dealt with in the section
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Polyspike and wave is a form of spike wave in which each slow wave is
accompanied by two or more spikes. The usual pattern is that the spike
and wave is faster than 3 Hz - usually 3.5 to 4.5 Hz. It is often associated
with myoclonus or myoclonic seizures. It should not be confused with 6 Hz
spike and wave, otherwise known as phantom spike and wave - a normal variant.
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PERIODIC LATERALISED EPILEPTIFORM
DISCHARGES
PLEDS - Periodic Lateralized Epileptiform Discharges - are a form of
discharge associated with acute brain injury or damage. The pattern
is also said to be most evident when acute brain injury is coupled with
some metabolic derangement. It is an evolving pattern starting out with
sharp waves occuring at regular intervals over one whole area or side
with relative flattening between. It evolves to slow transients and then
slow waves occuring periodically with improving background activity
between. It finally clears completely. It is often associated with severe
focal signs andmuch illness early on with some improvement later.
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Triphasic waves are as illustrated the 3 waves are seen outlined in
white. They often occur as long runs causing an appearance of
pseudoparoxysmal activity. The waveform was originally found with
hepatic encephalopathy but has subsequently been found in association
with many other forms of metabolic encephalopathy.
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Burst-suppression is a pattern of burst of slow and mixed waves often
of high amplitude alternating with a flat baseline. The pattern is bilateral
but not always symmetrical. It is usually seen after severe brain injury
such as postischemia or postanoxia. It is also seen in temporary form
in deep anesthesia in a stage prior to total flattening of the EEG.
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