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Vertex Sharp Transients (VSTs) and Interictal Epileptiform Discharges (IEDs) are both EEG patterns, but they have distinct characteristics that help differentiate them.
1.
Morphology:
§ VSTs:
Typically exhibit a triphasic waveform, consisting of two small positive waves
surrounding a larger negative sharp wave. They may also appear as diphasic or
monophasic but are most commonly recognized in their triphasic form.
§ IEDs:
Generally have a sharper contour and lower amplitude compared to VSTs. IEDs can
take various forms, including spikes and spike-and-wave complexes, and they do
not typically exhibit the triphasic morphology seen in VSTs.
2.
Localization:
§ VSTs:
Primarily recorded from midline electrodes, especially at the vertex (Cz), and
show phase reversal at this location. Their distribution is usually confined to
the parasagittal regions.
§ IEDs: More
commonly found in central or lateral regions of the scalp and can be
parasagittal but are not restricted to the midline. They may also show
different localization patterns depending on the type of epilepsy.
3.
Clinical Context:
§ VSTs:
Generally considered a normal finding during drowsiness and non-REM sleep. They
can occur spontaneously or be evoked by sensory stimuli, particularly auditory
stimuli.
§ IEDs:
Indicative of underlying epileptic activity and are associated with epilepsy.
They are typically observed in awake individuals or during sleep but are not
considered normal findings in the same way as VSTs.
4.
Amplitude and Background Activity:
§ VSTs: Can
vary in amplitude but typically do not exceed the amplitude of the background
activity. They maintain a consistent morphology during a train of
transients.
§ IEDs: Often
stand out against the background activity due to their sharper contour and can
exceed the amplitude of the background. They may also show significant
evolution in amplitude and frequency during a run of discharges.
5.
Response to Stimulation:
§ VSTs: May be
evoked by sensory stimuli, particularly auditory stimuli, and can reflect a
mechanism to maintain sleep after stimulation.
§ IEDs: Do not
typically respond to sensory stimuli in the same way and are more indicative of
a pathological process rather than a normal physiological response.
In
summary, Vertex Sharp Transients are generally benign EEG patterns associated
with normal sleep, characterized by their triphasic morphology and midline
localization. In contrast, Interictal Epileptiform Discharges are indicative of
epilepsy, with sharper contours, different localization, and a clinical context
that suggests underlying neurological issues. These differences are crucial for
accurate EEG interpretation and diagnosis.
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