![]() vertex waves from the central region) but basically never normal in the awake state. The central region is less complicated: discharges here are usually normal in the asleep state (ex. This isn’t always the case, but something to keep in mind when viewing frontal discharges.įurthermore, while anterior temporal interictals are perhaps the most common focal epileptiform discharges, because of the proximity of the F7 and F8 electrodes to the inferior frontal region, what appear to be anterior temporal discharges can, at times, actually be from the inferior frontal region. Deep frontal discharges can be missed on scalp EEG entirely, and mesial frontal discharges can appear on EEG as if they are from the contralateral frontal lobe due to the direction of the discharges’ dipole. The frontal lobes can be a confusing place for interictal discharges. Sometimes with rapid bisynchrony, with careful review you can find a small precedent change before the discharge, such as very low amplitude fast activity, to suggest a lateralized onset. You may also see discharges that appear generalized but are actually focal with rapid bisynchrony, in which they actually arise from a single location but the networks involved propagate the signal too quickly to trace that location, and they appear generalized. Note that on EEG generalized discharges do not have to be completely the same in every single lead there is often an anterior predominance to them, for example, but as long as the morphology of the discharge remains throughout all the leads (even if some are less well formed or lower amplitude) and the time of onset is the same in all the leads, you should consider it a generalized discharge. It is possible that deeper structures, such as the thalamus, may be involved with generalized discharges. Typically found with primary or symptomatic generalized epilepsies, generalized discharges begin in such a widespread fashion that they effectively involve the entire cortex simultaneously. First of all, generalized discharges cannot be localized. However, there are a few fine details or caveats to this rule. For example, a discharge at T4 suggests right mid-temporal hyperexcitability / epileptogenic potential. Generally speaking, the location of an epileptiform (or interictal) discharge suggests cortical irritability of that region. If you see a single discharge without a field, its good to make note of it but you probably shouldn't call it an interictal discharge (do, however, look for more of them and remain suspicious). The left temporal discharge above, for example, has a good field throughout the left temporal region, with the surrounding tracings "pointing to" the discharge site, as expected in bipolar montages. Whether an interictal has an appreciable slow wave or not, it should always disrupt the background and have a field this is to say, you should see "ripples" of a discharge in the surrounding EEG electrodes (as discussed in the technical section). Slow waves always immediately follow, and are often higher amplitude than, their precedent spikes or sharps. Realistically, the cutoff between them is not very important clinically, as one isn't known to be any more "severe" than the other.Īfter a spike or sharp, there is typically a slow wave, which represents the refractory period of the affected neuron population after the large and synchronized EPSPs that led to the spike or sharp itself. A spike is very similar to a sharp but faster, with a duration from 20-70ms. A sharp is a single epileptiform discharge defined by its duration lasting between 70-200ms, and by its disruption of the EEG background. Any epileptiform discharge is a disruption of the usual functioning of the brain, and sharps and spikes are perhaps the most classic type. ![]()
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