NCCEd: Neurocritical Care Education for Residents

The patient's EEG is very abnormal. The language used in the report here is helpful, as it calls out very specific things you need to consider when deciding whether a change in treatment strategy based on the electrographic record is indicated.

We should start with asking ourselves why we ordered the EEG in the first place. What clinical question are we asking of this test? If we skip this first step, we may very well end up with a useless test that doesn't actually help us. In this patient's case, with his sudden neurologic decline without a clear structural (HCT was unremarkable) or metabolic (labs overall seem normal) explanation, we are querying whether he is having non-convulsive seizures. (You can have encephalopathy resulting from intermittent non-convulsive seizures-- with post-ictal encephalopathy in between events-- without developing full-blown non-convulsive status epilepticus.) Knowing this, we realize that we have to monitor him for a good amount of time-- at least 24-48 hours, longer depending on what we end up seeing during this time period.

The description of the background activity fits with the summary of being an encephalopathic record. It's non-specific. You can have patients look relatively good clinically with an encephalopathic background (like us walking around when we're sleep deprived!). The words "rhythmic," "periodic," and "organized" should jump out to you whenever you see them in a report. The "quasi-" modifier means the finding didn't truly meet the criteria for these words, so the level of concern can be slightly lower. When you see that there's a rhythmic or periodic finding, the next questions should be: How fast? Did this evolve? Evolution in space and time indicate that the electrographic pattern is more concerning for an ictal (on the seizure end of the spectrum) phenomenon. Furthermore, per ACNS criteria, the general cut-off for frequency that is concerning is ≥ 2.5Hz. Patterns at this frequency or higher are more concerning for being ictal rather than not.

Finally-- and it's intentional that we're only talking about this part at the end-- there were no clinical events or seizures captured. If we had seem some concerning movements or fluctuations in his exam, it'd be helpful to refer back to the EEG to see if there was an electrographic correlate. If so, that would be concerning. The reason why this is the last part of the report about which we'll talk is because, yes, it's helpful to know if there were seizures. However, there are more very important findings about which to know-- the ones we covered above.

So, for this patient, there were times where the patient did develop rhythmic delta activity (RDA). However, the duration was brief (< 10seconds), and slower than our 2.5Hz threshold. Abnormal, but not ictal.

Now that we've seen the EEG report, we need to circle back and contextualize it in terms of the patient's clinical appeareance. He's still on light sedation-- dexmedetomidine-- which shouldn't suppress his mental status much. He still isn't very alert. However, his EEG isn't showing any ictal patterns. We don't need to treat with an antiseizure medication, but we do need to continue monitoring him on cEEG to see if these brief rhythmic patterns do end up becoming faster (meeting or exceeding that 2.5Hz threshold) and develop evolution.