A 71 year-old woman with left frontal WHO grade III astrocytoma (diagnosed one year prior, s/p gross total resection, chemoXRT) who originally presented to the ED with acute encephalopathy and right hemiparesis. Her hemiparesis improved, but her mental status did not. You were called to evaluate her in the ED. Initial vitals notable for BP 114/69, HR 68, RR 10, SpO2 99% on room air. Non-contrast head CT was already obtained and demonstrated no acute intracranial pathology; there were stable post-operative changes from her tumor resection.
On exam, you find her to be sleeping, but she briskly wakes up when you speak to her. She follows simple commands well, but then falls back asleep after a few minutes. She demonstrates right pronator drift, and some pyramidal weakness throughout that side as well (generally graded as 3/5).
Based on her history, you recommend initiation of cEEG and admit her to the floor for further care.
You continue your care for her the next day. Overnight, her weakness has improved to baseline, but her mental status has remained stably abnormal. No seizures were reported by the overnight epilepsy fellow. You review the record and the report.
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, she has a known focus for seizures-- left frontal astrocytoma s/p resection. With her [persistent] encephalopathy, we are querying whether she 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.)
The description of the background activity fits with the summary of being an encephalopathic record. It's non-specific. The words "rhythmic," "periodic," and "organized" should jump out to you whenever you see them in a report. 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.
This patient has continuous lateralized periodic discharges (LPDs)-- an epileptiform finding. How concerning is it though? Her LPDs do fluctuate between 1.5 and 2Hz. This doesn't meet the ≥ 2.5Hz threshold to be more concerning as a definitive ictal finding. However, the frequency of 1.5-2Hz, with continuous duration (thus > 10 seconds), is consistent with being on the ictal-interctal continuum (IIC). The electrographic pattern is not clearly ictal (i.e. seizure) and not clearly not ictal. So, we have to go back and contextualize this finding in terms of how the patient currently looks. Her mental status has remained abnormal. So, we do have to be a little worried about the possibility that this abnormal pattern is causing excessive metabolic demand that is negatively contributing to her mental status. (Conversely, if her mental status was great, then we could breathe a sigh of relief but would continue to monitor to ensure nothing on her record progresses.) Is there something we can do to figure this out?
We have this finding of IIC, and we don't know whether it's clinically relevant. Her mental status is not totally reassuring, so there is concern. This is a setting in which we should perform a benzodiazepine challenge. We can give a dose of IV lorazepam, and assess whether her clinical exam and electrographic record improve. If so, then that indicates that she was more on the ictal side of the ictal-interictal continuum, and we should be treating her with antiseizure medications. If not, then we can just continue the current course and monitor for any changes. (Alternatively, if we were really concerned about giving a benzodiazepine, then we could load with an ASM-- say 3g of IV levetiracetam or 400mg of IV lacosamide or 20mg/kg of IV valproic acid-- and assess for clinical and electrographic improvement.)
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