Reading EEG (Reports)

OK, so we’re not quite getting into the nuts and bolts of reading EEGs (although, I think we will attack that in a future post, at least a little). But, even the terminology on the EEG report can be confusing. with terms like “epileptiform discharges,” that sound like seizures but aren’t, and “generalized slowing,” how do you make sense out of all that?

Maybe you’re saying, “I don’t need an EEG. I don’t work in a neuro-ICU.” Or, “I can recognize seizures when I see them.” Well, firstly, if you work in a neuro-ICU, you probably have a lot more experience with EEGs and already understand how to read them (or at least the reports). Secondly, if working in neurocritical care has taught me one thing, it’s that almost ANYTHING can be a seizure. Seizures are often tonic-clonic and large muscle twitching, but just as often (probably more often), they look like anything but seizures. So, EEG is super helpful in any kind of encephalopathy or altered mental status that can’t be readily explained.

“When do I order a routine (spot) EEG and when do I want continuous/video EEG?” Well, that’s tricky and, like a lot in critical care, is somewhat institution dependent. Continuous EEG is probably better, it’s like just getting a 12-lead for a patient with arrhythmias but not putting them on some sort of continuous ECG. You may see some stuff, but you may miss some stuff. But, continuous is cost and labor intensive and lots of places have protocols for who needs the longer studies and when you can get away with a 1h.

This post from Casey Albin and Neha Dangayach over at EMCrit have written this great post on the basics of EEG and how to read the report. They go over when to order EEGs, when to do routine vs continuous, some of the basic terminology, and what they call the “not quite seizures.” So, check it out and hopefully it will help you make sense of the next EEG report you get.

One day soon, we’ll do a post on how to read (at least on a kindergarten level) the EEG yourself. Just so you can make sense of the squiggly lines before the epileptologist gets back with you. For now, I’ll leave you with what I was taught when I first started in neurocritical care. EEGs should be the opposite of ECGs. Rhythmic stuff is bad. You want the squiggly lines to be random-ish. Also, flat lines are bad (unless you’re trying to burst suppress someone). In that respect, I guess they’re exactly like ECGs.