Does anyone else have an EEG finding that instantly brightens their day? Bc I just saw both 14 Hz and 6 Hz variants of ctenoids back to back and I feel like I won the EEG lottery Maybe it's a good opportunity to discuss 14 & 6 Hz positive bursts? #EEG #tweetorial #neurology

When I first learned about "14 and 6 variant" I found it a bit confusing. 1st, because you usually either see 14 Hz or you see 6 Hz, so I didn't understand why they were grouped. 2nd, bc they often aren't exactly happening at 14 and 6 cycles per second. Oh, EEGers...

But recognizing them is important at all levels bc 1) they often get misinterpret as epileptiform discharges, 2) they are truly a lovely finding, and 3) standardized tests (including RITE) *love* this variant (can't blame them!). Let's start by defining it electrographically:

14 and 6 Hz positive bursts are:
1. very regular
2. arciform and spiky
3. broadly distributed but max over the posterior temporal regions
4. occurring unilaterally, bilaterally asynchronous, or bisynchronous
5. seen in (pre)teens in drowsiness/light sleep
6. brief (0.5-2 sec)

The key to not get confused is that the spiky component of these bursts occurs as downgoing deflection (thus, "positive" by convention) and that the frequency can be bt/ 5 and 7 Hz (aka "6 Hz") or 13 and 16-17 Hz (aka "14 Hz"). Look at my recordings from today:

They are grouped together because they share all of the features above but with variable frequency between those ranges. In fact, some authors think 6 Hz is a subharmonic of 14 Hz. On that note, 14 Hz variant is much more commonly seen than 6 Hz.

"Ctenoids" was used to refer to these bursts for their appearance of "ctenoid scales" which are overlapping fisch scales with the appearance of "teeth of a comb". Look at the picture!

These can be easily missed on bipolar montages, especially if electrodes are too close to each other (given broad distribution). It's a good idea to confirm on a contralateral ear montage. Look at the difference of my 6 Hz variant this morning on double banana vs. contralat ear:

The contralateral ear referential really shows the positive (downgoing) deflection of the spiky component. Is the appearance bothering you too much? Read this recent tweetorial where talked about arciform/notched patterns and their usual benign nature: https://twitter.com/e_gleich/status/1285193217961598977

On a related note, if you put it on ipsilateral ear, because it's closer to that posterior quadrant where ctenoids are maximal, you will likely decrease the amplitude posteriorly (they will look more frontal).

This morning, I tried "average ears" or "ears tied" referential (which tbh I never use), just for kicks... it actually really enhanced the 14 Hz variant. Compare it with longitudinal bipolar montage:

By the way, @AMoosaMD had a great thread a few months ago about the intracranial correlate of the 14-6 Hz variant, check it out: https://twitter.com/AMoosaMD/status/1260854689723224064 -- any other teaching points we should add?