“Things are seldom what they seem.” – W.S. Gilbert
Continuing with our Fall Quick Tips Series:What is a normal variant in an EEG?
Waves that are rare or unusual but not generally abnormal…
They are odd looking….they may be unusual in shape or in distribution…These variant waveforms are rare or unusual but are known to be generally benign. But that doesn’t mean they are not still interesting!
My favorite is the Mu Rhythm – I think it’s super interesting because of it’s relation to the Homunculus Man and it’s reactivity if you ask the patient to squeeze their fist or if you even touch their hand. The mu waveform, if it appears, occurs in the central regions in the awake patient…best seen with their eyes open. It’s often in the alpha range and can be asymmetrical.
A close second favorite of mine are Lambda Waves – Lambda waves occur in the occipital regions bilaterally as positive (upward) waves. They are triangular in shape and generally symmetric. They are most often seen when a patient is visually scanning something; such as, when they read.
Other normal variants include:
SREDA (Subclinical Rhythmic EEG Discharges in Adults)
RMTD (Rhythmic Mid-Temporal Theta of Drowsiness)
BETS (Benign Epileptiform Transients of Sleep)
14 and 6 Positive Spikes
and there are more…
It’s a great area to review and become familiar with – many of these are really interesting and often mistakenly referred to as abnormal.
What we are recording is the electrical activity of a highly complex system – so a variation is to be expected…occasional atypical waveforms that still fall within what would be considered normal is likely.