The EEG uses electrodes all over the brain to look at the patterns of brain wave activity, both at rest or sleep, and in response to various timuli like hyperventilating and strobe lights. They look for specific patterns of different kinds of brain waves. Most specifically they look for signs of an epileptic discharge to find a seizure disorder or generalized slowing to look for signs of encephalopathy, etc. More than a third of MS patients will have an abnormal EEG, from localized slowing of damaged areas, but they do not have a higher incidence of seizure disorder.
The EEG cannot diagnose MS. More often it is done to rule out a seizure disorder that is mimicking MS.
The Evoked Potential is looking at a specific sensory nerve pathway from somewhere in the body to the receptive part of the brain. the test may be testing the optic nerve pathway VEP, the auditory nerve pathway (AEP or BAER), sensory input from a limb called the SomatoSensory Evoked Potential. The stimulus is visual, auditory or stimulation in the limb. The electrodes are placed along the pathway - for the VEP around the scalp, same for the auditory and for the SSEP along the path of the sensory nerve leading to the brain and on the scalp.
In the EP they actually measure the time it takes for the nerve to conduct the signal and they see if the brain registers it. From huge studies with healthy people they know how fast that nerve should conduct the signal. If there has been demyelination the signal will be delayed and have a characteristic waveform. This test will often, but not always, point to MS as a diagnosis. It is considered a supporting test. The VEP is the most useful, then the SSEP, and last the AEP.
Actually, this is one of the best answers I have written on these two tests. Questio. Worthy of considering for the Info Section?
Just to let you know, that as Quix has given you all the info you need, when i had mine done both came back negative. The EVP really made my eyes sore after and gave me a migriane, but that's about it really.
OH..and have you been dx with MS?...I've had a couple of MRI and the lesions it's showed, didn't look like ms the dr say. I don't think I've had a EVP yet..guess it's another test I'll need to take.. thanks
I'm fairly new around here and I just read your explanation of EP. Thank you. I know my AEP was 3 SD below normal, which I know is very significant, since I'm a retired learning disabilities teacher. However, I couldn't wrap my head about how it differed from slower processing. Thank you. The time I see that you've taken explaining all this stuff, in just the few days I've been reading, is such a huge blessing to all others. I can tell everyone else feels the same way. Thank you.
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