Aa
Evoked Potentials Vs. EMG Vs. Nerve Cond. Studies
Help. What difference do they make?
My Evoked potentials were fine... and now they are wanting to do either an EMG or Nerve conduction Study becuase I can't move my feet.
What does the Evoked Potential actually test? I mean, for lesions? Or for electrical impulse?
I was told the NCS see how quickly the impulses travel between the nerves and the EMG assesse muscle function.
Is this true?
How exactly?
Which would test would be better in my case?
If my Evoked potentials are ok, so then why are they doing this? What more can it tell?
Thank you.
~Sunnytoday~
My Evoked potentials were fine... and now they are wanting to do either an EMG or Nerve conduction Study becuase I can't move my feet.
What does the Evoked Potential actually test? I mean, for lesions? Or for electrical impulse?
I was told the NCS see how quickly the impulses travel between the nerves and the EMG assesse muscle function.
Is this true?
How exactly?
Which would test would be better in my case?
If my Evoked potentials are ok, so then why are they doing this? What more can it tell?
Thank you.
~Sunnytoday~
I don't know, but I'd like to have more information on this myself. For instance, I was under the impression that an EMG and a nerve conduction study were the same thing, but evidently that's not exactly the case. Secondly, I've heard of three different common evoked potentials tests (visual, brainstem/auditory, and somatosensory, I think), but which one will tell us what information? What does it mean if we do well on one or another, but fail miserably on the other(s)? What have we learned?
Yes, you are right, EMG's and NCS are two different things, that is the only thing I know about the whole confusing matter.
well... we shall both await other minds to answer our questions....oh Quix, where art thou?
well... we shall both await other minds to answer our questions....oh Quix, where art thou?
Okay.
The three tests each test a different thing or a different part of the nerve.
The EMG tests the electrical environment inside the muscle, how well it can muster up the lectrical potentia needed for a proper contraction.
The EMG (Electro-Myo-Gram) is a test that measures the function and health of the muscle itself and, to some extent, the health of the nerve signal ARRIVING at the muscle. The EMG stimulates the muscle directly to see check a couple of things. The test is done by inserting a fine needle (which is wired to a recording device) into the belly of the muscle and recording the electrical activity of the muscle first at rest (as the needle is inserted) and then when the patient uses (contracts) the muscle smoothly. The electrical activity is recorded on paper or by a computer and also there is often a sound generated which may be recorded along with the measurement and which also gives auditory information.
1) A resting muscle is electrically quiet. There is a short burst of electrical activity from the irritation of the needle insertion. The needle is left to record the muscle at rest. The normal muscle should then become quiet. If there is spontaneous electrical activity when the muscle is at rest, this can indicate either muscle damage or disease or an abnormal nerve impulse arriving at the muscle.
2) The patient then begins to contract the muscle smoothly. The needle electrode measures what is called the "Action Potential" of the muscle. Initially just a few of the muslce fibers contract and their potential are measured. As the muscle contracts more and more fully, more muslce fibers join in and the EMG records more and more wave forms. The wave form of the electrical activity is examined for it's height (amplitude), it's shape, and it's duration.
3) Muscle disease is indicated by a short duration of the action potential and by abnormalities in calculated ratios between the various measurments.
In doing an EMG of a muscle, the needle is inserted deeply, analyzed, then pulled back a few miilimeters, analyzed again and such until the needlele is out of the muscle. It is then reinserted in other parts of the same muscle until enough data is collected.
4) EMGs can give indirect information on neurologic problems, that is problems with the nerve signal that is stimulating the muscle to contract. These findings might include a markedly prolonged action potential Also, there may be a greater amplitude in the action potential.
This procedure may be painful for some people and less so for others. The muscles tested may be sore for days after the test.
*************************************************
The Nerve Conduction Study measures the velocity of a PERIPHERAL nerve's conduction form the farthest point to some point closer to the brain, but outside the spinal column.
We know how fast a healthy peripheral nerve can carry a signal from point A to point B. the nerve is stimulated to see it it arrives in good time and intact. So if someone is having hand pain we can stimulate the median nerve in the hand and see if it arrives all healthy at the elbow and at the shoulder. This is how we test for Carpal Tunnel, for instance.
The important thing to know here is that a Nerve Conduction Study (aka Nerve Velocity Study) is a test of specific peripheral nerves, so that if it is positive we know the problem with the pain or numbness is out in the Peripherla Nervous System (so it is not MS).
If the problem is MS, then we would expect the NCS to be normal.
*************************************************
The Evoked Potentials have nothing at all to do with the muscles. The Evoked Potential testing in MS is a measurement of a set of SENSORY nerve signals. They measure the nerve signal from a sensory organ TO the brain. the conduction velocity is measured all the way from the origin of the stimulation to the brain itself. So this test mesures some of the peripheral system in the SSEP, but mainly evaluates whether the nerve is able to deliver a well-formed wave signal all the way to the brain and do it fast enough.
The three most common Evoked Potential (EP) tests are the:
1) Visual Evoked Potential (VEP), which measures the signal from the retina of the eye to the visual processing parts of the brain. The signal should arrive with a good wave form and in 100msec. In Optic Neuritis the signal is delayed, but the shape of the wave form received should be normal. This is the EP that is most frequently abnormal in MS. Approximately three quarters of people with MS will have an abnormal VEP AT SOME POINT in their disease course. A normal VEP cannot be used to rule out the diagnosis of MS (contrary to what a few of our neurologists have said!) The VEP may be annoying, but s painless.
2) SomatoSensory (meaning sensation of the body - as opposed to sensation of the internal organs) EP. The SSEP measures the nerve signal from a point of electrical stimulation and checks to see if the signal arrives in the brain. There are surface electrodes placed along the path of the signal so that if there is an interruption of the signal, they can see where the interruption occurs. In cases of MS the signal will be delayed, but the wave should arrive with a good shape. The SSEP is the second most commonly abnormal EP test in MS - I'm unsure of the numbers but it is around 50% or less.
3) Auditory EP (also known as the Brainstem Auditory Response, BAER, and a bunch of other acronyms) In this test the stimulus is a rapid repetition of clicks and the response is picked up by electrodes over the scalp. This test is used to detect deafness in babies and to detect MS lesions involving the auditory nerve (Cranial Nerve VIII) and pathway to the brain.
If the EPs are abnormal that is good evidence that some part of the Central Nervous System is damaged. It is good evidence pointing toward MS.
Quix
The three tests each test a different thing or a different part of the nerve.
The EMG tests the electrical environment inside the muscle, how well it can muster up the lectrical potentia needed for a proper contraction.
The EMG (Electro-Myo-Gram) is a test that measures the function and health of the muscle itself and, to some extent, the health of the nerve signal ARRIVING at the muscle. The EMG stimulates the muscle directly to see check a couple of things. The test is done by inserting a fine needle (which is wired to a recording device) into the belly of the muscle and recording the electrical activity of the muscle first at rest (as the needle is inserted) and then when the patient uses (contracts) the muscle smoothly. The electrical activity is recorded on paper or by a computer and also there is often a sound generated which may be recorded along with the measurement and which also gives auditory information.
1) A resting muscle is electrically quiet. There is a short burst of electrical activity from the irritation of the needle insertion. The needle is left to record the muscle at rest. The normal muscle should then become quiet. If there is spontaneous electrical activity when the muscle is at rest, this can indicate either muscle damage or disease or an abnormal nerve impulse arriving at the muscle.
2) The patient then begins to contract the muscle smoothly. The needle electrode measures what is called the "Action Potential" of the muscle. Initially just a few of the muslce fibers contract and their potential are measured. As the muscle contracts more and more fully, more muslce fibers join in and the EMG records more and more wave forms. The wave form of the electrical activity is examined for it's height (amplitude), it's shape, and it's duration.
3) Muscle disease is indicated by a short duration of the action potential and by abnormalities in calculated ratios between the various measurments.
In doing an EMG of a muscle, the needle is inserted deeply, analyzed, then pulled back a few miilimeters, analyzed again and such until the needlele is out of the muscle. It is then reinserted in other parts of the same muscle until enough data is collected.
4) EMGs can give indirect information on neurologic problems, that is problems with the nerve signal that is stimulating the muscle to contract. These findings might include a markedly prolonged action potential Also, there may be a greater amplitude in the action potential.
This procedure may be painful for some people and less so for others. The muscles tested may be sore for days after the test.
*************************************************
The Nerve Conduction Study measures the velocity of a PERIPHERAL nerve's conduction form the farthest point to some point closer to the brain, but outside the spinal column.
We know how fast a healthy peripheral nerve can carry a signal from point A to point B. the nerve is stimulated to see it it arrives in good time and intact. So if someone is having hand pain we can stimulate the median nerve in the hand and see if it arrives all healthy at the elbow and at the shoulder. This is how we test for Carpal Tunnel, for instance.
The important thing to know here is that a Nerve Conduction Study (aka Nerve Velocity Study) is a test of specific peripheral nerves, so that if it is positive we know the problem with the pain or numbness is out in the Peripherla Nervous System (so it is not MS).
If the problem is MS, then we would expect the NCS to be normal.
*************************************************
The Evoked Potentials have nothing at all to do with the muscles. The Evoked Potential testing in MS is a measurement of a set of SENSORY nerve signals. They measure the nerve signal from a sensory organ TO the brain. the conduction velocity is measured all the way from the origin of the stimulation to the brain itself. So this test mesures some of the peripheral system in the SSEP, but mainly evaluates whether the nerve is able to deliver a well-formed wave signal all the way to the brain and do it fast enough.
The three most common Evoked Potential (EP) tests are the:
1) Visual Evoked Potential (VEP), which measures the signal from the retina of the eye to the visual processing parts of the brain. The signal should arrive with a good wave form and in 100msec. In Optic Neuritis the signal is delayed, but the shape of the wave form received should be normal. This is the EP that is most frequently abnormal in MS. Approximately three quarters of people with MS will have an abnormal VEP AT SOME POINT in their disease course. A normal VEP cannot be used to rule out the diagnosis of MS (contrary to what a few of our neurologists have said!) The VEP may be annoying, but s painless.
2) SomatoSensory (meaning sensation of the body - as opposed to sensation of the internal organs) EP. The SSEP measures the nerve signal from a point of electrical stimulation and checks to see if the signal arrives in the brain. There are surface electrodes placed along the path of the signal so that if there is an interruption of the signal, they can see where the interruption occurs. In cases of MS the signal will be delayed, but the wave should arrive with a good shape. The SSEP is the second most commonly abnormal EP test in MS - I'm unsure of the numbers but it is around 50% or less.
3) Auditory EP (also known as the Brainstem Auditory Response, BAER, and a bunch of other acronyms) In this test the stimulus is a rapid repetition of clicks and the response is picked up by electrodes over the scalp. This test is used to detect deafness in babies and to detect MS lesions involving the auditory nerve (Cranial Nerve VIII) and pathway to the brain.
If the EPs are abnormal that is good evidence that some part of the Central Nervous System is damaged. It is good evidence pointing toward MS.
Quix
and again.
the EPs test for both electrical impulses AND lesions. If the electrical impulse doesn't arrive properly at the brain, then we know that a lesion has interrupted the electrical signal.
Clear as Mud?
Quix
the EPs test for both electrical impulses AND lesions. If the electrical impulse doesn't arrive properly at the brain, then we know that a lesion has interrupted the electrical signal.
Clear as Mud?
Quix
Thank you so much for that information, I have searched websites to try and gain that info without much avail. I could find plenty of information on the NCS but not the other tests like SSEP etc.
Thanks this is all relevant to me as I have had an abnormal VEP and I am about to do the NCS which I have never had done, I had the SSEP years ago. I hope perhaps all my problems (pain/sensory stuff) might just be over excitable peripheral nerves or something. :-)
Thanks Sunny Today for asking such a good question, now we are all more informed thanks to Quix's great reply.
Thanks this is all relevant to me as I have had an abnormal VEP and I am about to do the NCS which I have never had done, I had the SSEP years ago. I hope perhaps all my problems (pain/sensory stuff) might just be over excitable peripheral nerves or something. :-)
Thanks Sunny Today for asking such a good question, now we are all more informed thanks to Quix's great reply.
Yeah, what Udkas said.
Quix, you do have a gift for taking complex technical stuff and translating it into laypersons' language. In other words, that's some mighty clear mud.
Sunny honey, I hope this all answered your questions, since you brought it up! I know it helped me a lot.
Quix, you do have a gift for taking complex technical stuff and translating it into laypersons' language. In other words, that's some mighty clear mud.
Sunny honey, I hope this all answered your questions, since you brought it up! I know it helped me a lot.
Have an Answer?
You are reading content posted in the Multiple Sclerosis Community
Top Neurology Answerers
Australia
ON
Queensland, Australia
Queen Creek, AZ
Find out how beta-blocker eye drops show promising results for acute migraine relief.
In this special Missouri Medicine report, doctors examine advances in diagnosis and treatment of this devastating and costly neurodegenerative disease.
Here are 12 simple – and fun! – ways to boost your brainpower.
Discover some of the causes of dizziness and how to treat it.
Discover the common causes of headaches and how to treat headache pain.
Two of the largest studies on Alzheimer’s have yielded new clues about the disease
