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Difference between an EMG and Evoked Potentials
Is it possible for an EMG to come back ABNORMAL and Evoked Potentials to come back NORMAL? This has happened to me and I am really confused.
Adding to the confusion is the fact that I do not understand the difference between these obnoxious tests.
Challengecase
Adding to the confusion is the fact that I do not understand the difference between these obnoxious tests.
Challengecase
Hi,
man that was good doing those tests this week and had some before but you explain things so well. Can you add this to your health pages???
I am going to copy and paste good information.
thanks
m
man that was good doing those tests this week and had some before but you explain things so well. Can you add this to your health pages???
I am going to copy and paste good information.
thanks
m
Thank you for posting the answer to my question in terms I can understand!!!
winklewanger????? lol
Challengecase
winklewanger????? lol
Challengecase
This is such a confusing topic. I'll try here.
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 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.
*************************************************
Te Evoked Potentials have nothing at all to do with the muscles, for general discussion. At the bottom I will describe a MOTOR evoked potential that is sometimes performed.
The Evoked Potential testing in MS is a measurement of a set of SENSORY nerve signals. So instead of measuring a muscle receiving a signal FROM the brain, they measure the nerve signal from a sensory organ TO the brain. 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.
Finally there is a test called a Motor Evoked Potentials in which a stimulus (either magnetic or electrical) is applied at the scalp and the arrival of the signal at a muscle is measured.
*******************************
Now, to answer your question Yes, it is entirely possible for an EMG to be abnormal and for the EPs to be normal. This would point "away" from a diagnosis of MS. It does not rule it out, but it tells the doctors to look more closely for some process that is either damaging the muscles or interfering with the neuromuscular junction - the point at which the nerve ending touches the muscle.
Quix
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 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.
*************************************************
Te Evoked Potentials have nothing at all to do with the muscles, for general discussion. At the bottom I will describe a MOTOR evoked potential that is sometimes performed.
The Evoked Potential testing in MS is a measurement of a set of SENSORY nerve signals. So instead of measuring a muscle receiving a signal FROM the brain, they measure the nerve signal from a sensory organ TO the brain. 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.
Finally there is a test called a Motor Evoked Potentials in which a stimulus (either magnetic or electrical) is applied at the scalp and the arrival of the signal at a muscle is measured.
*******************************
Now, to answer your question Yes, it is entirely possible for an EMG to be abnormal and for the EPs to be normal. This would point "away" from a diagnosis of MS. It does not rule it out, but it tells the doctors to look more closely for some process that is either damaging the muscles or interfering with the neuromuscular junction - the point at which the nerve ending touches the muscle.
Quix
I learned something. I did not know Evoked Potentials were to check the hearing...knew about the eyes. I thought the EP'S would show more than just hearing & eyes. Now I'm wondering if the neuro should have taken more stock in the abnormal EMG, EEG. She reported to me it was a normal study. Since I do not think this neuro is "normal" I am wondering what her definition of normal is! BTW, she is no longer my neuro. I am seeing a MS expert next month.
According to my EMG report this is a nerve conduction study, Beth. Good luck tomorrow.
Wish I knew how to read these darn reports.
Challengecase
According to my EMG report this is a nerve conduction study, Beth. Good luck tomorrow.
Wish I knew how to read these darn reports.
Challengecase
I am having nerve conduction test tomorrow. I sort of know what to expect, but is that the same as EMG? Still trying to understand all this.
Hugs,
Beth
Hugs,
Beth
To my understanding the Evoked Potentials are checking your eyes and or hearing. I had the EMG yesterday, lower half. The EMG is looking to find any nerve damage in the legs, arms. They actually did the evoked for my eyes yesterday too which came back normal. They said they wont do the audio part if I wont do the test where they pour water into your ears, which right now I do not want any part of. There are folks here who have alot more knowledge than I about all of this, but I do believe you can have one normal and one not. I think both tests are looking for any nerve damage. All you experts out there set me straight if I'm wrong!
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