Abnormal Evoked Potentials, Normal MRI = What?

[Linda-James]

    
      Re: Abnormal Evoked Potentials, Normal MRI = What?
    


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Posted by ccfNeuro MD on July 21, 1997 at 15:55:44:

In Reply to: Abnormal Evoked Potentials, Normal MRI = What? posted by Linda James on July 03, 1997 at 01:48:24:

: My problem started with terrible headaches about three years ago.  This was determined to be related to a neck problem.  The symptoms progressed to included tingeling, burning and pain in my right arm and hand.  Then there came some of the same of the left side.  Three years later I am again having trouble with right side weakness including shoulder, arm and hip.  Last Oct I had the 3 evoked potentials and the auditory and brain stem tests were abnormal.  The report indicates that there were probably at least three lesions.  The MRI was normal except for one area on the right that seemed to be swollen.  My Doctor said must not be MS becasue of MRI and gave me muscle relaxers for spasms and pain meds.  My question is what exactly does the abnormal evokes mean?  Also, should I insist on a spinal to defintely rule out the MS.  The symptoms do leave at times, but each time the come back they are worse.  Sorry for such a long message.  Thanks in advance for your time.
  Linda
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Dear Linda,   Stimulating a nerve produces an electrical signal which travels along a predefined path through several “relay stations” to the cortex of the brain, the final destination.  Evoked potentials “track” the tiny electrical signals from a nerve impulse.  They measure the “latency”(the time from the stimulation to arrival of the impulse) along several points in the course of the electrical signals as they travel to the brain.  In this way they can provide information on the integrity of  these pathways.   By looking at where the latencies are abnormal, they can also help localize any problem along the pathway.    They CANNOT, however,  determine the cause of the abnormality.  There are several types of evoked potentials:  visual evoked potentials (VEPs) which examine the pathway from eye to the cerebral cortex, brainstem auditory evoked potentials (BAEPs) which look at the pathway between the ear and the cortex of the brain, and the somatosensory evoked potentials (SSEPs) which examine the pathway between the body (arm or leg) and the cortex.
Multiple sclerosis is a disease process in which myelin, the insulator covering the nerves, is attacked by the body’s immune system.  This leads to “disruption” of signal transmission and hence the symptoms.  The diagnosis of multiple sclerosis can be very difficult. It is made by looking at the history,  abnormalities on the neurological examination and various laboratory testing such as evoked potentials, MRI of the brain and spinal cord,  and testing of cerebrospinal fluid.    No single laboratory feature or test  is a totally reliable marker for MS.  The brain MRI is no exception to this: although it usually demonstrates abnormalities (I would say >80-90% cases)  not all people with MS will have an abnormal MRI.  It is difficult for me to comment on your problem.  There may be features of your history or examination which your physician believes is atypical for MS.  From the limited history I have, I cannot tell you to “insist” that you have a lumbar puncture to further evaluate the possibility of MS.  I will say that from what you have written, it sounds like a reasonable thing to do.  I do recommend that you go to a center which specializes in the diagnosis and treatment of MS for a thorough evaluation.  If you near the Cleveland area, I would recommend the  Mellen Center at the Cleveland Clinic, which is a large referral center which I believe provides excellent care. (To get in touch with them call 216-444-8600 ) Good luck to you.  This information is provided for general medical education purposes only.  Please consult your physician for diagnosis and treatment options of your specific medical condition.