Has anyone ever had a Central Motor Evoked Potential test?

The neurology clinic nurse called to let me know the doctor wants me to have a motor evoked potential test, which has been scheduled for next week.  

I have had an SSEP, BAER, EMG, NCS (sorry I don't know what the acronyms stand for) and now the doctor wants an MEP.  What is it like and what does it help with a diagnosis?

Thanks.

Julie

[Lulu54]

Hi Julie,
Which neurology clinic?  The NIH?  I thought you were done there for   while - I tke it this was a surprise. The only vague reference I found that might help here is the MEP is different in patients with RRMS vs SPMS and PPMS.  At least I think that's what a paper was saying.

So sorry that I'm not much help,
Lulu

[Sarahsmom46]

Thanks.  This is the NIH.  Just when you think they are done...This doctor has actually been very proactive for me.  He doesn't want to leave any stone unturned so to speak.  And, apparently even if I thought I was done I will be followed for as long as it takes to get another dx or meet the McD criteria. That is what they told me.

I tried to goodle it too, but didn't find anything about what the test entails.  I should have asked when they called me, but just not thinking that quickly anymore.  I was just wondering if it is like what they do for the SSEP.  Have you had that yet?

[Lulu54]

J-
No, I have had no evoked potential anythings done.  I honestly have had so few tests because my dx was a slam-dunk.  I got to skip all the *fun* of limbo and being poked and proded.   I just saved all that for the heart side of my diseases :-)

My ENT did say something about an ENG if this BPPV treatment doesn't stop my balance problems.
L

[Quixotic1]

The motor evoked potential is the same theory as the sensory evoked potential but it is done in the opposite direction.

First remember that sensory nerves carry their signal in the direction of the sensory organ (like the skin) TO the brain so that we can feel.  These are called afferent nerves.

Motor nerves carry their signals in the opposite direction.  They run from the command center of the brain TO the muscles that they effect   They are fittingly called the efferent nerves.  (I remembered this in med school by remembering that muscles take effort)

In a sensorey evoked potential the examiner stimulates a sense, like the vision, hearing or the sense of touch.  Then the length of time for the electrical potential (or signal) to travel to the brain is measured.

In a motor evoked potential we stimulate the brain to make the muscle work.  Ideally we would stick a probe into the brain and stimulate the exact place we want.  However, patients just aren't too keen on the idea of poking around in there and running the risk of brain damage.  Don't they realize it is for the sake of science???

So, what they do is generate an magnetic field over the scalp at a known spot and see what jumps.  Actually they see how long it takes for whatever to jump.  It is less precise than the sensory evoked potentials and not as often done.  But, it makes sense to do it when there is significant weakness and not so much in the way of paresthesias, or if you have the equipment to do it and a skilled tech.

I was kidding above.  They know what areas to do the test over in order to make certain larger muscle groups contract.

Does this explain it?

Quix

[rendean]

Try this link . It's very techinical in background and I'll be honest I only skimmed it as I am exhausted, I found it by just googling motor evoked potential and there were several  other sites: emedicine.  medscape.com/article/1139085-overview , just delete the space after emedicine.

Ren

[Quixotic1]

The MEP does the same thing as the SEP, but in the reverse direction.   If the signal is showed to be delayed between the source stimulus which is over the brain and where the motor nerve exits the spinal cord, then it is evidence of a site of demyelination in the central nervous system.

If the signal is of normal velocity between the brain and where it exits the spine, but delayed somewhere out in the body then the problem is in the peripheral nervous system.

I'll add the MEP to the HP on Evoked Potentials- when I get to it.  :((

Quix

[Sarahsmom46]

Thanks for your responses.  I kinda get it.

Overall, do you think this test is worthwhile?  I am pretty test fatigued right now and would prefer to skip it unless the information we could get will be significantly helpful.

Julie

[Quixotic1]

You need all the possible evidence that you can get.  I think one good result would put you over.

Quix

[mackemuk]

Hi Quix
I Hope You Are Keeping Well, Am I Right In Thinking What You Are Describing Is A Test Called A Transcranial Magnetic Stimulation (TMS) The New Neuro I Saw A Few Weeks Ago Wants Me To Have This Test Done And By All Accounts It Is A Pretty New Procedure.
Sorry Julie For Muscling In On Your Thread But I Think This Will Benefit Both Of Us
Take Care.
Regards Joe.

[Sarahsmom46]

No problem. Muscle away...Now you got me wondering the same thing.

[mackemuk]

Bump,
Anyone Care To Comment.
Take Care,
Joe.