Interpreting Nerve Conduction Studies

Interpreting Nerve Conduction Studies


Hopefully you will have watched the first
part of this video where I provided an overview of normative data. If you haven’t seen this
yet, please do so now, by clicking on the link via the i-card above. In this video,
I will provide an overview as to how we piece this information together. For any nerve, we measure the size of response,
called the amplitude which reflects the size of the underlying axons. The speed of the
response reflects the degree that the nerve is myelinated. So when the amplitude drops,
we generally attribute it to axonal loss and where the speed of conduction drops, we generally
attribute it to demyelination. There are exceptions, which we will eventually consider. But, for now, I just want to
highlight that that because, motor nerves are larger and more myelinated than sensory
nerves, they are better at showing conduction slowing. Let’s start with demyelinating mononeuropathies
at common compression sites. These are by far the commonest of the conditions we encounter
and include carpal tunnel, cubital tunnel and peroneal nerve lesions at the fibula neck.
Here, single nerves are being compressed and damaged. We test the nerves to look for focal
motor conduction slowing at the entrapment site. You can see videos on all 3 of these
conditions by following the i-cards above. Sometimes they can co-exist such as having
both carpal and cubital tunnel lesions. This is not rare and I see this in around 5% of
my carpal tunnel patients. So I keep an eye out for this and you can see me perform a
typical nerve conduction test in under 2 minutes by following the i-card above. If we see conduction slowing across all common
compression sites, especially in a young patient, then we need to consider a condition called
HNPP or hereditary liability to pressure palsies as a potential cause. Here a genetic mutation
in a myelin component, makes the nerves susceptible to being crushed. Keeping to the genetic neuropathy theme, when
we encounter conduction slowing which is uniform, symmetrical and outside entrapment sites,
we consider the hereditary motor and sensory neuropathies and you can see a video explaining
the different types of Charcot-Marie-Tooth disease by following the i-card above. Inflammatory demyelinating neuropathies, by
contrast, are more patchy, often more asymmetrical and tend to demonstrate phenomenon such as
conduction block and temporal dispersion where non-uniform dysfunction leads to reduction
or spread of the motor responses. You can see a more detailed explanation of this and
myelin function and nerve signalling by clicking on the i-card above as well as some videos
on the inflammatory demyelinating neuropathies. Any demyelinating neuropathy which is sufficiently
severe will eventually lead to underlying axonal fibre loss, recognisable as a drop
in response amplitude. So lets talk about the axonal neuropathies
and these can really subdivide into a few categories:
Length dependent, Generalised, Mononeuropathies and Mononeurtis multiplex patterns. The commonest are the length dependent neuropathies.
These occur to the more distal and smaller caliber nerves. Hence the sensory fibres tend
to be more affected than the larger motor fibres and so feet are affected first and
tend to clinically affect the hands by the time the impairment reaches the knees. Of
course, we can detect sub-clinical involvement earlier with NCS. Generalised neuropathies will lead to generalised
suppression of response amplitudes and will again affect sensory fibres more than motor
fibres. Perhaps the most interesting variation are the sensory neuronopathies where there
is a complete suppression of all sensory responses and I would advocate blink reflex studies
in these situations to look for trigeminal dysfunction. Single nerves lesions can also be detected
and these are called mono-neuropathies. These can be idiopathic or inflammatory in nature.
Where multiple single nerves are affected, this is called mono-neuritis multiplex and
tend to be associated with inflammatory or vasculitic processes. Pure motor neuropathies are very rare. These
primarily affect the motor responses and only rarely affect the sensory responses. Differentials
can include inflammatory neuropathies such as MMNCB / MMN without CB, distal HMN and
the motor neuronopathies such as Motor Neurone Disease Myopathies can lead to reduced motor responses,
but often as they are proximal processes, the distal motor amplitudes tend to be spared,
unless it is a distal myopathy. An interesting exception is critical care myopathy where
the motor responses reduce and become broad. However, what we do commonly encounter are
the radiculopathies. Here myotomal motor axonal loss is demonstrable without sensory fibre
loss. Take a look at the medical student tutorials, via the link above, where I explain how we
differentiate between pre and post ganglionic lesions which is a very important concept
in neurophysiology. So that’s the whistle stop tour and in the
coming series of videos I’ll work through specific examples.
Thanks for watching and I hope you enjoyed it. Please support this channel by liking,
sharing and subscribing.

12 Replies to “Interpreting Nerve Conduction Studies”

  1. Hi, very interesting videos. I have a question regarding electrical conduction test.

    I had a test on my left lower leg.The test of the tibial nerve was
    conducted measuring the signal at the abductor hallucis muscle, invoked
    at ankle and knee. The test was successful from the ankle, but, despite
    repeated attempts, the technician was unable to detect a signal when the
    pulse was from the knee. The technician called in the consultant, and
    again the test was attempted a number of times unsuccessfully. How
    often is there a problem with this test?

  2. Thanks for the interesting question. I can't give you a specific percentage as there are lots of variables at play. However, this specific stimulation point is often technically challenging because the tibial nerve at this point is deeply situated (unlike the ankle) and so the current may not adequately 'reach' it as there is lots soft tissues in the way.

    There are a number of ways to overcome this which can include changing the size of the stimulator, the material it's made from, pressure applied in and the characteristics of the stimulating impulse. All of which can make adequately testing that segment with adequate stimulation pretty uncomfortable. This is also coupled with the fact that it's fairly rare that this region yields sufficiently important extra information that cannot anyway be identified from the ankle stimulation point and EMG of Tibial innervated muscles (as well as studies of other nerves).

    Hence, I'm not a fan of routinely doing it as part of everyday practice and reserve it for specific situations.

    So in summary, this segment is recognised as being tricky but there are ways to overcome this, when sufficiently important to do so.

    Bw

    Simon

  3. Thank you so much for your earlier correspondence! ❀😻 My Dr.s office are now going to do new Nerve testing on my feet. Their consensus seems to be the Neuromas and Plantar Fascitiis with the injections and Physical therapy are resolved/improved leaving the Neuropathy and Muscle loss (I believe it is actually atrophy due to the pain). Do you think the Neuropathy could have been caused by having been stepped on by a 2000# Draft Horse while I was wearing sandles? Nothing broken, yet that seems to be when my issues started. For some reason the Dr.s seem to discount that, to me, significant event. Will the Nerve testing affirm or negate CMT if My Insurance will not pay for the Blood/Gene tests? What can I watch for? I can't tell you how much I appreciate your Channel as it has given me hope again!!!! Thank you! 😻❀

  4. Thank you so much for your earlier correspondence! ❀😻 My Dr.s office are now going to do new Nerve testing on my feet. Their consensus seems to be the Neuromas and Plantar Fascitiis with the injections and Physical therapy are resolved/improved leaving the Neuropathy and Muscle loss (I believe it is actually atrophy due to the pain). Do you think the Neuropathy could have been caused by having been stepped on by a 2000# Draft Horse while I was wearing sandles? Nothing broken, yet that seems to be when my issues started. For some reason the Dr.s seem to discount that, to me, significant event. Will the Nerve testing affirm or negate CMT if My Insurance will not pay for the Blood/Gene tests? What can I watch for? I can't tell you how much I appreciate your Channel as it has given me hope again!!!! Thank you! 😻❀

  5. Thank you so much for your earlier correspondence! ❀😻 My Dr.s office are now going to do new Nerve testing on my feet. Their consensus seems to be the Neuromas and Plantar Fascitiis with the injections and Physical therapy are resolved/improved leaving the Neuropathy and Muscle loss (I believe it is actually atrophy due to the pain). Do you think the Neuropathy could have been caused by having been stepped on by a 2000# Draft Horse while I was wearing sandles? Nothing broken, yet that seems to be when my issues started. For some reason the Dr.s seem to discount that, to me, significant event. Will the Nerve testing affirm or negate CMT if My Insurance will not pay for the Blood/Gene tests? What can I watch for? I can't tell you how much I appreciate your Channel as it has given me hope again!!!! Thank you! 😻❀

  6. i was told according to the full body nerve conduction studies i have MS and then now the neurologist my primary sent my records tobsaid only MRI can diagnose MS. and refused to see me because he siad my brain scan didnt say MS. however im still having the relapsing remitting symptoms and theyare getting worse i keep blacking out occaisionally and have hit my head. i have a mild concussion and had staples this time and yet the neurologist my primary sent my records too since he didnt see MS on my brain scan means i dont have it .really frustrated im an RN my pain is off the charts.i have severe bee sting type burning in the back of both legs all the way to the bottom of my knees .I just cant get a referral to anyone who wants to help .Any advice would be appreciated .i have my copy of the results of my nerve conduction studies if youd see them id love your interpretation .My private email is [email protected]

  7. Hi Dr Simon, I'm Dr Djenane Malek Saber From Algiers, i work with Medicatech Neurology on neurophysiology equipement. i wish to thank you for all your very interisting video. keep going on.

  8. Thank you for this video. Im told after have the EMT and nerve conductor test that I have Carpal Tunnel in both hands but my right hand has severe nerve damage and need surgery ASAP. I will be seeing the hand surgeon on 11/15. I'm wondering since it's so bad with my right hand will the surgery help? Thank you for your time!

  9. Hello
    greetings from Nepal
    My wife had a norve problem from 7 months, I visited to many neuro physician and they tested norve conduction test and suggest to take some medicine and do physiotherapy
    But she still have problems in her hand
    Now her fingers are not able to up and down easily but can up down by force
    So what will be the best solution for her recovery?

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