American Association for Hand Surgery · Transcript · · Updated
Beyond Carpal Tunnel: Nerve Compressions and Peripheral Nerve Diagnostics in the Upper Limb – Transcript
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Summary
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- Dr. Chris Dee explains that electrodiagnostic studies are an extension of the physical examination and evaluate parameters like latency, conduction velocity, and amplitude.
- Dr. Neil Lee discusses the utilization of ultrasound for upper extremity peripheral nerve conditions to provide real-time visual confirmation and cross-sectional area measurements.
- Ms. Megan Harrari reviews how an advanced practice provider uses history, physical examinations, and diagnostic tools to triage patients and handle peripheral nerve care.
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Good evening. I'm Warren Hammert and uh on behalf of my co-moderator for this webinar, uh Carrie Bethlack, I'd like to welcome everybody to the AAHS APP webinar series. This is our second uh webinar beyond carpal tunnel. These are uh recorded and they'll be available for viewing later on the AAHS website and uh certainly the previous one that we did would be available as well. So, you're uh welcome to go back and uh review any
of these. I think we have an outstanding program for you tonight. We're going to really be talking about peripheral nerve conditions. Carpal tunnel is kind of the thing you think about, but there's a lot of other things that will be touched on and what we want to do is kind of review ways to diagnose this and then think about how you take this information and input it into your practice. So, I would like to introduce our speakers. Uh starting off for us will be Dr. Chris Dee from
uh Washington University in St. Louis. He's a uh upper extremity and peripheral nerve surgeon. He's going to talk to us about electrodiagnostic studies, how to use and interpret these. And we're going to follow that with uh Dr. Neil Lee, who is an upper extremity and peripheral nerve surgeon at Duke University. And he's going to talk to us about understanding ultrasound and utilization for upper extremity uh peripheral nerve conditions. And then we're going to round this off with uh Ms. Megan
Harrari, who's a nurse practitioner at Yale University. And she's going to talk about how we take all this information and input it into clinical care and provide the best um care for our patients. If anybody has any questions, please uh put them in the chat. We'll have some uh question and answer as well as discussion either after the presentations or at the end uh based on how time uh allots for us. So, with that I'd like to turn it over to Dr. Dee and
have him uh share his screen and we'll uh talk about electrodiagnostic studies. Chris, thank you. >> All thank you, Warren. I appreciate it and thank you to to Grace for organizing and Carrie for again for the invitation as well.
Warren, if you could just give me a audio yes, you can see my slides. >> Yes. >> All right, excellent. So, we'll get started. I wanted to present this topic that Warren and Carrie asked me about understanding electrodiagnostic studies.
I am in in practice at Washington University in St. Louis. I'm fortunate enough to to work with David Brogan who we recruited back to St. Louis in 2018. And then we were also fortunate enough to recruit back one of our former fellows, David Wright, to join our Washington orthopedic nerve team last year.
And we are always looking for new ways and and opportunities to collaborate with our plastic surgery colleagues here at WashU. So, you can see us here at combined nerve education courses and who sees who knows what the future will hold. So, I I think that when I first started learning about this topic, I read this chapter back in Dr. Galberman's classic but very old now textbook from 1991. And this is from Dr. Lee Dellon who is a legend in nerve surgery. And I think this quote is really helpful.
For your EMG and nerve conduction studies, put in your consult only when your careful history taking and detailed sensorimotor testing indicate that electrophysiologic testing is necessary to answer a particular question. Have confidence in your clinical skills that your judgment, not Dr.
electrophysiology's printed report, will be the final authority. So, these are an extension of your physical examination. You know, so don't rely on it to make the entirety of your diagnosis. I think all of you if you have interest in this and have logged into the webinar have the clinical skills to get to the same answers. This just helps to have some additional information to corroborate your clinical exam.
But you know, whenever I start to talk about this with our residents, fellows, and students, and therapists in clinic, everybody is totally overwhelmed with what to do with it cuz it is a pretty intimidating topic to try to digest and I I do owe a lot of gratitude um to uh to uh the surgeon at that Carey works with uh Dr. McKinnon who taught me a lot about how to interpret this information.
But the underlying principles are that the nerve studies are a tool to complement your exam. The nerve studies are imperfect. They are as good as the person doing the nerve test and their usefulness relies on that interpreter as well as your interpretation. So like everything we do in in the practice of medicine, um it very much requires that you are looking at things from all angles and really appreciating some of the limitations that each of these tests have.
So the essential questions that I want to answer are where is the nerve injury or nerve compression? Are there any other lesions going on? How severe is that nerve injury? Will there is there a chance that there'll be any recovery uh spontaneously? And if not, what are my options? And for all of that, you need to combine both your history and your exam with your nerve studies and perhaps imaging as well.
So in terms of thinking about this nerve test, it's basically looking at how long it takes for uh one thing to get to the next point, point A to point B. So here is, you know, if you've ever been to St. Louis, uh you can see where Forest Park is and there is a zoo all the way on the right side of the screen. If I start my morning at conference, which is basically right around here on the right side, and I need to get to our satellite office, uh which is about 20 minutes away, sometimes 40 minutes away, you can see the different traffic uh patterns
that I might hit along the way. It's pretty much the same concept. So, you know, when you think about these parameters on the nerve conduction tests, the latency is how long it'll take you to get from point A to point B. How fast will we go is a conduction velocity. And are you driving a Tesla or you driving a jalopy? It's the amplitude, you know, the how strong is that uh um how strong is that signal?
And again, this is point A to point B. So this is a sensory nerve test. So this is assessing across the wrist for the median nerve. So they're going to stimulate the median nerve in this black uh electrode here and it's going to go from the left to right on the screen and you're going to be recording on the index finger the the sensation there. So again, pretty old picture, but it does the job.
So, how long does it take to get from the index finger to the median nerve? Or vice versa, how long does it take to go from the median nerve to the thenar musculature? That's your latency. So this is looking at this is actually my own hand that we recorded for an article.
Similar kinds of illustrations. So, every lab is different with their normal values. You know, just in terms of thinking about kind of classic articles that talk about normal values, the electrodiagnostic criteria for carpal tunnel syndrome are distal motor latency of greater than 4.5 milliseconds and a distal sensory latency of greater than 3.5 milliseconds. Again, this is how long it takes to get from point A to point B.
And then here's a classic article from Dr. Mackinnon looking at the testing criteria for cubital tunnel syndrome. She looked at her elbow flexion compression test, which is an excellent clinical examination maneuver, and compared it to electrodiagnostic studies. And the criteria is typically if the nerve goes less than 50 m/s across the elbow, you know, that that is suggestive if not diagnostic of ulnar nerve compression at the elbow or cubital tunnel syndrome. Again, that could be 45 in some labs, 55 in other
labs, but I just wanted to give you a general ballpark. But, you know, the nerve study is not, you know, infallible. It's looking at the usually the best running fibers. This is a so-called reporter in the sky pitfall. So that if the reporter in the sky doing the traffic report is looking only the fastest moving lanes of traffic, it's going to say everything is okay and it's going to ignore the the lanes of traffic that have pileups on the bottom part of the screen. So those nerve conduction studies, the latency and the conduction velocity, depend on
the first recorded impulse picked up from those large myelinated fibers. And again, looking at this traffic analogy, the large myelinated fibers are running really quickly, but you have no idea that these thinly myelinated smaller fibers, which typically are responsible for pain, um are are not being picked up. And this is why a lot of patients start with pain before they come with forward weakness or sensory deficits uh when they have early compression. So, you really have to trust your examination. Your clinical exam will get you all the information you need to help
diagnose and localize a lesion. So, there are important caveats. Uh there are no electrodiagnostic correlates to pain and paresthesias for the reasons I just mentioned. These are typically smaller and lesser or completely unmyelinated fibers that won't get picked up by the the nerve study, which is going to pick up the best runners in the pack.
And the nerve studies typically reflect the pathophysiology. Early on, carpal tunnel is a focal and demyelinating process, but if you let that go on for uh for years and years, that leads to axonal loss. Cubital tunnel is a combination of focal demyelinating compression and traction that that leads to axonal loss after early on being like a dynamic ischemic condition.
Um and then you can see Guyon's canal is axon loss. Neurapraxia is a demyelinating uh conduction block in the setting of a uh low-grade nerve injury. And axonotmetic injury, in which you have a higher severity nerve injury, does have axon loss on your nerve studies.
So, one of the analogy that tends to resonate pretty well with most people is you're thinking about again getting from point A to point B and you have a pack of runners. The conduction velocity and the latency only record the fastest runner's speed and time. So, the person leading this leading the pack in this race, that's going to be reflected in the conduction velocity and latency. But the amplitude is that the whole team is finishing cuz the amplitude tends to reflect the number of axons that are actually functioning in that nerve, not just the fastest one in the pack.
So, in the context of compressive neuropathy, um conduction velocity and latency again are the fastest runner's speed and time. So, that that's looking at you know in a scenario of early carpal tunnel or early cubital tunnel. But after a period of time where that compression on the nerve becomes so severe that there becomes some internal fibrosis or scarring in the nerve and you start to see those things like thenar atrophy, FDI weakness, um you know, just the static two-point changes. Um you know, that is reflected by the amplitude. You know, so the
number of functioning nerve fibers, the number of axons, that directly relates to your advanced clinical findings in the settings of long-standing carpal tunnel syndrome and cubital tunnel syndrome. So this is a great paper from Dr. Mackinnon and Holly Power, who was a fellow here at the time, um looking at the correlation between grip strength and pinch strength. So that's uh figure A and figure B and CMAP amplitudes and you can see there's a very linear relationship. The worse the CMAP amplitude is, the worse the grip strength is and the worse the pinch strength is.
So here's an example on a nerve study. So the amplitudes you can see here are on the right. You know, those the you can see the waveforms here and you can see the bottom to the top is the amplitude. And this is a conduction block of a healthy nerve because you've got normal amplitudes, okay?
Seen over here in this top top table on the second to right and it's far over the normal amplitude. But then if you look across the elbow, which is the bottom row of this table at the bottom, the velocity across the elbow is 42 m per second. So there is a conduction block as reflected by the 42 m per second of a healthy nerve, which is reflected by these normal CMAP amplitude levels right here. Now look at a different case. You can see that these CMAP amplitudes, which are illustrated with the italics in the underline and
the bold, and then you can see it on the right side with these waveforms. Look back at those waveforms from this last patient and then go back to these and you can see how small that waveform is. And then on top of that, you have conduction blocks at the wrist, so across Guyon's canal, and across the cubital tunnel of 21 m per second. So this is a conduction block at two levels as reflected here in the meters per second of an unhealthy nerve as reflected by