Hello, I'm Dr. Diana Kwan, Professor of Neurology at the University of Colorado School of Medicine. Welcome and thank you for joining us for the AANEM Advanced Practice Provider Webinar Series, the first of its kind. The presenting faculty will be available via the chat function to talk and answer your questions throughout and at the end of each presentation. Within the chat function, you may direct your questions or comments to the faculty exclusively or make them visible to all of the attendees and panelists. Faculty will appear at the end of the presentation to talk about questions in the chat box, and we look forward to reading your questions throughout the presentation. Welcome to Week 1. We have two presentations today. The first will be Peripheral Anatomy from Root to Muscle. Dr. Loretta Van Every will lead the session and be available for questions throughout the presentation. She is Chief of Neurology at the Indianapolis VA. Dr. Adam Comer will discuss Nerve Root and Plexus, Technologist Jerry Morris will discuss Peripheral Nerve, and Dr. Tristan Allen will conclude with Neuromuscular Junction and Muscle. Hello, everyone, and welcome. I'm Dr. Loretta Van Every, Acting Deputy Chief of Staff at the Richard L. Radabush VA in Indianapolis, Indiana, and Assistant Professor of Neurology at the IU School of Medicine. I'd like to welcome you to our lecture today, Peripheral Anatomy from Root to Muscle. I'd like to introduce our other speakers tonight. Our first speaker, who's going to talk to us about Nerve Root and Plexus, is Dr. Adam Comer. Dr. Comer is an Assistant Professor of Clinical Neurology at the IU School of Medicine. Joining us on a whirlwind version of the Peripheral Nervous System is Mr. Jerry Morris, Senior Electrophysiology Technician. He works at the Willis-Knighton Medical Center in Shreveport, Louisiana. The cleanup is Dr. Tristan Allen. Dr. Allen is the Clinical Associate Professor of Neurology, and she works at Duke University and the Duke Raleigh Hospitals. I have nothing to disclose. We'll start with our first lecturer. Thank you very much. Again, Adam Comer, I have the pleasure of presenting Nerve Root and Plexus. I have nothing to disclose. And I thought we'd start by just a brief review of the relevant anatomy. So the cervical nerve roots, C5, 6, 7, 8, and T1, contribute to innervation of the upper limbs. And from there, we have the dorsal root ganglion, and then that's followed by the trunks, divisions, cord, and then finally the terminal nerves, musculocutaneous, axillary, radial, median, and ulnar. And there will be a further review of that anatomy later. But from an electrodiagnostic perspective, what I wanted to point out is how we distinguish between radiculopathy and plexopathy, or at least one of the ways we distinguish between the two. So commonly with radiculopathy, the lesion is going to be proximal to the dorsal root ganglion, whereas with essentially any other lesion that would be more distal, it will be distal to the dorsal root ganglion. So that would be a lesion involving any of the trunks of the brachial plexus or distal to that in the divisions, cords, or terminal nerves. And how that affects what we do day-to-day is if the lesion is distal to the dorsal root ganglion, then we see that in the form of reduced sensory nerve conduction studies, reduced response amplitudes on our nerve conductions, on the sensory nerve conductions. Whereas with radiculopathy, the sensory responses are typically normal. And when we're concerned with radiculopathy, we like to work on the basis of some hypothesis. And so consider whether we're looking for upper trunk brachial plexopathy or whether we might be concerned about C5 radiculopathy, for instance. And that allows us to determine what nerve conduction studies are needed prior to the EMG needle examination. And so with a C5 radiculopathy, the culprit will often be due to a disc bulge or disc pathology at the C4-5 level. And that will manifest with sensory deficits involving the lateral arm, as well as motor deficits involving the proximal limb, deltoid, external rotators of the arm, and forearm flexors. And then in addition to that, we'll have decreased reflexes, often in the form of biceps or brachioradialis. At the C6 level, again, sensory deficits often involving the lateral arm, but also the lateral forearm and the first two digits, with weakness involving forearm flexion, arm pronation, finger and wrist extension, and then similar decreased reflexes. With C7 radiculopathy, digits three and four may have some sensory deficit with weakness in arm extension, finger and wrist flexors and extensors, and a decreased triceps reflex. And then finally, at the C8 level, the deficit is usually more medial forearm and medial hand with weakness of the intrinsic hand muscles. And so for the needle examination, there is significant overlap. And we use that to our advantage to try to determine the level, the myotome, all the muscles of the particular level that are responsible for the pathology. And so some muscles, such as biceps, may have some component of both C5 and C6, whereas other muscles tend to go along more with one particular level, such as the rhomboid, which tends to be more C5. And I think the sensory nerve conduction studies are particularly useful when we're trying to distinguish between brachial plexopathy and radiculopathy. And so this paper that was published in 1995, I think, is a worthwhile read if you have some time. And this is the result of that effort. With the upper trunk, the lateral antebrachial cutaneous sensory study, as well as the median anterodromic study recording at the thumb, those are both quite useful in distinguishing upper trunk plexopathy from middle or lower trunk. And so here, about 96% of the patients that they studied that had upper trunk pathology had abnormal lateral antebrachial cutaneous, and about a similar number when they looked at the recording at the thumb with the median sensory nerve. It is quite rare to have an isolated middle trunk plexopathy. If the middle trunk is involved, that's usually in combination with either the upper or lower trunks. But we would expect with middle trunk plexopathy, we believe that recording at the third digit, median sensory response recording at the third digit may be helpful in distinguishing that from upper or lower trunk plexopathy. With the lower trunk plexopathy, recording any of medial antebrachial cutaneous, dorsal ulnar cutaneous, or ulnar anterodromic at the fifth digit, those are all quite useful and would be abnormal lower trunk plexopathy. And so the way I typically use these are I look at both upper limbs, and you would expect at least a 50% decrease in the affected limb if there is a plexopathy compared to the normal limb. And then so I've just got them listed here again, as well as the lateral, posterior, or medial cords that we would expect to correlate with each of those sensory nerve conduction studies. And just briefly about examined brachial plexopathy, it can at times be a bit of a challenge to distinguish plexopathy from radiculopathy clinically, but with upper trunk, we'd expect to have weakness of deltoid and biceps with sensory loss involving the lateral arm and forearm. If there were an isolated middle trunk plexopathy, we'd expect weakness of elbow, wrist, and finger extension, as well as sensory loss involving the posterior forearm and middle finger. And then lower trunk, we'd expect weakness of the hand muscles in ulnar median and radial innervated hand muscles with sensory loss involving the medial forearm and hand. Needle EMG for brachial plexopathy, I have listed here the muscles that we'll commonly evaluate to try to distinguish between upper, middle, and lower trunk plexopathy. With regard to the lower trunk, or lower trunk, lower limb, we can divide that into the upper lumbar plexus, as well as the lower lumbosacral plexus. And so in the upper lumbar plexus, that would include the iliohypogastric, ilioinguinal, posterior cutaneous nerve of the thigh, femoral obturator, and genital femoral nerves, whereas the lower lumbosacral plexus, that would be the superior gluteal, inferior gluteal, posterior cutaneous nerve of the thigh, pudendal, and sciatic nerves. And then here, again, for lumbosacral radiculopathy, the clinical manifestations for L3, you'd expect sensory deficits involved in the anterior thigh with motor deficits of iliopsoas, hip adduction, and knee extension, L4, sensory deficit involving the knee and medial leg with weakness of knee extension. And with either of those, you may have a decreased patellar reflex. And then L5 radiculopathy, sensory loss of the lateral leg, dorsal foot, and large toe with weakness of the thigh adduction, knee flexion, and dorsiflexion of the foot and toes. And with S1 radiculopathy, lateral foot, sole of the foot, and small toe sensory deficits with weakness in hip extension, planar flexion of the foot and toes as well. And so the EMG needle examination can be a little bit challenging to distinguish between L3 and L4 radiculopathy. I think it's easier to distinguish either of those from L5 or from an S1 radiculopathy just because there's less overlap there. And just like the upper limb, the sensory nerve conduction studies can be helpful in lumbosacral plexopathy. I think that, however, these studies tend to be a bit more challenging technically. For the upper lumbar plexus, the saphenous, antedromic, and lateral femoral cutaneous responses may be reduced on the affected limb. And then that's assuming that you feel confident that you've gotten an adequate and reliable response. So I'll usually look at the unaffected side first to demonstrate that I can achieve an adequate response and then look at the affected side. Again, looking for about a 50% side-to-side difference. The more distal sensory nerve conduction studies are a bit more reliable. The seroantedromic or superficial fibular antedromic sensory responses. I thought I'd go through one case here. That of a 28-year-old male presents with right upper limb weakness and numbness after a gunshot wound about eight weeks prior. The nerve conduction studies show normal median ulnar motor responses. The lateral antebrachial cutaneous sensory response, the amplitude is decreased compared with the unaffected limb. The other sensory nerve conduction studies, median, radial, and ulnar are all normal. And EMG showed fibrillations and positive waves in infraspinatus, deltoid, biceps, and pronator teres. Whereas the other tested muscles, triceps, extensor digitorum communis, FDI, flexor carpi ulnaris, and abductor pollicis brevis were all normal. So I'll give you a second to think about where the lesion might be. You'd expect an acute right upper trunk brachial plexopathy. A component of that is the decreased lateral antebrachial cutaneous sensory response compared to the unaffected side and needle examination that is also consistent with an upper trunk plexopathy. And so I hope this has been helpful. I think the sensory responses can be particularly helpful because sometimes the needle examination evaluation of paraspinal muscles may be limited by prior cervical spine surgery or sampling error or other technical issues. So I think a hypothesis-driven approach to distinguishing plexopathy from radiculopathy is quite helpful. Good afternoon. It is good to be here and I'd like to speak today on the peripheral nerve anatomy in the upper and lower extremities. Dr. Comer has done such a wonderful job of the brachial plexus and the lumbosacral plexus. We won't be covering too much of that, although you will see some of the slides that I have for that. I have nothing to disclose. And the first thing that I would like to talk about is that in our lab, EMG lab, we consider median ulnar and radial motor and sensory nerves, the three major nerves of the upper extremity. Now, in our normal nerve conduction studies, we may not do radials unless there is some sort of extensor weakness. But our median and ulnar motor and sensory studies are just a hallmark of all of our studies that we have in the upper extremity and for a couple of the doctors, even for just a peripheral neuropathy screen, that's what they use. But we also today, I want to key in on some of the secondary nerves that we do use in isolated instances. Number one is the axillary, which provides motor to the deltoid. And again, it's a posterior cord coming from the posterior cord in the upper trunk and a good C5, C6 muscle. Musculocutaneous, again, anterior division of the lateral cord, another C5, C6 with the upper trunk. The medial antebranchial, which is a pure sensory nerve from the lower trunk and the medial cord. And then the dorsal ulnar cutaneous, or the DUC as we like to call it, is a sensory only from the lower trunk and the medial cord. And it'll be very helpful in a couple of, in a lesion of the ulnar nerve down at the wrist. And then there are a couple of other nerves that we don't do a lot in our lab, but are very, very helpful in getting to go through plexopathies and whether it's radiculopathy. And those things are like the thoracodorsal nerve, the suprascapular nerve, and the long thoracic nerve. Now, if you'll see the thoracodorsal and the suprascapular also are brachial plexus nerves, whereas the long thoracic is a pre-brachial plexus nerve, which makes it very helpful when the incidence or the possibility of a plexopathy is in the mix. And we'll talk about those a little bit later. Medial nerve, again, C5 through T1. The main thing about the medial nerve that I want to show you is as it tracks down the arm from the shoulder area down to the elbow, and then eventually to the hand, the one thing that if you'll notice in the forearm, it mainly innervates flexor muscles. Now that's, there are a couple that do have a, or one in particular, the flexor digitorum profundus that has a dual innervation, but by and large, what you see here is flexor flexor with a pronator caries muscle. And then it eventually ends in the abductor pollicis brevis, which is our normal nerve conduction study receptors where we do our nerve conduction studies from. Now, again, the palmaris longus is also in the mix in the forearm, but by and large, on the thenar eminence, the abductor pollicis brevis is the muscle that we use along with the opponents. And please remember that on that thenar eminence, that there are other, another nerve, the ulnar nerve that innervates things on that. Whereas when we go to the hypothenar eminence, the ulnar nerve is the only one that will innervate the abductor digiti minima. We'll get to that in just a second. The things that the pathology that we need to talk about or that we normally see when we have a medium nerve lesion is carpal tunnel syndrome, probably the most common entrapment that we see. Occasionally, we will see such things as pronator syndrome, anterior interosseous nerve syndrome, ligament of Struthers. I don't think in my career I've seen but maybe one ligament of Struthers and maybe others can chime in through the chat if that's something common that they do. But by and large, carpal tunnel is what we see mainly. And again, when we do these, we do sensories, the thumb, the second or the third fingers. We have doctors that like anadromic and some that like orthodromic. And the key thing about this is the little schematic and the little diagram showing what branches of that median sensory, the digital, the palmar cutaneous nerves of the median nerve. And then also here, this also shows the ulnar sensory innervation from the ulnar itself and from the dorsal ulnar cutaneous and the radial from the superficial radial. So this is a good little schematic diagram showing that cutaneous nerve supply of the hand. Again, as Dr. Comer talked about, certain ones of these doing sensory studies from either the thumb, the index finger or the middle finger, or even the lateral ring finger can help delineate plexopathy, plexus lesions from certain cords, from certain trunks. And each one of these digits has a specific cord supply and a specific trunk supply, and they may be different. So if you're looking for a C6 plexopathy, you may wanna do the medial thumb when you do the median sensory. And likewise, the ulnar nerve is the second nerve that we use, and again, it's medial cord and lower trunk of the brachial plexus. And again, as it courses down the upper arm, it goes around what we affectionately call the funny bone. And from there, it essentially goes to the muscles in the hand. Now there will be a couple flexors in the forearm that it innervates, especially the flexor carpi ulnaris and the flexor digitorum profundus, which it has dual innervation with a median nerve. But by and large, if you'll look at it, most of the ulnar innervation is down in the hand from the hypothenar group here, the abductor digiti minimi, the opponents, the interossei, and even over to the adductor pollicis on the thenar eminence of the hand. And when we look at these muscles, the key one EMG-wise that a lot of our doctors look at is the FTP, the flexor digitorum profundus, because of that dual innervation with the median nerve, and it can help delineate one way or the other. The syndromes that we look at when we talk and when we try to find out what the pathology is, is probably first and foremost is cubital tunnel or tardy ulnar palsy at the elbow. You can have entrapment at the canal of Guion. And when we get to the dorsal ulnar cutaneous nerve, you're gonna find that that's a very significant little nerve in sorting this out. And then you can also have ulnar lesions in the palm as the ulnar nerve crosses the palm all the way to the thenar eminence. Again, for the sensories, we do palmers, we do digits. So we do the fifth digit. If we wanna do comparison studies, we will do from the fourth, because as I showed on the, as you saw on the little diagram, the ulnar nerve and the median nerve have dual innervation on the fourth finger. And again, as you can see here, it's the one I kind of stay away from. If I'm wanting to do a pure ulnar sensory, I will go to the fifth digit. The radial nerve, again, this is not in our normal nerve study routine, but when we have a patient that comes in that has extensor weakness or extensor damage in the form, this is our go-to nerve. And the thing about the radial nerve, whereas the ulnar and the median pretty well are straightforward going down from the brachial plexus down to the arm and the hand, the radial nerve tends to wind around the upper forearm before it winds up in the extensors group in the hand. And again, once you see where the innervation, where the radial nerve winds up, you'll see extensory extensors, supinator. It also above the elbow innervates the triceps and a branch of the brachial radialis. But mainly you'll see these extensors and the hatch lines that I have here are gonna be where we usually see trauma, where we have pathology, either at the wrist, either at the posterior interosseous nerve here, or where we have honeymoon palsy here at the upper arm. Key muscles above the elbow for the radial nerve are the triceps and the ankineus with the forearm and the finger extensors being the most prevalent ones and the most likely ones for trauma there between the forearm and the hand. And again, with the wrist, we find handcuff palsy and with posterior, the pure posterior interosseous syndrome we'll have problems, you'll see problems with the posterior interosseous nerve. And at the spiral groove, you'll have what's called either Saturday night palsy or honeymoon palsy. Radial sensory, the little anadromic snuff box right there on the dorsum of the hand is a wonderful site for a sensory study. In fact, it's our third study that we use when we need a third sensory in the upper arm. The axillary, again, these are the ones, we only do these if they are asked for or if there is a plexopathy we're trying to figure out. And again, when we do ones like the axillary, like the musculocutaneous, things like that, we always do them side to side comparing the symptomatic and the asymptomatic side. But again, the axillary is motor study only and from the posterior core to the plexus. And again, where we put our active electrode is right on the deltoid and then stimulate at Erb's point. For the musculocutaneous nerve and its sensory continuation, the lateral antebrachial cutaneous, we will stimulate at Erb's point and we will record from the biceps. And again, this lateral antebrachial cutaneous nerve, as the motor innervation is done to the biceps, once that's done, this lateral antebrachial cutaneous goes on down into the forearm, which is a good sensory study that we can use. And again, here's the biceps and then here's as the lateral antebrachial cutaneous comes along on the lateral aspect. When we get to it, you'll see that the medial antebrachial, even though it's a pure sensory, will come along on the same direction, but almost parallel to the lateral antebrachial cutaneous. And again, the biceps is the key one here that we use when we do the motor studies. And with the medial antebrachial cutaneous, now, being a pure sensory nerve, it's very important in lower trunk medial cord lesions, and especially when you have the diagnosis of thoracicality. That's a very good, that's one of the go-to nerves that we use when we do that. And you'll see it follows right along with the ulnar nerve. I just wanna touch on this, that in the upper arm, you do have what's called Martin-Gruber anastomosis. And these are just normal variants that we have when we get to the lower extremity. We'll talk about the accessory fibular, the accessory peroneal. But again, this Martin-Gruber anastomosis can occur either at the ADM, either at the first dorsal interosseous, or either at the flexor pollicis brevis on the thenar eminence. And again, ADM is probably most common, but probably the FDI may be close to it. But a lot of people don't study ulnar from the FDI unless it's warranted. So that may be why we see more from the ADL. And here's just a picture of median fibers cross over to the ulnar side and go down into following the ulnar nerve. One thing I did wanna talk about, because we've had a couple of patients with this just recently, is the phrenic nerve. And again, it's from the C2-C4 roots through the cervical plexus, innervates the diaphragm. And years ago, I found this very hard to do, but now it's gotten to be easier. You simply put an active electrode on the xiphoid process and put your reference electrode on the eighth intercostal space and the ground somewhere in between, and you stimulate behind the sternocleidomastoid muscle. And once you do that, the characteristic is that you will get a hiccup, that you will make the patient hiccup. And in saying that, with it being in the cervical plexus, and it comes out right here, there is one other little nerve that is here that I need to talk just a little bit about, and that's a spinal accessory, because this is gonna be real key for us when we do repetitive stimulation studies. This is one of our nerves that we use when we have neuromuscular junction disorders. Again, here's the phrenic nerve, and here's where our stimulation site is and our ground and our active and our reference. And now with the crater lake in the background, we wanna get back to the lumbar plexus. And the lumbar plexus to me, the lumbar and the lumbosacral plexus are both much easier to talk about or much easier to see than the brachial plexus simply because there's not as much crossing over and winding around. And Dr. Comer, again, made a great talk on this. So I'm not gonna go too much about in the plexi itself, but just to say that with the lumbar plexus, the key nerve that we're gonna be looking at is really two, the lateral femoral cutaneous and the femoral nerve. The rest of that trunk, that lumbar trunk, will combine with the S1 to the S3 roots to form the sacral plexus, and from that, the sciatic nerve is given off. And from the sciatic nerve, just behind the knee at the popliteal fossa, the peroneal or fibular nerve, and the tibial nerve will split into their separate entities. Again, the sacral plexus, mainly L4, L5 roots. And again, it's a key thing when you're having to differentiate between sacral plexopathies or lumbosacral plexopathies and radiculopathies. Again, major nerves here, you will see both terms, fibular and peroneal and tibial. These two are our go-to nerves in the lower extremity and with the sural as a pure sensory. And now we have, as a second sensory nerd, most of my doctors like to do the superficial fibular sensory, not the motor, just the sensory. Again, secondary femoral, lateral femur cutaneous, saphenous. And when we talk about the sciatic nerve, once it starts down the back of the hip, it innervates the psoas muscle, and then it goes on down to the hamstring muscles. The short head of the biceps is gonna play a key part in part of the EMG studies and part of the nerve conduction studies, because this muscle is the only peroneal or fibular nerve innervated above the knee by the particular peroneal nerve. So that's very helpful in differentiating with peroneal, sciatic, and tibial nerve lesions. Again, as it courses down the back of the thigh, and when it splits, the fibular goes laterally, the tibial goes down the center of the leg, down toward the foot. Common peroneal, again, we study this routinely. And as it goes down, it innervates the... Common peroneal comes here, and here's where the tibial nerve goes down, giving off the serral as it goes on. The common peroneal will split, the deep peroneal will go on down to the extensor digitorum brevis after the split where the superficial peroneal comes off. And the superficial peroneal will go and innervate the peronea of the lateral leg. The tibialis anterior is gonna play a big part in our nerve conduction studies, simply because if we don't get anything bilaterally from the EDB or the abductor hallucis on nerve conduction studies on peroneal and tibial, I do a anterior tibial from, or I do a peroneal from the anterior tibial muscle and stimulate the same places that I would if my recording site was on the EDB. And again, the extensors of the leg, up and out, down and in is the way I kind of remember it, up and out for peroneal, down and in for tibial. The most common site of entrapment for the peroneal nerve is at the fibular head and you can have cross leg palsy. You can hear these people walk in the lab if you listen there because they have a foot drop and they kind of slap their feet as they walk. You do have anterior tarsal tunnel, which is very rare. And again, we have that anatomic variant accessory fibular in the leg. The sacral plexus also is, the superficial fibular comes from the sacral plexus. Again, it's a good little secondary sensory nerve that we use on the lateral aspect of the leg. It innervates motor-wise, the peroneus longus and brevis, but then as it goes to the dorsum of the foot and the anterior lateral foreleg, you'll find it makes a very good sensory nerve. And in some of the older clientele that we have, if the sural's not there, a lot of times you can get the superficial peroneal. Tibial nerve, back down the back of the leg, again, courses down to the foot where it innervates the abductor hallucis and then courses across the sole of the foot to eventually innervate the abductor digiti quinipedis. The key thing on that in the upper leg is the flexors of the foot and the gastroc and the soleus, which will play a big role when we do H reflexes in the upper, in the leg. And the medial plantar portion of that tibial nerve innervates the abductor hallucis. Baxter's nerve innervates the abductor ADQP and then the flexor digiti minimi brevis is innervated by the lateral plantar. The most common area of entrapment is tarsal tunnel at the ankle. Although you can have popliteal fossa trauma, which will cause not only the distal, but also the proximal stimulation sites to be either prolonged or they're not at all. And again, I compare side to side comparison and I always, my doctors must rule out first other diseases first. Serral nerve, our go-to sensory nerve with fibular and tibial components. And from there we go back up toward the plexus to the femoral nerve. And the femoral nerve is the one that innervates the quads of the leg, vastus lateralis, medialis, any of the four quads. And it is, becomes the saphenous nerve distally as it reaches the knee. The saphenous nerve goes down the medial aspect of the knee and the medial aspect of the leg, finally ending in the medial aspect of the foot. And again, here's your femoral nerve and here's the, as it goes past the knee, your saphenous nerve and as it goes on down to the foot. Sensory studies on the saphenous to me are a very difficult one to get. I tend to get it better at the lower leg than I do at the knee. One of the techniques was to stimulate at the knee, but I tend to stimulate at the lower leg just almost directly across from where I stimulate the superficial peroneal sensory nerve. And that would be in this area right here where I would put my active in reference and I would stimulate it 10 to 14 centimeters proximal to that. The lateral femur cutaneous is likened to the lateral or the medial antebranchial cutaneous nerve in the upper extremity because it's pure sensory nerve. It's a pure sensory nerve going down the lateral aspect of the thigh. This one is difficult to obtain even in the most thin people. Again, the disease process that occurs with it is myralgia parasitica. And it's a very, it's no motor problems whatsoever. It's strictly a sensory problem. And what I do when I have a patient that comes in with a diagnosis of myralgia parasitica, I give them a ballpoint pen or I give them a marker and I have a mark out their sensory loss here on the lateral aspect of the thigh. And then somewhere in that area is where I'm gonna put my active and reference electrodes and then stimulate at the hip. You can also have for, you can have the median and lateral plantar nerves, which is a mixed nerve from the tibial nerve. And again, the distal sensory branches go to the sole of the foot. And these are my big ones that I go to in patients with tarsal tunnel. And last but not least, the anatomic variant in the lower extremity is the accessory fibular, where the fibers from the fibular nerve leave the main trunk and instead of going along with the fibular nerve down to the EDB, they simply go around the lateral malleolus. They go from here, instead of going this way, they will go this way. And the way we find that is when we have a higher amplitude of studies here, then we do distally with everything being correct, temperature, super maximal and everything. So in order to make sure that that's what it is, go stimulate behind the lateral malleolus about somewhere along where you would think the sural nerve is and still record from the EDB and you'll pick up those fibers there. And we'll see these occasionally. In fact, a couple of weeks ago, I had someone that had bilateral. And that's it. Thank you for your time. It's been a pleasure giving this talk to you and I wish everyone well. Hello, everyone. My name's Dr. Tristan Allen, and I'm excited to finish up our lecture on peripheral nerve anatomy with the discussion of the anatomy of the neuromuscular junction and muscle and also talk about some practical applications for applying that knowledge in the electrodiagnostic lab. I have no financial disclosures. And so a couple of goals following this session, my hope is that everyone will be able to understand the anatomy and the function of a normal neuromuscular junction. We should be able to describe common findings on nerve conduction studies due to a neuromuscular junction or muscle disease. We should be able to describe how to perform repetitive nerve stimulation and when such testing is indicated. And finally, to discuss factors which may cause artifact on electrodiagnostic testing for these tests that we perform. So a couple definitions to start off with. When we talk about the neuromuscular junction, we're referring to the chemical synapse formed by the motor nerve and a muscle fiber. Synaptic transmission is the process by which signals are transmitted from the neuron to the target, which in this case is the muscle fiber. And acetylcholine is the neurotransmitter that's active in this space. So this is a schematic of what the neuromuscular junction looks like. So here we've got what's called the presynaptic nerve terminal down at the bottom here, we have the muscle fiber, which is the target. And so how neuromuscular junction transmission occurs, the first step is that presynaptic action potentials trigger influx of calcium into the presynaptic nerve terminal, which we see here. At that point, acetylcholine is released from these vesicles into the synaptic space. And then after that occurs, it fuses with the receptors here on the muscle fiber, we also refer to that as the postsynaptic end plate, and it produces a signal that then starts the synaptic activity that we're desiring. And then following this, the acetylcholine here in the synapse is then broken down for recycling. After acetylcholine fuses with the receptors, sodium channels are opened, which results in depolarization of the muscle fiber, and it creates a charge that's called the end plate potential. And this is important because the size of the end plate potential is dependent upon the amount of acetylcholine that binds to receptors. And there are diseases out there that affect the ability of acetylcholine to be released, so this has direct implications for what we see on electrodiagnostic studies. When we talk about the safety factor, this is the size of the end plate potential above the threshold to generate a normal muscle action potential. And I have a diagram that demonstrates this a little bit better on our next slide. The other important thing to know is that when acetylcholine is released, there are two groups that are mobilized. There's an initial primary store followed them by a secondary store. So this is a diagram here showing our end plate potential, which is the shaded areas. So if we stimulate a nerve repetitively or we're moving a muscle and the nerve is firing to tell the muscle, in a normal healthy neuromuscular junction, every time our end plate potential will be above this safety factor, which is the horizontal line here. So even though every time our end plate potential is going down a little bit because we're depleting those stores, our C-map over here on the right should look normal every time. And that's not the case with some neuromuscular junction diseases. So who should we test their neuromuscular junction in? Typically these disorders cause weakness, which is often fluctuating without any associated sensory symptoms. And these patients typically present with weakness in the bulbar region, with swallowing or weakness in the tongue or the eyes, or proximal weakness in the arms, the legs, or the neck flexors and extensors. So there's three primary diseases that we think of, although there are other things that can influence the neuromuscular junction that I wanna touch on a bit today. These include botulism and Lambert-Eaton myasthenic syndrome, which attack the presynaptic neuromuscular junction, and then myasthenia gravis, which is a postsynaptic disorder. As I stated previously, these diseases all cause muscle weakness. In myasthenia, the muscles that are most prominently affected are proximal muscles, the face, the upper trunk. In Lambert-Eaton myasthenic syndrome, this tends to be the intrinsic hand muscles or the hip abductors. And nerves that we typically evaluate by repetitive nerve stimulation involve those that I've listed, the facial nerve recording over the nasalis in the face, the spinal accessory nerve recording over the trapezius, or the ulnar nerve recording over the abductor digiti minimi. So going back to our schematic, I wanna demonstrate where each of these diseases affects the neuromuscular junction anatomically. So botulinum toxin works by inhibiting the release of acetylcholine. So normally we would get the vesicles that would bind and release the acetylcholine out into the synapse. Botulism does not allow that to happen. With Lambert-Eaton syndrome, this is caused by antibodies which target the voltage-gated calcium channel here on the right, and don't allow that initial calcium influx to start the depolarization process. And then typically, myasthenia gravis is most often caused by antibodies actually targeting the acetylcholine receptor here at the end. So it does not allow acetylcholine to bind. So there's a couple tests that we use for neuromuscular junction. The first of which is just doing our standard motor nerve conduction studies. Now, a low amplitude of a CMAP can suggest a presynaptic neuromuscular junction disorder. And that's because on the previous slide, we saw that both botulism and Lambert-Eaton syndrome don't allow the initial cascade that allows acetylcholine to be released out into the space and to cause a normal CMAP to occur. The other specific test that we can do for the neuromuscular junction is slow repetitive nerve stimulation. And this occurs at two to three hertz. These stimulations are administered in trains of 10 or five stimulations. And it's considered to be a positive test when we observe decrement or greater than a 10% drop in amplitude between the first and the fourth stimuli. And that has to do with how those stores of acetylcholine, the primary store and the secondary store are released. So what should our approach to a repetitive nerve stimulation study be or a neuromuscular junction study? In our lab, we initially always perform what we call our peripheral neuropathy screen, which includes one motor nerve and one sensory nerve and an upper and a lower limb. And the point of this is to make sure that there's not an underlying peripheral neuropathy or a compressive neuropathy that could potentially interfere with the results. If at all possible, you want to avoid quote unquote disease nerves. So this would include like carpal tunnel syndrome. You don't wanna repetitively stimulate the median nerve. And you always wanna make sure that you're stimulating at what we call supermaximal stimulation, which as you all know is stimulating. So the CMAP amplitude is at its highest and doesn't get any larger. For repetitive nerve stimulation, technique is of the utmost importance. And this includes making sure all the electrodes are well secured. Typically, I use a bar electrode for stimulation purposes because that can be secured with tape. Making sure that the patient knows ahead of time what to expect with the testing and making sure that they're resting the muscle. If we're doing the muscles in the hands, they're not making fists or moving around. And that's because when you're moving around, you're increasing calcium and that could interfere with the results. As with our usual testing, you always wanna make sure that the limb is warm, at least 33 degrees. And that you also wanna make sure the limb is immobilized that goes again to the movement. So when we do repetitive nerve stimulations, we establish a baseline with 10 stimulations in a row. Following that, we do 30 seconds of isometric exercise. And at that point, we're looking for facilitation of the response. So if there's decrement that we see, meaning the CMAP amplitude goes down, and then you exercise, and then there's an increase in the amplitude again, that's useful for identifying a disease of the neuromuscular junction. And then following the exercise, you repeat trains of five stimulations for about five minutes, again, looking for decrement. So this is a picture of the setup that I typically use. I'm holding a stimulator here just because our bar electrode had run off somewhere, but I will usually use the bar electrode over here on the right, tape it to where the stimulator is shown. Couple things I wanna point out, I've immobilized the digits here with a small piece of tape, and then I've rolled up a washcloth under the wrist here to support the wrist, so the arm's completely relaxed, the patient's relaxed. So this is an example of what a baseline training for repetitive nerve stimulation would look like. So we have 10 stimulations here. We look up here, this was done at two Hertz. This is our amplitude. I made sure that that was super maximal stimulation, and we don't have much of an amplitude difference between the fourth and the first stimulations. And so technically, this is a very good baseline. Now, this is an example of a baseline that's not so good. I had done a couple of stimulations here, but as you can see, this sort of, the bottom of the curve here, there's differing widths and lengths of the responses down here. And when we look over here at the amplitudes comparing the fourth and the first, there's not much rhyme or reason to it. There's not decrement, it kind of jumps around all over the place. And so that tells me that maybe there was some small movement with the patient, or that there was some muscle shortening, which moved the recording electrode, and we need to try again to get a better baseline. So, as we talked briefly about, presynaptic neuromuscular junction disorders may have low amplitude CMAPs during motor nerve conduction studies. And if you see this, particularly if there's not associated sensory changes pointing towards a polyneuropathy as a cause, an easy thing that you can do when you're in the lab is to perform 10 seconds of isometric exercise to look and see if there's facilitation. And with presynaptic neuromuscular junction disorders, so the problem is with generating that initial impulse to get acetylcholine released into the synaptic cleft, by doing the exercise, we're forcing calcium into that presynaptic nerve terminal. And when that happens, you can see a several hundred percent increase in CMAP facilitation. So I'm just showing you a picture of my hand. This is performing isometric exercise recording over the abductor digiti minimi. And this is just a diagram of what this would normally look like. So diagram A up here is showing the CMAP amplitudes of someone that has Lambert-Eaton syndrome just at rest. And then this is showing the increase in amplitude after they've done the 10 seconds of isometric exercise. And I actually have an example of this on this slide in a patient who I performed a study on in clinic that have Lambert-Eaton syndrome. So this is of the ulnar nerve, and you can tell that the wrist below elbow and above elbow stimulation sites, the amplitudes are all low. This is not an ulnar neuropathy at the elbow because the conduction velocity across the elbow is appropriate, and the ulnar sensory response was normal. So we did 10 seconds of isometric exercise stimulating at the wrist recording over the ADM. And I mean, the percentage increase in the amplitude was several hundred percent. So this is what you would expect to see. Now, post-synaptic neuromuscular junction disorders will have normal CMAPs because they don't have any trouble releasing the acetylcholine out into the cleft. It's just a matter of getting the acetylcholine to bind to the receptors. So usually if you're just doing one or two stimulations for a motor nerve, the CMAP will remain normal. But if you continue to repetitively stimulate the nerve and no more acetylcholine combined, that's when we start to see the drop in amplitude. Both pre and post-synaptic disorders affecting the neuromuscular junction will demonstrate either a 10% or greater decrement on repetitive nerve stimulation. So this is another example of a patient that has a neuromuscular junction disorder where we're doing the 10 stimulations in a row. And I've kind of pointed out here this classic saddle shape that we see in a positive study. So if we look up here at the table, we can see that with our baseline, the decrement was around 18%. When we exercise the patient, that caused some repair of the decrement, meaning that the differences between the amplitude decreased, and that's a direct effect of the exercise. But then again, as we continued to stimulate, the decrement became more profound. The reason why we have this saddle shape here is because there's some mobilization of the secondary stores of acetylcholine after about the fourth or fifth stimulation. And then this is another example just after five stimulations. I wanted to point out what's called post-exercise exhaustion where you don't get that saddle shape, it just continues going down in decrement. Okay, so I want everybody to take a look at this and kind of think to themselves what could have potentially caused this because I've reviewed some studies that had waveforms that look like this. This is a really good example of severe motion artifact on repetitive nerve stimulation. So it's always important to recognize when something doesn't look normal. So in this case, the first two stimulations don't look too bad, but then the morphology of the third and the fourth changes, and especially down here at the bottom, you can just tell nothing looks like it should. So can muscle diseases cause nerve conduction studies or repetitive stimulation or abnormalities? Absolutely. Motor nerve conduction studies can have low amplitude CMABS in muscle diseases, and this primarily attributes to muscle atrophy or wasting. So making sure that you kind of do an examination of the muscle or the limb prior to doing the study is always important. And in fact, repetitive nerve stimulation can be abnormal with any disease that affects the component parts of the neuromuscular junction. So the junction itself, the nerve, the muscle. So we can often see decrement in things like motor neuron disease, but if you take a careful history and exam, you should be able to differentiate those folks between those that have a primary neuromuscular junction. So if you're a neuromuscular junction, you should be able to differentiate between those that have a primary neuromuscular junction issue. So the take home points are that patients presenting with weakness without sensory changes in characteristic areas that we talked about should be considered for evaluation with repetitive nerve stimulation for a neuromuscular junction issue. Repetitive nerve stimulation is reliant upon excellent technique, and some patients just may not be able to tolerate this despite excellent coaching on your part. It's a difficult study to go through. If you do discover a low CMAP response on routine nerve conduction studies without associated changes in sensory nerves, a simple thing to do is to perform 10 seconds of isometric exercise to test for facilitation. Like that example we showed you with the Lambert-Eaton patient. And then any dysfunction of the nerve, the neuromuscular junction or the muscle can cause abnormalities in repetitive nerve stimulation studies. So it's always important to use this information in context of the bigger picture with the patient. Hello, everyone. Loretta Van Every coming to you live from beautiful downtown Indianapolis. Thank you for joining us today. I think we all can agree that that was a tremendous amount of information to receive over less than 90 minutes. And so one of the questions that was asked in the chat box for those of you who are streaming this after and not seeing it live is, will the slides be available to us? And yes, there will be a link making the slides available for you for the following year. I don't know if anybody has any questions for me today, anything that I can address following kind of all of those different topics that we discussed or that we watched my colleagues discuss. Today is gait examination for... Just watching the chat box to see if anybody sends anything. All right, well, in the absence of anything, I will thank you for your time and wish you good learning for the rest of this experience. Thank you so much, Dr. Avery. Thank you.

AANEM Advanced Practice Provider Webinar Series

peripheral neurology

peripheral anatomy

nerve root

plexus anatomy

neuromuscular junction

muscle anatomy

radiculopathy

plexopathy

repetitive nerve stimulation

nmj