Welcome to the next episode of Lessons from the Lab. My name is Devin Rubin. I'm a neurologist at Mayo Clinic in Jacksonville, Florida, and I'll be hosting this next episode. This is an educational program through AANEM in which we interview a special guest expert, we discuss a case, we learn from each other, and we hopefully will provide some practical information to those of you who are watching this and are practicing neuromuscular medicine and EMG. Today we're going to go international. We have a superb guest, a really outstanding educator and outstanding electromyographer. He's someone that I'm really excited to speak with. He has such a vast knowledge of EMG. He has had a whole career not only of EMG but of developing some of the tools that we use in the EMG laboratory. And I'm going to give him a case and pick his brain and have him maybe grade me on how well I did on a case. And I hope you enjoy this. Welcome to the next episode of Lessons from the Lab. My name is Devin Rubin from Mayo Clinic in Jacksonville, Florida, and I am extremely excited to introduce the guest expert for this episode of Lessons from the Lab. This is someone that I don't think needs any introduction. For any of those of you who are watching this and are involved in EMG, you know Professor Erik Stahlberg from Uppsala, Sweden. He is extremely well known in the field of EMG. It's someone that when I hear him talk, when we talk together, I always learn something and I've been looking forward to chatting. So welcome, Erik. It's wonderful to have you with me. Thank you very much. Thank you, Devin. How have you been this summer? We have had a good summer. In Southern Europe, it has been extremely hot, but up north here, it has been very reasonable. So I can say I have enjoyed a long vacation, a long Swedish vacation. Well, I should have booked a plane ticket to do this recording with you because in Florida, it's been extremely hot and it's going to probably be hot for another two months. So next time we do this, I'll come to you and we can chat there. That is not a very good temperature for patients with myasthenia, I tell you. It's not, but instead of warming people up, we have to cool them down, it seems. Yes, they can eat ice cream and they can go into cold Swedish churches. That is better than hot soup and sauna. Yes, right. Yes, we're in the wrong space, wrong place. So it's been great seeing you this year. I know I've seen you at a couple of meetings, I think, earlier in the year and it's always nice. So you're active, you're still going to meetings, you're still teaching, but you haven't been practicing EMG in a while, right? You've been retired for a while? That's right. When COVID came and the laboratory more or less had more and more restrictions and I'm an old man, then I found it good to stay away from the laboratory. And after that, I have not seen patients. Do you go into the laboratory at all just to say hi? Not very much, but some occasionally, particularly for teaching. Okay. Well, even though you don't see patients now, I'm sure you can teach me something. One of the goals of this webinar is to teach the viewers and I'd like to learn something about a case and how I approach a case and see if you would do the same or do something different. So I'm hoping I can present a case to you and I can pick your brain. We can talk about it. Yes, that's right. It's very good to have a dialogue about these things because very often there are no absolute truths around, but we have to discuss and find an optimal way forward. Yeah. And I think that's what's been beneficial as we've been doing these, that you're right, that as I found that there isn't a truth and when I'm discussing it with other experts that we might have some variations, even though we come to the same conclusion, we have different ways to get there. And so I think that's enlightening and eye-opening. So I'm going to present a case to you. This is a patient we had in our lab several months ago, and it was a 63-year-old woman who was referred to the EMG lab because she was having some vision difficulty and some ptosis. And she basically had had it for about six months. She noted that it came on kind of suddenly and she noted her vision was sort of blurred. She didn't really say it was completely double, but when she would look off, I believe to the left, the vision seemed blurry. And her left eyelid, I think it was her left eyelid, would droop a little bit. It wasn't severe. It wasn't closing completely, but she felt that it was droopy. And that was it. She had no other symptoms, no slurring of speech, swallowing problems, limb or extremity problems. It was just really the visual difficulties. So she was, I think it's no surprise, she was referred to the EMG lab with a question of, could this be ocular myasthenia gravis? So I guess my first question for you is, I assume you've seen, had many patients over the years referred similar to this. Absolutely, yes. Yeah. And so in your lab or in your practice, when you're seeing patients, I'm curious how you would initially approach the patient from an electrophysiologic standpoint. Well, with these symptoms, first of all, you have to think about what kind of common, what is the most common reason for this type of symptomatology with a rather long history and not coming from the childhood, but developing more or less acutely and then developing slowly and it's drooping eyelids and probably double vision that is explaining her blurred sight. Then I think you have two good alternatives and certainly one is the ocular myasthenia and the other is probably some kind of myopathy. And when we now start with our battery of tests, I think it's in general very important to all of us for every study that we do that we are going to apply a test that can answer, include, I mean, confirm or exclude a certain diagnosis. I mean, it's not like fishing that you expose all your tests and see what you've got in the net today, but rather be very, you decide what you really want to look at today. And therefore, now I come to the question. In this case, I should make a suspicion of myasthenia and I want to confirm or exclude that. And since long time decades have used single fiber EMG, that will be my first test. And I certainly start with that in frontal muscles and orbicularis oculi and a few facial muscles. So interesting. So that would be your first test, but would you do repetitive nerve stimulation before that in this kind of patient? Devon, in this particular type of myasthenia, as you know, the repetitive nerve stimulation is not that sensitive. Don Sanders and Massey and the colleagues, for example, made the statistics of it and they found that the RepStim in the face gives 48% hit rate. So it's very low hit rate. So that should not be the first test to do. And so if we have access to single fiber EMG, then I start with that. If it is generalized myasthenia, I may start with single fiber EMG, but I like to have the RepStim as well, because then you get an easy overview of many muscles in a short period of testing. I have one more comment. It's not every laboratory and every practice that have single fiber EMG. And then we have to think in other terms. Then we at least have to do RepStim. That is the best we have for that question. Okay. So we're going to talk more about, I'm going to ask you more about single fiber EMG, but I'm going to show you what we did to start with before we got to that point. I'm going to just share my screen for a second. And certainly the clinical test is, we should not forget to say that. Right, right. It's important. Right. And her exam was similar to what I described. She really didn't have any obvious eye movement abnormality. Maybe there was a slight deviation of one of the eyes, and maybe slight ptosis. So it was one of these that was, it wasn't real obvious clinically as to what was going on. So we, so I agree with you, what you said, but despite my agreement, we still sometimes do repetitive nerve stimulation first. And part of that for us, I think, is because our techs room the patient and we're in another room doing another study. And so they'll go ahead and do the repetitive stimulation in case we find an abnormality. And in this case, they actually did spinal accessory and facial repetitive nerve stimulation. So are we bad at, for doing that? Would you, would you fault us for doing that? Not at all. This is, first of all, the way you have to do, if it was another laboratory than yours or mine, where we don't have single fiber EMG. So that is good. And, and the choice of muscles, it has to be proximal muscles. And the three that you mentioned, nasalis and, and sternocleidom, and maybe you had one more is, is good muscles. The, the outcome from a REP stim in hand muscle in this case is more than zero. Right. And I would even think that the outcome of spinal accessory is probably low. And as you said, even facial is, is only 50% if, if that. So, but this was, this was the spinal accessory from the trapezius. These are, I think you're familiar with this. So this is, these are the histograms at three at rest and then after exercise. And so I'm curious what you think about this is this. Yeah. I, I have, I have only one, well, I have a comment about the, the train of four. That was what we did in earlier days. And you have kept that, that protocol many laboratories in, in the world do more stimuli. We have gone over since many years to do 10. And you say, why should you do 10 when you still measure between number one and number four? Well, first of all, you can have a surprise with, with the changes later on in some conditions that they are more decrement later. And you really want to get that nice profile, the general shape of this, the saddle shape with the later slight facilitation, intratitanic facilitation, is it called? So I like to do that, but I measure like you do here between number one and four. And, and I think that's a good point. And I think, I think Don Sanders and maybe you, there were some studies in cases where you're trying to sort out myasthenia gravis from Lambert-Eaton myasthenic syndrome. So not necessarily this patient where seeing the continued the pattern where after shock five, six, seven, eight and Lambert-Eaton syndrome, often that doesn't start to repair. Whereas in myasthenia gravis, you might start to see the repair. Is that kind of what you were alluding to? Yes, yes, exactly. And other, I mean, more, more seldom conditions like, like McArdle, they continue to go down and down. So I, I, I feel more confident with the total quality of the, of the study. If you see the 10 and it's not that painful, we have not had to, to stop a study after four stimuli because it was too painful. It worked well. Okay. So in, in this study, the, it may be hard to see, but the amplitude decrement after exercise was somewhere right between five, three and six, but the area was a little higher here, 10, 11 to 13. Do you think this is technical, a technical problem, or could you think this is real? There's a discrepancy between amplitude and area. Yeah, there is, there is a discrepancy in the normal subjects and also in, in, in patients with some kind of disease. So now I think this is absolutely perfect. And I don't know what you consider abnormal. This is very different in, in the world also. In earlier days, we said 20% and that was due to the width of, of the ink line in the, in the, in the ink writer. Later, we came to 15 and 12 and then somebody, some people have stopped at around 10%. You know, the neuromuscular junction in itself has no decrement at all. In a normal, you cannot see that. It is actually the other way around that the amplitude may increase for, for many different reasons within the muscle fiber. So we should have zero, but that is not possible. We must add some, some technical possibility for, for errors and so on. So I made a summary of a group of patients retrospectively, and I found that 5% covered, covered the, the normal material. So we have used 5%, but many use 10% and I think you use 10%. But remember that if we, if we move that figure up to 12 or 15, then we allow kind of artifact, more artifacts and, and we lose some of the sensitivity. So I think it's instead of just increasing the number for normality, it's better to improve the quality as much as possible. Yeah, I think those are fantastic points. And, and, you know, I think the point that normal decrement is zero is an important point. Whenever I ask that to our residents or they always say, Oh, it's 10%, but you're right. It should be zero. And, and in our lab, I'm, I'm a little cautious about calling 5% because I know because of technical factors, but I'm not, but it's not an absolute 10% as the cutoff. And we, we did a study at Mayo and a series of our myasthenic patients and found the optimal sensitivity without, without reducing specificity was about seven. So, you know, kind of, if I see consistent real decrement of 7%, 8%, I'm comfortable, and even five percent, but I'm a little more cautious with that. Yeah, absolutely, that is really the lower limit, so I agree with you. Seven percent is fine, and that is the standard of your laboratory, so we buy that. And one thing that both you and I are very keen about is to look at the signals themselves to the left in this panel here, so that you see takeoff and you see late components and this and that, and to the right you see the bars, and that is a harmonic change in amplitude, not jumping up and down. I'm sure that in the near future we will define how much of jumping up and down we can allow, which is indicating movement of electrodes and so on. So quality can be quantitated from these bars. Yeah, and especially even with AI and computer learning, hopefully that will be something that we can have some type of warning that this is not a normal pattern, so people who aren't as familiar with it will not over-diagnose based on a technical problem. Yeah, so okay, so we did the trapezius, and then we did a facial, same thing, facial repetitive stimulation, and here there isn't really much decrement, really isn't any, so kind of… Are you proud of this? No, I'm never proud. The techs know I'm never proud, never perfectly proud. I think what happens, I mean if you're asking me, well I'll ask you, what would you not be proud of? Well I mean, you see the problems we have with the REPSTIM in the last four runs there, it's increasing a little, the light green, I think that is a positive decrement of something, and I think that is technical. Yeah, and the amplitude, if you just look at the first trace in the numbers, the amplitude is dropping, just the absolute amplitude, so maybe there was some movement of the stimulator or something, the amplitude goes down, so yeah. Nosalis is certainly a very difficult muscle, because in all the studies we want to have supra-maximal stimulation, and that is more or less hopeless when it comes to facial muscles, because if you activate nosalis to a good point, then you increase the stimulus a little, and then all of a sudden you activate rhizorius and zygomaticus and other neighboring muscles, so it's very difficult to get the clean supra-maximal nosalis, so we have to allow this kind of quality. The quality here is acceptable, I think. Yeah, acceptable but not perfect. So but anyway, I think with the, I felt with these two repetitive nerve stimulations, there was not sufficient, it was not definite decrement to, at least certainly not enough to say with certainty that this is a neuromuscular junction disorder, and as you said, it's not specific even if there was for neuromuscular junction disorder, but I wasn't too impressed from a pathology standpoint with these two nerves, I don't know if you would agree with that or not. Yeah, I agree with that, and are you going to show something more on RepStim, otherwise I have two comments. No, that was the only RepStim that I did. Very good. One question is, did you do a short or long-term activation? I mean, I remember in one of your webinars you had, you talked about the one-minute exhaustion and to see a more definite decrement, because in the previous picture, I mean, it is in tendency to decrement there, I think. Yeah. With activation, wouldn't that have been coming out much better? Yeah, actually, this is post-activation, so it's difficult to see on these slides, so the first three traces are at rest, and then the fourth is immediately after one minute of exercise, and then 30 seconds, one minute, two minute, three minute. Oh, wonderful. So, I think you're right, that if there's worse, somewhat worse decrement here, that's about two or three minutes after exercise. Okay, okay. The short-term activation, except when we use it for presynaptic conditions like Lambert-Eaton, I have played around with 10-second activation in the way like you get the feeling for the conduction in the motor end plate. That is like a booster dose of Tensilon or whatever. If you activate just 10 seconds, then you get an increase in release of acetylcholine, and if a questionable decrement, like in yellow four bars there, if that all of a sudden after 10 seconds of activation is abolished and you have no decrement at all, then I tend to believe that the yellow there is a kind of decrement. That is how I use the 10 seconds to see if I can facilitate the neuromuscular transmission. So, would you usually have the patient exercise for 10 seconds, and then after that have them, and then give a set, and then after that have them exercise for a longer period of time and take it out for a few minutes? You would do both? In the one-minute test is definitely in the cases where the RepStim is not showing an abnormality, or if it is showing a questionable abnormality, we want to provoke the failure by long-term activation. Okay. Good. So, that was all the repetitive nerve stimulation, and then we did go on to the needle exam, and you mentioned at the beginning that your primary test would be single fiber EMG. Do you perform a routine needle EMG of the muscle first before you go into single fiber, or do you just go right into single fiber? Unfortunately, I should say, I go right into single fiber EMG, and people say, you must do EMG before. I do the other way around, that when I do the single fiber EMG, we get a very good sense of the distribution of muscle fibers in the motor unit. I'm talking about re-innovation, because that is the problem with single fiber EMG, because jitter is seen also in early re-innovation. So, when I do the single fiber, and it's unusually easy to get pairs, then I say, is this a tendency to neurogenic involvement? Then I do EMG afterwards, for sure, but we do not usually start with EMG in all cases, and not nerve conduction. Certainly, nerve conduction has more nothing to do with the symptomatology in this patient, I should say, but EMG is reasonable. But to your question, we do not, unfortunately, perhaps, do EMG before. We do it after, if it is unexpected findings in SFEMG. Okay, so you made a comment, and I'm going to ask you, and it's either going to make me feel bad or feel good, but you said, when it's relatively easy to collect pairs, I was under the assumption, every time it was easy for you. Single fiber, how long would it take you to do a study? 20 minutes per muscle for 20 good pairs, that is a kind of routine, sometimes easier, sometimes more difficult. I'm preferring the facial muscles in these types of cases. I sit behind the head, at the head and behind the patient, and just lift my hands down to the forehead or around the eyebrows or the clavicle. And instead of sitting in front and coming, approaching the patient from front side, it's not so easy. So you said you would sit next to the patient, you said, like you're next to him, and then you're coming in. Yeah, I have my chair behind the coach. Would you typically do frontalis or orbicularis oculi as your first choice? We do the two, a little depending. Often I start with frontalis and then we do the orbicularis oculi, if frontalis was normal. If frontalis was abnormal, it does not add anything to test another muscle also. But you have to think of facial palsy in the history and think of Botox, which is the important thing. Then if frontalis is normal, I go to orbicularis oculi. There is a little more tendency to have a hematoma, perhaps one per 20 patients. We see a little bruise here. And if that is also normal, we don't go on to number three. I have done that before and I looked at statistics. It doesn't really add anything. So two muscles. What's the most unusual muscle that you've done single fiber on? Well, it's... Have you ever done the tongue? Yes, yes. And also you can do EMG and single fiber in levator palpebrae or rectus superior. A very high frequency is difficult to get low frequencies for analysis. But in some laboratories, I know an article from Nogves and Antonio Rivero in Argentina. They published an article about doing EMG in these types of patients by putting a needle either through the eyelid and get the thin levator palpebrae and the rectus superior and get very nice recordings there. Ah, interesting. I always thought, I didn't realize that, I'm not familiar with that, but I always made sense to me that that would be a higher yield muscle if you could reliably do it when patients have ptosis, because that's the muscles that that's weak. So exactly. Well, I'm going to show you three clips of a single fiber. This is with concentric needle that were recorded from this patient. And maybe you can grade them A, B, C, D, or an F as a recording. And comment on it. So is that OK? Yeah. And you can be as hard as you as harsh as you want in your grading. But this was one, this was one. Yeah. Good quality is A the best. A is the best. Yeah, A is the best. F is fail. Then this is fantastic. I have the comment that the amplitudes are very low. Which filter do you use? This is a thousand hertz for frequency. I see that here. Sorry. Yes. And now I have and this is normal. And the sweep speed, I usually use 0.5. And you see, you have plenty of room for 0.5 milliseconds per division here. And that helps to look at the jitter a little better. OK. So this amplitude on the second spike, it is low. But not so low that, I mean, you would feel that this is a reliable pair, even though it's a low amplitude. I think this is really very reliable. And the disturbances are really minor. So this is fine. Yeah. OK. I like to say, I like you have superimposed at the bottom there a number of these charges. And I don't think they are so many. Perhaps 10 or so. If you should have a setup that the bottom panel has a superimposition of all your 100 discharges, for example. That is not so good, because if you have a slight trend in the time interval between spike one and spike two, and you have a slow, slow trend, then you will see a very wide distribution down at the bottom there and misjudge this to be a high jitter. So I like you to do that. You did this superimposed low number, 10 or 15, not more. Right. OK. OK, that's one. This is the second one. I'll try to stop it here, right there. So that is a little more difficult because of the combination of three spikes. And I can say that a disturbance, if you consider this as a variable shape and all that, we can look at the jitter. And the jitter of the green one on the middle, there is only 13. So that is normal. And it's very little chance that an artifact should reduce the jitter falsely. So I think it's correct. In the bottom line, it looks like some individual... You see a line there? Right here. Yeah, on number two. Yes, exactly. Yeah. It could look like another single unit, a single spike is also triggering. But in the raster display, you see all the three spikes together. So I think this is correct. And the value is very reasonable. It fits to what the eye is saying. And also the numbers. The thing is that if the spikes are closer than 150 microseconds, they interfere so much that the jitter in that case is a little reduced. But the setup, I think I know the machine you have here. The setup is such or can be set up so that if the interval is too short, then the system will cancel the recording. And here, obviously, it has at least occasionally measured green dots, but not all the time. Not all of them. Yeah. So you're talking just for the listeners, this second spike, which does seem to be separated from the third spike. But if it was a little more to the right, sort of more on the slope of that, that might not be reliable to measure. You might have the jumping. It might be jumping and measuring that spike differently. OK. So good quality. OK. And then let me show you one more. So here's the third one. I'll play it. I'll play it again here. So it doesn't sound like an A. Yeah, what do we do with this? I think that, I think that this is in essence a normal jitter. I think, let's see the sweep speed is also yes, and the, there is one that is green. Yeah, this little one right here. That one should not be accepted, I think, because that is definitely not a clean spike and that you can remove from the plot to the right. Yeah, yeah, you can, this is just a still video, but yeah, you can, right. It's good, but I really think that these two high spikes are good. The problem with this recording, if there is a problem, is the degree of activation, perhaps a little too much, and one should ask the patient to relax a little. That is the most common command I have to patients, relax, relax. So that's kind of my question for, and reason for showing this, that, you know, what happens if the patient relaxes and then this spike stops the fire, stops firing, and then they activate a little bit and you get this again, but you get the, there's a second and maybe a third motor unit, separate motor unit. Are you, would you be okay keeping this and now with the machines, you can, you know, you can edit, you can click and drag a box and get rid of the background one. Is that fair to do that or is it, should this be thrown out because of that? It is probably fair, but I don't, I don't like the post editing very much. First of all, it takes time. Secondly, it is not really statistically fair to do manipulations of the sickness afterwards. The best is, I'm sure that you let the patient listen to the sound because it's so great difference to have a silent machine or have the sound on. Patient can train and learn to slow down a little. And so my answer is try one minute more and train the patient and see if they can relax a little more. Okay. So you'll get, you'll give me a C on this one, a C or a V? C. Okay. Okay. Good. So, so this, you know, there were, and there were other pairs that were collected and, and I guess the next, the question then, the other question for you is in this patient, things all looked good, the collecting more pairs looked good. They were all within normal limits. If you look down here, I think that was one that I threw out. It was not a clean pair. But if, if someone's having trouble collecting 20 pairs for whatever reason, do you, are you a proponent of the futility studies that say if the first 12 or 15 pairs are normal, the chance of you getting two abnormal or three abnormal pairs for the last group is so low that you can stop without collecting 20 pairs or do you think you have to always collect 20 pairs, at least 20? If all, all the chances are equal, then you can statistically decide whether 12 is enough and how big a chance it is to, to, to find more later on. I don't use that. I make it simpler. If we consider three or more pairs, if three or more pairs are abnormal, then the study will be normal. And you see, if you have done, if you have done four recordings and, and two of them are abnormal, then the study will be abnormal. Right. Because 50% are abnormal. Yeah. Is that what you're saying? Yes. And I don't use percent. I really don't. The reference values are, and the rule of having more than two is dependent on that we record from 20, that the cutoff is 20. So if, if we have three abnormal, then the study is likely to be abnormal. And I tried to, I tried to, so we can stop earlier if, if five recordings are abnormal, you can stop there. Even if you only had studied 12 recordings. If we want to exclude an abnormality, I think we have to go up to a reasonable number. I aim for 20 and in, in statistics and in publications and so on, I have accepted 15 and write that clearly that we have based the study on down to 15. I aim for 20. Okay. And do you have any advice, and this may be hard to answer verbally without this being a demonstration, but you, you seem like someone who never gets flustered, never gets frustrated. But I think as we all know, sometimes, at least for me, when, when I'm doing a single fiber study and patients, I'm just can't find pairs very well. It's taking time. I'm trying not, trying to not get frustrated. Do you, do you have any advice or technique or anything you do if, if you're searching and you're just not getting good pairs after several minutes? Devin, I can tell you when Ekstedt and I worked on developing this technique in the sixties, we said it must be possible to get a single fiber. Theoretically with this needle that we build ourself, we inserted that in my, my thinner muscles and we were poking and poking for 18 hours without sleep and dinner. And then finally we got the single fiber potential. So the, the, the, the first, first recording took 18 hours per pair. And then it has been reduced very much. I say it's definitely a matter of training, but, but in your case, I mean, you have years of training in, in this. So it's certainly the patient's degree of cooperation also, if they move or if they have too much activity, which is the most common problem, but I think we can usually get enough with, with, well, I don't know what I should say. Yeah. And I think, I mean, we've had situations where, you know, I think for our fellow when they're training and even for staff where we, you can't go into the study having, having to be rushed, you know, if you have another patient or you have, you know, you know, I have a meeting to go to in 15 minutes, that's not going to work that. And I think that's advice that I would share with trainees or someone learning this as you just understand, this may take some time. And I tell patients this, it might, this might take me a half an hour to collect what I need to collect and not feel rushed because that doesn't do anyone any good. And it can be worth it because in the other situation where you have a patient and you, you do a rep stim and that is borderline and then you try after three months and it's borderline again, it can take a long time until you arrive at the diagnosis with single-fiber EMG. If you spend a few more minutes, 15 minutes or even 30 minutes more, you may be able to get the correct situation. Right. Well, I want to, before we end, I want to show one more clip because I want to end on an A, an A plus. This was not from this patient, but it is a single-fiber study from a patient that had similar findings, similar symptoms. And this was the, the study. Yeah. So do I get an A plus for that one? Okay. Let's close from here. Do you want to comment, make any comments about what this is showing? I think it is, it's a very nice recording and listen to the sound. It is, you can actually tell when you're out in the corridor and hearing that your colleague must have a myasthenic patient in the room. So this is wonderful. And we, we, we try to at least make one of the spikes optimal in amplitude and trigger on that, and then see the jitter displayed either on a preceding signal or a follower. Like this, it is a follower. And here you want to see if there are any blocking. That means a line through the base of the signal. And you don't see that here. And the jitter is something like 70. If the jitter is more than a hundred, then it should also be blocking. Yeah. And I do have one other clip since you mentioned blocking that does show, it may not be as good of a clip, but I think this one shows blocking. Yeah. Oh, this is nice. Very nice. Lot of blocking. So you can see a lot of blocking and the jitter, yeah, was 150, I believe here on this one. So yeah, here, here, yes, yes, very, very nice. So if you did, if I, if this patient, we did those, this example, and the one I just showed you, both of those were highly abnormal, and maybe you collect one of their parenets abnormal, you could just stop and say, this is an abnormal study. Yeah. Yeah. As long as you have more than, more than two. But then if you got this, would you then, would then you, would you just flip over and do a concentric needle to make sure there wasn't myopathic findings or would you, no, you wouldn't say this is enough. Myopathy, they have a little, little jitter as, as, as a group of patients, but not, not a pronounced jitter at all. And so we, I mean, the myopathy diagnosis with EMG in the face is very difficult, isn't it? So, yeah. It's all right. I mean, I must add one thing, the two things, the RepStim can confirm a disturbed neuromuscular transmission, but we cannot exclude it, particularly in the face. I mean, we talked about 50%, the single fiber EMG has a sensitivity in certain hands and certain publications, 99% in generalized and 97% in ocular. So it is possible to make the diagnosis very, very unlikely with single fiber EMG. I hate to use the word exclude, but it's a very, very unlikely. That is not true for, for RepStim. And another thing, if you go into a weak muscle, if the weakness is due to neuromuscular problem, then you must see that in jitter and blocking, blocking. If you have a weak muscle, man, no blocking, a little jitter, but no blocking, then the weakness is due to other things. For example, a myopathy where the weakness is due to the contractile properties and the loss of fibers and so on. That's not a neuromuscular problem. Do you think that if someone has a weak muscle that you should be, and it's due to a neuromuscular junction problem, you should be able to identify unstable motor unit potentials with a concentric needle and not need single fiber? Yeah. Yes, absolutely. And that was the very first sign of EMG abnormality in 1934, when the first publication came about the variation in amplitude in motor unit potentials. And that can be used. You put in an ordinary concentric electrode and see the shape of the motor unit potential. You don't need to make them to single fiber, but you can see the compound motor unit potential. Yeah. And I think that's a good point for people who don't do single fibers to not ignore the motor unit stability or instability when you're doing your routine EMG. Well, this has been enlightening and terrific. I'm wondering if you have any final words of advice for anyone watching this related to EMG or based on your career or history or anything that they can take with them. If you like to go into this, the most difficult is to do it on your own arm. First of all, you are normal and secondly, you are not so good to be both examiner and patient at the same time. Try on a colleague, try an extensor digitorum communis or facial muscle. And the easiest is to have a patient with a slight polyneuropathy, for example, where you can get a lot of pairs and you can try to hold them for a few seconds to get enough discharges. We want to have 50 discharges for a recording. Yeah. I think that's a great point that when we teach our fellows, it doesn't have to be a myasthenic patient that you do single fiber. You can do it on any patient, especially since we use a concentric needle now, just flip over to the program and collect a few pairs at a time. And that's a good way to help train and improve the skills. So when you asked about the funny muscle to test, I've seen a few myasthenic dogs. They were just lying flat on the coach without any anesthesia or anything. And I lifted up the foreleg and made the recording from deltoid that I can grade a little, got beautiful recordings and the diagnosis of myasthenia was within 10 minutes. So that was fantastic. So I had quite a number of those, or a low number, six, seven, and horses I've seen, and horses have the same motor unit potentials than men, but that is another topic. Wow. Well, that's, if I get bored, you know, seeing all the patients, I might have to bring some animals to the lab and try that out. Well, it's, this has been wonderful. I really appreciate you taking the time, having this great discussion. I think there's so much information and you have so much knowledge. It's great to learn from you. I'm glad you gave me at least an A on a couple of those, those clips. Beautiful. Beautiful. And thank you again, and I look forward to seeing you soon again at, at a meeting. Yeah. Thank you very much, Devon. Have a good time. Thanks. You too. Bye-bye. Well, I hope you've enjoyed this episode of Lessons from the Lab. Professor Stahlberg is just a wonderful, knowledgeable person, and I always learn something when I chat with him and hear him speak. I did learn that I'm doing okay with single fiber. I was graded pretty well, but I think that the points he made are important points, that it's not an easy technique. It takes practice, and it's important both with single fiber EMG and repetitive nervous stimulation to really scrutinize the recordings to ensure that they're technically reliable in the assessment and interpretation of the findings. It is interesting, but makes sense that single fiber EMG may be the go-to test, particularly in patients who have only ocular symptoms. And I think, as I said, in our experience, repetitive stimulation doesn't usually help us a whole lot, and we ultimately go to single fiber EMG in the ocular myasthenia patients anyway. But both techniques are useful. They're complicated techniques, and it is important to ensure technical reliability. So I hope you enjoyed it. Hopefully none of you will go out and bring your pets to the EMG lab and practice single fiber EMG on your dogs, but if you do, you can always contact Dr. Stahlberg for tips on doing it on your pets. So enjoy, and we'll see you next time.

Lessons from the Lab

Devin Rubin

neurologist

EMG

ocular myasthenia gravis

diagnosis

single fiber

repetitive nerve stimulation

technical reliability

electromyography