Continuum Audio

• Myotonic Dystrophy With Dr. Paloma Gonzalez Perez

  Myotonic dystrophies (DM), in addition to muscle weakness and myotonia, are associated with broad and variable multiorgan involvement. Neurologists need to recognize DM to ensure prompt diagnosis, effective symptom management, and prevention of life-threatening events. In this episode, Casey Albin, MD, speaks with Paloma Gonzalez Perez, MD, PhD, author of the article "Myotonic Dystrophy" in the Continuum® October 2025 Muscle and Neuromuscular Junction Disorders issue. Dr. Albin is a Continuum® Audio interviewer, associate editor of media engagement, and an assistant professor of neurology and neurosurgery at Emory University School of Medicine in Atlanta, Georgia. Dr. Gonzalez Perez is an assistant professor at Harvard Medical School in Boston, Massachusetts. Additional Resources Read the article: Myotonic Dystrophy Subscribe to Continuum®: shop.lww.com/Continuum Earn CME (available only to AAN members): continpub.com/AudioCME Continuum® Aloud (verbatim audio-book style recordings of articles available only to Continuum® subscribers): continpub.com/Aloud More about the American Academy of Neurology: aan.com Social Media facebook.com/continuumcme @ContinuumAAN Host: @caseyalbin Full episode transcript available here Dr Jones: This is Dr Lyell Jones, Editor-in-Chief of Continuum. Thank you for listening to Continuum Audio. Be sure to visit the links in the episode notes for information about earning CME, subscribing to the journal, and exclusive access to interviews not featured on the podcast. Dr Albin: Hello everyone, this is Dr Casey Albin. Today I'm interviewing Dr Paloma Gonzalez-Perez about her article on myotonic dystrophy, which appears in the October 2025 Continuum issue on muscle and neuromuscular junction disorders. Welcome to the podcast, Dr Gonzalez-Perez. I'd love for you to introduce yourself to our listeners. Dr Gonzalez-Perez: Thank you very much for the invitation. My name is Paloma Gonzalez-Perez. I'm a neuromuscular neurologist at Massachusetts General Hospital in Boston since 2018. And I'm originally from Spain. I did residency there and also here in Iowa City. And then I did the neuromuscular fellowship here at Mass General Brigham, and then I stayed here as a faculty. So, my focus is myopathies, and more specifically muscular dystrophies, and more particularly myotonic dystrophy, which is what we are going to talk today. Dr Albin: Wonderful. And this is a really fantastic tour de force article about myotonic dystrophy. And in reading your article, it really did stand out to me that these myotonic dystrophies are probably under-recognized. And so, I was hoping that, just to start, you could tell us a little bit about, what is a myotonic dystrophy, and how should we sort of situate that within the larger context of all muscular dystrophies? Dr Gonzalez-Perez: Yes, so muscular dystrophies, we have many of them, right? And mostly affecting the skeletal muscle. And basically, the definition of muscular dystrophy is a genetic or inherited muscle disease that causes a progressive muscle weakness. And also, in the muscle biopsies of patients with muscular dystrophies, we see some fractures that are characteristic of this category of muscle diseases, such as, for example, the nuclei of the muscle fibers are in the center---that's what we call internal nuclei---or maybe fat infiltration or increased connective tissue or a variability in the size of the muscle fibers. So, now in the last few years, the genetic testing is more accessible to us. So, we don't need muscle biopsies all the time to diagnose patients with muscular dystrophy. So many times, we go directly to genetic testing. And this is basically the category of muscular dystrophies. Myotonic dystrophy is very fascinating muscular dystrophy in the sense that many times not only affect the skeletal muscle, but other organs can be affected. And it is true that other muscular dystrophies can affect other organs such as, for example, the brain and the heart, which is something that we always have in mind as a clinician to make sure this muscular dystrophy affect the heart or affect the brain, because it is important for patient care. But myotonic dystrophy actually can affect any organ in the body. I think it is one of these muscular dystrophies in which there is a multisystem involvement of the body. So, the immune, immunological system can be affected and the endocrine system can be affected, the GI system can be affected. In addition to, obviously, to the brain, to the heart, to the skeletal muscle. And sometimes that is why it is under-recognized because of course, if there is a very severe phenotype, maybe the patient comes very easily to a neurologist who is very familiar with myotonic dystrophy. But if the phenotype is a little bit milder, and maybe it doesn't affect much the skeletal muscle. So, these patients probably are in the care of other specialists, such as, for example cardiology or GI doctors, and obviously these specialists are not really aware of this muscular dystrophy. So, I think it is a complex disease because it is very variable in phenotype, can affect many organs and can be also mild. Dr Albin: That is fantastic. That is just a wonderful overview of, really, muscular dystrophy. One of the things I was really curious about: the name includes myotonia. Is myotonia, like, always present, or is that a little bit misleading? Dr Gonzalez-Perez: Yeah. I would say that it is a little bit misleading---maybe not too much in myotonic dystrophy type one, because it is true that in adults with myotonic dystrophy type one, many times they have the myotonia, but not many times they complain about the myotonia. This is the thing. So, it is a diagnostic clue that we have at bedside when we ask the patient, for example, to squeeze the hands and then release and we see the myotonia there. And then, obviously, this can actually give you the diagnosis at bedside, but the patients usually don't come to the clinic complaining of this myotonia, which is delaying the relaxation of the muscles. Sometimes they don't- they are not bothered by that. They don't need treatment for that. But it is a very important clue at bedside. I have to say, adults, myotonic dystrophy type one, because the congenital myotonic dystrophy type one you don't see myotonia, clinical myotonia. These babies, right, are born with severe muscle weakness and we don't see myotonia. And then myotonic dystrophy type two, many patients don't have clinical myotonia. And then, you know, the absence of myotonia, the absence of this delay in the muscle relaxation doesn't rule out a myotonic dystrophy, and especially doesn't rule out a myotonic dystrophy type two. Dr Albin: Fantastic. So probably is going to be a feature of the adult-onset type one. May or may not be present in type two. And then the congenital forum where children are presenting as infants, they're not going to tell you that, oh, I have delayed relaxation. That's not going to be part of that. Dr Gonzalez-Perez: Exactly. Dr Albin: This is one of those things that I think, unless you're in neuromuscular clinic, you might not think to ask people about. Maybe the patient isn't actually saying, oh, I have this delayed reaction. How do you get them to give you that history? Like, what are the questions that you ask? Dr Gonzalez-Perez: Sometimes I will say, do your hands get locked? You know, this could be the first question that they noticed something there, and then they can give you maybe the clue. But actually, it's the exam more than the question. I will say it's more do the exam and, you know, intentionally test for myotonia. And you test for spontaneous myotonia and percussion myotonia. So spontaneous myotonia, we tell the patient to squeeze the hands very strongly and then open the hands quickly. And then if they cannot open the hands quickly, this is a delay in muscle relaxation. We call it grip myotonia, spontaneous grip myotonia. Or sometimes close your eyes very, very, very strongly and then open the eyes quickly. And if they have this delay in the eye opening, we call it eyelid myotonia. This eye is spontaneous myotonia, you don't touch the patient and you don't use your hammer yet. And then if we don't find anything, we go to the hammer. We use our reflex hammer, and then we try to test for percussion myotonia. And sometimes we with the reflect hammer, we tap the thinner eminence of the hand, and we can see that you tap, there is a contraction, and then the thumb goes up and then takes a while to go down again. It is a delay in the relaxation of the thinner eminence muscles. Or sometimes in the posterior aspect of the forearm, if we tap the extensor digitorum communis muscle. Again, so, there is a contraction of that muscle, the fingers go up and then take a while to go down. It is also a perfusion myotonia of the extensor digitorum communis muscle. Sometimes people do it even in the tongue. I don't do that because could be very painful. But you can, you know, use a tongue depressor and put it in the tongue, and you tap the tongue depressor and sometimes there is contraction of the tongue, which can be very painful. I don't do it. So- but this is the perfusion myotonia, that can give you also a clue. Dr Albin: That's fantastic. I think this is one of the most memorable things that I saw in pediatric neurology. I remember very distinctly a kid coming in, and then us also examining the mother and having that delayed relaxation. And just one of those really great neurologic exams, those little findings to tuck away to really make a diagnosis, recognizing that not all patients with muscular dystrophy or myotonic dystrophy will have that finding. But so beautiful. And I think that's a really great explanation. And I will also direct our listeners, if you are a Continuum subscriber, she has some really wonderful videos in her article from the EMG sounds of this, which is another layer of being able to appreciate the physical exam finding. One of the things that I was really struck by, and that you've already mentioned, is that there is this really incredible spectrum of disease. That some of the myotonic dystrophy patients may barely have any skeletal involvement, and the ones with congenital myotonic dystrophy may have significant mortality even within the first year of life. Given how many subtypes of this disease there are in that varied presentation, let's just walk through sort of starting with congenital myotonic dystrophy. What are some of the clues to that diagnosis? Dr Gonzalez-Perez: Yes. So, you know, these babies with congenital myotonic dystrophy, actually when they are born, the phenotype is what we call a floppy baby. Floppy baby syndrome right? So, they are very weak. There is generalized weakness, including the swallowing muscles and the respiratory muscles. So sometimes, you know, these patients, these babies have to be intubated---to have a feeling tube, right---to survive. So, that's why the mortality can be so high during the first year of life, because obviously swallowing and breathing is affected because the muscle, those muscles, are also affected. So, one of the clues, actually- you know, sometimes these patients may have, like, a tented mouth, which could be a sign of congenital myotonic dystrophy. The differential diagnosis for a floppy baby syndrome is very broad and can be caused by central nervous system problems or peripheral nervous system problems. So, it's very broad, but maybe the tented mouth can be a clue to suspect the congenital myotonic dystrophy type one. And I will say that also, examine the mom. Because sometimes the mom is not diagnosed with myotonic dystrophy, and as simple as going into the mom who is an adult and can have already the myotonia that we talked about before and maybe, you know, try to do, like, a grip myotonia, eyelid myotonia, or use your reflex hammer and tap a few muscles, and then can give you the diagnosis of potential congenital myotonic dystrophy in the baby. And I have to say that there is no newborn screening for myotonic dystrophy type one yet. Maybe in the future it's going to be, but not at this time. So, I'm pretty sure that pediatricians probably rule out other things before unless there is distinctive mouth or unless the mom is affected. Dr Albin: Great pearls about how to take it to the bedside and try to look for that hereditary nature of this. Let's move up a little bit in sort of the childhood and adolescent onset. What are some of the clues that you're seeing for those children who come to presentation a bit later in life, but still probably more likely to be seen in pediatric clinic? Dr Gonzalez-Perez: Yes. So, the childhood and adolescent onset in myotonic dystrophy type one, it is interesting because the skeletal muscle may not be the organ that is more affected or the organ that impacts the life of the patient and the family of the patient. So, it's- the phenotype is predominantly focused on behavioral and intellectual disabilities. They may develop at some point myotonia, and they may develop also muscle weakness. But for the most part they are ambulatory. They eat by themselves, they breathe okay, and there is not too much problem with the skeletal muscle, but mostly with behavioral problems such as, for example, ADHD or intellectual disability. So, they may need some help in school and things like that. So, it is more, I will say, a central nervous system phenotype at this age. Dr Albin: Yeah, I love that that this is- to me, this was part of the complexity of this was that, while we call it myotonic dystrophy, the muscle part of this disease really may not be the main issue for the patients and their families. And that we're actually looking for something that involves the central nervous system, endocrine system, GI system. And knowing that maybe the muscle is not the main problem here, why is it so important that these patients actually get the correct diagnosis? Dr Gonzalez-Perez: Exactly. So, it is very important. And I always think about the heart. You know, the heart can be affected in the sense like the rhythm of the heart can be abnormal. And sometimes, you know, the patient doesn't have symptoms. But it's important to detect this because, you know, an abnormal rhythm in the heart can cause sudden death. So that's why it's so important. The diagnosis of this muscular dystrophy at this time, and of course in the future when we have a treatment, right, will be very important also to have the diagnosis, the earlier is the better, because probably the treatment is going to be more effective in the earlier stages than in the later stages. But I will say that right now making sure that the heart is in a good shape and the patient has a cardiologist on board if they have myotonic dystrophy. And also, you know, there are consensus-based care recommendations for myotonic dystrophy type one for the pediatric population and the adult population, and also for myotonic dystrophy type two for the adult population, that are published. And I also included in the chapter because they are very important to look for things that maybe the patient it doesn't complain about, but it's important to look for them in the case that we can prevent some future complications. Dr Albin: Absolutely. I really love that. This is a systemic disease that has multiple manifestations, and while the skeletal muscle involvement may or may not be causing problems, we really do have to get the right diagnosis, particularly as it impacts the heart and preventing fatal cardiac arrhythmias. Up to this point, we've mostly been talking about type one myotonic dystrophy. What sets type two apart? Dr Gonzalez-Perez: Yes. So, type two is, I think, even more under-recognized, probably because the phenotype is even more variable than type one and can be much milder in some sense. We are not aware of, you know, like, there are some pediatric cases that have been reported, but for the most part it's an adult muscular dystrophy, type two. So, we diagnose these muscular dystrophies usually in the forties, fifties. The thing is, like, sometimes patients actually may only have muscle pain. And not even muscle weakness. And so… and actually some of these patients may receive a diagnosis of fibromyalgia, for example, just because of the muscle pain. And it is more difficult to obtain myotonia on exam, actually. I think there is a delay in diagnosis in this population, and also the multisystem involvement, which is present but maybe even more variable than that in type one. And we have less patients, so we understand less the phenotype of these patients. But for the most part it is, I think, more under-recognized in the type one. Dr Albin: Fascinating. So again, could have pretty mild skeletal involvement and may just have cramps and muscle pain. So, you have to be really sort of mindful of keeping this on the differential for people with multiple areas of pain in the muscles. When is this suspected? Are you usually sending genetic tests to confirm? How do we get to the diagnosis? Dr Gonzalez-Perez: In the history, in the past medical history, you have probably- sometimes you have the clue. For example, a patient with muscle pain, imagine like for example a forty-eight-year-old male with muscle pain comes to the clinic, and then he tells you that he had cataract surgery at the age of twenty. And then you see a CK that is a little bit more elevated than usual. And then at that time I will go for genetic testing right away, for my myotonic dystrophy type two. Because of the muscle pain is so characteristic of myotonic dystrophy type two, and the multiorgan involvement sometimes includes a very early cataracts, the same as in type one. But the muscle pain is much more typical for type two than for type one. So, that's why I will go, in this specific scenario to type two. If I still think that my alternative dystrophic type two is a possibility, although I'm not totally convinced if it is or not, I usually go for EMG. I mean, if you don't see myotonia at the side, maybe with the EMG and the needle in the muscle, you can see this electrical myotonia that I have some videos in the chapter to see if there is this motorcycle sound of the electrical discharges from the muscle that are consistent with- they can be seen in myotonic dystrophy type two. They are not as specific, but can be seen in myotonic dystrophy type two. So if I have a patient with muscle pain and then I see this electrical myotonia on EMG, so then I will go then next to a genetic testing for myotonic dystrophy type two. Sometimes if there are some family history, it gives you also clues about the possibility of myotonic dystrophy in general, but also myotonic dystrophy type two. Myotonic dystrophy type two, usually the muscle weakness, when it is present, it's more proximal. While in myotonic dystrophy type one it's more distal. So, this also, you know, helps you to differentiate. But specifically in this myotonic dystrophy area, I think the past medical history helps you a lot and the family history helps you too. If you see an autosomal dominant inheritance of muscle or other organ problems, you suspect this type of muscular dystrophy. And I have low threshold to test for this if it is possible because, as we mentioned before, knowing what the patient has helps a lot in their care. Dr Albin: Absolutely. I love that. Spoken like a true neurologist, using the history, the physical, thinking about the family history, using EMG as an extension of our physical to really find and clinch that diagnosis, and then using genetic tests as a confirmation to get to the right answer. I love the mention of early-onset cataract. Are there any other things that pop into your mind or when you're reading the chart and you look at the medical history that, like cataracts, stand out to you as, this really clues me into myotonic dystrophy? Dr Gonzalez-Perez: Yes. So, for example, a pacemaker at early age---in their thirties, in their forties---; a family history of sudden death---for example, having a surgery for whatever reason, having a surgery like for example, surgery for appendicitis and have complications from general anesthesia, like a delay in the awakening from the general anesthesia because patients with melatonin dystrophy are very sensitive to anesthetics and also any sedative medication. So, that gives me a clue that, you know, patients with melatonin dystrophy can have this type of history. I think that those will be the main ones. Sleep apnea is very common, but we know it's also common in the general population. So, maybe sometimes, actually, we may think too much and it is, you know, normal for the general population, more frequent in the general population. But, yeah. And daytime sleepiness that can be caused by the sleep apnea. But sometimes these patients have profound daytime sleepiness. Like, they really complain about that. You know, I need to nap very often during the day because of this. Those features, I think, increase my suspicion for myotonic dystrophy. Dr Albin: Fantastic. So, in the brief time that we have left, I'd love for you to tell us a little bit about what's on the horizon for treatment for these patients. Dr Gonzalez-Perez: Yes, we have exciting preclinical and clinical trials in myotonic dystrophy type one; not yet in myotonic dystrophy type two. And these trials try to target the genetic defect at the level of the DNA or at the level of RNA. So, we have small molecules in clinical trials. We have also some antisense oligonucleotides in clinical trials. We have some small interfering RNAs in clinical trials. And then the CRISPR, which is another new technology, that is trying, you know, to repair this long function that causes myotonic dystrophy type one. And the important thing is, like, once we know what works for myotonic dystrophy type one, we may have good clues also for myotonic dystrophy type two because they share the common pathogenic mechanism. Dr Albin: Fantastic. So, it sounds like there's some genetic therapy in the pipeline. There is some small molecule treatments that are going to be available. So, really an exciting time. There's going to be a lot of changes coming forward to these patients. Again, today I've been interviewing Dr Paloma Gonzalez-Perez about her article on myotonic dystrophy, which appears in the October 2025 Continuum issue on muscle and neuromuscular junction disorders. Be sure to check out Continuum Audio episodes from this and other issues, and thank you so much to our listeners for joining again today. Dr Gonzalez-Perez: Thank you very much for the invitation. My pleasure. Dr Monteith: This is Dr Teshamae Monteith, Associate Editor of Continuum Audio. If you've enjoyed this episode, you'll love the journal, which is full of in-depth and clinically relevant information important for neurology practitioners. Use the link in the episode notes to learn more and subscribe. AAN members, you can get CME for listening to this interview by completing the evaluation at continpub.com/audioCME. Thank you for listening to Continuum Audio.

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• Muscle Channelopathies and Rhabdomyolysis with Dr. Hani Kushlaf

  Genetic variants that underlie skeletal muscle channelopathies and rhabdomyolysis can also cause persistent and progressive muscle weakness. The availability and expanded use of genetic testing allows for the identification of new genes causing periodic paralysis and rhabdomyolysis. In this episode, Teshamae Monteith, MD, FAAN speaks with Hani Kushlaf, MD, MS, FAAN, author of the article "Muscle Channelopathies and Rhabdomyolysis" in the Continuum® October 2025 Muscle and Neuromuscular Junction Disorders issue. Dr. Monteith is the associate editor of Continuum® Audio and an associate professor of clinical neurology at the University of Miami Miller School of Medicine in Miami, Florida. Dr. Kushlaf is a professor of neurology and pathology as well as the director of the Neuromuscular Division, director of Neuromuscular Research, and director of the Neuromuscular Medicine Fellowship in the Department of Neurology and Rehabilitation Medicine and the Department of Pathology and Laboratory Medicine at the University of Cincinnati College of Medicine in Cincinnati, Ohio. Additional Resources Read the article: Muscle Channelopathies and Rhabdomyolysis Subscribe to Continuum®: shop.lww.com/Continuum Earn CME (available only to AAN members): continpub.com/AudioCME Continuum® Aloud (verbatim audio-book style recordings of articles available only to Continuum® subscribers): continpub.com/Aloud More about the American Academy of Neurology: aan.com Social Media facebook.com/continuumcme @ContinuumAAN Host: @headacheMD Guest: @HaniKushlaf Full episode transcript available here Dr Jones: This is Dr Lyell Jones, Editor-in-Chief of Continuum. Thank you for listening to Continuum Audio. Be sure to visit the links in the episode notes for information about earning CME, subscribing to the journal, and exclusive access to interviews not featured on the podcast. Dr Monteith: This is Dr Teshamae Monteith. Today I'm interviewing Dr Hani Kushlaf about his article on muscle channelopathies and rhabdomyolysis, which appears in the October 2025 Continuum issue on muscle and neuromuscular junction disorders. Hi, Hani. How are you? Dr Kushlaf: Good. How are you doing? Thank you for having me. Dr Monteith: Well, thank you for coming on our podcast. So why don't you introduce yourself? Dr Kushlaf: So, I'm Hani Kushlaf. I'm a professor of Neurology and Pathology in the Department of Neurology and Rehabilitation Medicine at the University of Cincinnati in Cincinnati, Ohio. Dr Monteith: And what got you interested in muscle disorders? Dr Kushlaf: So, this is a long story. At first in residency, I was interested in epilepsy, but the moment I started doing a rotation in neuromuscular, I became enamored with neuromuscular disorders. I remember seeing the first patient in the rotation who had myofibrillar myopathy, and I found out that there is very little known about muscle disease at the time. So, I became very interested and I immediately changed direction as I started doing nerve conduction studies and EMGs and having that procedure base, I just decided that I want to pursue neuromuscular disorders. Dr Monteith: Well, that doesn't sound like a long story. It sounds like love at first sight. Dr Kushlaf: Yes, I think part of it is not very far from neuromuscular disorders and that it does have some electrophysiology involved. But muscle disease and nerve disorders, they need that detailed neurologic examination, which I love in terms of doing the localization exercise. Dr Monteith: Great. So why don't we talk about the objectives of your article? Dr Kushlaf: This article was written to review muscle channelopathies that include myotonic disorders and periodic paralysis, and also rhabdomyolysis, with emphasis on genetic causes of rhabdomyolysis more than acquired causes. Dr Monteith: So, why was this update so important? Dr Kushlaf: I think this area of muscle disorders hasn't seen a lot of progress in recent years, but there are interesting findings that we're learning that spark, hopefully, more research into the area, because we do have significant gaps that are related to understanding pathophysiology of some of these disorders. For example, in patients with periodic paralysis, it's clearly known now that these patients over time develop muscle weakness, and the muscle weakness is unrelated to how many episodes of weakness they have---basically, the episodic paralysis part of the disease. So, this is an important finding that I think we need to look more into it and understand that these disorders actually progress, even though that they may not have episodes of paralysis. In addition, there are genetic therapies that have been introduced into most of neuromuscular medicine at this time, including muscle disorders, while this specific part of muscle diseases has not had that luxury yet. And I'm hoping over time that there will be an introduction of gene therapies for these diseases. Dr Monteith: Great. So, it sounds like there's some clinical advances, then, as well as genetic advances. Now, you also spoke about rhabdomyolysis and that there's newer ways of thinking about that from perhaps when I was in residency. So why don't you update me on these newer approaches? Dr Kushlaf: The rhabdomyolysis… first, the definition of it is changing. We used to use a cut off, a CK of about a thousand, to call it rhabdomyolysis. And very recently it's clear that that level of CK is not sufficient to call it rhabdomyolysis. So, now the level went up in terms of exertion of rhabdomyolysis, up to ten thousand, has to be more than ten thousand. And in patients who haven't had exercise, the level is up to five thousand. So, it's no longer actually one thousand. And that refinement in the definition is important because there are some patients who exercise all the time and they may exercise at an athletic level and they have very high CK's. And those patients should not be labeled as having rhabdomyolysis. Basically, they are doing strenuous physiologic exercise. In addition, not only the definition of rhabdomyolysis is changing, it is our approach to which disorders to consider first and how we should work up patients with rhabdomyolysis. So, acquired rhabdomyolysis remains the most important etiology to be ruled out first. So, I always tell my fellows and residents that, think about acquired rhabdomyolysis first before you think about the genetic disorder. After you rule out the fact that it is not a toxic or metabolic or medication-induced rhabdomyolysis, then think about a genetic etiology. But when you get that consultation from the hospital that the patient has rhabdomyolysis and we want you to figure it out, always look at the medication list and make sure that there isn't anything on it that causes, actually, a rhabdomyolysis. And in many instances, you find out that it's actually a toxic or metabolic etiology for the rhabdomyolysis. And as part of this article, there's also an acronym that's now being used to identify those patients who would benefit from genetic testing. The acronym is called RHABDO. It's as is the word, RHABDO. R refers to Recurrent exertion of rhabdomyolysis. So, it's not just one episode. And the H refers to HyperCKemia, and the hyperCKemia should persist more than eight weeks after the episodes of rhabdomyolysis. And if it is exertional, then the person has not done an unaccustomed exercise. So, they have changed the way that they do exercise and now they are exercising for two hours instead of one hour or they have introduced a new way of exercise into their exercise regimen. Then that should not be considered. It's not considered necessary to test these patients for a genetic cause. Also, the muscle enzyme typically, in genetic causes of rhabdomyolysis, goes more than fifty times above the upper limit of normal, which is more than a thousand. So that has to be taken into account. And then for the D it's Drugs and medications. This has to be ruled out before you say yes, we need to find the genetic cause of rhabdomyolysis. And then the O, it's basically family history. If you find that there is other family members who are affected or they have a high CK, then of course that would point you toward doing genetic testing. Dr Monteith: Great. So, it sounds like there's some advances there in how we approach these patients. In what way is this practice changing? You mentioned, you know, really important to rule out these potentially reversible causes first. Dr Kushlaf: Yeah. So, once you identify the theology, it becomes easier to manage the patient. So, if it is a statin-induced rhabdomyolysis, you know that you want to stop the statin and you are not going to have this problem again. So, that's quite important. The statins, of course, will have to not be reintroduced in the future for that specific patient who developed statin-induced rhabdomyolysis. But for the genetic causes of rhabdomyolysis, if you go down the path of genetic rhabdomyolysis, of course we have no cures for these disorders. We may have treatments. One of the conditions that I have alluded to as one of the case presentations in the article is a patient who has riboflavin responsive multiple acid CoA dehydrogenase deficiency, and I wanted to highlight this disorder because it's a disorder not to be missed. It does have a treatment, which is riboflavin, and that comes from the name riboflavin-responsive. So that's why I put there in the article as part of the manuscript. However, some of these disorders, once you find the genetic etiology, there may be a way of preventing it in the future generation. Family planning, reproductive medicine technologies, can help in this instance and prevent this disease from occurring in the future generations. Dr Monteith: So, why don't we move on to episodic skeletal disorders? What is your general approach for these types of diseases? Dr Kushlaf: Muscle channelopathies, skeletal muscle channelopathies, are ultra-rare disorders. And part of the issue is not giving them a high index of suspicion in the diagnostic process. So, these patients typically come to us in clinics with very vague symptoms, and they may have lived with these symptoms for a very long time. So, they may have muscle pain, they may have fatigue, they may have muscle stiffness. Even though in most instances they do not tell you that they have muscle stiffness, they will tell you that when I wake up in the morning, I feel like I walk like a robot. My legs feel rigid, something like that. The word stiffness is not usually in the vocabulary of patients. When they come to see you and you examine them and you find out that the muscle strength is normal, you may not think much about the myotonic disorder. And that's where the issue is. You always have to keep these disorders in your differential diagnosis. So, you elicit for myotonia and for paramyotonia on examination, look at the muscle size, see if there is any muscle hypertrophy that happens in fluoride channelopathies, and that will typically guide you toward the diagnosis. And also ask about whether their symptoms get worse in a cold environment. So, sometimes they tell you they don't like winter because during winter everything is not doing well. They may report that they even feel like they cannot move their face because of facial stiffness in wintertime, especially in states where it snows outside and patients will be walking outside. So, these are things, typically, that give you clues about the diagnosis. But in patients who are affected minimally with the disease, sometimes you do not catch them, really, till they come to the EMG lab because of another reason. If they develop a neck pain and someone thinks that they may have a cervical radiculopathy and they want to do an EMG on them, or if they develop carpal tunnel symptoms, they send them to the EMG lab for carpal tunnel. And the moment we see them in the EMG lab, we start doing the needle examination and we find out that there is myotonic discharges in every muscle that we stick with the needle. And we're like, well, this person must have a myotonic disorder. And you ask them more about their symptoms. They may have symptoms, but they will tell you that they have ignored them for too long because it's something that they live with throughout their lives since childhood. They thought this is what is normal for them and this is what normal people might have. They may have aches and pains here and there and that is normal. So, these are clues, typically, for the diagnosis. Once you find the myotonia, your next bet to identify the exact genetic abnormalities to do genetic testing. And nowadays I think the field has benefited from the availability of free genetic testing so we can find out which channel is affected and then move on toward freezing that disorder. Dr Monteith: So, you spoke about nondystrophic myotonia. What are some bedside tips to try and really get at the diagnosis? Dr Kushlaf: So as I said, first is, look at the muscle build of the patient. So, these disorders, chloride channelopathies---so, the autosomal dominant and autosomal recessive chloride channelopathies---can cause muscle hypertrophy. So, these patients can have an athletic appearance even though when you ask them, do you exercise? I don't exercise at all. Do you lift weights? I don't lift weights at all. And they look like bodybuilders, so that's something to think about. Also eliciting the myotonia and typically we elicit the myotonia by using, of course, the reflex hammer. You can either tap on the phenol eminence and notice the myotonia in the thumb as it moves inward and stays in that position for some time. Depending on the severity of the myotonia, you can tap on the extensor digitorum in the forearm and notice the middle finger as it gets up and gets stuck for some time before it goes down. You can also ask patients to squeeze your fingers and then release quickly. Squeeze forcefully, of course, and find out how long does it take them to release their fingers, and that way you can identify the myotonia. Also, you may need to repeat the elicitation of myotonia several times because it can be not myotonia but paramyotonia, which is the opposite of myotonia. It's basically worsening of the myotonia as you keep doing the eliciting activity. So, the more they squeeze your fingers, the more difficult it is for them to improve. While the warm up phenomenon, which is the opposite of paradoxical myotonia, is, for them, as they repeat squeezing, they are able to do it better and better. They would be able to release more quickly with each attempt. In some patients, you can also ask them to close their eyes if they have facial myotonia, to close their eyes forcefully and see how quickly does it take for them to open their eyes. You may see that they do not open their eyes quickly. Or if you repeat in patients with paramyotonia, if you ask them to close and open, close and open, close and open, there will come a point where they really cannot open their eyes anymore, and that tells you there is paramyotonia. Of course, if you find paramyotonia, then you know that this is a sodium channel abnormality, that the genetic testing would just confirm that. Dr Monteith: And what about for periodic paralysis? Is there anything new in the field? Dr Kushlaf: Periodic paralysis… if I can say one thing about periodic paralysis, it's to talk about Andersen Tawil syndrome. It's an ultra-rare disorder also, but the episodes of paralysis that happens in patients with Andersen Tawil syndrome, they occur either with hypokalemia, so it can be hypokalemic---like, exactly hypokalemic periodic paralysis---or with hyperkalemia. So, it's hyperkalemic periodic paralysis. It doesn't really matter whether it's hyperkalemic or hypokalemic. These patients they typically have dysmorphic features. And the most common dysmorphic feature, and I chose a picture for the article, is a patient who has a small mandible. That is the most common dysmorphic feature. There are other dysmorphic features which include short stature, hypertelorism---which is the distance between eyes, the eyes become widened. Also, scoliosis and low-set ears. So, the ears are lower than the level of the eyes. So, these are dysmorphic features one can look for, but they do not exist in every patient with Andersen Tawil syndrome. The problem with Andersen Tawil syndrome is that these patients, as opposed to hyperkalemic and hypokalemic periodic paralysis, they have cardiac involvement. And the cardiac involvement can be deadly. So, it's very important that these patients are identified quickly. And anyone who has episodic weakness should have an EKG and should have halter monitoring to recognize if there are any arrhythmias or EKG abnormalities. So, one can identify anything that needs to be corrected from the cardiac standpoint. I think that is the most important point about periodic paralysis. Overall, these disorders… I mean, they are disabling and they can have huge effect on patient's life in terms of productivity and employment. And the diagnosis can be very difficult, especially that we do not know all the genes that are associated with periodic paralysis. Right now, the genetic testing that's available to us includes five genes that are associated with periodic paralysis. But I think we need to know more. There's a proportion of patients who do not have an identifiable abnormality at this time. So, I think as time goes on, we'll recognize more causes for periodic paralysis. Dr Monteith: I'm just reading your really great article, and it sounds like there's a lot of variability in presentation from I'm not feeling that well or I'm not feeling my best for mild disease, and then very severe disease where the whole body can be weak without alteration in consciousness. Dr Kushlaf: That's correct. So, my patients tell me that you never know when you're going to develop episodes of weakness. And sometimes they can recognize the precipitant, sometimes they cannot. Stress, sometimes, is a precipitant. At times, they really cannot tell what happened. And the weakness can be affecting one limb or more than one limb. It can be isolated to an arm or isolated to one leg. And that is the issue with the diagnosis, is that for those who do not suspect periodic paralysis, they are labeled as a functional neurologic disorder and they do not get the care that they need. I'm hoping that this article will shed a light on how to think about these disorders and how to diagnose them because treating them can have a significant impact on patient's life. Dr Monteith: How useful are these laboratory tests? Dr Kushlaf: So, in any patients where I suspect periodic paralysis, I would always do thyroid function testing to rule out hyperthyroidism because it can cause episodes of paralysis similar to hyperkalemic and hypokalemic paralysis. And I also do EKG and halter monitoring to make sure that I'm not missing the cardiac manifestations of Andersen Tawil syndrome. On top of that, then I would do genetic testing. And the genetic testing, as I said, at this time includes five genes. So, we will recognize any genetic abnormality that comes on that genetic testing. And if it is negative and I still have a high suspicion for the disease, I will do a long exercise test. The long exercise testing is, we record from a muscle in the hand---it's called the productive digit minimi---and stimulate the unknown nerve. We record, typically, baseline responses and then exercise the muscle for five minutes and keep recording after five minutes of exercise for up to forty minutes after. We're looking for a change in the amplitude of the motor response that typically happens over time. Dr Monteith: Great. Well, thank you so much for being on our podcast. Dr Kushlaf: I appreciate it. Thank you very much. Dr Monteith: Again, today I've been interviewing Dr Hani Kushlaf, whose article on episodic skeletal muscle disorders, muscle channelopathies, and rhabdomyolysis appears in the most recent issue of Continuum on muscle disease. Be sure to check out Continuum Audio episodes from this and other issues, and thank you to our listeners for joining today. Dr Monteith: This is Dr Teshamae Monteith, Associate Editor of Continuum Audio. If you've enjoyed this episode, you'll love the journal, which is full of in-depth and clinically relevant information important for neurology practitioners. Use the link in the episode notes to learn more and subscribe. AAN members, you can get CME for listening to this interview by completing the evaluation at continpub.com/audioCME. Thank you for listening to Continuum Audio.

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• Idiopathic Inflammatory Myopathies With Dr. Anthony Amato

  Inflammatory myopathies are a large group of disorders associated with an inflammatory response targeting skeletal muscle. Treatment hinges on the use of evolving immunotherapies and diagnostic tools to quickly identify inflammatory myopathy, initiate appropriate therapy, and exclude underlying malignancy or infection of other organs. In this episode, Katie Grouse, MD, FAAN speaks with Anthony A. Amato, MD, an author of the article "Idiopathic Inflammatory Myopathies" in the Continuum® October 2025 Muscle and Neuromuscular Junction Disorders issue. Dr. Grouse is a Continuum® Audio interviewer and a clinical assistant professor at the University of California San Francisco in San Francisco, California. Dr. Amato is the Brigham and Women's Hospital Distinguished Chair in Neurology and the director of neuromuscular research at Mass General Brigham, and is a professor of neurology at Harvard Medical School in Boston, Massachusetts. Additional Resources Read the article: Idiopathic Inflammatory Myopathies Subscribe to Continuum®: shop.lww.com/Continuum Earn CME (available only to AAN members): continpub.com/AudioCME Continuum® Aloud (verbatim audio-book style recordings of articles available only to Continuum® subscribers): continpub.com/Aloud More about the American Academy of Neurology: aan.com Social Media facebook.com/continuumcme @ContinuumAAN Full episode transcript available here Dr Jones: This is Dr Lyell Jones, Editor-in-Chief of Continuum. Thank you for listening to Continuum Audio. Be sure to visit the links in the episode notes for information about earning CME, subscribing to the journal, and exclusive access to interviews not featured on the podcast. Dr Grouse: This is Dr Katie Grouse. Today I'm interviewing Dr Anthony Amato about his article on idiopathic inflammatory myopathies, which he wrote with Dr Kian Salajegheh. This article appears in the October 2025 Continuum issue on muscle and neuromuscular junction disorders. Welcome to the podcast, and please introduce yourself to our audience. Dr Amato: Thank you. And I am Tony Amato. I'm in Boston at Mass General Brigham. Dr Grouse: It is a distinct pleasure to have you here with us today, and I'm really excited to talk with you about your article. I thought it was a fantastic overview of the subject. And I'd like to start by asking what you hope will be the key takeaway for those who are reading this article. Dr Amato: I think it's kind of basic: how to make a diagnosis, describe about the inflammatory myopathy as approach to, again, diagnosis, and then a little bit on pathogenesis, which… and kind of leading to the treatments, and hopefully we'll have more treatments based on the distinct pathogenesis in the future. Dr Grouse: Can you give a brief overview of the categories of inflammatory myopathies you reviewed in your article? Dr Amato: So, I mean, the major inflammatory myopathies, radiopathic inflammatory myopathies, are dermatomyositis, antisynthetase syndrome, immune-mediated necrotizing myopathy, inclusion body myositis, and polymyositis. Now, that's been a big change, as you know. I mean it used to be, you know, we all started off it was dermato or poly. But I've kind of made a name for myself- a bad name for myself in the early 2000s saying, I'm not sure there's much of a thing called polymyositis. I think it's a hodgepodge and it's not distinct. And that's come to be, now most of those cases are- now we find out having antisynthetase syndrome or necrotizing myositis or IBM. Dr Grouse: Could you walk us through your diagnostic approach with a patient in your clinic presenting with symptoms that are suspicious for inflammatory myopathy? Dr Amato: So, you want to really make sure that they have inflammatory myopathy as opposed to some other kind of myopathy, a muscular dystrophy, for example. Taking family history first is going to be important, clueing in are they really weak or what they're complaining of is fatigue or muscle pain? Are they feel weak but what they really are complaining of is stiffness and rigidity from parkinsonism, or they have a sensory ataxia so they can't modulate? I want to know about other organ system involvement. Do they have a rash? Do they have joint swelling and pain that you might see with arthritis? Do they have shortness of breath that you might see with interstitial lung disease or ventilatory muscle weakness? Or do they have a cardiomyopathy? What kind of weakness do they have? Is it proximal weakness in the arms or legs? Getting out of a chair, climbing stairs. Do they have problems lifting their arms over their head---so, proximal weakness---or do they have more problems with grip, finger flexion, holding a pen, tripping? Do they have swallowing problems? Do they have ocular problems? So that's the big history on the exam. Again, I'm looking for pattern of involvement. So, on my exam, is there atrophy or weakness in muscles---you know, fasciculations---which would take it out of the motor? Is it mainly proximal? Is it distal? Again, is there ocular bulbar involvement? Is it symmetric, particularly in, like, the IBM? Most of the other inflammatory myopathies are going to be mainly and proximal and mainly symmetric. IBM is different, and that the- at least in the hands it's more distal, and it's finger flexors. So, you're looking at flexing the tips of the fingers, you're looking at the forearms, best looked at in a semipronated position to see if it's atrophied. And that leads you to an IBM if you see that. So that's the main things on exam. Dr Grouse: That's a really helpful overview. I was wondering, in earlier training days, the convention was you- once you've suspected myopathy, you get your CK, you get your EMG, then that may give you the information you need for your diagnosis. It seems that things have been turned a little on their head. We're often skipping those things to go straight to the antibody testing. When should we be going for the myositis-specific antibodies before considering other things like EMG or muscle biopsy? Dr Amato: I would always get a CK first. You know, in somebody who's weak. You know, the EMG, I don't need an EMG if the CK is two or three thousand. I mean, EMG is- localize it to, is it muscle, nerve, neuromuscular junction. If it's very elevated CK, it really doesn't help me there.  Sometimes if I have myotonic discharges or something that might make me think of a myotonic dystrophy or something else like that. But you can see that with the inflammatory myopathy. So, if I'm pretty sure of a myositis, I don't always do an EMG, or- unless I really need it to help guide what muscle biopsies I do. if I'm suspicious then on my exam and I see the CK---or they come to me already with the CK, which often happens, and it's very elevated---that's when I'll do the myositis-specific antibody panels if I'm really thinking that. And the important thing to know from that is, you have antibodies for dermatomyositis and antisynthetase that are on the panel that are available, and even signal recognition particle, which is a necrotizing myositis. But what's not on the panel is HMGCR antibodies, which is important because that's 70% of the necrotizing myocidites are HMGCR, and then the IBM antibody and T5-C1A is not on that. So, you need to order those separately. If somebody doesn't know, they order a myositis-specific antibody and think that it's all-inclusive, but it doesn't have IBM or the HMGCR antibody. And the other test that I sometimes will do is a skeletal-muscle MRI to help in the evaluation. Sometimes, not all the time, but I'm not sure it's a dystrophy, is it a myositis when I see a lot of STIR signal, which is edema. And you can still see STIR signal in a dystrophy and toxic. But sometimes I'll do it depending on whether I need a biopsy or not. Dr Grouse: What is the benefit of an open biopsy versus a needle biopsy, and when should we be considering using one over the other? Dr Amato: So, it really is not our decision. It's the pass lab. So, it's the technicians and the pathologists who read the biopsies need to be able to process a needle biopsy, which might be much smaller. Needle biopsies show to be fairly accurate in a lot of the hereditary disorders where you might just look for central nuclear core, and they might be- so, mainly in kids, but in the inflammatory myopathies, it's really patchy. So, if I'm thinking of an inflammatory, I like an open biopsy. I think it's hit and miss. And so, I like open biopsies for the adults that I'm thinking of inflammatory. Dr Grouse: Do you have any other tips or tricks in the diagnosis of inflammatory myopathies that you could share with our listeners? Dr Amato: I would say first, in terms of what muscle to biopsy, you're not doing them yourself, but you're referring to a surgeon. You have to tell them what to do with the biopsy. And you want to pick a muscle that's about an MRC grade 4 because if it's a normal muscle, the muscle strength, the biopsy, is likely to be normal. If it's less than a 4, you might just have end-stage muscle. And saying you can't tell end-stage muscle from a bad myositis, from a dystrophy, from a severe end-stage neurogenic. If I don't have a muscle that I would typically biopsy that's an MRC grade 4---for example, somebody with an early weakness and they're only weak, say, in their in their hip girdle. So hip flexors, abductors, extensors, and we're usually not biopsying the iliopsoas or the gluteal muscles. Then what do you pick? That's when I like to do an EMG on one side of the body and look at proximal and distal muscles and select one that's irritable, you know, some fibs and positive sharp waves that I might biopsy. And then maybe consider doing a skeletal muscle MRI to go from muscle that's abnormal, that has a lot of edema in it, to increase the yield. Dr Grouse: That's really helpful. And then, I think, jumping from that, what are pitfalls that you've seen neurologists fall into in this diagnosis or other challenging aspects of the diagnosis that you could review with us? Dr Amato: Some of the things that we see are hard to pick up. It might be hard to pick up a rim vacuole. They're very rare, too. And so, you might miss it, particularly if you don't see a lot. Sometimes, like looking at the dermato and that's the, on the exam question, perifascicular atrophy, but that's a late stage, usually. And so, if you're really attuned and you're a good clinician, you make that diagnosis really quick. You do a biopsy, you might not see that paraphysical atrophy. So, they don't know that in a necrotizing myopathy, the pathologists often think of what they see in a toxic myopathy or a metabolic where there's a lot of necrotic fibers. But in most of the autoimmune necrotizing, it's not. It's actually what you see is more regenerating fibers, a few necrotic fibers. It's because it's usually been smoldering along for a while, and so you have many more regenerating fibers than ones that are actively, and that can fool a lot of people. So, that's a pitfall from that end of things. Some of these myositis specific antibodies aren't specific and at a low titer, particularly if you have more than one antibody being positive, that would be a red flag that it could be false. That's another pitfall. I think a lot of people don't, when they're examining people, really look at the finger flexors and stuff. And again, if I have somebody over the age of fifty, the most common muscle disease is IBM. Number two is IBM, number three is IBM. If you don't- and you have to think about that, and you need to examine the distal finger flexors because it doesn't get better with immunotherapy. You don't want to put people at the risk of immunotherapy when they're not going to get better. I talked a lot about the biopsies, and biopsy, biopsy, biopsy. But you know, sometimes you can make the diagnosis without a biopsy. So, if somebody's like a classic dermato rash and they have a dermato antibody, do they need a biopsy? No. If they have, you know, CKs of ten thousand proximal weakness, they're on a statin and they have HMGCR antibody, do they need us have a biopsy to confirm? Probably not. Dr Grouse: Those are some really great pearls that you've shared with us, and I think will be very helpful to many of our listeners. Now, you mentioned earlier about the diminishing category of polymyositis as other types of myosidites have been discovered and better described. Do you think that is the most controversial aspect of this field currently, or are there other controversial areas or areas of ongoing debate that exist? Dr Amato: It was very controversial twenty years ago, or maybe ten years ago. So, the rheumatology guidelines, they're the ones that are often saying, oh yeah, we were right. Polymyositis, it's just hodgepodge, and it's ever-shrinking. So that's not so controversial anymore. I mean, the controversies that we have, what's the pathogenesis of dermato? It's still a little debated, some- the old theory was that it was a complement-mediated microangiopathy and the damage was caused by ischemia. That's probably not the case. It looks more and more like it's a type 1 interferonopathy, and that's toxic to the vessels in the muscle. There's still a little bit of a debate about that or, you know, you have complement might be on it, but how much that might be damaging, or it's just a secondary phenomenon. I think in the antisynthetase things, I think there's some interesting things also with that these antibodies. We used to think of that they're just diagnostic biomarkers. But there's some recent studies suggesting that these antibodies which are directed against intracellular targets, which is interesting and applies to other autoimmune diseases and that are in the brain too. And we would think that, oh, if it's a intracellular target, it it's secondary. But there's suggestion now that- again, it did demonstrate that the antibodies actually get into muscle fibers. And they bind to these targets. So maybe they're just not epiphenomenon, but they might be binding to a target and causing pathology. And that's what there's some preliminary studies that are impressed, I will say, that have antibodies, anti-HMGCR, that actually go into the cell and they inhibit the enzyme. And that might be causing the pathology. And so that's interesting. And then IBM is a big field. Is this a primary autoimmune disease that has these other kinds of degenerative features like REM vacuoles, or is it a primary degenerative that has secondary inflammation, or is it a combination of both? So, that's probably the biggest controversy these days. It is probably with IBM. What the heck is causing it? Dr Grouse: Sounds like a lot that we still have to understand about these diseases. This does lead me to wonder, though, have some of these new discoveries and ideas led to or will lead to any new breakthroughs, either in diagnostics or in therapeutics? Dr Amato: So, certainly in therapeutics. So, the discovery of dermato being an interferonopathy, probably a beta-interferonopathy, has led to development of monoclonal antibodies that target interferon, and there's trials underway. And in phase 2 studies, I can tell you from talking to colleagues that participate just melted away the rash of dermato. So, I think that's going to be a very, very good drug in the future for dermato. There's others, like JAK. JAK inhibitors work on that interferon pathway too. So, I think we'll be going towards, like, less broad-spectrum steroids, IVIG, to going, let's go to the target. Certainly, in dermato, I mean, IBM, we don't know. There is an inflammatory cell that we see in IBM that has a receptor, KCRRN receptor, and there's a monoclonal antibody that targets that in IBM, and that's a phase 3 trial right now. Hopefully that study should be ending in December, and so early next year we'll have results about that. The fact that these antibodies might be pathogenic of themselves is other ways to get rid of the antibodies. So, getting rid of plasma cells and B cells, and FCRN receptors which have been approved or antagonists that are approved for myasthenia. Now CIDP might work in some of the inflammatory myopathies where we think the antibodies might be pathogenic. So, FCRN receptor antagonist and they're in trial now as well. And there's CAR-T therapies to knock out the antibody-producing lymphocytes and plasma cell. So, I think we're going to move into the field of individualized therapies as we find the distinct pathogenesis of these disorders. Dr Grouse: That's really exciting to hear and I can't wait to see what's coming down the pipeline as more of these discoveries are made and the clinical trials advance. It has been such a pleasure. I've learned so much. So much is packed into the article. So again, I can't stress enough, please take the time to check out this article. I think you'll learn a lot, and it'll really help you fine-tune your diagnostic pathway in relation to myopathies. Dr Amato: Oh, my pleasure. Thank you. Anybody has questions, please feel free to send me an email. Dr Grouse: We may just take you up on that. Again, today I've been interviewing Dr Anthony Amato about his article on idiopathic inflammatory myopathies, which he wrote with Dr Kian Salajegheh. This article appears in the October 2025 Continuum issue on muscle and neuromuscular junction disorders. Be sure to check out Continuum Audio episodes from this and other issues, and thank you to our listeners for joining today. Dr Monteith: This is Dr Teshamae Monteith, Associate Editor of Continuum Audio. If you've enjoyed this episode, you'll love the journal, which is full of in-depth and clinically relevant information important for neurology practitioners. Use the link in the episode notes to learn more and subscribe. AAN members, you can get CME for listening to this interview by completing the evaluation at continpub.com/audioCME. Thank you for listening to Continuum Audio.

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• Inclusion Body Myositis With Dr. Elie Naddaf

  Inclusion body myositis (IBM), the most common myopathy in adults, is a disease of aging characterized by slowly progressive weakness. Diagnosis of IBM requires the integration of historical, clinical, and laboratory data, while management consists of a multidisciplinary approach to address comorbidities and potential complications. In this episode, Aaron Berkowitz, MD, PhD, FAAN speaks with Elie Naddaf, MD, author of the article "Inclusion Body Myositis" in the Continuum® October 2025 Muscle and Neuromuscular Junction Disorders issue. Dr. Berkowitz is a Continuum® Audio interviewer and a professor of neurology at the University of California San Francisco in the Department of Neurology in San Francisco, California. Dr. Naddaf is an associate professor of neurology at the Mayo Clinic College of Medicine in Rochester, Minnesota. Additional Resources Read the article: Inclusion Body Myositis Subscribe to Continuum®: shop.lww.com/Continuum Earn CME (available only to AAN members): continpub.com/AudioCME Continuum® Aloud (verbatim audio-book style recordings of articles available only to Continuum® subscribers): continpub.com/Aloud More about the American Academy of Neurology: aan.com Social Media facebook.com/continuumcme @ContinuumAAN Host: @AaronLBerkowitz Guest: @ElieNaddaf3 Full episode transcript available here Dr Jones: This is Dr Lyell Jones, Editor-in-Chief of Continuum. Thank you for listening to Continuum Audio. Be sure to visit the links in the episode notes for information about earning CME, subscribing to the journal, and exclusive access to interviews not featured on the podcast. Dr Berkowitz: This is Dr Aaron Berkowitz, and today I'm interviewing Dr Elie Naddaf about his article on inclusion body myositis, which appears in the October 2025 Continuum issue on muscle and neuromuscular junction disorders. Welcome to the podcast, Dr Naddaf, and would you please introduce yourself to our audience? Dr Naddaf: Thank you for having me. I am Elie Naddaf, a neuromuscular neurologist at Mayo Clinic in Rochester, Minnesota, and one of my main focus research-wise is about inclusion body myositis. Dr Berkowitz: Fantastic. Well, this is a great article on inclusion body myositis, or IBM, as we may refer to it today. It has a lot of clinically practical tips for examining patients at the bedside and a lot of important updates for us on how to diagnose this condition. So, I encourage our listeners to check out the article, and I look forward to discussing some of the key aspects here and learning from your expertise. First, tell us about the classic presentation of IBM, when the disease is pretty easy to recognize at the bedside based on the history and exam. Dr Naddaf: Luckily, IBM is one of those diseases that has a very particular pattern of weakness that makes it easier to diagnose. However, in real life it can be very challenging for several reasons, which we will cover in this podcast and in the article. However, a typical presentation of IBM is that of an older patient, more likely to be a male---twice more likely to be a male---,presenting with slowly progressive weakness over a couple years or so. And the weakness predominantly affects the deep finger flexors in the hand. So, they most commonly present with hand grip weakness, or the quadriceps muscle presenting with some lower limb weakness. However, some patients can present with one or the other, not necessarily with both at the same time. It is usually a painless disease,, and because of the lingering course, patients tend to present within two to three years from their symptom onset. So, with that, on examination, if the patient is presenting with the hand weakness, they would demonstrate weakness in the deep finger flexors, which are the muscles that we use to flex the distal intralaryngeal joints. This weakness is often asymmetric and can be in only one hand; and also, even within the same hand, you can have a variable severity from one finger to the other. And that's one reason, although it sounds a classic phenotype, if you can imagine a patient just presenting with hand weakness, a lot of other things come to mind, whether it's a compressive neuropathy or whether it's a radiculopathy or motor neuron disease. Similarly, in the leg, the quadriceps is a big and strong muscle. So, it's often that patients' symptoms originally or in the beginning get dismissed because the physician did not demonstrate any weakness on manual motor testing. Because it's a strong muscle, it needs to lose a certain amount of strength to be able to demonstrate that weakness by just pushing against the patient trying to extend their knee from about a 90 degree or so. That's why another way in those cases would be to examine them more functionally whether they're kneeling or squatting. It is usually a pure motor disease, although patients can commonly have a peripheral neuropathy. But typically, on exam, you mainly see muscle weakness. Dr Berkowitz: Perfect. So, if we see a patient who's an older man with progressive painless weakness of the finger flexors, quadriceps, this is sort of the classic presentation where we would consider IBM. But you mentioned in your article that some patients can present somewhat atypically when we might not immediately think of this diagnosis. What are some of the atypical presentations we should be aware of that should lead us to think about IBM as a possible etiology for the patient's pattern of weakness? Dr Naddaf: So, IBM indeed can present in any muscle group. That's why about 14% of patients may have the weakness onset beyond the finger flexors or knee extensions. And there are very particular phenotypes that stand out. Especially the most common in that scenario would be patients presenting with pure difficulty swallowing, isolated dysphasia that can sometimes precede the limb weakness by several years, and that's especially common in females. Other phenotypes including just a proximal weakness, like a limb-girdle weakness; an axial weakness, for example, head drop or camptocormia or a foot drop. And because it's an asymmetric disease, you can see the challenge there---if someone just presenting with a foot drop on one side, that it could be challenging to just think of IBM. So, those are the main phenotype. One particular phenotype that is super interesting is, patients present with severe facial weakness as if they have severe bilateral Bell's palsy. And that's the, usually, the most common first misdiagnosis. And all these patients reported so far in the literature are only females. This has not been reported in any male patients. So yes, the finger flexor quadriceps weakness is the most common typical presentation. However, IBM can present, technically, in any other muscle in the body. Dr Berkowitz: Great. Well that's very helpful information that especially comes from experts like you who see a lot of these patients and are able to make these diagnoses of these rare phenotypes. Whereas many of us general neurologists, like myself, might think of IBM only with finger flexor weakness and quadriceps weakness, perhaps with some foot drop dysphagia associated. Sounds like this is a diagnosis to consider in atypical presentations or atypical presentations of myopathy that aren't fitting other phenotypes or aren't yielding diagnostic results for other phenotypes. And you have in your article a very helpful table that goes through some of the common sites of weakness in IBM and the differential diagnosis for myopathies and other conditions to consider in patients who have the classic and less typical presenting features. So, let's say that we see a patient with clinical features suggestive of IBM. How do we go about confirming the diagnosis? What are the main diagnostic tests we would use to try to make a firm diagnosis here? Dr Naddaf: So, the gold standard so far for diagnosis for inclusion body myositis, as it is an acquired disease, has been a muscle biopsy. So, muscle biopsy is the probably most important tool in the diagnostic approach to IBM. Even in patients with a classical phenotype, that all like in any other test, it depends on your pretest probability and how sure you are the patient has IBM. But even with the classic phenotype, it is characteristic of IBM, but not pathognomic of IBM. Because if we see a high number of patients with similar phenotypes, we will run into a lot of other disorder that present similarly. And some patients---especially for instance, with myotonic dystrophies, specially type two---may be very difficult to distinguish from IBM, especially those that present in adulthood that they don't have the classic picture of a myotonic dystrophy patient you would think of. And some of them may not even have percussion myotonia. Because of that, the biopsy is very important to confirm your diagnosis in that regard. And on the biopsy, you want to see evidence of inflammation, basically, and the mesial inflammation, without going into a lot of details, to set it apart from those genetic ones. But in IBM it's not a pure inflammatory disease. There are other features on the biopsy that are very particular to IBM, two main other things we need to find. One is that of the accumulation of autophagic vacuole and protein aggregates and that of mitochondrial dysfunction. So, the other test for patients, presenting with weakness---again that depends on your clinical suspicion---would be first to establish that the underlying process is a myopathy; and hence, the EMG. And also, that's particularly important in patient with symptoms in one limb to differentiate it from compressive neuropathies or from a motor neuron disorder or other. So, the EMG tells you it's a myopathy with fibrillation potential, helps you also choose a muscle for biopsy. So as far as blood tests, the main blood test is that of the cytosolic nucleosidase 1A, or people call them IBM antibody. That's present in about half of the patients with IBM, 50%. Specificity originally reported to be high in the 90s, but in real-life practice with commercial lab it's probably lower in the 70s. There is a growing interest in the use of muscle imaging as well and IBM is one of those diseases similar to the clinical phenotype that has some distinctive pattern on imaging on MRI. But again, like the clinical phenotype, it is helpful, it is characteristic. It's not diagnostic on its own. Other blood tests in IBM include creatine kinase level. As long as you're not seeing creatine kinase in the 10,000 or 20,000, that would be very unusual in IBM and other routine blood tests that are discussed in the article. Dr Berkowitz: Right. That's a very helpful overview of the testing we would consider when we're trying to make this diagnosis that can include, as you mentioned, EMG, muscle MRI, and this five-prime cytosolic nucleosidase 1A antibody. As you said, many of these have variable sensitivity and specificity. We can diagnose a myopathy generally, or muscle inflammation more specifically, using EMG and muscle MRI respectively. It's interesting to hear that that antibody, I know there was a lot of excitement about that originally. Sounds like less sensitive and less specific than one would have hoped. In your article, you discussed sort of how to use some of these tools to try to meet the diagnostic criteria that were updated in 2024 for diagnosing IBM. And correct me if I'm wrong, this is my first time reading about these. I want to make sure I understand that essentially, you always require a biopsy for definitive diagnosis of this disease. Is that right? Dr Naddaf: That's correct. That's because of the issues that you raised with the antibody and because, even with people with the classic phenotype, you still could have other diseases that can mimic IBM that are associated with different complications, comorbidity profiles. For instance, myotonic dystrophy requires very close monitoring of cardiac rhythm, which is usually not affected in IBM. Hence, there is still the need for a biopsy, as we don't have a better test so far. The antibody has its own challenging, but I still find it very helpful in certain situations, and that's also reflected in the new criteria. It's definitely not a standalone diagnostic test. I don't think you can just draw the antibody, if it's positive, tell the patient they have IBM. To me, it's helpful in two ways, at least in my practice. One way is, it makes me think of IBM in situations where I was not considering IBM. In the end IBM is the most common disease in adulthood, so it's not a bad habit to just check the antibodies in any unusual case. Or where inconclusive case, it's just me saying, huh, that could be IBM that I missed. Then I go and try to confirm it. The other scenario that it helps me, there are a lot of cases that remain inconclusive. For instance, you just saw inflammation on biopsy, you have some pattern on MRI. You just need another piece of information to further make the case for the diagnosis. And that's where I find the antibodies helpful. And that's reflected in the new criteria. Dr Berkowitz: I see. So, if you- Yeah, so just to pick up on the antibody here, since I'm sure people be interested in when or whether to send this. You sort of use this in atypical cases where you know it's a myopathy or not. You haven't yet made a diagnosis. And you think, well, if I send this and it's positive, that's not 100% specific, but going to tip me a little more towards thinking this could be an atypical IBM case. But if it's negative, it doesn't sort of tell you either way, since you said it's only about 50% sensitive, right? Am I understanding correctly how you use the antibody? Dr Naddaf: Yes, this is correct. So basically, you don't have to check it if you think it is IBM; that also depends on your style of practice. To me, I think at some stage, with all the progress we're seeing in research in systems biology, so far there's no indication that the antibody predicts severity, and I don't think it does. But there could be at some time down the road that there are different underlying pathways or disease mechanisms that are associated with people that have the antibodies. So, it's more like for the future, it's good to know if the patient is positive or not. Dr Berkowitz: Okay. So, if biopsy is really necessary to make this diagnosis, if you see a classic presentation with an older man, as we've said before, with slowly progressive painless finger flexor weakness and quadriceps weakness, do we even need EMG or muscle MRI or this antibody or do you just go straight to biopsy in those cases when the clinical phenotype looks relatively certain? Do you still think one or more of those tests are helpful in the classic presentation? Or are those EMG, muscle MRI, and the antibody ones used more when you think, this looks sort of like IBM but it's either it's maybe early and it's not sort of fully kind of developed into the classic phenotype or it's very asymmetric, which you can see in IBM, or whether it's sort of has more atypical features or only one of the classic features? How do you use EMG muscle MRI in the antibodies when you know you're going to need biopsy ultimately, if this is the diagnosis you have in mind? Dr Naddaf: That's a great question. And all of the above would be correct depending on the setting you practice in. If I were practicing in a community where I have the privilege to do things step by step, I might approach it a little bit differently. Being at the referral center with many patients coming with a one-stop shop and they need to do everything possible rather than returning, that's also another different practice scenario. But in general, you want the EMG if you're not sure it's a myopathy, especially that these patients are asymmetric and sometimes the findings are in a single limb. So, you would want the EMG when you're not sure it's a myopathy, or also you need a little bit more information on what muscle to biopsy, you could use the EMG. If those questions have already been answered, you don't have to do the EMG. Now regarding the biopsy, if it is the classic phenotype and you think it's going to be a bingo with the biopsy, you might not need to do any antibody or MRI or any further testing. Now with one caveat that the biopsy might not give you the full picture or all the features, then you could go back and do the rest. And that's actually all integrated in the new criteria. So, in the new 2024 revised European Neuromuscular Center diagnostic criteria for IBM, the main differences are the following: now you can use additional test measures to support the diagnosis in addition to the biopsy. So that will probably reduce the need to have a repeated muscle biopsy. Two, you could have an atypical form and still have the diagnosis. You don't have to wait until your finger flexor or knee extensors are involved. And that's very important also, because criteria generally are made for clinical trials where you want to know for sure who you are treating. But at the same time, you don't want to wait till advanced stages of the disease where treatments might not work. Diagnostic criteria are not made to be used in clinical practice, but at the same time they offer a good framework, a good suggestion for people to use in their clinical practice. And just always remember to tailor it to your particular patients that you're seeing. In those criteria, basically, we go by scenario depending on your level of suspicion. There is no possible probable. You either make the diagnosis or you don't make it. And as you said, if you have a classic phenotype patient with deep finger flexor weakness in the upper limb and knee extends her weakness in the lower limb, your pretest probability is very high, and the chances that you're wrong are low. They're not zero, they're low. That's why I was just showing in the mesial inflammation on the biopsy, which would rule out your genetic mimicor. You're pretty confident of the diagnosis. And the other scenarios, then let's say you have only one limb, then you need a little bit more support. And you have an atypical form where the differential is very wide. You want to provide more supportive criteria, and the supportive criteria could be other features in the biopsy, whether it's the CCO negative fibers or derma vacuoles, or you could use MRI and antibodies if they're available to you. In many countries, these are still not available, but if they're available, that's good. You could use them as supportive criteria. That was the logic behind those revised criteria that are discussed by scenario in detail in the article. Dr Berkowitz: Fantastic. That's very helpful. Yeah, as you mentioned this- the criteria reviewed in the article, you have a very helpful figure there with all the branch points of how to get to the diagnosis, but very helpful to hear how you think about combining these tests in practice in different scenarios to get to the final diagnosis. So, IBM is considered an inflammatory myopathy, right? Like dermatomyositis and antisynthetase syndrome and immune-mediated necrotizing myopathy. And yet it gets its own separate article each time we do a Continuum issue on muscle disorders, right? Because it's unique in that it doesn't respond to any immune- immunomodulatory or immunosuppressive therapy like these other inflammatory myopathies. So why do you think, or why is it thought by experts in the field like yourself, that this is an inflammatory myopathy but it, at least from a treatment perspective, appears to behave so differently from the other inflammatory myopathies and doesn't respond to immunomodulatory therapy---or at least we haven't found the right key in the right block of immunomodulatory therapy to treat this disease? Dr Naddaf: That's a great question, and it's an area that I'm particularly interested in from a research standpoint. So, all these entities were classified as idiopathic inflammatory myopathies because they had inflammation on muscle biopsy. And IBM does have inflammation on muscle biopsy. Even when we study gene expression, all the immunoglobulin, interferon-related genes, the data are very, very highly expressed in IBM. However, IBM histopathology is not just inflammation. There are other features of IBM that are shared with other diseases of aging, and IBM only affects the aging population. So, by definition it is a disease of aging, and it shares a lot of similarities with other diseases of aging such as Alzheimer's disease or Parkinson's disease or those others that occur with aging. And IBM, unlike any other idiopathic inflammatory myopathy, it is twice more common in males and does not have a juvenile form. Taking all of this together, we could argue that IBM is a disease of aging, and those diseases usually are very complex and have involvement of different pathways---including but not restricted to inflammatory pathways, disrupted protein homeostasis, mitochondrial abnormalities and so on and so forth. And that's why so far we have not had any luck with any immunosuppressive or immunomodulatory therapy in IBM. Now the type of inflammation in IBM is also different, that's mediated by highly differentiated cytotoxic CD8 cells that may not respond to the other treatment. But again, IBM is not just inflammation, and unfortunately in these complicated disorders, we're still at early stages of understanding them, let alone intervene on them. There have been a lot of progress in the last few years in the area of aging in general, and hopefully we would see some new developments in IBM and in other diseases that would help at least slow down the progression. Dr Berkowitz: Fantastic. Well, we've only gotten an opportunity to scratch the surface of your article today talking about the clinical presentation, diagnosis, and a little bit about some of the challenges in treatment. But there's a lot more for our listeners to refer to in your article related to some of the aspects of management, not yet a disease-modifying therapy, but other important aspects of management and many other clinical pearls in this article. So, I encourage our listeners to take a look at your article in this issue. Dr Naddaf: Thanks a lot. Dr Berkowitz: Again, today I've been interviewing Dr Elie Naddaf about his article on inclusion body myositis, which appears in the October 2025 Continuum issue on muscle and neuromuscular junction disorders. Be sure to check out Continuum Audio episodes from this and other issues, and thank you again to our listeners for joining us today. Dr Monteith: This is Dr Teshamae Monteith, Associate Editor of Continuum Audio. If you've enjoyed this episode, you'll love the journal, which is full of in-depth and clinically relevant information important for neurology practitioners. Use the link in the episode notes to learn more and subscribe. AAN members, you can get CME for listening to this interview by completing the evaluation at continpub.com/audioCME. Thank you for listening to Continuum Audio.

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• Limb-Girdle Muscular Dystrophies With Dr. Teerin Liewluck

  Limb-girdle muscular dystrophies (LGMDs) encompass a group of genetically heterogeneous skeletal muscle disorders. There has been an explosion of newly identified LGMD subtypes in the past decade, and results from preclinical studies and early-stage clinical trials of genetic therapies are promising for future disease-specific treatments. In this episode, Gordon Smith, MD, FAAN, speaks with Teerin Liewluck, MD, FAAN, FANA, author of the article "Limb-Girdle Muscular Dystrophies" in the Continuum® October 2025 Muscle and Neuromuscular Junction Disorders issue. Dr. Smith is a Continuum® Audio interviewer and a professor and chair of neurology at Kenneth and Dianne Wright Distinguished Chair in Clinical and Translational Research at Virginia Commonwealth University in Richmond, Virginia. Dr. Liewluck is a professor of neurology at the Division of Neuromuscular Medicine and Muscle Pathology Laboratory at Mayo Clinic College of Medicine in Rochester, Minnesota. Additional Resources Read the article: Limb-Girdle Muscular Dystrophies Subscribe to Continuum®: shop.lww.com/Continuum Earn CME (available only to AAN members): continpub.com/AudioCME Continuum® Aloud (verbatim audio-book style recordings of articles available only to Continuum® subscribers): continpub.com/Aloud More about the American Academy of Neurology: aan.com Social Media facebook.com/continuumcme @ContinuumAAN Host: @gordonsmithMD Guest: @TLiewluck Full episode transcript available here Dr Jones: This is Dr Lyell Jones, Editor-in-Chief of Continuum. Thank you for listening to Continuum Audio. Be sure to visit the links in the episode notes for information about earning CME, subscribing to the journal, and exclusive access to interviews not featured on the podcast. Dr Smith: This is Dr Gordon Smith with Continuum Audio. Today I'm interviewing Dr Teerin Liewluck, a good friend of mine at the Mayo Clinic, about his article on the limb girdle muscular dystrophies. This article appears in the October 2025 Continuum issue on muscle and neuromuscular junction disorders, a topic that is near and dear to my heart. Teerin, welcome to the podcast, and maybe you can introduce yourself to our listeners. Dr Liewluck: Thank you very much, Gordon, and I want to say hi to all the Continuum fans. So, I'm Dr Teerin Liewluck, I'm the professor of neurology at Mayo Clinic in Rochester, Minnesota. So, my practice focus on all aspects of muscle diseases, both acquired and genetic myopathies. Glad to be here. Dr Smith: I just had the great pleasure of seeing you at a seminar in Houston where you talked about this topic. And so, I'm really primed for this conversation, which I'm very excited about. I find this topic a little hard, and I'm hoping I can learn more from you. And I wonder if, as we get started, recognizing many of our listeners are not in practices focused purely on muscle disease, maybe you can provide some context about why this is important for folks doing general neurology or even general neuromuscular medicine? Why do they need to know about this? Dr Liewluck: Yes, certainly. So, I would say limb girdle muscular dystrophy probably the most complex category of subgroup of muscle diseases because, by itself, it includes thirty-four different subtypes, and the number's still expanding. So, each subtype is very rare. But if you group together, it really have significant number of patients, and these patients present with proximal weakness, very high CK, and these are common patients that can show up in the neurology clinic. So, I think it's very important even for general neurologists to pick up what subtle clues that may lead to the diagnosis because if we are able to provide correct diagnosis for the patients, that's very important for patient management. Dr Smith: So, I wonder if maybe we can talk a little bit about the phenotype, Terran. I mean, your article does a great job of going over the great diversity. And you know, I think many of us here, you know, limb girdle muscular dystrophy and we think of limb girdle weakness, but the phenotypic spectrum is bananas, right? Rhabdomyolysis, limb girdle distal myopathy. I mean, when should our listeners suspect LGMD? Dr Liewluck: Yes, I think by the definition to all the LGMD patients will have limb girdle of proximal weakness and very high CK. So, these are common phenotypes among thirty-four different subtypes. But if it did take into details, they have some subtle differences. In the article, what I try to simplify all these different subtypes that we can categorize at least half of them into three main group that each group the underlying defect sharing among those subtypes and also translate into similar muscles and extra muscular manifestations. You will learn that some of the limb girdle muscular dystrophy may present with rhabdomyolysis. And we typically think of this as metabolic myopathies. But if you have a rhabdomyolysis patient, the CK remain elevated even after the acute episode, that's the key that we need to think this could be LGMD. That's for an example. Dr Smith: So, I wonder if maybe we can start there. I was going to go in a different direction, but this is a good transition. It's easy to see the opportunity to get confused between LGMD or, in that case, a metabolic myopathy or other acquired myopathies. And I think particularly adult neurologists are more accustomed to seeing acquired muscle disease. Are there particular clues that, or pearls that adult neurologists seeing patients with muscle disease can use to recognize when they should be thinking about LGMD given the diverse phenotype? Dr Liewluck: Yes. What I always tell the patient is that there are more than a hundred different types of muscle diseases, but we can easily divide into groups: acquired and genetic or hereditary. So, the acquired disease is when you encounter the patients who present with acute or subacute cause of the weakness, relatively rapidly progressive. But on the opposite, if you encounter the patient who present with a much more slowly progressive cause of weakness over several months or years, you may need to think about genetic disease of the muscle with also including limb-girdle muscular dystrophy. The detailed exam to be able to distinguish between each type of muscular dystrophy. For example, if proximal weakness, certainly limb girdle muscular dystrophy. If a patient has facial weakness, scapular winking, so you would think about facial scapular hematoma dystrophy. So, the slowly progressive cause of weakness, proximal pattern of weakness, CK elevation, should be the point when you think about LGMD. Dr Smith: So, I have a question about diagnostic evaluation. I had a meeting with one of my colleagues, Qihua Fan, who's a great peripheral nerve expert, who also does neuromuscular pathology. And we were talking about how the pathology field has changed so much over the last ten years, and we're doing obviously fewer muscle biopsies. Our way of diagnosing them has changed a lot with the evolution of genetic testing. What's your diagnostic approach? Do you go right to genetic testing? Do you do targeted testing based on phenotype? What words of wisdom do you have there? Dr Liewluck: Yes, so, I mean, being a muscle pathologist myself, it is fair to say that the utility of muscle biopsies when you encounter a patient with suspects that limb girdle muscular dystrophy have reduced over the year. For example, we used to have like fifteen, seventeen hundred muscle biopsies a year; now we do only thirteen hundred biopsies a year. Yes, as you pointed out, the first step in my practice if I suspect LGMD is to go with genetic testing. And I would prefer the last gene panel that not only include the LGMD, but also include all other genetic muscle disease as well as the conjunctive myopic syndrome, because the phenotype can be somehow difficult to distinguish in certain patients. Dr Smith: So, do you ever get a muscle biopsy, Teerin? I mean you obviously do; only thirteen hundred. Holy cow, that's a lot. So, let me reframe my question. When do you get a muscle biopsy in these patients? Dr Liewluck: Muscle biopsy still is present in LGMD patients, it's just we don't use it at the first-tier diagnostic test anymore. So, we typically do it in selected cases after the genetic testing in those that came back inconclusive. As you know, you may run into the variant of unknown significance. You may use the muscle biopsy to see, is there any histopathology or abnormal protein Western blot that may further support the heterogenicity of the VUS. So, we still do it, but it typically comes after genetic testing and only in the selected cases that have inconclusive results or negative genetic testing. Dr Smith: I'd like to ask a question regarding serologic testing for autoantibodies. I refer to a really great case in your article. There are several of them, but this is a patient, a FKRP patient, who was originally thought to have dermatomyositis based on a low-titer ME2 antibody. You guys figured out the correct diagnosis. We send a lot of antibody panels out. Wonder if you have any wisdom, pearls, pitfalls, for how to interpret antibody tests in patients with chronic myopathies? We send a lot of them. And that's the sort of population where we need to be thinking about limb-girdle muscular dystrophies. It's a great case for those, which I hope is everyone who read your article in detail. What do you have to say about that? Dr Liewluck: Yes, so myositis antibodies, we already revolutionized a few of muscle diseases. I recall when I finished my fellowship thirteen years ago, so we don't really have much muscle myositis antibodies to check. But now the panel is expanded. But again, the antibodies alone cannot lead to diagnosis. You need to go back to your clinical. You need to make sure the clinical antibodies findings are matched. For example, if the key that- if the myocytes specific antibodies present only at the low positive title, it's more often to be false positive. So, you need to look carefully back in the patient, the group of phenotypes, and when in doubt we need to do muscle biopsies. Now on the opposite end, the other group of the antibody is the one for necrotizing autoimmune myopathy; or, the other name, immune-mediated necrotizing myopathy. This is the new group that we have learned only just recently that some patients may present as a typical presentation. I mean, when even thinking about the whole testing autoimmune myopathy, we think about those that present with some acute rapidly progressive weakness, maybe has history of sudden exposures. But we have some patients that present with very slowly progressive weakness like muscular dystrophies. So now in my practice, if I encounter a patient I suspect LGMD, in addition to doing genetic testing for LGMD, I also test for necrotizing doing with myopathy antibodies at the same time. And we typically get antibody back within what, a week or two, but projected testing would take a few months. Dr Smith: Yeah. And I guess maybe you could talk a little bit about pitfalls and interpretation of genetic tests, right? I think you have another case in your article, and I've certainly seen this, where a patient is misdiagnosed as having a genetic myopathy, LGMD, based on, let's say, just a misinterpretation of the genetic testing, right? So, I think we need to think of it on both sides. And I like the fact that the clinical aspects of diagnosis really are first and foremost most important. But maybe you can talk about wisdom in terms of interpretation of the genetic panel?  Dr Liewluck:Yes. So genetic testing, I think, is a complex issue, particularly for interpretation. And if you're not familiar with this, it's probably best to have your colleagues in genetics that help looking at this together. So, I think the common scenario we encounter is that in those dystrophies that are autosomal recessive, so we expect that the patient needs to have two abnormal copies of the genes to cause the disease. And if patients have only one abnormal copy, they are just a carrier. And commonly we see patients refer to us as much as dystrophy is by having only one abnormal copy. If they are a carrier, they should not have the weakness from that gene abnormality. So, this would be the principle that we really need to adhere. And if you run into those cases, then maybe you need to broaden your differential diagnosis. Dr Smith: I want to go back to the clinical phenomenology, and I've got a admission to make to you, Teerin. And I find it really hard to keep track of these disorders at, you know, thirty-four and climbing a lot of overlap, and it's hard to remember them. And I'm glad that I'm now going to have a Continuum article I can go to and look at the really great tables to sort things out. I'm curious whether you have all these top of mind? Do you have to look at the table too? And how should people who are seeing these patients organize their thoughts about it? I mean, is it important that you memorize all thirty-four plus disorders? How can you group them? What's your overall approach to that? Dr Liewluck: I need to admit that I've not memorize all twenty-four different subtypes, but I think what I triy to do even in my real-life practice is group it all together if you can. For example, I think that the biggest group of these LGMD is what we call alpha-dystroglycanopathies. So, this include already ten different subtypes of recessive LGMD. So alpha-dystroglycan is the core of the dystrophin-associated glycoprotein complex. And it's heavy glycosylated protein. So, the effect in ten different genes can affect the glycosylation or the process of adding sugar chain to this alpha-dystroglycan. And they have similar features in terms of the phenotype. They present with proximal weakness, calf pseudohypertrophy, very high CK, some may have recurrent rhabdomyolysis, and cardiac and rhythmic involvement are very common. This is one major group. Now the second group is the limb-girdle muscular dystrophy due to defective membrane repair, which includes two subtypes is the different and on dopamine five. The common feature in this group is that the weakness can be asymmetric and despite proximal weakness, they can have calf atrophy. On muscle biopsy sometimes you can see a myeloid on the muscle tissues. And the third group is the sarcoglycanopathy, which includes four different subtypes, and the presentation can look like we share. For the rest, sometimes go back to the table. Dr Smith: Thank you for that. And it prompts another question that I always wonder about. Do you have any theories about why such variability in the muscle groups that are involved? I mean, you just brought up dystroglycanopathy, for instance, as something that can cause a very distal predominant myopathy; others do not. Do we at this point now have an understanding given the better genetics that we have on this and work going on in therapeutic development, which I want to get to in a minute, that provides any insight why certain muscle groups are more affected? Dr Liewluck: Very good question, Gordon. And I would say the first question that led me interested in muscle disease---and this happened probably back in 2000 when I just finished medical school---is why, why, why? Why does muscle disease tend to affect proximal muscles? I thought by now, twenty-five years later, we'd have the answer. I don't. I think this, you don't know clearly why muscle diseases, some affect proximal, some affect distal. But the hypothesis is, and probably my personal hypothesis is, that maybe certain proteins may express more in certain muscles and that may affect different phenotypes. But, I mean, dysferlin has very good examples that can confuse us because some patients present with distal weakness, some patients present with proximal weakness, that's by the same gene defect. And in this patient, when we look at the MRI in detail, actually the patterns of fatty replacements in muscle are the same. Even patient who present clinically as a proximal or distal weakness, the imaging studies show the same finding. Bottom line, we don't know. Dr Smith: Yeah, who knew it could be so complex? Teerin, you brought up a really great point that I wanted to ask about, which is muscle MRI scan, right? We're now seeing studies that are doing very broad MR imaging. Do you use some muscle MRI very frequently in your clinical evaluation of these patients? And if so, how? Dr Liewluck: Maybe I don't use it as much as I could, but the most common scenario I use in this setting is when I have the genetic testing come back with the VUS. So, we look at each VUS, each gene in detail. And if anything is suspicious, what I do typically go back to the literature to see if that gene defect in particular has any common pattern of muscle involvement on the MRI. And if there is, I use MRI as one of the two to try to see if I can escalate the pathogenicity of that VUS. Dr Smith: And a VUS is a "Variant of Unknown Significance," for our listeners. I'm proud that I remember that as a geneticist. These are exciting times in neurology in general, but particularly in an inherited muscle disease. And we're seeing a lot of therapeutic development, a lot going on in Duchenne now. What's the latest in terms of disease-modifying therapeutics and gene therapies in LGMD? Dr Liewluck: Yes. So, there are several precritical and early-phase critical trials for gene therapy for the common lymphoma of muscular dystrophies. For example, the sarcoglycanopathies, and they also have some biochemical therapy that arepossible for the LGMD to FKRP. But there are many things that I expect probably will come into the picture broader or later phase of critical tryouts, and hopefully we have something to offer for the patients similar to patients with Duchenne muscular dystrophy. Dr Smith: What haven't we talked about, I mean, holy cow? There's so much in your article. What's one thing we haven't talked about that our listeners need to hear? Dr Liewluck: Good questions. So, I think we covered all, but often we get patients with proximal weakness and high CK, and they all got labeled as having limb-girdlemuscular dystrophy. What I want to stress is that proximal weakness and high CK is a common feature for muscle diseases, so they need to think broad, need to think about all possibilities. Particularly don't want to miss something treatable. Chronic, slowly progressive cause, as I mentioned earlier, we think more about muscle dystrophy, but at the cranial range, we know that rare patients with necrotic autonomyopathy and present with limb good of weakness at a slowly progressive cost. So, make sure you think about these two when suspecting that LGMD patient diabetic testing has come back inconclusive. Dr Smith: Well, that's very helpful. And fortunately, there's several other articles in this issue of Continuum that help people think through this issue more broadly. Teerin, you certainly don't disappoint. I enjoyed listening to you about a month ago, and I enjoyed reading your article a great deal and enjoy talking to you even more. Thank you very much. Dr Liewluck: Thank you very much, Gordon. Dr Smith: Again, today I've been interviewing Dr Teerin Liewluck about his article on limb-girdle muscular dystrophy, which appears in the October 2025 Continuum issue on muscle and neuromuscular junction disorders. Please be sure to check out Continuum Audio episodes for this and other issues. And thanks to our listeners for joining today. Dr Monteith: This is Dr Teshamae Monteith, Associate Editor of Continuum Audio. If you've enjoyed this episode, you'll love the journal, which is full of in-depth and clinically relevant information important for neurology practitioners. Use the link in the episode notes to learn more and subscribe. AAN members, you can get CME for listening to this interview by completing the evaluation at continpub.com/audioCME. Thank you for listening to Continuum Audio.

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