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Essential tremor is the most common movement disorder, although it is often misdiagnosed. A careful history and clinical examination for other neurologic findings, such as bradykinesia, dystonia, or evidence of peripheral neuropathy, can reveal potential alternative etiologies. Knowledge about epidemiology and associated health outcomes is important for counseling and monitoring for physical impairment and disability. In this episode, Lyell Jones, MD, FAAN, speaks with Ludy C. Shih, MD, MMSc, FAAN, author of the article "Essential Tremor" in the Continuum® August 2025 Movement Disorders issue. Dr. Jones is the editor-in-chief of Continuum: Lifelong Learning in Neurology® and is a professor of neurology at Mayo Clinic in Rochester, Minnesota. Dr. Shih is clinical director of the Parkinson's Disease and Movement Disorders Center at Beth Israel Deaconess Medical Center in Boston, Massachusetts. Additional Resources Read the article: Essential Tremor 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: @LyellJ Guest: @ludyshihmd 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 Jones: This is Dr Lyell Jones, Editor-in-Chief of Continuum: Lifelong Learning in Neurology. Today, I'm interviewing Dr Ludy Shih, who recently authored an article on essential tremor for our latest issue of Continuum on movement disorders. Dr Shih is an associate professor of neurology at Harvard Medical School and the clinical director of the Parkinson's Disease and Movement Disorder Center at Beth Israel Deaconess Medical Center in Boston. Dr Shih, welcome, and thank you for joining us today. Why don't you introduce yourself to our listeners? Dr Shih: Thank you, Dr Jones, for having me. It's a real pleasure to be here on the podcast with you. I'm a neurologist, I trained in movement disorders fellowship, and I currently see patients and conduct clinical research. We offer a variety of treatments and diagnostic tests for our patients with movement disorders. And I have developed this interest, a clinical research interest in essential tremor. Dr Jones: And so, as an expert in essential tremor, the perfect person to write such a really spectacular article. And I can't wait for our listeners to hear more about it and our subscribers to read it. And let's get right to it. If you had, Dr Shih, a single most important message for our listeners about caring for patients with essential tremor, what would that message be? Dr Shih: Yeah, I think the takeaway that I've learned over the years is that people with essential tremor do develop quite a few other symptoms. And although we propose that essential tremor is this pure tremor disorder, they can experience a lot of different comorbidities. Now, there is some debate as to whether that is expected for essential tremor or is this some part of another syndrome, which we may talk about later in the interview. But the fact of the matter is, it's not a benign condition and people do experience some disability from it. Dr Jones: And I think that speaks to how the name of this disorder has evolved over time. right? You point out in your article, it used to be called benign essential tremor or benign familial tremor. But it's really not so straightforward as it. And fairly frequently these symptoms, the patient's tremor, can be functionally limiting, correct? Dr Shih: That is correct. In fact, the reason I probably started getting interested in essential tremor was because our center had been doing a lot of deep brain stimulation for essential tremor, which is remarkably effective, especially for tremor that reaches an amplitude that really no oral medication is going to satisfyingly treat. And if you have enough upper limb disability from this very large-amplitude tremor, a surgical option may make a lot of sense for a lot of patients. And yet, how did they get to that point? Do they continue to progress? These were the sort of interesting questions that got raised in my mind as I started to treat these folks. Dr Jones: We'll come back to treatment in just a minute here, because there are many options, and it sounds like the options are expanding. To start with the diagnosis- I mean, this is an extraordinarily common disorder. As you point out, it is the most common movement disorder in the US and maybe the world, and yet it seems to be underrecognized and frequently misdiagnosed. Why do you think that is? Dr Shih: Great question. It's been pretty consistent, with several case series over the decades showing a fairly high rate of quote/unquote "misdiagnosis." And I think it speaks to two things, probably. One is that once someone sees a postural and kinetic tremor of the arms, immediately they think of essential tremor because it is quite common. But there's a whole host of things that it could actually be. And the biggest one that we also have to factor in is also the heterogeneity of the presentation of Parkinson's disease. Many people, and I think increasingly now these days, can present with not a whole lot of the other symptoms, but may present with an atypical tremor. And it becomes actually a little hard to sort out, well, do they have enough of these other symptoms for me to suspect Parkinson's, or is the nature of their tremor suspicious enough that it would just be so unusual that this stays essential tremor and doesn't eventually develop into Parkinson's disease? And I think those are the questions that we all still grapple with from time to time in some of our clinics. Dr Jones: Probably some other things related to it with, you know, our understanding of the pathophysiology and the availability of tests. And I do want to come back to those questions here in just a minute, but, you know, just the nomenclature of this disorder… I think our clinical listeners are familiar with our tendency in medicine to use words like essential or idiopathic to describe disorders or phenomena where we don't understand the precise underlying mechanism. When I'm working with our trainees, I call these "job-security terms" because it sounds less humbling than "you have a tremor and we don't know what causes it," right? So, your article does a really nice job outlining the absence of a clear monogenic or Mendelian mechanism for essential tremor. Do you think we'll ever have a eureka moment in neurology for this disorder and maybe give it a different name? Dr Shih: It's a great question. I think as we're learning with a lot of our neurologic diseases---and including, I would even say, Parkinson's disease, to which ET gets compared to a lot---there's already now so much more known complexity to something that has a very specific idea and concept in people's minds. So, I tend to think we'll still be in an area where we'll have a lot of different causes of tremor, but I'm hopeful that we'll uncover some new mechanisms for which treating or addressing that mechanism would take care of the tremor in a way that we haven't been able to make as much progress on in the last few decades as maybe we would have thought given all the advances in in technology. Dr Jones: That's very helpful, and we'll be hopeful for that series of discoveries that lead us to that point. I think many of our listeners will be familiar with the utility---and, I think, even for most insurance companies, approval---for DAT scans to discriminate between essential tremor and Parkinsonian disorders. What about lab work? Are there any other disorders that you commonly screen for in patients who you suspect may have essential tremor? Dr Shih: Yeah, it's a great question. And I think, you know, I'm always mindful that what I'm seeing in my clinic may not always be representative of what's seen in the community or out in practice. I'll give an example. You know, most of the time when people come to the academic Medical Center, they're thinking, gosh, I've tried this or that. I've been on these medicines for the last ten years. But I've had essential tremor for twenty years. We get to benefit a little bit from all that history that's been laid down. And so, it's not as likely you're going to misdiagnose it. But once in a while, you'll get someone with tremor that just started a month ago or just started, you know, 2 or 3 months ago. And you have to still be thinking, well, I've got to get out of the specialist clinic mindset, and think, well, what else really could this be? And so, while it's true for everybody, moreso in those cases, in those recent onset cases, you really got to be looking for things like medications, electrolyte abnormalities, and new-onset thyroid disorder, for example, thyroid toxicosis. Dr Jones: Very helpful. And your article has a wonderful list of the conditions to consider, including the medications that might be used for those conditions that might result or unmask a tremor of a different cause. And I think being open-minded and not anchoring on essential tremor just because it's common, I think is a is a key point here. And another feature in your article that I really enjoyed was your step-by-step approach to tremor. What are those steps? Dr Shih: Well, I think you know first of all, tremor is such common terminology that even lay people, patients, nonclinicians will use the word "tremor." And so, it can be tempting when the notes on your schedule says referred for tremor to sort of immediately jump to that. I think the first step is, is it tremor? And that's really something that the clinician first has to decide. And I think that's a really important step. A lot of things can look superficially like tremor, and you shouldn't even assume that another clinician knows what tremor looks like as opposed to, say, myoclonus. Or for example a tremor of the mouth; well, it actually could be orolingual or orobuccal dyskinesia, as in tardive dyskinesia. And another one that tremor can look like is ataxia. And so, I think- while they sound obvious to most neurologists, perhaps, I think that---especially in the area of myoclonus, where it can be quite repetitive, quite small amplitude in some conditions---it can really resemble a tremor. And so, there are examples of these where making that first decision of whether it's a tremor or not can really be a good sort of time-out to make sure you're going down the right path to begin with. And I think what's helpful is to think about some of the clinical definitions of a tremor. And tremor is really rhythmic, it's oscillatory. You should see an agonist and antagonist muscle group moving back and forth, to and fro. And then it's involuntary. And so, I think these descriptors can really help; and to help isolate, if you can describe it in your note, you can probably be more convinced that you're dealing with the tremor. The second step that I would encourage people to really consider: you've established it's a tremor. The most important part exam now becomes, really, the nontremor part of the exam. And it should be really comprehensive to think of what else could be accompanying this, because that's really how we make diagnosis of other things besides essential tremor. There really should be a minimum of evidence of parkinsonism, dystonia, neuropathy, ataxia- and the ataxia could be either from a peripheral or central nervous system etiology. Those are the big four or five things that, you know, I'm very keen to look for and will look pretty much in the head, neck, the axial sort of musculature, as well as the limbs. And I think this is very helpful in terms of identifying cases which turn out to have either, say, well, Parkinson's or even a typical Parkinson disorder; or even a genetic disorder, maybe even something like a fragile X tremor ataxia syndrome; or even a spinal cerebellar ataxia. These cases are rare, but I think if you uncover just enough ataxia, for example, that really shouldn't be there in a person, let's say, who's younger and also doesn't have a long history of tremor; you should be more suspicious that this is not essential tremor that you're dealing with. And then the last thing is, once you've identified the tremor and you're trying to establish, well, what should be done about the tremor, you really have to say what kind of tremor it is so that you can follow it, so you can convey to other people really what the disability is coming from the tremor and how severe the tremor is. So, I think an example of this is, often in the clinic, people will have their patients extend their arms and hands and kind of say, oh, it's an essential tremor, and that's kind of the end of the exam. But it doesn't give you the flavor. Sometimes you'll have a patient come in and have a fairly minimal postural tremor, but then you go out, take those extra few seconds to go grab a cup of water or two cups of water and have them pour or drink. And now all of a sudden you see this tremor is quite large-amplitude and very disabling. Now you have a better appreciation of what you really need to do for this patient, and it might not be present with just these very simple maneuvers that you have at bedside without props and items. And then the severity of it; you know, we're so used to saying mild, moderate, severe. I think what we've done in the Tremor Research Group to use and develop the Essential Tremor Rating Assessment Scale is to get people used to trying to estimate what size the tremor is. And you can do that by taking a ruler or developing a sense of what 1 centimeter, 2 centimeters, 3 centimeters looks like. I think it'd be tremendously helpful too, it's very easy and quick to convey severity in a given patient. Dr Jones: I appreciate you, you know, having a patient-centered approach to the- how this is affecting them and being quantitative in the assessment of the tremor. And that's a great segue to a key question that I run into and I think others run into, which is when to initiate therapy? You know, if you see a patient who, let's say they have a mild tremor or, you know, something that quantitatively is on the mild end of the spectrum, and you have, you know, a series of options… from a medication perspective, you have to say, well, when does this across that threshold of being more likely to benefit the patient than to harm the patient? How do you approach that question? What's your threshold for starting medication? Dr Shih: Yeah. You know, sometimes I will ask, because---and I know this sounds like a strange question---because I feel like my patients will come for a couple of different reasons. Sometimes it's usually one over the other. I think people can get concerned about a symptom of a tremor. So, I actually will ask them, was your goal to just get a sense for what this tremor is caused by? I understand that many people who develop tremor might be concerned it might be something like Parkinson's disease. Or is this also a tremor that is bothering you in day-to-day life? And often you will hear the former. No, I just wanted to get checked out and make sure you don't think it's Parkinson's. It doesn't bother me enough that I want to take medication. They're quite happy with that. And then the second scenario is more the, yeah, no, it bothers me and it's embarrassing. And that's a very common answer you may hear, may be embarrassing, people are noticing. It's funny in that many people with essential tremor don't come to see a doctor or even the neurologist for many years. And they will put up with it for a very long time. And they've adopted all sorts of compensatory strategies, and they've just been able to handle themselves very admirably with this, in some cases, very severe tremor. So, for some of them, it'll take a lot to come to the doctor, and then it becomes clear. They said, I think I'm at the point where I need to do something about this tremor. And so, I think those three buckets are often sort of where my patients fall into. And I think asking them directly will give you a sense of that. But you know, it can be a nice time to try some as-needed doses of something like Propranolol, or if it's something that you know that they're going to need something on day-to-day to get control of the tremor over time, there are other options for that as well. Dr Jones: Seems like a perfect scenario for shared decision-making. Is it bothersome enough to the patient to try the therapy? And I like that suggestion. That's a nice pearl that you could start with an a- needed beta blocker, right, with Propranolol. And this is a question that I think many of us struggle with as well. If you've followed a patient with essential tremor for some time and you've tried different medications and they've either lost effectiveness or have intolerable adverse effects, what is your threshold for referring a patient for at least considering a surgical neurostimulator therapy for their essential tremor? Dr Shih: Yeah, so surgical therapies for tremor have been around for a long time now, since 1997, which was when it was approved by the FDA for essential tremor and Parkinson tremor. And then obviously since then, we have a couple more options in the focus ultrasound thalamotomy, which is a lesioning technique. When you have been on several tremor medications, the list gets smaller and smaller. It- and then chance of likely satisfying benefit from some of these medications can be small and small as you pass through the first and second line agents and these would be the Propranolol and the primidone. And as you say, quite a few patients- it's estimated between 30 to 50% of these patients end up not tolerating these first two medications and end up discontinuing them. Some portion of that might also be due to the fact that some of our patients who have been living with essential tremor for decades now, to the point that their tremor is getting worse, are also getting older. And so, polypharmacy and/or some of the potential side effects of beta blockers and anticonvulsants like primidone may be harder to bear in an older adult. And then as you talk about in the article, there's some level of evidence for topiramate, and then from there a number of anticonvulsants or benzos, which have even weaker evidence for them. It's a personal decision. As I tell folks, look, this is not going to likely extend your life or save your life, but it's a quality of life issue. And of course, if there are other things going on in life that need to be taken care of and they need that kind of care and attention, then, you know, you don't need to be adding this to your plate. But if you are in the position where those other things are actually okay, but quality of life is really affected by your being unable to use your upper limbs in the way that you would like to… A lot of people's hobbies and applications are upper limb-based, and enjoying those things is really important. Then I think that this is something- a conversation that we begin and we begin by talking about yes, there are some risks involved, but fortunately this is the data we have on it, which is a fairly extensive experience in terms of this is the risk of, you know, surgery-related side effects. This is the risk of if you're having stimulation from DBS stimulation-related side effects, which can be adjustable. It's interesting, I was talking with colleagues, you know, after focused ultrasound thalamotomy was approved. That really led more people to come to the clinic and start having these discussions, because that seemed like a very the different sort of approach where hardware wasn't needed, but it was still a surgery. And so, it began that conversation again for a bunch of people to say, you know, what could I do? What could I tolerate? What would I accept in terms of risk and potential benefit? Dr Jones: Well, I think that's a great overview of a disorder where, you know, I think the neurologist's role is really indispensable. Right? I mean, you have to have this conversation not just once, this is a conversation that you have over time. And again, I really want to refer our listeners to this article. It's just a fantastic overview of a common disorder, but one where I think there are probably gaps where we can improve care. And Dr Shih, I want to thank you for joining us, and thank you for such a great discussion on essential tremor. I learned a lot from your article, and I learned even more from the interview today. I suspect our readers and listeners will too. Dr Shih: Well, thank you again for the invitation and the opportunity to kind of spread the word on this really common condition. Dr Jones: Again, we've been speaking with Dr Ludy Shih, author of a fantastic article on essential tremor in Continuum's latest issue on movement disorders. Please check it out, 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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