HD phenocopies and targeted testing

Chorea describes involuntary movements that are random, abrupt, and unpredictable, flowing from one body part to another. The most common cause of genetic chorea in adults is Huntington disease, which requires comprehensive, multidisciplinary care as well as support for care partners, who may themselves be diagnosed with the disease.

In this episode, Aaron Berkowitz, MD, PhD FAAN speaks with Kathryn P. L. Moore, MD, MSc, author of the article "Huntington Disease and Chorea" in the Continuum® August 2025 Movement 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. Moore is an assistant professor and director of the Parkinson's Disease and Movement Disorders Fellowship in the department of neurology at Duke University in Durham, North Carolina.

Additional Resources

Read the article: Huntington Disease and Chorea

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Host: @AaronLBerkowitz

Guest: @KatiePMooreMD

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 with Continuum Audio, and today I'm interviewing Dr Kathryn Moore about her article on diagnosis and management of Huntington disease and chorea, which appears in the August 2025 Continuum issue on movement disorders. Welcome to the podcast, Dr Moore. Could you please introduce yourself to our audience?

Dr Moore: Yeah, thank you so much. I'm so excited to be here. I'm Dr Moore. I'm an assistant professor of neurology at Duke University, where I work as a movement disorder specialist. I run our fellowship there and help with our residency program as well. So, I'm excited to speak with our listeners about chorea today.

Dr Berkowitz: Fantastic. And we're excited to talk to you about chorea. So, as a general neurologist myself, I only see chorea pretty rarely compared to other movement disorders like tremor, myoclonus, maybe the occasional tic disorder. And like anything I don't see very often, I always have to look up the differential diagnosis and how to evaluate a patient with chorea. So, I was so glad to read your article. And next time I see a patient with chorea, I know I'll be referring to your article as a great reference to have a framework for how to approach it. I hope our readers will look at all these helpful tables on differential diagnosis based on distribution of chorea in the body, potential etiologies, time course of onset and evolution, associated drug-induced causes, what tests to send. So, I highly recommend our listeners read the article. Keep those tables handy for when a patient comes in with chorea. I'm excited to pick your brain about some of these topics today. First, how do you go about distinguishing chorea from other hyperkinetic movement disorders when you see a patient that you think might have chorea?

Dr Moore: One of the wonderful things about being a movement disorder specialist is we spend a lot of time looking at movements and training our brain to make these distinctions. The things that I would be looking out for chorea is involuntary, uncontrolled movements that appear to be brief and flowing from one part of the body to another. So, if you can watch a patient and predict what movements they're going to do, this probably isn't chorea. And it should be flowing from one part of the body to another. So, not staying just in one part of the body or having sustained movements. It can be difficult to distinguish between a tic or dystonia or myoclonus. Those things tend to be more predictable and repetitive than the chorea, which tends to be really random and can look like dancing.

Dr Berkowitz: That's very helpful. So, once you've decided the patient has chorea, what's your framework for thinking about the differential diagnosis of the cause of the patient's chorea?

Dr Moore: Well, that could be really challenging. The differential for chorea is very broad, and so the two things that I tend to use are age of the patient and acuity of onset. And so, if you're thinking about acute onset of chorea, you're really looking at a structural lesion like a stroke or a systemic issue like infection, hyperglycemia, etc. Where a gradually progressive chorea tends to be genetic in nature. When you're thinking about the difference between a child and an adult, the most common cause of chorea in a child is Sydenham's chorea. And actually, the most common cause of chorea that I tend to see is Parkinson's disease medication. So, if anybody's seen dyskinesia in Parkinson's disease, you've seen chorea. But it's those two things that I'm using, the age of the patient and the acuity. Somewhere in the middle, though---so, if you have subacute onset of chorea---it's important to remember to think about autoimmune conditions or paraneoplastic conditions because these are treatable.

Dr Berkowitz: That's very helpful. So, like in any chief concern in neurology, we're using the context like the age and then the time course. And then a number of other helpful points in your article about the distribution of chorea in the body. Any comments you'd like to make about- we have this very helpful table that I thought was very interesting. So, you really get deep into the nuances of chorea and the movement disorder specialist expert level. Are there any aspects of parts of the body affected by chorea or distribution of chorea across the body that help you hone your differential diagnosis?

Dr Moore: Certainly. I think where the chorea is located in the body can be helpful, but not as helpful as other conditions where you're localizing a lesion or that sort of thing. Because you can have a systemic cause of chorea that causes a hemichorea; that you can have hyperglycemia causing a hemichorea, or even Sydenham's chorea being a hemichorea. But things that we think about, if the forehead is involved, I would think about Huntington's disease, although this is not pathognomonic. And if it's involving the face or the mouth, you can think about neuroacanthocytosis or, more commonly, tardive dyskinesia. Hemichorea would make me think about some of those systemic issues like hyperglycemia, Sydenham's chorea, those sorts of things, but I would rely more on the historical context and the acuity of presentation than the distribution itself.

Dr Berkowitz: Got it. That's very helpful. So those can be helpful features, but not sort of specific for any particular condition.

Dr Moore: Exactly.

Dr Berkowitz: Yeah, I often see forehead chorea mentioned as sort of specific to Huntington's disease. Since I don't see much Huntington's disease myself, what does forehead chorea look like? What is the forehead doing? How do you recognize that there is chorea of the forehead? It's just sort of hard for me to imagine what it would look like.

Dr Moore: It's really tricky. I think seeing the eyebrows go up and down or the brows furrow in an unpredictable way is really what we're looking for. And that can be hard if you're having a conversation. My forehead is certainly animated as we're talking about one of my favorite topics here. One of the tricks that I use with the fellows is to observe the forehead from the side, and there you can see the undulation of the forehead muscles. And that can be helpful as you're looking for these things. I think where it's most helpful to use the forehead is if you're trying to determine if someone with a psychiatric history has tardive dyskinesia or Huntington's disease, because there can be quite a lot of overlap there. And unfortunately, patients can have both conditions. And so, using the forehead movement can be helpful to maybe direct further testing for Huntington's disease.

Dr Berkowitz: Oh, wow, that's a very helpful pearl. So, if you see, sort of, diffuse chorea throughout the body and the forehead is involved, to my understanding it may be less specific. But in the context of wondering, is the neuropsychiatric condition and movement disorder related by an underlying cause in the case of seeing orofacial dyskinesias, is the relationship a drug having caused a tardive dyskinesia or is the whole underlying process Huntington's, the absence of forehead might push you a little more towards tardive dyskinesia, presuming there is an appropriate implicated drug and the presence of forehead chorea would really clue you in more to Huntington's. Did I understand that pearl?

Dr Moore: That's exactly right, and I'm glad you brought up the point about making sure, if you're considering tardive dyskinesia, that there has been an appropriate drug exposure. Because without that you can't make that diagnosis.

Dr Berkowitz: That's a very helpful and interesting pearl, looking at the forehead from the side. That is a movement disorders pearl for sure. Sort of not just looking at the forehead from one angle and trying to figure out what it's doing, but going to look at the patient in profile and trying to sort it out. I love that. Okay. So, based on the differential diagnosis you would have crafted based on whether this is sort of acute, subacute, chronic, the age of the patient, whether it's unilateral, bilateral, which parts of the body. How do you go about the initial evaluation in terms of laboratory testing, imaging, etc.?

Dr Moore: Well, certainly in an acute-onset patient, you're going to get a number of labs---and that's listed out for you in the paper---and consider imaging as well, looking for an infarct. One thing our learners will know is that sort of the typical answer to what's the infarct causing hemichorea would be the subthalamic nucleus. But really, those infarcts can be almost anywhere. There are case reports for infarcts in a wide variety of places in the brain leading to hemichorea. So, I think some general blood work and an MRI of the brain is a good place to start. For someone who has a more chronic course of the development of chorea, there are certain labs that I would get---and an MRI, because if you get an MRI and there's heavy metal deposition or other disease, structurally, that indicates a certain condition, that can help you pretty considerably. But otherwise, I'm looking for inflammatory markers, heavy metals, HIV, some general other things that are outlined, to help make sure that I'm not missing something that's treatable before I go down the route of genetic testing. And we may talk about this in a little bit, but if you start out with genetic testing and then you sort of have to back up and do more systemic testing, that can be very disjointed when it comes to good patient care.

Dr Berkowitz: That's very helpful. So yeah, if it's acute, obviously this is the most straightforward scenario, acute and unilateral. We're imagining something lesional, as you said, either a stroke or---not sort of sudden, but fast, but not sudden---you might think of another structural lesion. Toxoplasmosis, right, has an affinity for the basal ganglia if you were seeing this in a patient who is immunocompromised. But in a case that, probably as you alluded to, sort of what we would see most commonly in practice, those still relatively rare, sort of subacute to chronic symmetric chorea. There's a long list of tests that are recommended. In your article and in other texts, I've read lupus testing, anti-phospholipid antibodies… but the list is long. I'll refer readers to your article. Out of curiosity as a specialist, how often do you see any of these labs come back revealing any underlying diagnosis in a patient who's otherwise healthy and just has developed chorea and comes to you with that chief concern? I feel like I've sent that mega-workup a few times; I'm obviously a general neurologist, but not nearly as many times as you have been. It's- I can't remember a time where something has come up, maybe an ANA one to forty or something like this that we don't think is relevant. But in your practice, how often do you end up finding a reversible cause in the laboratory testing versus ending up starting to go down the genetic testing route, which we'll talk about in a moment?

Dr Moore: It's not common, but it is important that we capture these things. Because for a lot of those laboratory tests, there are treatments that are available, or other health implications if those come back positive. So, the case I think of is a polycythemia vera patient who had diffused subacute onset chorea and was able to be treated, was temporarily managed with medication for her chorea, and as her PV improved, she was able to come off those medications. As I was alluding to before---and I'm sure we'll talk about genetic testing---if you test for HD and it's negative, do you go down the route of additional expensive genetic testing, or do you then circle back and go, oops, I missed this treatable condition? As we talk about genetic testing as well, getting HD testing is a pretty involved process. And so, we want to make sure we are checking all those boxes before we move forward. So, it's not common, but we do catch some treatable conditions, and that's really important not to miss.

Dr Berkowitz: That's very interesting. So, you diagnosed that polycythemia vera by blood smear, is that how you make the diagnosis?

Dr Moore: Yes.

Dr Berkowitz: And is that a once-in-a-career-so-far type of thing, or does that happen time to time?

Dr Moore: For me, that's a once-so-far, but I don't doubt that I'll see it again.

Dr Berkowitz: Great. And how about lupus and some of these other things we look for in the absence of other systemic features? Have you picked up any of these or heard of colleagues picking up something on laboratory testing? They said, oh, this patient came in for a referral for genetic testing, negative Huntington's disease. And good news, we found polycythemia vera; good news, we found undiagnosed lupus and we reversed it. I'm just curious, epidemiologically, seeing these long lists and not having the subspecialty practice that you do, how often you find a reversible cause like we do for neuropathy all the time, right? Oh, it's diabetes, it's B12---maybe not reversible, but preventing progression---or reversible dementia work up. You get so excited when you find low B12 and you replete the patient's B12, and they get better when they had been concerned they were developing an irreversible condition. How often does one in your subspecialty find a reversible cause on that initial mega-lab screen?

Dr Moore: I think it's really uncommon, and maybe the folks that do are caught by someone else that never make it to Huntington's clinic, but I don't tend to see those cases. There are, of course, case reports and well-described in the literature about lupus and movement disorders and things of that nature, but that doesn't come to our clinic on a regular basis for sure.

Dr Berkowitz: Got it. That's helpful to hear. Well, we've alluded to genetic testing a number of times now, so let's go ahead and talk about it. A lot of your article focuses on Huntington disease, and I was thinking about---in the course of our medical training in medical school, and then neurology residency, for those of us who don't become movement disorder experts like yourself---we learn a lot about Huntington disease. That's sort of the disease that causes chorea, until we later learned there are a whole number of diseases, not just the reversible causes we've been talking about, but a number of genetic diseases which you expertly reviewing your article. So, what are some of the red flags that suggest to you that a patient with chronically progressive chorea---and whom you're concerned for Huntington's or another genetic cause---what are some things you notice about the history, about the exam, the symptoms, the signs, the syndrome, that suggest to you that, actually, this one looks like it might not turn out to be HD. I think this patient might have something else. And as you have alluded to, how do you approach this? Do you send HD testing, wait for it to come back, and then go forward? Are there genetic panels for certain genetic causes of chorea? Do you skip just a whole exome sequencing, or will you miss some of the trinucleotide repeat conditions? How do you approach this in practice?

Dr Moore: I'll try to tackle all that. One thing I will say is that a lot of patients with chorea, regardless of the cause, can look very similar to one another. So, if you're looking at chronic onset chorea, perhaps with some neuropsychiatric features, I'm going to most often think about HD because that's the most common cause. Certainly, as we mentioned before, if there's a lot of tongue protrusion, I would think about the acanthocytic conditions, neurocanthocytosis and McCloud syndrome. But generally in those conditions, we're looking at HD as the most likely cause. Certainly, if there is epilepsy or some other syndromic types of things going on, I may think more broadly. But it's important to know that while HD, as you mentioned, is the cause of chorea, many of our patients will have parkinsonism, tics, dystonia, a whole host of other movement phenomenologies. So, that wouldn't dissuade me from thinking about HD. When we think about the kind of patients that you're describing, upwards of 95% of those people will have Huntington's disease. And the process for genetic testing is fairly involved. The Huntington's Disease Society of America has organized a set of recommendations for providers to go about the process of genetic testing in a safe and supportive way for patients and their families. And so that's referred to in the article because it really is important and was devised by patients and families that are affected by this disease.

And so, when we're thinking about genetic testing for HD, if I reveal that you have HD, this potentially affects your children and your parents and your siblings. You can have a lot of implications for the lives and health and finances of your family members. We also know that there is high suicidality in patients with HD, in patients who are at risk for HD; and there's even a higher risk of suicidality in patients who are at risk but test negative for HD. So, we do recommend a supportive environment for these patients and their families. And so, for presymptomatic patients or patients who are at risk and don't have chorea, this involves making sure we have, sort of, our ducks in a row, as it were, when we think about life insurance, and, do you have somebody supportive to be with you through this journey of genetic testing, no matter what the results are? So, oftentimes I'll say to folks, you know, there's this 20-page policy that I encourage you to look at, but there are Huntington's Disease Centers of Excellence across the country that are happy to help you with that process, to make sure that the patients are well supported. This is an individual genetic test because, as you mentioned, it is a CAG repeat disorder. And unfortunately, there is no chorea panel.

So, if an HD test comes back negative, what we'll do then is think about what's called the HD phenocopies. As I mentioned before, some of these patients who look like they have HD will have a negative HD test. And so, what do you do then? Well, there's a handful of phenocopies---so, other genetic mutations that cause a very similar presentation. And so, we try to be smart, since there's not a panel, we try to be smart about how we choose which test to do next. So, for instance, there's a condition called DRPLA that is present in an African-American family here in my area, in North Carolina, as well as in Japan. And so, if someone comes from those backgrounds, we may decide that that's the next test that we're going to do. If they are white European descent, we may consider a different genetic test; or if they're sub-Saharan African, we may choose a different one from that. However, even if you do a really thorough job, all those blood tests, all those genetic tests, you will occasionally get patients that you can't find a diagnosis for. And so, it's important to know even when you do a good job, you may still not find the answer. And so, I think trying to do things with this complex of the presentation in a systematic way for yourself so you're not missing something. So, going back to our answer about, how do I look at lupus and polycythemia vera and all of that, to think about it in a systematic way. That when you get to the end and you say, well, I don't have an answer, you know you've tried.

Dr Berkowitz: That's very helpful to hear your approach to these challenging scenarios, and also how to approach the potential challenging diagnosis for patients and their families getting this diagnosis, particularly in the presymptomatic phase. And your article touches on this with a lot of nuance and thoughtfulness. So, I encourage our listeners to have a read of that section as well. So, last here, just briefly in our final moments, you discuss in your article the various symptomatic treatments for chorea. We won't have time to go into all the details of all the many treatments you discussed, but just briefly, how do you decide which medication to start in an individual patient with chorea for symptomatic management? What are some of the considerations related to the underlying condition, potential side effect profiles of the particular medications, or any other considerations just broadly, generally, as you think about choosing one of the many medications that can be used to treat chorea?

Dr Moore: Certainly. So, there is a group of FDA-approved medications, VMAT2 inhibitors, that we can choose from, or the off-label use of neuroleptics. And so, there's a lot of things that go into that. Some of that is insurance and cost and that sort of thing, and that can play a role. Others are side effects. So, for the VMAT2 inhibitors, they all do have a black box warning from the FDA about suicidality. And so, if a patient does struggle with mental health, has a history of suicidality, psychiatric admissions for that sort of thing, then I would be more cautious about using that medication. All patients are counseled about that, as are their families, to help us give them good support. So, the neuroleptics do not tend to have that side effect and can help with mood as well as the chorea and can be helpful in that way. And some of them, of course, will have beneficial side effects. So, olanzapine may help with appetite, which can be important in this disease. So, the big considerations would be the black box warning and suicidality, as well as, are we trying to just treat chorea or are we treating chorea and neuropsychiatric issues?

Dr Berkowitz: Fantastic. Thank you for that overview. And again, for our listeners, there's a lot more detail about all of these medications, how they work, how they're used in different patient populations, their side effects, etc, to be reviewed in your excellent article. Again, today, I've been interviewing Dr Kathryn Moore about her article on diagnosis and management of Huntington's disease in chorea, which appears in the August 2025 Continuum issue on movement disorders. Be sure to check out Continuum Audio episodes from this and other issues. And thank you so much to our listeners for joining today. And thank you again, Dr Moore.

Dr Moore: Thanks for having me.

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.