Navigating Diagnostic Challenges in Cognitive Disorders

Although Alzheimer disease (AD) is the most common neurodegenerative cause of dementia, other etiologies can mimic the typical amnestic-predominant syndrome and medial temporal brain involvement. Neurologists should recognize potential mimics of AD for clinical decision-making and patient counseling.

In this episode, Kait Nevel, MD, speaks with Vijay K. Ramanan, MD, PhD, an author of the article “LATE, Hippocampal Sclerosis, and Primary Age-related Tauopathy,” in the Continuum December 2024 Dementia issue.

Dr. Nevel is a Continuum® Audio interviewer and a neurologist and neuro-oncologist at Indiana University School of Medicine in Indianapolis, Indiana.

Dr. Ramanan is a consultant and assistant professor of neurology in the Division of Behavioral Neurology at Mayo Clinic College of Medicine and Science in Rochester, Minnesota.

Additional Resources

Read the article: LATE, Hippocampal Sclerosis, and Primary Age-related Tauopathy

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Host: IUneurodocmom

Guest: @vijaykramanan

Full episode transcript available here

Dr Jones: This is Dr Lyle Jones, Editor-in-Chief of Continuum, the premier topic-based neurology clinical review and CME journal from the American Academy of Neurology. Thank you for joining us on Continuum Audio, which features conversations with Continuum 's guest editors and authors who are the leading experts in their fields. Subscribers to the Continuum Journal can read the full article or listen to verbatim recordings of the article and have access to exclusive interviews not featured on the podcast. Please visit the link in the episode notes for more information on the article, subscribing to the journal, and how to get CME.

Dr Nevel: This is Dr Kait Nevel. Today I'm interviewing Dr Vijay Ramanan about his article he wrote with Dr Jonathan Graff-Radford on LATE hippocampal sclerosis and primary age-related tauopathy, which appears in the December 2024 Continuum issue on dementia. Welcome to the podcast. Vijay, can you please introduce yourself to the audience?

Dr Ramanan: Thanks so much, Kait. I'm delighted to be here. So, I am a cognitive neurologist and neuroscientist at the Mayo Clinic in Rochester, Minnesota. I have roles in practice, education and research, but amongst those I see patients with cognitive disorders in the clinic. I help direct our Alzheimer's disease treatment clinic and also do research, including clinical trial involvement and some observational research on genetics and biomarkers related to Alzheimer's and similar disorders.

Dr Nevel: Great, thanks for that. So, I'd like to start off by talking about why is LATE hippocampal sclerosis, why is this important for the neurologist practicing in clinic to know about these things?

Dr Ramanan: That's a great question. So, if we take a step back, we know that degenerative diseases of the brain are really, really common, and they get more and more common as we get older. I think all neurologists, and in fact most clinicians and large swaths of the general public, are well aware of Alzheimer's disease, which is the most common degenerative cause of cognitive impairment in the population. But there are non-Alzheimer’s degenerative diseases which can produce cognitive difficulties as well. And it's important to be aware of those disorders, of their specific presentations and their implications, in part because it's always a healthy thing when we can be as precise and confident about diagnosis and expectation with our patients as possible. I'll look to the analogy of a patient presenting with a myelopathy. As neurologists, we would all find it critical to clarify, is that myelopathy the result of a compressive spondylotic change? The result of an inflammatory disorder, of a neoplastic disorder, of an infectious disorder? It's critical to guide the patient and choose appropriate management options based on the cause of their syndrome. It would potentially harm the patient if you treated an infectious myelopathy with steroids or other immune-suppressant drugs. So, a similar principle holds in cognitive neurology. I accept with humility that we can never be 100% crystal clear certain about things in medicine, just because when you think you got it all figured out there's a curveball. But I want to get as close to that 100% as possible. And recognizing that disorders like LATE or PART can mimic the symptoms, sometimes even the imaging features of Alzheimer's disease. I think it's critical to have heightened awareness of those disorders, how they look, to be able to apply appropriate counseling and management options to patients. I think this becomes particularly critical as we move into an era of disease-specific, and sometimes disease-modifying, therapies, where applying a choice of a treatment option could have significant consequences to a patient if the thing you're treating isn't the thing that the drug is trying to accomplish. So, having awareness and spreading awareness about some of these non-AD causes of cognitive difficulty, I think, is a big mission in the field. 

Dr Nevel: Yeah, that makes total sense. And kind of leaning into this, you know, trying to differentiate between these different causes of late-life amnestic cognitive impairment. You know, I'll point out to the listeners today to please read your article, but in addition to reading your article, I'd like to note that there's a really nice table in your article, Table 6-1, where you kind of go through the different causes of amnestic cognitive impairment and the different features that better fit with diagnosis X, Y, or Z, because I think it's a really nice table to reference and really easy to look at and reference back to. But on that note, what is your typical approach when you're seeing a patient in clinic, have a new referral for an older patient presenting with a predominantly progressive amnestic-type features?

Dr Ramanan: Excellent question. And this is one that I think has relevance not just in a subspecialty memory clinic, but to all the clinicians who help to diagnose and manage cognitive disorders, including in primary care and general neurology and others. One principle that I think it's helpful to keep in our minds is that in cognitive neurology, no one data point takes precedence over all the others. We have a variety of information that we can gather from history, from exam, from imaging, from fluid biomarkers. And really the fun, the challenge, the reward is in piercing together that information. It's almost like being a lawyer and compiling the evidence, having possibilities on your list and raising and lowering those possibilities to get as close to the truth as you can. So, for patients with a cognitive syndrome, I think the first plank is in defining that syndrome. As you mentioned, if I'm seeing someone with a progressive amnestic-predominant syndrome, I first want to make sure, are we talking about the same thing, the patient, the care partner, and I?  Can often be helpful to ask them for some examples of what they see, because sometimes what patients may report as memory troubles may in fact reflect cognitive difficult in other parts of our mental functioning. For example, executive functioning or naming of objects. And so helpful to clarify that in the history to get a sense of the intensity and the pace of change over time, and then to pair that with a good general neurologic exam and some type of standardized assessment of their cognitive functioning. At the Mayo Clinic, where partial to the short test of mental status. There are other ways to accomplish that, such as with an MMSE or a MoCA. If I understand that the syndrome is a progressive amnestic disorder, Alzheimer's disease is the most common cause of that presentation in older adults, it deserves to be on my differential diagnosis. But there might be some other features in the story that could raise or lower those mimics on my list. So, in patients who are, say, older than the age of seventy five, disorders like LATE or PART start to rise higher on the likelihood for me, in particular if I know that their clinical course has been more slow brewing, gradually evolving. And again, most degenerative disorders we expect to evolve not over days or weeks, but over many months to many years. But in comparison with Alzheimer's disease, patients with LATE or with PART would be expected to have a little more slow change where maybe year over year they or their care partners really aren't noticing big declines. Their daily function is relatively spare. There might not be as much involvement into other non-memory cognitive domains. So, these are some of the pieces of the story that can help to perhaps isolate those other non-AD disorders on the list as being more likely and then integrating, as a next level, diagnostic testing, which helps you to rule in and rule out or support those different causes. So, for example, with LATE there can be often out of proportion to the clinical picture, out of proportion to what you see on the rest of their imaging or other profiles, very predominant hippocampal and medial temporal volume loss. And so that can be a clue in the right setting that you may not be dealing with Alzheimer's disease or pure Alzheimer's disease, but that this other entity is there. So, in the big picture, I would say being systematic, recognizing that multiple data points being put together helps you get to that confident cause or etiology of the syndrome. And in particular, taking a step back and thinking about big picture factors like age and course to help you order those elements of the differential, whether AD or otherwise.

Dr Nevel: Great, thanks. In your article, you talk about different imaging modalities that can be used, as you mentioned, you know, just another piece of the puzzle, if you will, to try and put together what may be going on with the patient, and recognizing that some of these imaging techniques are imaging is special imaging, not available in a lot of places.  You know, and maybe other diagnostic type tests that could be helpful in differentiating between these different disorders may not be available, you know, for the general neurologist practicing in the community. So, what do you suggest to the general neurologist maybe practicing somewhere where they don't have access to some of these ancillary tests that could assist with a diagnosis? 

Dr Ramanan: Critical question. And here I think there's not likely to be one single answer. As with most things, awareness and recognition is a good place to start. So, some of those clues that I mentioned earlier about the clinical course, about the age, the- we're talking about clinical setting there. So, comfort with and understanding that the clinical setting can help you to be more confident about, for example, LATE or PART being present in contrast to AD. That's important information. It deserves to be part of the discussion. It doesn't necessarily need other tests to have value on its own. A second piece is that tests help, in some cases, to rule in and rule out causes for cognitive difficulty. As part of a standard cognitive evaluation, we would all be interested in getting some blood tests to look for thyroid dysfunction or vitamin deficiencies. Some type of structural head imaging to rule out big strokes, tumors, bleeds. Head CT can accomplish some of that perspective. It's ideal if a brain MRI can be obtained, but again, keeping in mind, what's the primary goal of that assessment? It's to assess structure. Occasionally you can get even deeper clues into a syndrome from the MRI. For example, that very profound hippocampal or medial temporal atrophy. So, increasing awareness amongst clinicians throughout our communities to be able to recognize that change and put it in the context of what they see in other brain regions that can be affected by Alzheimer's or related disorders. For example, the parietal regions can be helpful. And recall that MRI can also be helpful in assessing for chronic cerebrovascular disease changes. This is another mimic that shows up in that table that you mentioned. And so multiple purposes can be satisfied by single tests. Now, you're absolutely right that there are additional test modalities that, perhaps in a subspecialty clinic at an academic medical center, we're very used to relying on and finding great value on; for example, glucose PET scans or sometimes fluid biomarkers from the blood or from the spinal fluid. And these are not always as widely available throughout our communities. Part of the challenge for all of us as a field is therefore to take the expertise that we have gathered in more subspecialty settings and tertiary care settings and translate and disseminate that out into our communities where we need to take care of patients. That's part of the challenge. The other challenge is in continued tool and technological development. There's a lot of optimism in our field that the availability of blood-based biomarkers relevant for Alzheimer's disease may play a part in helping to address some of the disparities in resource and access to care. You can imagine that doing a blood test to give you some high-quality information, there are going to be less barriers to doing that in many settings compared to thinking about a lumbar puncture or a PET scan, both in terms of cost to the patient as well as infrastructure to the clinicians and the care team. So I'm optimistic about a lot of those changes. In the meantime, I think there are, through both clinical evaluation and some basic testing including structural head imaging, there are clues that can help navigate these possibilities.

Dr Nevel: So, let's say you have your patient in clinic, you've done your evaluation, maybe gotten some ancillary testing, and you highly suspect either LATE or PART. How do you counsel those patients and their families? How do you manage those patients moving forward who you really suspect don't have, you know, some sort of co-pathology?

Dr Ramanan: So, it's- I think it's helpful to remember when patients are coming to see us, either they or the people around them have noticed an issue. And very likely it's an issue that's been brewing for a little while. I think it can be very valuable, very helpful for patients to have answers. What's the cause for the issue? Once you have answers, even if sometimes those answers are not the most welcome things or the things that you'd be looking forward to, answers give you an opportunity to grab hold of what's going on, to define a game plan. So, understanding there is a degenerative disease there, it sheds light on why that individual had had memory symptoms over the years. And it gives them a general expectation that over time on an individualized basis, but generally expecting gradually over many months to many years, there may be some worsening in some of those symptoms helps them to plan and helps them to make the adaptations that are a-ok and great to make to just help you to do the things you want to do. As much as I can, I try to put the focus here closer to how we would view things like high blood pressure or high cholesterol. Those are also chronic issues that tend to be more common as we get older, tend to get more troublesome as we get older. The goal is, know what you're dealing with and take the combination of lifestyle modifications, adaptations in your day-to-day and maybe medications to keep them as mild and as slow-changing as possible. With something like LATE, we don't have specific medication therapies to help support cognitive functioning at this time. There's a lot of hope that with additional research we will have those therapies. But even so, I think it's an important moment to emphasize some of those good healthy lifestyle habits. Staying mentally, socially and physically active, getting a good night's sleep, eating a healthy, balanced diet, keeping good control of vascular risk factors, all of that is critical to keeping the brain healthy, keeping the degenerative disease as mild and slow-brewing as possible. And understanding what some of the symptoms to expect could be. So, with LATE the syndrome tends to be very memory-predominant. There may be some trouble with maybe naming of objects or perhaps recall of emotionally salient historical knowledge, world events, but you're not expecting, at least over the short to medium term, huge intervening on other cognitive functioning. And so that can be helpful for patients to understand. So, the hope is once you know what what you're dealing with, you understand that the disease can look different from person to person. Having a general map of what to expect and what you can do to keep it in check, I think, is the goal.

Dr Nevel: I agree with you 100% that it really can be helpful even if we can't, quote unquote, fix it, that for people, family, the patient have a name for what they have and kind of have some sort of idea of what to expect in the future. And they may come in thinking that they have Alzheimer's or something like that. And then, so, to get that information that this is going to be a little different, we expect this to go a little bit differently then it would if you had a diagnosis of Alzheimer's, I can see how that would be really helpful for people. 

Dr Ramanan: I completely agree. And here's another challenge for us in the field when most patients have heard about Alzheimer's disease and many have perhaps even heard of dementia with Lewy bodies or frontotemporal dementia, but may not have heard of things like LATE. And they're not always easy to go online or find books that talk about these things. Having a name for it and being able to pair that with patient-friendly information is really critical. I see our appointments where we're sharing those diagnosis and making initial game plans as an initial foray into that process. 

Dr Nevel: Yeah, absolutely. What is the greatest inequity or disparity that you see in taking care of patients with progressive amnestic cognitive impairment?

Dr Ramanan: Yeah, great question. I think two big things come to mind. The first, you hinted at very well earlier that there are disparities in access to care, access to diagnostic testing, access to specialists and expertise throughout our communities. If we want diagnostics and therapeutics to be broadly applicable, they do need to be broadly available. And that's a big challenge for us as a field to work to address those disparities. There's not going to be one single cause or contributor to those iniquities, but as a field, I'm heartened to see thought and investment into trying to better address those. Another big weakness, and this is not just limited to cognitive neurology, it's a challenge throughout neurology, is that too many of our research studies are lacking in diversity. And that impacts our biological and pathophysiological understanding of these disorders. It also impacts our counseling and management. Again, if we want a new drug treatment to be broadly applicable throughout all of the patients that we take care of, we need to have data which guides how we apply those treatments. And so again, I'm heartened. This is a big challenge. It's a long standing challenge. It will take deep and long standing committed efforts to reverse. But I'm heartened that there are efforts in the field to broaden clinical trial enrollment, broaden observational research enrollment, and again, broaden access to tools and expertise. As a neurologist, I got into this field because I want to help people, use my expertise and my training to help people. These are steps that we can take to make sure that that help is broadly applicable throughout everybody in our communities.

Dr Nevel: Yeah, absolutely. So, kind of segueing from you mentioning research and how we can better include patients in research. What do you think the next breakthrough is going to be? What do you think the next big thing is going to be in these disorders? What do we still need to learn?

Dr Ramanan: There's a lot. I think for LATE and PART, the development of specific biomarkers would be top of the agenda. Now, biomarkers are by their nature imperfect. Even with Alzheimer's disease, where in comparison, we know quite a lot. We have a variety of imaging and fluid biomarkers that we can use to support or rule out a diagnosis. There are nuances in how you interpret those biomarkers. Patients can have signs of amyloid plaques in their brain and have completely normal cognition. They may be at risk for developing cognitive trouble due to Alzheimer's disease in the future, but it's one piece of the puzzle. Patients can have the changes of Alzheimer's disease amyloid plaques and tau tangles in the brain. We can confirm that through biomarkers. But at the end of the day, their cognitive syndrome might be driven by something else. Maybe it's Lewy body disease, maybe it's LATE, maybe it's a combination of factors. So, integrating and interpreting those biomarkers is challenging. But I do think, again, from the standpoint of giving patients answers with a diagnosis, having those biomarkers is really critical to just kind of closing the loop. It will also be critical to have those biomarkers as we're assessing for treatment response. So, for example, patients who may have coexistent Alzheimer's disease and LATE, I don't think we know the answer fully as to how likely they are to benefit from, say, newer antiamyloid monoclonal antibodies for Alzheimer's disease in the setting of that second pathology. So, wouldn't it be great if, similar to an oncologic setting where you engage in a treatment and then you're tracking two or three or four plasma measures and you're tracking tumor size with imaging, if we had this multimodal ability to track neurodegenerative pathology through biomarkers? I think that'll be a critical next step. And so, filling out that for non-Alzheimer’s diseases, including LATE and PART, I think is item number one on the agenda.

Dr Nevel: Wonderful, thank you so much. I really appreciate you taking the time to chat with me today about your article. I really enjoyed our conversation, certainly learned a lot.

Dr Ramanan: Thank you so much, Kait. Love talking with you. And again, it was an honor to write this article. I hope it's helpful to many out in the field who take care of patients with cognitive issues. 

Dr Nevel: Yeah, I think it will be. So again, today I'm interviewing Dr Vijay Ramanan about his article that he wrote with Dr Jonathan Graff-Radford on LATE hippocampal sclerosis and primary age-related tauopathy, which appears in the most recent issue of Continuum on dementia. Be sure to check out Continuum audio episodes from this and other issues. And thank you, Vijay, and thank you 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 this 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.