Although rare, recognizing NMOSD is crucial for improving patient outcomes through correct diagnostic and treatment approaches. Reports of atypical forms and increasing knowledge of clinical, imaging, and laboratory-specific features are fundamental for the accurate recognition of this condition. Research on targeted therapies and biomarkers measuring and predicting disease activity will improve NMOSD management. In this episode, Gordon Smith, MD, FAAN, speaks with Sara Mariotto, MD, PhD, coauthor of the article "Neuromyelitis Optica Spectrum Disorder" in the Continuum® April 2026 Multiple Sclerosis and Related 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. Mariotto is a neurologist in the Neurology Unit in the Department of Neurosciences, Biomedicine, and Movement Sciences at the University of Verona in Verona, Italy. Additional Resources Read the article: Neuromyelitis Optica Spectrum Disorder 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 Full episode transcript available here Dr Smith: Neurology is an increasingly therapeutic specialty, and across many of our subspecialty areas, lots of new drugs are being approved. Are you interested in learning more about a historically disabling disorder for which we now have a spectrum of new therapies that, if used appropriately and promptly in the right clinical situation, promise to dramatically improve patient outcomes? If so, keep listening. My name's Dr Gordon Smith. Today I'll be talking with Dr Sara Mariotto about her article on neuromyelitis optica spectrum disorder or NMOSD, which she wrote with Dr Romain Marignier. This article appears in the April 2026 Continuum issue on multiple sclerosis. 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. Today, I'm interviewing Dr Sara Mariotto about her article on neuromyelitis optica spectrum disorder or NMOSD, which she wrote with Dr Romain Marignier. This article appears in the April 2026 Continuum issue on multiple sclerosis. Sara, welcome to the podcast, and maybe you can start by introducing yourself to our audience. Dr Mariotto: Yes. Thanks, Gordon. I'm Sara Mariotto. I'm a neurologist, and I work at the Neurology Unit, University of Verona, where I do both clinical diagnosis and research into neuroimmunology---so, in particular, autoimmune encephalitis, NMOSD, and MOGAD. Dr Smith: Well, this is a super exciting area. Whenever I hear about NMOSD, I think of one specific patient I had, and I always think of her when I come across something like your article, which is really fantastic. So, before we dive into the details, I wonder if maybe you can just explain to our listeners who aren't up to speed on what NMOSD is, what the disorder is, and maybe why it's so important that all of our listeners learn how to recognize it quickly and get people started on therapy. Dr Mariotto: Yes, sure. So, neuromyelitis optica is an inflammatory autoimmune CNS disorder usually associated with aquaporin-4 antibodies, although there are a few cases, around 10%, who can be antibody-negative. And I think it's very much important to have in mind this disease and recognize it because it can be severe, as you pointed out; can present with very severe optic neuritis, myelitis, the brain stem, or area postrema syndrome. So, it can be really severe, affect quite young people around 40 years of age---although it can affect also the pediatric population and elderly people---and, importantly, it can be treated. It's very much important to treat this patient in the acute stage very quickly with steroids or plasma exchange in addition, and then to start a chronic treatment. So, we have treatment for this condition. So, it's very much important to, to recognize it quickly and treat the patient properly. Dr Smith: So, I wonder if we can talk a little bit about the diagnostic criteria and boundaries of NMOSD, right? So, someone who comes in with bilateral op- severe long segment optic neuritis or long segment myelitis, we think about it. But what are the boundaries? Should we be looking for this, for instance, in someone who comes in with a unilateral optic neuritis or looks like typical multiple sclerosis? Is it important to get aquaporin-4 antibodies in those patients? What do the diagnostic criteria say about this? Dr Mariotto: So, I wouldn't test aquaporin-4 antibodies in all patients with demyelinating conditions because although aquaporin-4 antibody assay is very specific, as for all assay and all antibody testing---also for MOG antibodies, for example---some false positive results can come out. So, I would suggest to test aquaporin-4 antibodies not in typical MS cases but in those who could be suggestive for not being MS, so in all those cases with atypical optic neuritis and myelitis or other syndromes. For those cases, it's important to test aquaporin-4 antibodies, but I wouldn't test them in all typical, classical MS cases. As I said, it's quite specific, the assay, so it's uncommon to have false positive results, but it can be. Dr Smith: Serum, CSF, both? Dr Mariotto: So, for aquaporin-4 antibodies, they're usually present in serum. They can be positive also in the CSF. And there are a few reports of isolated CSF positivity. But if we analyze larger samples volume, then it becomes clear that isolated CSF positivity is so, so rare that it's not recommended to test them in the CSF when serum is negative. So, for aquaporin-4 antibodies, the recommended matrix of testing is serum, which is different for MOG, which is not the topic of our article but is important to mention because MOG antibodies should be tested in serum and CSF. But aquaporin-4, I would recommend to test serum. Dr Smith: What are the boundaries between MOGAD and NMOSD? And you talked about the differential testing of antibodies, which I was going to ask about. But when should we think of NMOSD relative to MOG? Dr Mariotto: Yeah. There are aspects which are the one mentioned in the criteria, highly suggestive for NMOSD. But the clinical spectrum can be similar to that of MOGAD. Usually, although there are some clinical aspect---like, for example cortical encephalitis or ADEM, which is more typical for MOGAD, or others like area postrema syndrome, which are more typical of NMOSD. The spectrum can be similar among the two conditions, so that's why in our clinical experience, usually they ask both aquaporin-4 and MOG antibodies in patients. It's- for experts, it can be easy to differentiate the two conditions, but for nonexperts can not be so easy. Dr Smith: Can you define area postrema syndrome? I think not all of our listeners see that every day. Dr Mariotto: Yeah, sure. This is a syndrome which is highly suggestive of NMOSD. That's why I mention it. And it's characterized by nausea, vomiting, hiccups are known as the syndrome. And it is very, very suggestive because of the expression of aquaporin-4 in that area of NMOSD. That's why I strongly recommend for all patients who comes out to have this syndrome to test for aquaporin-4 antibodies. MOGAD is hardly ever positive for that, so I think that whenever you see a patient with that syndrome, you should think about NMOSD. Dr Smith: I'm just curious, aquaporin-4 is a water channel, which is kind of an interesting concept. Our conversation, I really want to make sure we give clinically important information to folks, but it's so curious to me at least, how does this actually result in a inflammatory demyelinating syndrome? For a simple neuromuscular guy, what's the immunopathogenesis of this? Dr Mariotto: Yeah, the immunopathogenesis is quite complicated, as in all CNS disorders. And of course, aquaporin-4 antibodies are the main focus, but they are not the only one. As you said, aquaporin-4 antibodies have a target, this water channel, which is at the basis of the disease, and they are produced by the interplay between T cells, B cells, and plasma cells. But then also eosinophils, macrophages, cytokines, and chemokines are involved, enter the CNS, and then another important component is complement, which is highly activated in this disease. At the end, we have astrocyte damage because astrocytes are the main target of the disease, but also axon and myelin are involved. So, it's a quite complex pathogenesis based on the antibodies, but not only on that. Dr Smith: And this will become important when we start talking about treatment. There seems to be a recurring theme of long segment demyelination, right? Optic neuritis is typically a large percentage of the length of the optic nerve, and obviously the myelitis se- more than three segments. Do you see other long segment areas of CNS demyelination, corpus callosum or things like that? Any ideas why that is, if that's true? Dr Mariotto: Of note, this is quite interesting because usually when we have NMOSD, we have a longitudinal involvement, especially of the optic nerve and spinal cord, while brain lesions are quite different. Like, we usually do not have the typical Dawsen fingers-like lesions that we have in MS, for example, or the classical periventricular or subcortical extensive