Understanding Normal Pressure Hydrocephalus

Normal pressure hydrocephalus (NPH) is a clinical syndrome characterized by the triad of gait apraxia, cognitive impairment, and bladder dysfunction in the radiographic context of ventriculomegaly and normal intracranial pressure. Accurate diagnosis requires consideration of clinical and imaging signs, complemented by tests to exclude common mimics.

In this episode, Lyell Jones, MD, FAAN speaks with Abhay R. Moghekar, MBBS, author of the article “Clinical Features and Diagnosis of Normal Pressure Hydrocephalus” in the Continuum® June 2025 Disorders of CSF Dynamics 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. Moghekar is an associate professor of neurology at Johns Hopkins University School of Medicine in Baltimore, Maryland.

Additional Resources

Read the article: Clinical Features and Diagnosis of Normal Pressure Hydrocephalus

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Host: @LyellJ

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 Abhay Moghekar, who recently authored an article on the clinical features and diagnosis of normal pressure hydrocephalus for our first-ever issue of Continuum dedicated to disorders of CSF dynamics. Dr Moghekar is an associate professor of neurology and the research director of the Cerebrospinal Fluid Center at Johns Hopkins University in Baltimore, Maryland. Dr Moghekar, welcome, and thank you for joining us today. Why don't you introduce yourself to our listeners?

Dr Moghekar: Thank you, Dr Jones. I'm Abhay Moghekar. I'm a neurologist at Hopkins, and I specialize in seeing patients with CSF disorders, of which normal pressure hydrocephalus happens to be the most common.

Dr Jones: And let's get right to it. I think most of our listeners who are neurologists in practice have encountered normal pressure hydrocephalus, or NPH; and it's a challenging disorder for all the reasons that you outline in your really outstanding article. If you were going to think of one single most important message to our listeners about recognizing patients with NPH, what would that be?

Dr Moghekar: I think I would say there are two important messages. One is that the triad is not sufficient to make the diagnosis, and the triad is not necessary to make the diagnosis. You know these three elements of the triad: cognitive problems, gait problems, bladder control problems are so common in the elderly that if you pick 10 people out in the community that have this triad, it's unlikely that even one of them has true NPH. On the other hand, you don't need all three elements of the triad to make the diagnosis because the order of symptoms matters. Often patients develop gait dysfunction first, then cognitive dysfunction, and then urinary incontinence. If you wait for all three elements of the triad to be present, it may be too late to offer them any clear benefit. And hence, you know, it's neither sufficient nor necessary to make the diagnosis.

Dr Jones: That's a really great point. I think most of our listeners are familiar with the fact that, you know, we're taught these classic triads or pentads or whatever, and they're rarely all present. In a way, it's maybe a useful prompt, but it could be distracting or misleading, even in a way, in terms of recognizing the patient. So what clues do you use, Dr Moghekar, to really think that a patient may have NPH?

Dr Moghekar: So, there are two important aspects about gait dysfunction. Say somebody comes in with all three elements of the triad. You want to know two things. Which came first? If gate impairment precedes cognitive impairment, it's still very likely that NPH is in the differential. And of the two, which are more- relatively more affected? So, if somebody has very severe dementia and they have a little bit of gait problems, NPH is not as likely. So, is gait affected earlier than cognitive dysfunction, and is it affected to a more severe degree than cognitive dysfunction? And those two things clue me in to the possibility of NPH. You still obviously need to get imaging to make sure that they have large ventricles. One of the problems with imaging is large ventricles are present in so many different patients. Normal aging causes large ventricles. Obviously, many neurodegenerative disorders because of cerebral atrophy will cause large ventricles. And there's an often-used metric called as the events index, which is the ratio of the bitemporal horns- of the frontal horns of the lateral ventricles compared to the maximum diameter of the skull at that level. And if that ratio is more than 0.3, it's often used as a de facto measure of ventriculomegaly. What we've increasingly realized is that this ratio changes with age. And there's an excellent study that used the ADNI database that looked at how this ratio changes by age and sex. So, in fact, we now know that an 85-year-old woman who has an events index of 0.37 which would be considered ventriculomegaly is actually normal for age and sex. So, we need to start adopting these more modern age- and sex-appropriate age cutoffs of ventriculomegaly so as not to overcall everybody with big ventricles as having possible NPH.

Dr Jones: That's very helpful. And I do want to come back to this challenge that we've seen in our field of overdiagnosis and underdiagnosis. But I think most of us are familiar with the concept of how hydrocephalus could cause neurologic deficits. But what's the latest on the mechanism of NPH? Why do some patients get this and others don't?

Dr Moghekar: Very good question. I don't think we know for sure. And it for a long time we thought it was a plumbing issue. Right? And that's why shunts work. People thought it was impaired CSF absorption, but multiple studies have shown that not to be true. It's likely a combination of impaired cerebral blood flow, biomechanical factors like compliance, and even congenital factors that play a role in the pathogenesis of NPH. And yes, while putting in shunts likely drains CSF, putting in a shunt also definitely changes the compliance of the brain and affects blood flow to the subcortical regions of the brain. So, there are likely multiple mechanisms by which shunts benefit, and hence it's very likely that there's no single explanation for the pathogenesis of NPH.

Dr Jones: We explored this in a recent Continuum issue on dementia. Many patients who have cognitive impairment have co-pathologies, multiple different causes. I was interested to read in your article about the genetic risk profile for NPH. It's not something I'd ever really considered in a disorder that is predominantly seen in older patients. Tell us a little more about those genetic risks.

Dr Moghekar: Yeah, everyone is aware of the role genetics plays in congenital hydrocephalus, but until recently we were not aware that certain genetic factors may also be relevant to adult-onset normal pressure hydrocephalus. We've suspected this for a long time because nearly half of our patients who come to us to see us in clinic with NPH have head circumferences that are more than 90th percentile for height. And you know, that clearly indicates that this started shortly at the time after birth or soon afterwards. So, we've suspected for a long time that genetic factors play a role, but for a long time there were not enough large studies or well-conducted studies. But recently studies out of Japan and the US have shown mutations in genes like CF43 and CWH43 are disproportionately increased in patients with NPH. So, we are discovering increasingly that there are genetic factors that underlie even adult onset in patients. There are many more waiting to be discovered.

Dr Jones: Really fascinating. And obviously getting more insight into the risk and mechanisms would be helpful in identifying these patients potentially earlier. And another thing that I learned in your article that I thought was really interesting, and maybe you can tell us more about it, is the association between normal pressure hydrocephalus and the observation of cervical spinal stenosis, many of whom require decompression. What's behind that association, do you think?

Dr Moghekar: That's a very interesting study that was actually done at your institution, at Mayo Clinic, that showed this association. You know, as we all get older, you know, the incidence of cervical stenosis due to osteoarthritis goes up, but the incidence of significant, clinically significant cervical stenosis in the NPH population was much higher than what we would have expected. Whether this is merely an association in a vulnerable population or is it actually causal is not known and will need further study.

Dr Jones: It's interesting to speculate, does that stenosis affect the flow of CSF and somehow predispose to a- again, maybe a partial degree for some patients?

Dr Moghekar: Yeah, which goes back to the possible hydrodynamic theory of normal pressure hydrocephalus; you know, if it's obstructing normal CSF flow, you know, are the hydrodynamics affected in the brain that in turn could lead to the development of hydrocephalus.

Dr Jones: One of the things I really enjoyed about your article, Abhay, was the very strong clinical focus, right? We can't just take an isolated biomarker or radiographic feature and rely on that, right? We really do need to have clinical suspicion, clinical judgment. And I think most of our listeners who've been in practice are familiar with the use and the importance of the large-volume lumbar puncture to determine who may have, and by exclusion not have, NPH, and then who might respond to CSF diversion. And I think those of us who have been in this situation are also familiar with the scenario where you think someone may have NPH and you do a large-volume lumbar puncture and they feel better, but you can't objectively see a difference. How do you make that test useful and objective in your practice? What do you do?

Dr Moghekar: Yeah, it's a huge challenge in getting this objective assessment done carefully because you have to remember, you know, subconsciously you're telling the patients, I think you have NPH. I'm going to do this spinal tap, and if you walk better afterwards, you're going to get a shunt and you're going to be cured. And you can imagine the huge placebo response that can elicit in our subjects. So, we always like to see, definitely, did the patient subjectively feel better? Because yes, that's an important metric to consider because we want them to feel better. But we also wanted to be grounded in objective truths. And for that, we need to do different tests of speed, balance and endurance. Not everyone has the resources to do this, but I think it's important to test different domains. Just like for cognition, you know, we just don't test memory, right? We test executive function, language, visuospatial function. Similarly, walking is not just walking, right? It's gait speed, it's balance, and it's endurance. So, you need to ideally test at least most of these different domains for gait and you need to have some kind of clear criteria as to how are you going to define improvement. You know, is a 5% improvement, is a 10% improvement in gait, enough? Is 20%? Where is that cutoff? And as a field, we've not done a great job of coming up with standardized criteria for this. And it varies currently, the practice varies quite significantly from center to center at the current time.

Dr Jones: So, one of the nice things you had in your article was helpful tips to be objective if you're in a lower-resource setting. For you, this isn't a common scenario that someone encounters in their practice as opposed to a center that maybe does a large volume of these. What are some relatively straightforward objective measures that a neurologist or someone else might use to determine if someone is improving after a large-volume LP?

Dr Moghekar: Yeah, excellent question, Dr Jones, and very practically relevant too. So, you need to at least assess two of the domains that are most affected. One is speed and one is balance. You know, these patients fall ultimately, right, if you don't treat them correctly. In terms of speed, there are two very simple tests that anybody can do within a couple of minutes. One is the timed “up-and-go” test. It's a test that's even recommended by the CDC. It correlates very well with faults and disability and it can be done in any clinic. You just need about ten feet of space and a chair and a stopwatch, and it takes about a minute or slightly more to do that test. And there are objective age-associated norms for the timed up-and-go test, so it's easy to know if your patient is normal or not. The same thing goes for the 10-meter walk test. You do need a slightly longer walkway, but it's a fairly easy and well-standardized test. So, you can do one of those two; you don't need to do both of them. And for balance, you can do the 30-second “sit-to-stand”; and it's literally, again, 30 seconds. You need a chair, and you need somebody to watch the patient and see how many times they can sit up and stand up from a seated position. Then again, good normative data for that. If you want to be a little more sophisticated, you can do the 4-stage balance test. So, I think these are tests that don't add too much time to your daily assessment and can be done with even trained medical assistants in any clinic. And you don't need a trained physical therapist to do these assessments.

Dr Jones: Very practical. And again, something that is pretty easily deployed, something we do before and then after the LP. I did see you mentioned in your article the dual timed up-and-go test where it's a simultaneous gait and executive function test. And I’ve got to be honest with you, Dr Moghekar, I was a little worried if I would pass that test, but that may be beyond the scope of our time today. Actually, how do you do that? How do you do the simultaneous cognitive assessment?

Dr Moghekar: So, we asked them to count back from 100, subtracting 3. And we do it particularly in patients who are mildly impaired right? So, if they're already walking really good, but then you give them a cognitive stressor, you know, that will slow them down. So, we reserve it for patients who are high-performing.

Dr Jones: That's fantastic. I'm probably aging myself a little here. I have noticed in my career, a little bit of a pendulum swing in terms of the recognition or acceptance of the prevalence of normal pressure hydrocephalus. I recall when I was a resident, many, many people that we saw in clinic had normal pressure hydrocephalus. Then it seemed for a while that it really faded into the background and was much less discussed and much less recognized and diagnosed, and less treated. And now that pendulum seems to have swung back the other way. What's behind that from your perspective?

Dr Moghekar: It's an interesting backstory to all of this. When the first article about NPH was published in the Newman Journal of Medicine, it was actually a combined article with both neurologists and neurosurgeons on it. They did describe it as a treatable dementia. And what that did is it opened up the floodgates so that everybody with any kind of dementia started getting shunts left, right, and center. And back then, shunts were not programmable. There were no antibiotic impregnated catheters. So, the incidence of subdural hematomas and shunt-related infections was very high. In fact, one of our esteemed neurologists back then, Houston Merritt, wrote a scathing editorial that Victor and Adam should lose their professorships for writing such an article because the outcomes of these patients were so bad. So, for a very long period of time, neurologists stopped seeing these patients and stopped believing in NPH as a separate entity. And it became the domain of neurosurgeons for over two or three decades, until more recently when randomized trials started being done early on out of Europe. And now there's a big NIH study going on in the US, and these studies showed, in fact, that NPH exists as a true, distinct entity. And finally, neurologists have started getting more interested in the science and understanding the pathophysiology and taking care of these patients compared to the past.

Dr Jones: That's really helpful context. And I guess that maybe isn't rare when you have a disorder that doesn't have a simple, straightforward biomarker and is complex in terms of the tests you need to do to support the diagnosis, and the treatment itself is somewhat invasive. So, when you talk to your patients, Dr Moghekar, and you've established the diagnosis and have recommended them for CSF diversion, what do you tell them? And the reason I ask is that you mentioned before we started recording, you had a patient who had a shunt placed and responded well, but continued to respond over time. Tell us a little bit more about what our patients can expect if they do have CSF diversion?

Dr Moghekar: When we do the spinal tap and they meet our criteria for improvement and they go on to have a shunt, we tell them that we expect gait improvement definitely, but cognitive improvement may not happen in everyone depending on what time, you know, they showed up for their assessment and intervention. But we definitely expect gait improvement. And we tell them that the minimum gait improvement we can expect is the same degree of improvement they had after their large-volume lumbar puncture, but it can be even more. And as the brain remodels, as the hydrodynamics adapt to these shunts… so, we have patients who continue to improve one year, two years, and even three years into the course of the intervention. So, we’re, you know, hopeful. At the same time, we want to be realistic. This is the same population that's at risk for developing neurodegenerative disorders related to aging. So not a small fraction of our patients will also have Alzheimer's disease, for example, or go on to develop Lewy body dementia. And it's the role of the neurologist to pick up on these comorbid conditions. And that's why it's important for us to keep following these patients and not leave them just to the neurosurgeon to follow up.

Dr Jones: And what a great note to end on, Dr Moghekar. And again, I want to thank you for joining us, and thank you for such a wonderful discussion and such a fantastic article on the clinical diagnosis of normal pressure hydrocephalus. I learned a lot reading the article, and I learned a lot more today just in the conversation with you. So, thank you for being with us.

Dr Moghekar: Happy to do that, Dr Jones. It was a pleasure.

Dr Jones: Again, we've been speaking with Dr Abhay Moghekar, author of a wonderful article on the clinical features and diagnosis of NPH in Continuum's first-ever issue dedicated to disorders of CSF dynamics. 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.