There is an order to it that families remember afterwards. The walking changed first: small steps, feet that seemed to stick to the kitchen floor, a slow shuffle when turning at the top of the stairs. Months later came the quietness, less interest in the crossword, slower answers. Then the accidents to the toilet, which nobody wanted to discuss. Every piece was filed under getting older, and each went somewhere different: the walking to the physiotherapist, the memory to the GP, the bladder to nobody.
Idiopathic normal pressure hydrocephalus is the condition that produces exactly that sequence, and it is one of the very few causes of this picture where an operation can give somebody their walking back. It is also one of the most reliably missed diagnoses in older adults, in Ireland and everywhere else.
TL;DR
- Normal pressure hydrocephalus (NPH) is a build-up of cerebrospinal fluid in the brain’s ventricles causing a distinctive walking difficulty, slowed thinking and bladder urgency, usually in that order.
- It is common and badly under-found. An MRI study of 791 Swedish 70-year-olds found 1.5% met international criteria, yet only around 13% of affected people in Europe are thought to receive appropriate care.
- Waiting for all three classic symptoms is the central mistake. In a 2025 survey of 274 healthcare professionals, only 16.8% knew NPH can present with just one of them.
- The first placebo-controlled trial of shunt surgery, in the New England Journal of Medicine in 2025, found real improvement in walking but no significant benefit for memory or continence. “Reversible dementia” oversells it.
- Ireland has two adult neurosurgical centres. An Irish frailty team reported that even after a confirmed response to fluid drainage, referral for a shunt “can take months to years”.
What is actually going on
Your brain sits in cerebrospinal fluid, which is made and reabsorbed continuously, and which fills four connected chambers inside the brain called the ventricles. In normal pressure hydrocephalus, that circulation stops balancing. The ventricles enlarge and press outwards on the brain tissue immediately around them. The name comes from the fact that pressure measured at a lumbar puncture usually reads normal, which is precisely why the condition hid for so long.
The reason the legs suffer first is anatomical. The nerve fibres carrying instructions to the legs run closest to the ventricles, so they are the first to be stretched and squeezed. “Idiopathic” means no cause is found, which is the usual situation after 65; a secondary form can follow a bleed on the brain, meningitis or a serious head injury.
The three signs, and the mistake of waiting for all three
The walking is the giveaway. It is not the cautious, stiff walk of arthritis or the general slowing of age. Steps become short and wide-based, the feet seem magnetised to the floor, and turning takes several small shuffling steps instead of one pivot. Starting is hard: the person stands, intends to move, and nothing happens. Tellingly, the arms are usually fine. Someone can swing their arms normally and still not get their feet to co-operate.
The thinking slows rather than shatters. This is not the dense forgetting of Alzheimer’s disease, where recent events vanish. It is slowness, apathy and loss of initiative. Families describe the person going quiet, losing interest, taking a long time to answer a simple question. They often still know exactly what day it is.
The bladder comes last. Urgency first, then accidents, and some of that is simple mechanics: the urge arrives and the legs cannot get there in time.
Generations of medical students learned this as a triad, and the teaching has done real harm, because it implies you wait for all three. You should not. Gait trouble typically comes first and can be the only sign for a long time. A 2025 study in Scientific Reports surveyed 274 healthcare professionals across neurology, neurosurgery, geriatrics and primary care: 78.5% knew the condition is treated with a shunt, but only 16.8% knew it can present with one of the three signs rather than all three. NPH also commonly sits alongside Alzheimer’s disease, vascular changes or Parkinson’s disease. Having one does not rule out the other.
How common, and how rarely found
Estimates vary widely with the criteria used, so treat these as orders of magnitude. A population-based MRI study of 791 seventy-year-olds in Gothenburg, published in Neurology in 2024, found 1.5% met international diagnostic criteria. A Swedish community study in PLOS One found 3.7% of people aged 65 and over met modified criteria, rising from 2.1% in the 65 to 79 group to 8.9% among those aged 80 and over. Of the 25 people that second study identified, exactly one had already been treated with a shunt.
A 2026 analysis in the European Journal of Health Economics puts the consequence plainly: only around 13% of affected people in Europe receive appropriate care, despite clinical improvement in up to 80% of properly selected patients. Ireland had 891,063 people aged 65 and over in April 2026, according to CSO estimates, so even that analysis’s conservative 1.3% prevalence points to something like eleven thousand people here.
Getting to a diagnosis
Diagnosis has two halves, and the scan alone is not enough. First, imaging: a CT or MRI looks for ventricles enlarged out of proportion to the rest of the brain, measured as an Evans index above 0.3, plus supporting features such as tight, crowded folds over the top of the brain. The catch is that plenty of people in their seventies and eighties have roomy ventricles simply because brain tissue has shrunk around them. That pattern will not respond to a shunt, and telling the two apart is specialist work.
Second, and more important, the functional test. A large volume of cerebrospinal fluid is drained, either by a high-volume lumbar puncture, known as a tap test, or by leaving a temporary drain in place for a few days. Walking is measured before and after, usually as timed walking speed. If it improves, that is the single best predictor that a shunt will help, though the test is demanding for a frail person.
What a shunt does, and what it does not
Treatment is a ventriculoperitoneal shunt: a thin tube from a ventricle, under the skin, draining excess fluid into the abdomen, with an adjustable valve controlling the flow. For decades the evidence for it was observational, so nobody could separate genuine benefit from the improvement that often follows any operation. That changed in 2025. The PENS trial, published in the New England Journal of Medicine, randomised 99 people who had all already responded to temporary fluid drainage to either a working valve or one set so high it drained nothing. Neither patients nor their doctors knew which they had.
At three months, walking speed in the working-shunt group had risen by 0.23 metres per second against 0.03 on placebo, a difference of 0.21. For context, 0.10 metres per second is the widely used benchmark for a substantial meaningful change in an older adult’s walking speed, so this is roughly double that. A gait and balance score improved too. Memory scores and bladder questionnaires did not.
Read that honestly in both directions. It is strong evidence that the walking improvement is real rather than wishful, and walking is not a small thing: it is the difference between getting to the shop and not leaving the house. It is not evidence that a shunt reverses dementia, and the popular label “reversible dementia” promises families something this operation did not deliver in a controlled trial. There are risks too. Bleeding under the surface of the brain occurred in 12% of the shunted group against 2% on placebo, and positional headaches in 59% against 28%, though falls were far more common on placebo, at 46% against 24%.
The Irish picture
The structural problem is that this condition presents to three services at once and belongs to none of them. Walking goes to physiotherapy or a falls clinic, memory to a memory assessment service, bladder symptoms to continence services if they are mentioned at all. The person most likely to join the three together is a geriatrician or a frailty team taking a whole-person look.
Irish clinicians have shown that joining them up works. A Roscommon frailty intervention team reported in Age and Ageing in 2023 that it diagnosed ten cases of probable NPH in a single year in one county, using a structured diagnostic pathway and CT scoring alongside a trial of high-volume fluid drainage. Ten cases from one small service tells you how much is sitting undetected elsewhere. The sting is in their own honest note: three of those people were not suitable for surgery, two were still waiting for a shunt, and even with measurable improvement after drainage, referral for shunting “can take months to years”.
That bottleneck has a simple explanation. Adult neurosurgery in Ireland runs from two centres: Beaumont Hospital in Dublin, the National Neurosurgical Centre, and Cork University Hospital. On the memory side, the HSE’s memory assessment services and regional specialist memory clinics exist precisely for complex or atypical presentations, which is exactly what a gait-led picture is.
If this sounds like someone you know
Three practical things, none of which need a doctor.
Write down the order and the timing. Which came first, and roughly when. A GP hearing “his walking changed eighteen months ago and the memory followed” is handed a different problem than one hearing “he’s getting forgetful”. That sequence is the most useful single thing you can bring.
Film the walking. Thirty seconds on your phone of the person walking down a hall and turning at the end. Gait is hard to describe and easy to recognise on screen, and in a ten-minute appointment where the person has been sitting throughout, it may be the only chance anyone gets to see it.
Ask the question by name. “Could this be normal pressure hydrocephalus? Has a brain scan been done, and what did it say about the ventricles?” You are not being difficult, and given what the research shows about awareness of this condition, you may be adding something useful.
Be realistic too. Not everyone will be suitable for surgery, and long-standing symptoms respond less well than recent ones, which is the argument for asking early. If the answer turns out to be a form of dementia after all, that is still worth knowing properly and worth support: the Alzheimer Society of Ireland’s National Helpline is free on 1800 341 341, Monday to Friday 10am to 5pm and Saturday 10am to 4pm.
At Críonna Health we keep coming back to a single habit of mind, because it keeps proving useful: treat “it’s just their age” as the beginning of a question rather than the end of one. A walk that changed over a few months is not ageing. Ageing does not have a start date. This has a name, a scan, a test and, for some people, an operation that gives them the length of the road back.
This article is for general information and is not a substitute for medical advice. If you are worried about changes in your own or a family member’s walking, thinking or bladder control, speak to your GP.
📷 Photo by Khanh Do (@donguyenkhanhs) on Unsplash
