Normal pressure hydrocephalus (NPH) is a neurological condition where cerebrospinal fluid builds up in the brain’s ventricles, enlarging them, even though the fluid pressure measured during testing appears normal. It primarily affects adults over 65 and is estimated to occur in about 3.7% of that population. The prevalence climbs sharply with age, reaching nearly 9% in people over 80. NPH is one of the few causes of dementia-like symptoms that can be reversed with treatment, which is why recognizing it matters.
How Fluid Builds Up Without High Pressure
Your brain constantly produces cerebrospinal fluid (CSF), a clear liquid that cushions the brain and spinal cord. Normally, this fluid circulates through chambers in the brain called ventricles, flows around the brain and spinal cord, and gets reabsorbed into the bloodstream. In NPH, something disrupts this cycle. The ventricles gradually stretch and enlarge, pressing on surrounding brain tissue.
What makes NPH unusual is that when doctors measure the fluid pressure with a spinal tap, it reads within the normal range. This paradox is actually where the condition gets its name. The exact mechanism behind this remains unclear, but the leading theory is that the pressure may spike intermittently, particularly during sleep, causing gradual ventricular stretching over time while single-point measurements appear normal. Some research points to dysfunction in the tiny hair-like structures (cilia) lining the ventricles, which normally help move fluid along. When these cilia don’t beat properly, fluid flow stalls and the ventricles expand under chronic, low-grade stress.
NPH can be idiopathic, meaning it develops without a known trigger. This is the most common form. Secondary NPH develops after a specific event that disrupts normal fluid circulation: a brain hemorrhage, meningitis, traumatic brain injury, or prior brain surgery.
The Three Core Symptoms
NPH produces a recognizable cluster of three symptoms known as Hakim’s triad: trouble walking, urinary problems, and cognitive decline. These symptoms typically emerge gradually and worsen over months or years. Not everyone develops all three at once, and they don’t always appear in the same order.
Walking Difficulty
Gait problems are the earliest and most common symptom, appearing in 80% to 95% of people with NPH. The walk becomes slow, shuffling, and unsteady. People describe feeling “stuck to the floor,” with their feet barely lifting off the ground. The gait is characteristically wide-based, meaning the feet are spread farther apart than normal for balance. This can look similar to Parkinson’s disease, but a key difference is that NPH walking problems typically affect only the legs and feet, while arm swing and upper-body movement remain relatively normal early on.
Urinary Incontinence
Bladder symptoms often start subtly. You might notice needing to urinate more frequently or feeling sudden, hard-to-control urges. Over time, this can progress to full loss of bladder control. Some people with NPH seem unaware of or unbothered by the incontinence, which itself can be a sign of the cognitive changes the condition causes.
Cognitive Decline
The thinking changes in NPH tend to involve mental and physical slowness: taking longer to respond to questions, difficulty with planning and organizing tasks, and reduced motivation. This pattern differs from Alzheimer’s disease, where short-term memory loss is usually the dominant early feature while attention and executive function stay relatively intact. In NPH, it’s closer to the opposite, with slowed processing and poor executive function appearing before significant memory loss.
Why NPH Gets Misdiagnosed
NPH shares symptoms with several common conditions of aging, which is why it’s frequently mistaken for Alzheimer’s, Parkinson’s, or simply “getting old.” Studies show that about 70% of NPH patients have parkinsonian features like slow movement and balance problems. However, the resting tremor that’s a hallmark of Parkinson’s is uncommon in NPH. Parkinson’s also tends to produce a narrow-based gait with reduced arm swing, often asymmetric, while NPH produces the broad-based, magnetic gait described above.
The overlap with Alzheimer’s is another diagnostic trap. Both conditions cause cognitive decline in older adults, and they can even coexist in the same person. The sequence of symptom onset is one important clue: NPH typically causes walking problems before noticeable cognitive decline, while Alzheimer’s usually begins with memory difficulties. Brain imaging also helps, since NPH produces a specific pattern of enlarged ventricles that looks different from the widespread brain shrinkage seen in Alzheimer’s.
How NPH Is Diagnosed
Diagnosis starts with brain imaging, either CT or MRI. Doctors look for enlarged ventricles and calculate something called the Evans Index, which compares the width of the front horns of the ventricles to the widest diameter of the skull. A value of 0.3 or greater indicates abnormal ventricular enlargement. Under the current diagnostic guidelines, this imaging finding combined with gait problems plus either urinary or cognitive symptoms points toward NPH.
The most important diagnostic step is the lumbar tap test. A doctor inserts a needle into the lower spine and removes 30 to 50 milliliters of cerebrospinal fluid. (In the original studies from the 1960s, improvement was seen after removing as little as 10 to 15 ml.) Before and a few hours after the procedure, the patient walks a timed course and completes cognitive tests. If walking speed, stride length, or thinking improves after the fluid is removed, that’s considered a positive result and a strong predictor that surgical treatment will help. The test isn’t perfect, though. Some people who don’t improve after a single tap still benefit from surgery, so doctors sometimes use extended lumbar drainage over several days for borderline cases.
Shunt Surgery and What to Expect
The primary treatment for NPH is a surgically implanted shunt, most commonly a ventriculoperitoneal (VP) shunt. This is a thin tube placed into one of the brain’s ventricles, running under the skin down to the abdominal cavity, where excess cerebrospinal fluid drains and gets absorbed by the body. The surgery itself typically takes about an hour under general anesthesia.
Success rates are encouraging. Up to 80% of well-selected patients experience meaningful improvement. In one study tracking outcomes over two years, about 91% of patients showed symptom improvement at six months, and roughly 91% of those followed to two years maintained that improvement. Gait tends to respond best and fastest. Cognitive symptoms may improve more slowly, and urinary control often follows gait improvement.
Modern shunts come in two types: fixed-pressure and programmable. Fixed-pressure valves drain fluid at a single, preset rate. Programmable valves allow doctors to adjust the drainage setting externally, using a magnetic tool placed against the scalp, without additional surgery. This flexibility makes a measurable difference. Patients who receive programmable valves have a revision rate of about 13%, compared to 24% for fixed-pressure valves. They’re also far less likely to need the valve swapped out entirely (2% vs. 12%). Despite the higher upfront cost of programmable valves, total treatment costs end up nearly identical because fewer revision surgeries are needed.
Risks and Complications
Shunt surgery is not risk-free. In one large study, some type of complication occurred in 58% of patients, though about half of those complications were minor and resolved without additional surgery. Around 26% of patients experienced a problem directly related to the shunt hardware. Mechanical malfunctions requiring a second operation have been reported in up to 41% of cases in some studies, and shunt infections occur in roughly 7%. Overdrainage, where too much fluid is removed, can cause headaches or, less commonly, a collection of blood between the brain and skull. Programmable valves help reduce overdrainage because the flow rate can be fine-tuned after surgery.
The timing of treatment matters. People who are diagnosed and treated earlier in the course of the disease, particularly before significant cognitive decline sets in, tend to have better outcomes. Gait improvement can sometimes be noticeable within days of shunt placement, while cognitive gains may take weeks to months to become apparent.