NPH, or normal pressure hydrocephalus, is a brain condition where cerebrospinal fluid builds up in the brain’s ventricles (hollow chambers), causing them to enlarge and press on surrounding tissue. Unlike other forms of hydrocephalus, the fluid pressure measured during a spinal tap reads as normal or only slightly elevated, which is what makes the condition tricky to identify. NPH primarily affects people over 60 and is one of the few causes of dementia that can be reversed with treatment.
The Three Hallmark Symptoms
NPH produces a distinctive cluster of three symptoms known as the Hakim triad, named after the neurosurgeon who first described the condition in 1965. Between 50% and 75% of people with NPH have all three symptoms at the same time, though they don’t always appear together early on.
The first and most recognizable symptom is a change in walking. People with NPH develop a shuffling, wide-based gait, sometimes described as “magnetic” because their feet seem glued to the floor. They walk with feet turned outward and take short, slow steps, with a side-to-side pattern sometimes compared to a penguin’s walk. As the condition progresses, balance worsens, especially when turning.
The second symptom is urinary problems. Early on, this shows up as a sudden, hard-to-control urge to urinate or needing to go more frequently than usual. The underlying cause is overactivity in the bladder muscle, which contracts when it shouldn’t. Over time, this can progress to full loss of bladder control.
The third symptom is cognitive decline. The type of mental slowing seen in NPH is different from Alzheimer’s disease. Rather than the severe memory loss typical of Alzheimer’s, NPH tends to cause sluggish thinking, difficulty with planning and decision-making, forgetfulness, and a general sense of mental inertia. People may seem apathetic or slow to respond rather than confused.
What Causes It
Your brain constantly produces cerebrospinal fluid, which cushions the brain and spinal cord, delivers nutrients, and carries away waste. Normally, this fluid circulates through the ventricles and is reabsorbed into the bloodstream at a steady rate. In NPH, that reabsorption slows down. Fluid accumulates, the ventricles gradually expand, and the enlarged chambers compress the nerve fibers that control walking, bladder function, and cognition.
In most cases, there’s no clear reason why this happens. This form is called idiopathic NPH, and it accounts for the majority of diagnoses. In a smaller number of cases, NPH develops after a specific event that disrupts normal fluid circulation: a brain hemorrhage, meningitis, a serious head injury, or prior brain surgery. This is called secondary NPH and can occur at younger ages.
How Common NPH Is
NPH becomes more common with age. In people aged 70 to 79, roughly 0.2% meet the diagnostic criteria. That number jumps to about 5.9% in people 80 and older, with no significant difference between men and women. These numbers suggest NPH is more common than many clinicians realize, and studies from different countries have found varying prevalence rates, likely because the condition is frequently misdiagnosed as Parkinson’s disease, Alzheimer’s, or simply “normal aging.”
How NPH Differs From Parkinson’s Disease
The walking problems in NPH can look a lot like Parkinson’s disease at first glance. Both conditions slow walking speed and shorten stride length. But there are important differences. NPH produces a wide-based gait with feet turned outward and reduced step height, so people tend to scuff or drag their feet. Parkinson’s gait is typically narrow-based with small, quick, shuffling steps.
One practical distinction: people with Parkinson’s often improve dramatically when given visual cues, like lines on the floor to step over. These cues have little effect on the gait problems caused by NPH. This difference can help clinicians tell the two conditions apart during evaluation.
How NPH Is Diagnosed
Diagnosing NPH involves matching symptoms with brain imaging findings. On an MRI or CT scan, doctors look for enlarged ventricles that are disproportionate to overall brain shrinkage. The standard measurement is called the Evans index: the ratio of the widest part of the front ventricle chambers to the widest internal diameter of the skull. A value above 0.30 confirms ventricular enlargement. Normal values fall between 0.20 and 0.25.
Imaging alone isn’t enough. Doctors also look for a specific pattern where the grooves on the brain’s upper surface appear tighter than expected, while the ventricles below are expanded. This combination helps distinguish NPH from other causes of large ventricles, like brain tissue loss from Alzheimer’s.
Diagnosis follows a stepped approach. A “possible” NPH diagnosis requires at least two of the three hallmark symptoms, plus imaging showing enlarged ventricles, with no other obvious explanation for the symptoms. A “probable” diagnosis adds two more requirements: the cerebrospinal fluid pressure must be normal when measured, and either the brain imaging shows that characteristic pattern of tight upper grooves with enlarged ventricles, or the patient improves after a spinal tap test.
The Spinal Tap Test
The large-volume lumbar tap test is one of the most widely used tools for predicting whether someone with suspected NPH will benefit from surgery. During the procedure, a doctor removes a large volume of cerebrospinal fluid through a spinal needle, typically 40 to 50 mL, though research suggests that amounts in the 28 to 50 mL range produce similar results.
Gait is tested before the tap, then again one to four hours later and the following day. If walking noticeably improves after the fluid is removed, that’s considered a positive sign that surgical treatment will help. Interestingly, when the condition was first described in 1965, the original doctors noted improvement after removing only 10 to 15 mL. If there’s no improvement after the tap, it doesn’t necessarily rule out NPH, but it does prompt further testing before considering surgery.
Treatment With a Shunt
The primary treatment for NPH is a surgically implanted shunt, a thin tube that drains excess cerebrospinal fluid from the brain’s ventricles to the abdominal cavity, where the body absorbs it naturally. The shunt includes a valve that regulates flow, and modern programmable valves can be adjusted after surgery without another operation.
Shunting works well for many people. A systematic review of outcomes found an overall improvement rate of about 71% at both three months and one year after surgery, with individual studies reporting success rates ranging from 33% to 91%. In one study of 116 patients, gait improved in the majority, while improvements in bladder control and cognition were less common but still meaningful.
What Recovery Looks Like
Walking problems, mild cognitive symptoms, and bladder control issues often start improving within days of shunt surgery. Walking and balance tend to respond first. With physical therapy, many people see meaningful gains in mobility within a few weeks. Reaching the full benefit of surgery, however, can take weeks to months.
Memory and thinking skills are the slowest to recover, and some people are left with lasting cognitive deficits even after successful shunt placement. The general pattern holds that the earlier NPH is caught and treated, and the shorter the duration of symptoms before surgery, the better the outcome. This is one of the key reasons awareness of NPH matters: it’s a treatable condition that is too often dismissed as untreatable dementia or the inevitable decline of aging.