NPH stands for normal pressure hydrocephalus, a condition where cerebrospinal fluid (CSF) builds up in the brain’s ventricles, enlarging them, even though fluid pressure measurements come back normal or only slightly elevated. It primarily affects adults from their 60s onward and is one of the few causes of dementia-like symptoms that can actually be reversed with treatment. Because its symptoms overlap with Parkinson’s disease and Alzheimer’s disease, NPH is frequently missed or misdiagnosed.
How Fluid Builds Up Without High Pressure
Your brain continuously produces cerebrospinal fluid, which cushions the brain and spinal cord before being reabsorbed into the bloodstream. In NPH, that reabsorption process doesn’t work efficiently. The fluid accumulates gradually, and the ventricles (fluid-filled chambers deep inside the brain) slowly stretch outward. What makes NPH unusual is that a standard pressure reading during a spinal tap often looks normal, which is how the condition gets its name.
The enlarging ventricles create mechanical stress on surrounding brain tissue and blood vessels. This compression reduces blood flow to nearby areas, causing a kind of chronic, low-grade oxygen deprivation. Over time, this damages the nerve pathways that control walking, bladder function, and thinking. Abnormal patterns of fluid flow through the narrow channel connecting the ventricles (the aqueduct) may also generate ongoing shearing forces that worsen the dilation, creating a cycle where the damage feeds itself.
When a clear cause can be identified, such as a previous brain hemorrhage, meningitis, or head trauma, the condition is called secondary NPH. When no cause is found, it’s classified as idiopathic NPH, which is the more common form.
The Three Classic Symptoms
NPH produces a well-known trio of symptoms called Hakim’s triad: difficulty walking, cognitive decline, and urinary incontinence. Not every patient develops all three, but at least two of the three need to be present for a diagnosis, and gait problems are considered essential.
The walking difficulty is often the earliest and most noticeable symptom. People with NPH develop a distinctive “magnetic gait,” where their feet seem stuck to the floor. Steps become short and shuffling, the stance widens, and the feet tend to turn outward. It looks somewhat like the walk seen in Parkinson’s disease, but there are key differences. In Parkinson’s, visual cues on the ground (like lines to step over) can dramatically improve stride length. In NPH, those same cues help only slightly. NPH also produces a wider base and lower step height than Parkinson’s typically does.
The cognitive changes in NPH primarily affect short-term memory and executive functions like planning, organizing, and multitasking. The decline tends to be slower and less severe than Alzheimer’s disease in its early stages, but it can worsen significantly if untreated.
Bladder problems affect roughly 45 to 90 percent of NPH patients. The pattern usually starts with needing to urinate more frequently, then progresses to urge incontinence (a sudden, overwhelming need to go that arrives too late). Part of this is neurological: the brain loses its ability to properly regulate bladder muscle contractions. Part of it is practical: when walking is already difficult, getting to the bathroom in time becomes its own challenge. In advanced cases, patients may lose awareness of the urge entirely. Fecal incontinence is rare and only appears in late-stage disease.
How NPH Is Diagnosed
Diagnosis starts with brain imaging. An MRI or CT scan will show ventricles that are disproportionately large compared to the rest of the brain. Neurologists use a measurement called the Evans Index to quantify this: it compares the width of the frontal horns of the ventricles to the maximum width of the skull. A ratio greater than 0.3 is the established threshold for ventriculomegaly (abnormally large ventricles) in both Japanese and international guidelines.
Imaging alone isn’t enough, though, because enlarged ventricles can also result from brain atrophy in conditions like Alzheimer’s. The key distinguishing test is the CSF tap test (also called a large-volume lumbar puncture). A doctor removes about 40 milliliters of spinal fluid through a needle in the lower back, then evaluates whether the patient’s symptoms improve over the following hours or days. Walking is the primary measure: clinicians typically assess walking speed, step length, and performance on the Timed Up and Go test, where the patient stands from a chair, walks a short distance, turns, and sits back down. An improvement of at least 10 percent in walking speed or Timed Up and Go time is generally considered a positive response.
A positive tap test serves two purposes. It supports the NPH diagnosis, and it predicts whether the patient is likely to benefit from surgery. Not everyone who has NPH will show an immediate response, so a negative tap test doesn’t completely rule out the condition, but a clear positive result is a strong signal that treatment will help.
Treatment With a Shunt
The primary treatment for NPH is surgery to implant a shunt, a thin tube that redirects excess cerebrospinal fluid away from the brain to be absorbed elsewhere in the body. The most common type is a ventriculoperitoneal (VP) shunt, which routes fluid from a brain ventricle into the abdominal cavity. Alternatives include ventriculoatrial (VA) shunts, which drain into a vein near the heart, and lumboperitoneal (LP) shunts, which connect the spinal canal to the abdomen.
A large meta-analysis published in The Lancet found that more than 74 percent of patients improved after shunt surgery overall. VP and VA shunts both showed a 75 percent success rate, while LP shunts came in at about 70 percent. A less invasive procedure called endoscopic third ventriculostomy, which creates a small opening in the ventricle floor to improve fluid flow, had a 69 percent success rate, though its effectiveness remains debated.
Modern shunts often include programmable valves that allow doctors to adjust the drainage rate after surgery without additional operations. This matters because over-drainage is one of the more common complications. When too much fluid drains too quickly, the brain can shift inside the skull, stretching and tearing small bridging veins. This can cause subdural hematomas (collections of blood between the brain and skull), which occur in 3 to 33 percent of cases depending on the study. Overall complication rates for shunt surgery range from about 17 to 52 percent across published research, though many of these are relatively minor. In one large study, infection rates were 3 percent, shunt malfunction occurred in 11 percent, and about a third of patients were readmitted within six months for some type of issue. Programmable valves showed significantly lower malfunction and total complication rates compared to fixed-pressure valves.
Which Symptoms Improve After Treatment
Gait problems respond best to shunting. Walking speed, step length, and balance often show measurable improvement, sometimes within days of the tap test and continuing over weeks to months after surgery. Slowness in both the arms and legs can also improve.
Cognitive symptoms are more variable. Patients who are treated earlier, before significant brain damage has accumulated, tend to see better results. When NPH coexists with Alzheimer’s disease, which happens more often than you might expect given the overlapping age group, walking may still improve after shunting but the dementia typically does not. This is one reason early and accurate diagnosis matters so much: the longer the brain tissue is compressed and oxygen-deprived, the less reversible the damage becomes.
Bladder symptoms generally fall somewhere in between. Many patients see meaningful improvement, especially if incontinence was primarily driven by the combination of urgency and impaired mobility rather than complete loss of bladder awareness.
Why NPH Is Often Missed
NPH remains underdiagnosed largely because its symptoms are common in older adults for many other reasons. Slow walking, memory problems, and bladder issues are often attributed to “normal aging,” Parkinson’s disease, or Alzheimer’s disease without further investigation. The condition’s gradual onset makes it easy to overlook, and many primary care physicians encounter it infrequently enough that it doesn’t come to mind as a possibility.
Formal diagnostic guidelines were first published in Japan in 2004 and internationally in 2005. These frameworks significantly improved outcomes by giving clinicians clearer criteria for when to suspect NPH and how to confirm it. Updated guidance published in 2025 continues to refine these recommendations, emphasizing that the diagnosis should be actively considered in any older adult with unexplained gait disturbance, particularly when accompanied by cognitive changes or bladder dysfunction. The fact that NPH is one of the few treatable causes of dementia makes the cost of missing it especially high.