How a Reversible Type of Dementia Can be Mistaken for Alzheimer’s Disease

Updated: Oct. 10, 2022

Normal pressure hydrocephalus is a treatable form of dementia that targets more than 700,000 Americans, yet about 80 percent of cases are undiagnosed.

A mysterious malady

Memory and mental sharpness can decline as we get older. Struggles with walking and bladder control can also become issues. Although these can be manageable problems, they can erode a person’s quality of life and isolate them from the support they need. What many people don’t realize is that the three problems—cognitive decline, gait troubles, and urinary incontinence—may indicate a devastating but treatable condition known as normal pressure hydrocephalus (NPH).

While symptoms like these can arise from a variety of health issues, including diseases such as Alzheimer’s or Parkinson’s, NPH can also be a culprit: Experts estimate that more than 700,000 people in the United States may have the condition, yet about 80 percent of cases are unrecognized and untreated. In hopes of shedding more light on this mysterious malady, including why it’s so difficult to diagnose, here is a closer look at normal pressure hydrocephalus.

What is normal pressure hydrocephalus?

The fluid surrounding your brain and spinal cord, called cerebrospinal fluid (CSF), performs several important functions. It serves as a cushion for your brain and spine, for example, and helps distribute nutrients and remove waste products from the brain. An adult produces about one pint (500 milliliters) of CSF every day, continuously reabsorbing it into the bloodstream.

Hydrocephalus is a condition in which too much CSF builds up, potentially elevating pressure within the brain. This can happen in young children due to birth defects, but it also can develop later in life. As some people age, their brains seem to struggle with the daily production and recycling of CSF, causing the ventricles—cavities in the brain that contain CSF—to become enlarged.

This process is not fully understood. And even though patients often have normal or only slightly elevated CSF pressure (hence the name “normal” pressure hydrocephalus), they can experience a range of serious health problems.

Normal pressure hydrocephalus is further split into two subtypes based on the cause. Secondary NPH is associated with a known trigger, such as a tumor, infection, traumatic brain injury, or complications from surgery, and can occur at any age. Primary NPH, on the other hand, occurs without any of these triggers, typically in older people. It’s also known as “idiopathic” NPH, which means the cause is unknown.

What are NPH symptoms?

There are three main NPH symptoms: mild dementia, gait changes (and difficulty walking), and impaired bladder control. Not all cases of NPH involve all three symptoms at the same time, and some people experience only one or two, according to the Hydrocephalus Association.

Who is likely to have NPH?

“Age is definitely a risk factor,” says Guy McKhann, MD, professor of neurological surgery and director of the Adult Hydrocephalus Center at the Columbia University Irving Medical Center in New York City.

In fact, most people with idiopathic NPH are more than 60 years old. Some genes identified in recent years seem to predispose people to idiopathic NPH, he adds, but that represents a minority of patients. Based on his own experience treating NPH patients, Dr. McKhann suspects socioeconomic risk factors might play a role, as well.

“Because it’s a difficult diagnosis that requires good access to medical care, the majority of patients I see with NPH are people who have good medical access and resources,” he says. “I don’t believe this is primarily a condition of that demographic. Are we missing a whole subpopulation of patients who may have idiopathic NPH in our less advantaged communities in terms of lack of medical access?”

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Why is NPH so rarely diagnosed?

Normal pressure hydrocephalus is already “vastly underdiagnosed” overall, says Alexandra Golby, MD, professor of neurosurgery and radiology at Harvard Medical School. Some neurologists don’t believe in the condition, she notes, which helps explain why it isn’t diagnosed more often. But it’s also obscured behind symptoms like dementia, mobility issues, and urinary incontinence, which are already common in older patients.

“Those symptoms seem like the kinds of things that happen to older people. The patients themselves think, ‘This must be old age,'” Dr. Golby says. “Their families think that, and their primary care physicians often don’t put it together. It also can have an insidious presentation, and it can sneak up on people like old age does.” (This man’s undiagnosed normal pressure hydrocephalus left him stumped for two decades.)

Even when people do seek treatment for their symptoms, she adds, NPH is commonly misdiagnosed by primary care physicians who lack familiarity with the condition; they may instead blame dementia on Alzheimer’s or gait deviations on Parkinson’s. Patients with NPH often visit several doctors before they hear anything about hydrocephalus. (Don’t miss how this woman pressed for answers until she got her normal pressure hydrocephalus diagnosis.)

“By the time patients get to me as a surgeon, they’ve often gone through many layers of care,” Dr. Golby says. Some do come in without a referral, though, after learning about NPH on their own. “They look on the internet because they’re frustrated with the lack of progress, and they self-refer,” she says. “And that’s great when that happens.”

What are the risks?

When NPH is missed or misdiagnosed, a patient can lose valuable time to intervene. “The biggest consequence is people continue to get worse. It’s a progressive condition, and the worse off someone is, the harder it is to get them better in terms of a functional status,” Dr. McKhann says. “It’s always easier in the brain to protect function than it is to recover function.”

Even before someone with NPH has severe symptoms, such as inability to walk or great difficulty standing up, the early stages of the disease can pose significant health risks, Dr. Golby points out.

“Before they get that bad, when they’re still trying to walk, they’re at great risk for falls due to poor balance,” she says. “We’ve seen patients with fractured bones, broken teeth, and other traumas from falling. Not being able to walk safely really limits your quality of life.”

What causes it?

While the origins of secondary NPH are relatively clear, idiopathic NPH is, by definition, more mysterious.

“We don’t really know what causes it, nor do we really understand the pathophysiology of it,” Dr. Golby says. There are theories about the mechanisms involved, she adds, but none are well-established.

Although the cause may be too much CSF in the ventricles, research has yet to reveal exactly how that generates the symptoms of NPH, or what exactly causes the accumulation of CSF in the first place. “It’s not really a blockage per se,” Dr. Golby explains. “It’s better to characterize it as an imbalance in the fluid system.”

Idiopathic NPH may also be better characterized as a syndrome than a single disease. “What we probably see in idiopathic NPH is a common endpoint of a number of different common ways to get there,” Dr. McKhann says. “Whatever the absolute micro cause is, when someone becomes symptomatic, the symptoms look the same.”

The mystery of idiopathic NPH may be vexing, but it doesn’t necessarily hinder treatment, Dr. Golby points out. “It’s much better to have a disease that we don’t really understand but have a great (treatment) for it, than something we understand, but can’t do much for it.”

The medical community understands a lot about brain tumors, for example, but is often limited in ways to treat them. NPH, on the other hand, can be surprisingly easy to treat—at least in certain patients.

How is NPH treated?

The primary treatment option for NPH is to surgically implant a shunt, which diverts CSF away from the brain so it can be absorbed. A shunt is not suitable in every case. But for some patients who’ve spent years struggling with NPH, this relatively simple procedure can be life-changing.

“Shunt treatment is pretty mundane from a surgical perspective—it’s a very routine procedure,” Dr. Golby says. “But the results are so nearly miraculous in the right patients that it’s one of the things that I love about my job.”

The surgery may be mundane, but it can still be risky for some people, so there are important tests to conduct before deciding to try a shunt. Most patients come into the hospital for two or three days for a spinal drainage trial, Dr. McKhann says. By draining a little CSF fluid from the brain, doctors can test how much the patient improves under those conditions.

“Just in that brief window, that provides a much better predictor of whether they will subsequently improve with a shunt,” he says. “If you preface it with a spinal drainage trial, then more than 80 percent of patients you treat with a shunt with benefit from the shunt.”

What happens after treatment?

Some of those patients may improve for years or even decades with a shunt, while others may see their benefits fade after just a couple of years. Some patients lose responsivity to the shunt, Dr. McKhann says, but it’s not yet clear why that happens in some patients and not others.

“Not everyone is going to have a home run,” Dr. Golby says. “We have a process about how to decide who should have the surgery. We basically triage patients to have surgery versus not. Sometimes we hit a double, sometimes a triple, and sometimes a home run. We sometimes hit singles, but we usually try to triage the patients who might be borderline out. Because these patients are older, they do have a lot of co-morbidities, and surgery is not without risk.”

If someone suspects they may have NPH, the first step should be finding a clinician who is familiar with the condition, Dr. Golby says. “It’s not a disease as much as a syndrome. It’s kind of a grab bag. That’s why you want to go to someone who treats a lot of this, so they understand the whole spectrum of possibilities.”

In the right patients, though, at least some aspects of NPH can rapidly improve after surgery. “I don’t feel that it’s as much a memory thing—or at least the aspect that we are able to reverse with surgical treatment—but more of a kind of engagement with life,” she adds. “One of the really wonderful things about treating this is when the spouse says, ‘I got my husband back,’ or ‘I got my wife back.'” To learn more about NPH, visit the Hydrocephalus Association.