Some people suffer from a rare condition known as normal pressure hydrocephalus. This condition is characterised by a decline in cognitive ability, changes in thinking, mild dementia, loss of bladder control, and impaired walking and motor skills. While these symptoms resemble those of Alzheimer’s and Parkinson’s diseases, normal pressure hydrocephalus is caused by a buildup of cerebrospinal fluid in the brain leading to normal or slightly elevated intracranial pressure.

So what is normal pressure hydrocephalus? 

This article will address this question and more about normal pressure hydrocephalus, including how to identify its symptoms, understand its effects, and navigate its diagnosis and treatment.

Introduction

Normal pressure hydrocephalus (NPH), also called idiopathic normal pressure hydrocephalus (INPH), is most commonly seen in adults in their 60s and 70s. The estimated incidence of the condition is 0.003% in people under 65 and 0.2% to 2.9% in people aged 65 or older.¹

Hydrocephalus refers to a condition in which there is an abnormal buildup of cerebrospinal fluid (CSF) in regions of the brain. Typically, hydrocephalus is associated with elevated intracranial pressure, which damages the brain tissue resulting in severe symptoms, including headaches, impaired motor abilities, blurred vision, nausea, and others. In NPH, the ventricles of the brain also swell with accumulated fluid; however, this does not cause the expected increase in intracranial pressure. It is likely because the fluid accumulates slowly and gradually, giving the tissues sufficient time to accommodate the swelling ventricles.

While the symptoms of NPH are similar to other forms of hydrocephalus, early diagnosis is important as the disorder tends to worsen over time. Timely diagnosis allows for treating the NPH properly, decreasing the chance of developing severe symptoms, and improving the overall prognosis.

Causes of normal pressure hydrocephalus 

While certain factors have been identified as leading to the development of NPH, the majority of cases occur for unknown reasons. As such, occurrences of NPH have been categorised as primary NPH, which occurs for unknown reasons, and secondary NPH, which may occur as a secondary result of another disorder, damage, or lesion.

Secondary NPH can be caused by a number of factors, most commonly:

• Brain trauma: Injuries to the head can cause brain bleeds that block the flow of CSF²
• Subarachnoid haemorrhages: Severe bleeds on the surface of the brain into the subarachnoid space, which contains the CSF, can disrupt normal fluid dynamics³
• Tumours: The tumours in the brain region may lead to the overproduction of CSF, resulting in its buildup and swelling. Alternatively, tumours can obstruct the flow of CSF
• Infections and inflammation: Infections can cause inflammation, leading to scarring and fibrosis of brain tissue, which blocks the flow of CSF⁴ 

While these factors are present in some people with NPH, the cause remains unknown for the majority of sufferers. Furthermore, the disorder predominantly affects people aged 65 and older. 

Risk factors

You are at a higher risk for NPH if you:

• Are over 65 years old
• Have had a brain or head injury
• Have had a brain infection
• Have undergone brain surgery
• Have a brain tumour

However, NPH can still occur without any of these risk factors. Thus, further research into patients is necessary to better characterise the disorder.

Sign and symptoms

In 1964, Dr. Salomon Hakim identified the main symptoms of NPH, calling them the “classic triad”.⁵ These symptoms include:

• Gait apraxia: Instability and an unusual walking pattern, often resembling a person walking unsteadily on the boat deck, shuffling forward with their feet spread and torso leaning forward⁶
• Urinary incontinence: Loss of control over bladder function
• Cognitive impairment: Similar to that seen in dementia, including memory problems, personality changes, and reduced thinking ability

These symptoms are accompanied by a swelling of the ventricles, which are cavities in the brain filled with CSF. This swelling occurs due to an accumulation of CSF. However, the swelling of the ventricles and increased CSF volume are characteristic of this condition, which is accompanied by little to no increase in intracranial pressure.

Further, it is often observed that the swelling of the ventricles and accumulation of CSF without an increase in pressure might occur without developing all three symptoms.

A study conducted by the Mayo Clinic found that among 41 adults suspected of NPH, all suffered from gait apraxia, 30 showed signs of cognitive impairment, and only 14 had urinary incontinence. Despite NPH being characterised by this triad of symptoms, only 12 patients out of 41 had all three symptoms. 

Diagnosis

In NPH, identifying the disorder early is of utmost importance. As time progresses, the symptoms become more severe, and early diagnosis enables timely treatment. Notably, dementia caused by NPH is one of the few forms of dementia that can be reversed with treatment.⁷

However, diagnosing NPH can be challenging due to its symptoms overlapping with those of other neurological disorders such as Parkinson’s and Alzheimer’s diseases. To confirm NPH, your physician may conduct the following tests:

Physical and neurological assessment

Your neurologist may assess your cognition, motor ability, and senses, including sight, hearing, and reflexes. Due to the overlap of symptoms with other neurological and neurodegenerative disorders, a high degree of experience and skill is necessary to properly distinguish the disorder based on these clinical aspects.

Furthermore, as with all disorders, your doctor will assess your medical history to identify any risk factors as well as any previous instances of brain trauma or other conditions that may have contributed to the development of NPH.

Brain imaging

Brain imaging methods like Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scans, help your doctor to differentiate between neurodegenerative diseases and NPH. In NPH, the ventricles are enlarged and swollen without shrinkage of the brain tissue. In contrast, in disorders like Alzheimer’s disease, shrinkage of brain tissue is the major sign, while the ventricles are not enlarged.

Lab test

Testing the CSF can help rule out other potential causes, such as meningitis. CSF is obtained through a lumbar puncture procedure.

Shunt responsiveness

By inserting a shunt and diverting the flow of CSF, shunt pressure can be determined. Further, any improvement of symptoms following shunt insertion could confirm the diagnosis of NPH.

Lack of response to levodopa

Levodopa, a dopamine precursor, is prescribed to treat gait apraxia in Parkinson's patients with dopamine deficiency. However, since dopamine deficiency is not the cause of symptoms in NPH, patients with NPH would not respond to levodopa treatment.

Treatment options

Shunt insertion

NPH is most commonly treated with surgical insertion of a shunt, aiming to redirect excess CSF from the brain into the abdomen for reabsorption and clearance. To test the effectiveness of this method, doctors may initially extract a high volume of CSF. If improvements in motor ability, cognition, reasoning, etc., are observed over the following hour, shunt insertion may be considered. However, complications may arise from shunts, including infections, shunt malfunction, or valve displacement. If excessive CSF is drained via the shunt, it could result in reduced intracranial pressure.

Endoscopic third ventriculostomy 

It may be proposed as an alternative to shunt insertion in patients diagnosed with aqueductal stenosis. In these individuals, the normal clearance of excess CSF through the shunt is obstructed. Therefore, a neurosurgeon may use an endoscope inserted into the brain to create a different route for draining CSF.

NPH caused by a secondary factor is also treatable, but only to the extent that the underlying cause can be treated. For example, NPH resulting from low-grade brain trauma is more manageable than NPH caused by a tumour.

Prognosis

NPH can be successfully treated and reversed with early diagnosis and proper treatment during its developmental stages. The disorder progresses slowly and gradually, with CSF accumulation over 3-6 months. The surrounding brain tissue adapts to this swelling, which explains the slight or no increase in intracranial pressure. However, as NPH progresses, the symptoms worsen. Thus, early treatment is crucial, otherwise, no improvement will be observed, potentially resulting in severe or permanent brain damage.

When shunting is successful, the diversion and removal of excess CSF allow the brain swelling to reduce rapidly and relax the stressed tissues. Patients usually experience signs of improvement within a few hours to a few days. However, recovery from the surgery itself may take weeks to months. Shunting is usually an effective treatment for primary NPH, while the prognosis for secondary NPH depends on the primary cause. In addition, outcomes are influenced by other factors, including:

• Onset of cognitive impairment: Certain NPH cases where cognitive decline appears later, or after the other triad symptoms, are more likely to be reversible
• Comorbidities: Individuals affected by other neurological disorders like Alzheimer’s disease are more resistant to treatment
• Early diagnosis: Late detection of the disorder is often the most common cause of complications in NPH

Therefore, the prognosis of NPH can be significantly improved by promptly responding to symptoms and diagnosing the condition early. This should be followed by taking quick action while the disorder is still in its early stages.

Summary

Normal Pressure Hydrocephalus (NPH) is a neurological disorder characterised by the enlargement of the brain's ventricles due to the gradual accumulation of CSF. NPH progresses slowly, allowing the surrounding brain tissue to adapt, resulting in minimal or no increase in intracranial pressure. NPH presents with a classic triad of symptoms including gait instability, urinary incontinence, and cognitive decline, although not all patients suffer from all three. While NPH can be secondary to brain trauma, tumour, or bleeding, the majority of cases have unknown causes. Treatment often includes surgical insertion of a shunt to redirect excess CSF from the brain into the abdomen for removal. Early diagnosis is crucial, as it greatly improves the prognosis; untreated NPH can lead to severe and permanent brain damage. Therefore, early detection is of paramount importance in managing this condition.