What is Normal Pressure Hydrocephalus?
Idiopathic normal pressure hydrocephalus (iNPH), listed as G91.2 by the International Classification of Diseases (abbreviated as ICD-10), is a condition that can potentially reverse dementia. It is the most common form of a condition called hydrocephalus in adults, where there is an abnormal build-up of fluid in the brain.
iNPH usually affects older people and is known for causing a steady decline in walking ability, cognitive functions like memory, and an urgent or uncontrollable need to urinate, sometimes accompanied by accidental leakage (otherwise known as the Hakim-Adams triad). This condition’s name, Hakim-Adams triad, was coined after the Colombian neurosurgeon, Salomon Hakim, and R D Adams who first described it in 1965.)
For a person to be suspected of having iNPH, they usually present with difficulty walking and at least one other symptom. Although these symptoms can give a hint towards the diagnosis of iNPH, further assessment like brain imaging and checking of the cerebrospinal fluid (which protects the brain and spinal cord) is required to confirm it.
Interestingly, some experts have raised viewpoints that the term iNPH may not be entirely accurate since not all people with the condition actually have normal brain pressure. As such, a new term “idiopathic adult hydrocephalus syndrome” (iAHS) has been proposed as a replacement.
What Causes Normal Pressure Hydrocephalus?
Normal pressure hydrocephalus, or NPH, is a condition where there is too much fluid in the brain, but the pressure remains normal. There are two main types of NPH:
1. Idiopathic NPH: This is when the cause of the condition is unknown.
2. Symptomatic NPH: This happens when certain risk factors are present, such as a previous brain infection, brain bleeding, a traumatic brain injury, or exposure to radiation.
Both idiopathic and symptomatic NPH share common traits. They are both types of hydrocephalus where the fluid can still flow within the brain, and they both have generally the same outcomes. The main difference between them is that symptomatic NPH can occur at any age, while idiopathic NPH mainly occurs in older adults.
To develop NPH, the pressure inside the skull needs to be slightly higher than normal for at least a short period.
Risk Factors and Frequency for Normal Pressure Hydrocephalus
Idiopathic Normal Pressure Hydrocephalus (iNPH) is a condition that tends to affect older individuals, particularly those over the age of 70. An extensive study conducted in Western Sweden provided significant insight into this disorder. Findings of the study indicate that this condition is prevalent in around 0.2% of people aged 70 to 79 and 5.9% of those aged 80 and above. Importantly, the average age at which iNPH tends to manifest is around 70 and it affects both men and women equally.
iNPH is also thought to be responsible for about 6% of all dementia cases. It is estimated to occur at a rate of 0.2 to 5.5 per 100,000 person-years. For individuals under 65, the prevalence of iNPH is at a lower 0.003%. For those aged 65 and older, the figures range from 0.2% to 2.9%.
- iNPH often affects individuals over the age of 70.
- An extensive research in Western Sweden found that 0.2% of people aged 70-79 and 5.9% of those aged 80 and older, match the guideline criteria for probable iNPH.
- The average age of onset is approximately 70 years.
- Men and women are affected equally by iNPH.
- iNPH contributes to roughly 6% of all dementia cases.
- The estimated occurrence rate is between 0.2 to 5.5 per 100,000 person-years.
- For people under 65, the prevalence of iNPH is 0.003%.
- For those aged 65 and older, the prevalence ranges from 0.2% to 2.9%.
Signs and Symptoms of Normal Pressure Hydrocephalus
NPH, or Normal Pressure Hydrocephalus, is a condition that sometimes affects people over 40 years old. The main symptoms of NPH are problems with walking, thinking and urination. These are also known as the Hakim triad. Not everyone with NPH shows all three symptoms at once, but between 50% and 75% of patients do. 80% to 95% experience issues with walking and cognitive function, and 50% to 75% have issues with bladder control. These symptoms develop gradually and don’t have a clear cause.
The first symptom that usually appears is difficulty walking, described as a shuffle-like gait. As the disease progresses, the walk becomes slower, wider, and the person can find it difficult to lift their feet, as if they’re glued to the floor. Other common features include:
- Pivoting foot posture
- Difficulty clearing foot off the ground
- Trouble turning around
- Difficulty starting to walk or freezing while walking
There can be balance issues, particularly when the eyes are closed, although they may still need a wide base for standing even with their eyes open. Their upper body may be slightly bent over, and they can experience slow movement in their arms and legs. However, some patients may also have a tremor in their limbs, which won’t improve with treatment.
Bladder issues usually stem from overactive bladder muscles, leading to frequent and urgent urination or even incontinence.
The dementia linked with NPH can lead to inertia, forgetfulness, and trouble with multitasking. These cognitive issues are due to impaired function in the frontal and subcortical areas of the brain. It is important to evaluate these cognitive deficits with specific tests, such as the grooved pegboard test, the Stroop test, the digit span test, the trail-making A/B test, and the Rey auditory-verbal learning test.
Testing for Normal Pressure Hydrocephalus
While a CT scan, which uses X-rays to create detailed pictures of the inside of your body, can show us some changes in the brain, it’s not enough on its own to diagnose a condition called normal pressure hydrocephalus, or NPH.
In contrast, an MRI, which uses a large magnet and radio waves to look inside your body, is the best method we have for identifying the structural changes in the brain that occur with NPH. A couple of additional procedures, known as CSF flow studies and magnetic resonance spectroscopy, can help support this diagnosis.
Several signs that we see on an MRI brain could suggest NPH:
The Evans index, which measures the space of a specific area in the brain, can signify brain swelling if it’s greater than or equal to 0.3.
The Callosal angle, another measurement in the brain, should range from 40 to 90 degrees in patients with NPH.
A disproportionate widening of some areas of the brain compared to others.
A narrowing of spaces surrounding the outer brain surface and narrow internal passages.
Dilated – or widened – Sylvian fissures, which are spaces in the brain.
Certain types of widened spaces in the brain.
A bulging of the roof of a particular part of the brain.
In a CSF flow study, a flow rate higher than 24.5 mL/min is 95% typical of NPH.
Several factors indicate a good outcome following a surgical procedure known as shunting:
The volume of CSF moving through a particular part of the brain greater than 42 microliters.
A lack of white matter lesions, or damage, on MRI.
At least half of the time spent monitoring intracranial pressure showing a specific pattern called B-waves.
Resistance to CSF outflow over 18 mmHg.
There are also factors that suggest shunt surgery may not have a favorable outcome:
Severe dementia.
Dementia being a first symptom.
MRI abnormalities, brain shrinkage, and multiple white matter lesions.
Misdiagnosis and delayed detection.
There are also a few non-specific signs of NPH we can see in a procedure called nuclear medicine studies. These include:
An unusual ‘heart-shaped’ appearance of a part of the brain called the lateral ventricles.
Slowed removal of a tracer due to impaired absorption.
Lack of tracer on the top side of the lateral ventricles.
Backflow of CSF into lateral ventricles.
FDG-PET, another imaging method, is a promising technique for diagnosing NPH and identifying any additional degenerative disease.
Certain invasive diagnostic tests can improve the accuracy of diagnosis and prognosis to above 80%. One of these tests is the spinal tap test, where experts remove 30 to 70 mL of CSF, the fluid that surrounds the brain and spinal cord, by getting a sample from your lower spine. Continuous withdrawal of this fluid from the lumbar spine can also be very beneficial. These tests are considered positive if the patient shows at least a 20% improvement in walking speed and steps or a 10% improvement in psychometric testing, which measures your ability to concentrate, reason, and solve problems. These tests should be conducted by experienced health professionals before and after fluid drainage.
Treatment Options for Normal Pressure Hydrocephalus
Several scientific studies have been conducted relating to a condition called Idiopathic Normal Pressure Hydrocephalus (iNPH), a type of brain disorder where cerebrospinal fluid builds up in the brain’s ventricles, or cavities, causing pressure.
In the SINPHONI-1 study, certain features observed in brain scans indicated a high success rate for ventriculoperitoneal shunt surgery, a procedure where a tube is inserted into the brain to drain the excess fluid.
The subsequent study, SINPHONI-2, found that another type of surgery, lumboperitoneal shunt surgery (LPS), could also be beneficial for iNPH patients. However, more comprehensive research is needed before LPS can be considered a first-line treatment.
Other studies focused on particular aspects of shunt surgery. The SVASONA study supported the use of a particular type of valve to reduce over-drainage complications, while other research found no significant difference in outcomes if the valve pressure was gradually reduced or fixed at a certain level. The Dutch Evaluation Programme Strata Shunt trial provided evidence that using a programmable shunt with a high opening pressure could yield better results.
Alongside these studies, an ongoing trial is assessing the complication rates of programmable compared to fixed anti-siphon devices, which are used to prevent over-drainage in shunt operations.
In addition to these surgeries, there is another treatment method known as endoscopic third ventriculostomy (ETV). It is a procedure used when there’s a specific type of blockage to fluid flow in the brain. Unfortunately, a study comparing ETV with shunt surgery did not provide clear results, implying that the effectiveness of these two methods still needs further investigation.
Aside from the surgical options, non-surgical treatments include taking carbonic anhydrase inhibitor drugs or having regular lumbar punctures to drain the excess fluid. Such treatments might be appropriate for patients who cannot undergo surgery.
When deciding on the best approach for a patient with iNPH, medical professionals consider several factors, such as how the patient responds to a large volume lumbar tap (i.e., removal of some cerebrospinal fluid), and the results from brain scans and other tests.
Overall, the preferred treatment for iNPH is usually a ventriculoperitoneal shunt operation, where a tube with an adjustable valve is implanted to drain the excess fluid. Nevertheless, the right choice can vary based on the individual’s condition.
What else can Normal Pressure Hydrocephalus be?
There are two main types of dementia: cortical and subcortical. Each of these types can be broken down into specific diseases:
Cortical Dementias include:
- Alzheimer’s disease
- Frontotemporal dementia
Subcortical Dementias include:
- Lewy-body dementia
- Parkinson’s disease and vascular parkinsonism
- Progressive supranuclear palsy
- Corticobasal degeneration
- AIDS dementia complex
- Age-related depression
- Mixed dementias
- Vascular dementia
What to expect with Normal Pressure Hydrocephalus
Before and after a shunt surgery, doctors use several trusted tools to measure the patient’s progress. These include the NPH Japanese Scale, the Berg Balance Scale, the Dynamic Gait Index, the Functional Independence Measure, the Mini-Mental Status Examination, and the Timed Up and Go test. These tools help the doctors understand how the patient is responding to the surgery.
Cytokines, certain types of proteins like CSF IL-10 and IL-33, may be helpful in diagnosing and monitoring patients with NPH (Normal Pressure Hydrocephalus). This is a condition where fluid builds up in the brain, which these proteins can help identify and track.
Possible Complications When Diagnosed with Normal Pressure Hydrocephalus
Patients with iNPH, or Idiopathic normal pressure hydrocephalus, are often found to also have high blood pressure and type 2 diabetes. The condition of type 2 diabetes also increases their risk of death. In a Finnish study, it was found that diseases like schizophrenia are three times more common in people with iNPH compared to the elderly general population.
Surgery-related complications can also occur in patients with iNPH. These complications can either be directly related to the shunt put in place to treat hydrocephalus, including its failure (occurs in 3% of cases), over-drainage or under-drainage, subdural hematoma (3-4%) and infection (less than 1%). There are also complications that are not directly related to the shunt like seizures, and hemorrhage in the brain, which occur in less than 5% of the patients.
- Increased rates of hypertension and type 2 diabetes
- Mortality from diabetes
- Schizophrenia three times higher than in the general elderly population
- Shunt-related complications such as failure, over/under-drainage, subdural hematoma and infection
- Non-shunt related surgical complications like seizures and inner brain hemorrhage
Preventing Normal Pressure Hydrocephalus
The doctor should let the patient know about the likelihood of their symptoms getting better after undergoing shunt surgery. Here’s a breakdown of the potential improvements:
Walking difficulties – There’s an 85% chance of improvement
Bladder problems – There’s an 80% chance of improvement if the condition is caught early. However, if the condition is in the late stages, the chance of improvement drops to between 50% and 60%
Problems with mental functions like memory and concentration (also known as cognitive deficits) – There’s an 80% chance of improvement.
