What is Normal Pressure Hydrocephalus?
Normal pressure hydrocephalus (NPH) is a neurological disorder that causes dementia. It is characterized by walking abnormalities, cognitive dysfunction (i.e., dementia), and urinary incontinence.
NPH is relatively rare. According to the Hydrocephalus Association, an estimated 375,000 Americans suffer from NPH (Hydro Assoc). However, it is difficult to diagnose NPH because its symptoms resemble other neurological diseases. Doctors must consider your symptoms and run numerous tests to make the diagnosis. For this reason, many sufferers go undiagnosed.
There are two forms of the disorder. The first is idiopathic (iNPH). The cause of iNPH is unknown. The second is caused by secondary disorders or symptoms. The risk of NPH increases after age sixty.
The only effective treatment is ventricular shunting. In cases of severe dementia, the risks of surgery do not outweigh the benefits. Most people show significant improvement after shunt placement. In fact, this condition is one of only a few causes of dementia that are potentially reversible.
Risk Factors for NPH
The risk of developing NPH increases after the age of 60. As you grow older, you may have more risk factors.
Risk factors of NPH include:
- cerebrovascular disease
- vascular disorders
- Alzheimer’s disease
Causes of NPH
The cause of idiopathic NPH is unknown. Doctors believe it is related to:
- weakening of veins that impairs the flow of cerebral spinal fluid (CSF) to the brain
- swelling in the brain that stops blood flow
- swelling in the brain that stops metabolism of vital pathways
The second type of NPH is known as secondary or symptomatic form.
Conditions that may cause this type include:
- mass lesions
- traumatic brain injury (TBI)
Symptoms of NPH
The three symptoms that characterize NPH are walking abnormalities, cognitive dysfunction (dementia), and urinary incontinence. Minor symptoms may indicate the onset of NPH. Over time these symptoms will become more noticeable.
Minor symptoms in early NPH include:
- difficulty in walking slopes or stairs
- difficulty in rising/sitting on a chair
Examples of walking abnormalities include:
- disequilibrium (feeling unsteady) when walking
- slowness from short steps
- gait apraxia (walking with shuffling, halting steps)
Bladder symptoms caused by NPH include:
- urinary frequency
- urinary urgency
- complete incontinence
Cognitive dysfunction (dementia) symptoms include:
- psychomotor slowing
- impaired attention
- executive dysfunction
- visuospatial dysfunction
Diagnosis of NPH
It can be hard to diagnose NPH because it appears similar to other neurodegenerative diseases. Multiple tests must be used to gather sufficient evidence for a diagnosis of NPH.
Neurodegenerative diseases with symptoms similar to NPH:
- Alzheimer’s disease (AD)
- multi-infarct dementia (MID)
- lewy body dementia
- frontotemporal dementia
To help rule out other neurological conditions, your doctor may test your mental function with neuropsychological tests.
Types of neuropsychological tests include:
- MMSE (mini-mental state examination): test for cognitive function
- digit spat spatial span: test of attention
- word fluency: test of executive function
- frontal assessment battery: test of executive function
Imaging tests of the brain are helpful. However, they are insufficient for a diagnosis.
Examples of these include:
- computer tomography (CT)
- positron emission tomography (PET)
- magnetic resonance imaging (MRI)
Invasive Diagnostic Tests
Invasive diagnostic tests are another option. These include:
- Cerebrospinal fluid (CSF) removal: lumbar spinal catheter is implanted to drain CSF over a 72-hour period for testing
- spinal tap test: removes CSF for testing
- continuous spinal drainage: catheter is implanted to drain CSF at time intervals over a two- to seven-day period
Treatment of NPH: Ventricular Shunting
The only successful treatment for NPH is ventricular shunting. Ventricular shunts are surgically implanted to drain excess cerebrospinal fluid (CSF).
Three types of shunts are used:
- ventriculoatrial (used rarely because of tendency to cause long-term complications)
After the shunt is surgically implanted, it will have valves to control the amount of CSF drainage. The options for valves include:
- adjustable-shunt valves: the valve pressure can be adjusted without another operation
- gravity-controlled valves: valve pressure is determined by the position of the body and adjusts to avoid over-drainage (recommended for mobile patients)
All surgery carries the risk of complications. Shunt surgery has serious risks that include:
- shunt malfunction
- subdural hemorrhage
Long-Term Outlook for NPH
An individual’s outlook will vary according to his or her age, previous health problems, and surgery. Recovery becomes more difficult as age increases.
Surgery is not an option for every patient with NPH. Those with severe dementia are discouraged as the risks of surgery outweigh the benefits. Surgery itself carries over a 30 percent chance of complications in the first year.
A healthy individual who received an early diagnosis has the best outlook. People who are able to have the surgery without complications may see up to a 70 percent improvement in function.