Normal Pressure Hydrocephalus (NPH)

Normal pressure hydrocephalus or NPH is a brain disorder. The term hydrocephalus means extra fluid in brain cavities. All human brains have a central cavity called ventricles, filled with cerebrospinal fluid or CSF. Ventricles are divided into different parts and are connected to each other. The big ones in the cerebral cortex are called lateral ventricles. They drain into a single cavity called 3^rd ventricle in the middle of the brain, which is connected to the 4^th ventricle in the brainstem.

In young age and in a normal brain these cavities look relatively small. With aging, as brain degenerates or shrinks, these cavities may look bigger. But sometimes they look abnormally big, out of proportion to the amount of brain shrinkage, which may be due to NPH. This contrasts with enlargement of ventricles due to a blockage within the ventricles, when ventricles get large due to high pressure, e.g., by a tumor.

 

What is the difference between ventriculomegaly and NPH?

The ventriculomegaly means, enlarged ventricles, which may or may not be due to NPH. Neurologists used this term to avoid confusion and to suggest that though ventricles may be enlarged, it is not NPH.

 

What are the symptoms of NPH?

NPH causes three types of symptoms or problems:

1. Gait disorder: Patients walk in a wide-based gait with difficulty in lifting their feet. It is like their feet are magnetically attached to the ground, so is the name given to it, magnetic gait. Patients may also look like having some symptoms of Parkinson disease.
2. Loss of bladder control: Patients develop urgency and frequency of urination. In untreated cases and in later stages, it may lead to incontinence.
3. Dementia: It may also cause mild to moderate dementia.

It is important to know that NPH is not the only reason for these symptoms, separately or together. It is not uncommon to see patients with this set of symptoms with alternate explanation, even when the ventricles seem larger than normal. Clinical experience and acumen are needed to tease things out and to figure out exact diagnosis and right course of action.

 

What causes NPH?

NPH seems to be a problem with absorption of spinal fluid or its flow, resulting in too much fluid in the ventricles, which increases their size. Large amount of fluid in the ventricles put pressure on the surrounding brain, distorting the white matter connections and blood vessels, affecting its function, and causing degeneration or loss of brain cells. Rarely, there is a congenital narrowing of a CSF pathway within the ventricles, which may cause NPH later in life. Some cases are triggered by meningitis or a type of brain bleed. In most cases, no such cause is found.

 

Who is at risk for NPH?

Aging is the main risk factor. Rarely, a relatively large head may suggest this diagnosis, in which case one may find a relatively narrow ventricular aqueduct. NPH typically is middle to old-age disease.

 

Is NPH a genetic disorder?

There probably is a genetic component and at least one gene has been identified for NPH. Genetic variations may affect anatomical microstructures within the ventricles affecting its secretion or absorption.

 

How is NPH diagnosed?

Diagnosis of NPH is not a straight-forward process. With its typical symptoms, a brain scan is ordered. Both CT and MRI scan may help to make the diagnosis, but MRI is better to provide further detail about any other pathology that may also be present. If CT or MRI of brain reveals enlarged brain ventricles or cavities, out of proportion to the amount of brain shrinkage, the diagnosis can be made. At the same time, one must be careful to not overemphasize this finding or not ignore other pathologies that may cause similar symptoms. Once the diagnosis is made, further testing is required to figure out if patient may benefit from its treatment or not.

 

What is large volume tap?

Once the clinical diagnosis of NPH is made, a lumbar puncture is performed and a relatively large volume of CSF, 15-30cc, is removed, which in medical slang is called “large volume tap.” In a patient with NPH, and especially who might benefit from its treatment, significant improvement of symptoms is noted for a few hours to a day or two. If that happens, patient is referred to a neurosurgeon for a shunting procedure.

 

What additional methods can be utilized to assess the likelihood of success for a shunting procedure?

An expert review of brain MRI and some specialized MRI imaging techniques are helpful. There are some findings and calculations made on MRI scan, which can help to determine if the shunting procedure is going to be successful or not. This kind of expertise, available in specialized places, is not critical to diagnose and manage a patient with NPH.

 

What happens if NPH is not treated?

Without treatment, NPH usually progresses causing more problems, and may ultimately result in inability to walk, bladder incontinence, and significant dementia. On the other hand, with treatment all these symptoms may significantly improve, especially walking and bladder control.

 

What treatment options are there for NPH?

There is no medicine to treat NPH. The available treatment at this time is surgical by inserting a thin tube, a shunt, in brain cavities with its other end in the patient’s belly. The shunt continuously drains the spinal fluid and patient feels better.

 

Are there different types of shunts?

This is a neurosurgical question and not fully answered here. Newer shunts have a valve to control CSF flow, to avoid excessive drainage that may affect some patients, which by itself create some problems. Older shunts did not have the valve. Also, newer shunts are compatible with MRI.

 

What may be the complications of NPH shunting procedure?

Other than risks associated with any other surgery, it may cause intracranial bleeding. Its risk is about 5-10%. The shunt may get blocked or infected, and sometimes may have to be replaced. In some cases, over drainage may cause positional headaches, which can be fixed by adjusting the shunt valve. My long experience of dealing with patients with NPH, especially the ones treated with shunting, is that it is a reasonably safe and effective treatment.

 

Are there different types of NPH?

It is generally divided in 3 types:

1. Idiopathic: With unknown cause.
2. Delayed-onset congenital: From congenital cause.
3. Secondary, after meningitis or sub-arachnoid bleed.

 

How long does the shunting procedure remain effective?  

It remains effective if there was no technical malfunction and if NPH was the only problem. As most patients are elderly and are commonly affected by other brain problems. A patient with associated Alzheimer or vascular disease of brain, Parkinson, arthritis, neuropathy or neck problems, may not improve as much or may deteriorate despite shunting.

 

Where can I get more information about Normal Pressure Hydrocephalus (NPH)?

American Academy of Neurology

American Neurosurgery Association