Normal Pressure Hydrocephalus (NPH)
By Dr. Virginia Cummings

Question: I recently saw a special on 60 Minutes about Normal Pressure Hydrocephalus (NPH). I am concerned that someone I know might have NPH, and not dementia or Alzheimer’s disease. How can we rule this out as a diagnosis?

Answer: This is a very important topic—the segment on 60 Minutes may have been a little misleading for some people. Let’s begin by defining dementia. Dementia is a progressive decline in cognitive functioning. Many people associate dementia with memory loss, but there are many other cognitive functions that can be affected, such as language, calculation, insight, judgment, constructional ability and spatial relations. Dementia is not a diagnosis, but a description of what is happening to the brain’s functioning.

Dementia has many possible causes. Alzheimer’s Disease is the most common cause, but dementia and Alzheimer’s disease are not synonymous. There are numerous other conditions that may result in dementia, including Huntington’s disease, Lewy body disease, Parkinson’s disease, alcoholism, head trauma, strokes and Pick’s disease.

It is important to remember that dementia occurs as the result of a disease process, because some diseases or conditions that cause dementia are curable. Unfortunately, Alzheimer’s disease is not currently curable, but we do have treatments that delay its progression. Having the correct diagnosis for dementia is vital to ensure that reversible, curable causes are not missed. NPH is one of the potentially curable causes of dementia and it is important that health care professionals rule out this diagnosis when treating a patient with dementia. NPH is most likely to be curable when diagnosed and treated early (it is important not to ignore the signs of dementia, because all types of dementia respond best to treatments when diagnosed early).

NPH is a condition in which the fluid that surrounds the brain and the spinal cord, called cerebrospinal fluid (CFS), does not drain properly. The fluid is made and stored in hollow pockets in the brain called ventricles. If the CSF does not drain out of the ventricles, it will build up, enlarging the ventricles and pushing on the surrounding brain tissue. If the fluid is not drained, damage occurs to this sensitive tissue, which, over time, can become permanent. That is why it is so important to diagnose and treat this early.

The tissue around the ventricles contains white matter, which is the type of brain tissue responsible for relaying information. It is damage to this white matter that causes the characteristic triad of symptoms seen in NPH: problems with gait (the ability to walk), incontinence (involuntary loss of urine) and dementia. Because the white matter can not relay information from the brain to the legs as quickly, the gait with NPH is slowed and shuffling. The person may look “stuck to the ground” and have trouble getting started. The balance and turning ability is also impaired.

The incontinence occurs because brain signals fail to reach the bladder, which then becomes unstable and irritable, prone to more frequent contractions. The signal from the bladder that a contraction is about to occur may not reach the brain, and urine is expelled.

The dementia seen in NPH usually arises after the gait and incontinence problems occur, and is mild at first, progressing slowly. As expected, the cognitive functions that become impaired have to do with the information processing and retrieval. The person may be excessively slow to recall data, have poor attention, speak slowly or be unable to solve problems. Because dementia often occurs later in the disease process, damage to the white matter may be permanent at that point and these symptoms may not respond as well to treatment of NPH.

NPH is diagnosed based on the presence of the clinical triad, as well as the presence of enlarged ventricles on a CT scan or MRI. Unfortunately, the scans can sometimes be misleading. In many other dementias, the brain shrinks, making extra space in the ventricles, which then fill up with CSF. This excess CSF is not putting pressure on the brain tissue.
The enlarged ventricles of NPH have a different appearance, because the brain has not shrunk. An experienced radiologist can usually tell the difference between “too much fluid” and “not enough brain” when looking at a scan with enlarged ventricles. An experienced physician will take both the scan and the clinical history into account when making the diagnosis. If the triad of symptoms is not present, enlarged ventricles are not likely to be caused by NPH.

The treatment of NPH involves placing a shunt, a hollow tube, into one of the ventricles of the brain. The tube then tunnels under the skin down to the abdomen, where it drains CSF into the abdominal cavity. This a serious surgical procedure, and carries a high risk of infection, bleeding and stroke. It should only be done in patients who have been definitively diagnosed with NPH and who have responded to a trial of removal of some CSF via a spinal tap. NPH is very rare, accounting for 1 case per 25,000 cases of dementia. Only about 40% of these patients will be helped by a shunt. Overall, less than 1% of patients with dementia will turn out to have curable NPH. Unfortunately, the 60 Minutes special may have raised the hopes of many patients and their families who do not have NPH. However, given the poor prognosis of other types of dementia, it is important for all patients with cognitive problems to have a thorough evaluation, including an MRI or CT scan, to avoid any missed diagnosis.