Normal Pressure Hydrocephalus (NPH)
What is NPH?
Normal pressure hydrocephalus (NPH) occurs when cavities in the brain become filled with cerebrospinal fluid because the normal flow is blocked. This puts pressure on the brain as the cavities, called ventricles, enlarge. NPH is most common in elderly people.
How is NPH diagnosed?
NPH diagnosis is difficult. There is no gold standard in determining if the syndrome is a cause for the symptoms other than response to shunting (see below). If someone does not respond to shunting, it is unclear whether this is because they never had the syndrome in the first place, the shunt was placed too late or there is a malfunction of the shunt system.
Making an NPH diagnosis involves consideration and treatment of other potential causes of the symptoms. Those who do best with shunting have the following characteristics:
- Presence of the complete clinical triad of gait disturbance, urinary incontinence and dementia
- Gait disturbance preceding the other features
- Short duration of symptoms
However, it is still difficult to know whether shunting will help. Other conditions can cause the triad symptoms. Shunting may still help if these other conditions are present, but outcomes may not be as good without treating those conditions first. For example, people with Alzheimer's disease can develop NPH and improve with shunting.
In addition to a complete history and physical, there are supplemental tests which seem to be helpful in predicting who will benefit from surgery. Imaging characteristics on MRI or CT can be helpful. Before committing someone to have a permanent shunt, temporary drainage of cerebrospinal fluid (CSF) can be performed, either with a single high volume spinal tap or with more prolonged CSF drainage over two or three days (prolonged lumbar drainage). Collecting CSF can also be helpful in diagnosing other disease processes which might be causing the symptoms. We perform comprehensive cognitive and gait testing before and after procedures to obtain more objective data and to follow our patients over time.
How is NPH treated?
There are currently no drug or therapy treatments that seem to be effective means of NPH treatment. For now, NPH is a surgical disease.
- Shunting: A drainage tube is placed into the ventricles of the brain and connected to a valve. The valve is then connected to more tubing that drains into another part of the body, most commonly the abdominal cavity or the bloodstream. The procedure takes 60 to 90 minutes. Programmable valves on the shunt allow the drainage to be adjusted slowly to avoid bleeding in the brain. The adjustments are made after surgery in the office using a magnet.
- Endoscopic third ventriculostomy (ETV): In a small percentage of patients with NPH (less than 10%), there is a blockage of the normal pathway through which CSF flows. In such patients, an alternative pathway can be created through an endoscope. This procedure takes 15 to 60 minutes.
What is the likelihood of successful NPH treatment?
In general, walking improves, although thinking does not to the same extent. Previous studies estimate that between 45 and 80% of people gain significant improvement from surgery. Risks of surgery are about 15%. In our clinic, we evaluate many factors and try and estimate the risks and benefits of surgery for each of our patients, to help them and their families make an informed decision about whether or not to proceed.