Diagnosis
"The .. major question is whether an operation will help.."
Information
With over 30 years of investigation into Normal Pressure Hydrocephalus, several things have become clear. Firstly, although the classical problems are walking difficulty, incontinence and dementia, there is considerable variation. People sometimes only have one or two of these symptoms. Therefore physicians should be suspicious about NPH even if you do not fit the classical description. Secondly, within the syndrome of NPH there are very probably several different disease states. We know this because the treatment of choice (see under Treatment) does not work for everyone, and predicting who will or won't benefit from being treated is one of the greatest challenges your physicians face.
There is no simple diagnostic test to determine who has NPH, however several features make the diagnosis more likely. A combination of the cardinal symptoms described above should be present, an MRI or CT scan will likely show excess fluid in the head, and the CSF pressure must be normal. If these criteria are satisifed then a diagnosis of NPH is justified. An assessment of the CSF "fluid dynamics" (see under Evaluation) can also yield information which supports the diagnosis. The diagnosis of NPH has important implications and therefore consultation with an expert in the field is highly advisable (see VCUABC-NPH Service).
The next major question once you have been diagnosed with NPH, is whether or not an operation will help. There is only one true way to determine this at present, and it requires skill and experience from the physicians involved. The only treatment which has any success is to have a little valve implanted which connects your CSF to your abdominal cavity. This allows any excess CSF which builds up to drain away. This valve can quite safely stay with you for many years. In order to test whether you would benefit from a valve, you need to come into hopsital for a few days, and have a test amount of the CSF drained away (called External Lumbar drainage, see under Evaluation) without permanently fitting a valve. If this procedure improves your symptoms, then you are likely to be one of the people who can benefit from the simple operation.
A logical question is "why don't you give everyone the operation then?". Well, simply put, any operation has its risks, and as a surgeon you NEVER want to operate unless it will benefit the patient. There are some very small risks of having the valve placed, and these include infection, brain hemorrhages, stroke, and worsening of symptoms.
Infection, bleeds and stroke happen only rarely, however sometimes the symptoms of NPH do not improve or even worsen with the valve. Most importantly, the external lumbar drainage procedure can help identify patients most likely to benefit from a shunt.
A second type of test is available, which can also yield some very important information. The test is very simple to perform, it involves the injection of a small amount of fluid into the back, with a few minutes of pressure measurement afterwards (CSF pressure dynamics). The results of the test however are very difficult to interpret, and this can only be effectively done by someone with considerable experience and knowledge about the CSF. The test was devised and characterised by Anthony Marmarou Ph.D, a member of the MCV-NPH Service, and he is considered a world authority on its application and interpretation.
The results of CSF pressure testing can provide two pieces of information. Firstly CSF absoroption / outflow pressure can be directly measured - this information assists with the diagnosis of NPH. However it is important to state that in someone who has obvious symptoms a negative test would not alter the diagnosis. The second important piece of information the test yields is an idea of what sort of setting a valve would need if it were to be fitted. There are many types of valves, and some valves have variable settings. Fitting of the correct valve at the correct setting is extremely important in the success of the treatment, and also helps to avoid the need for further surgery. There are no standard criteria for determining the correct valve from CSF pressure dynamics, and again the success or failure solely relies on the experience of the person interpreting the test.
In summary, the most important features in diagnosing NPH are clinical symptoms. There are other tests available which can be performed, and these are important to determine the likely success of treatment. Although these other tests are easy to perfom, they can be difficult to interpret. For this reason you should ensure the person recommending treatment to you has substantial experience in treating people with NPH.