The diagnosis of NPH can at times be quite difficult, and as with most conditions in medicine which have an ill-defined pathology, significant diagnostic grey areas exist. The principal reason for intervention in NPH is the patients symptoms, and these form one of the strongest guides for diagnosis. The classical triad of symptoms is a sensitive marker for NPH, however there are many cases in which only one symptom may be present or a different symptom complex appears.

As described in "Background", the finding of dilated ventricles on a CT or MRI scan is also non-specific, and can be seen in several neurodegenerative conditions. Consequently considerable effort has been expended over the years in trying to find a more objective method for diagnosis. Proposals have included assessment of CSF pressure dynamics using either bolus or continuous lumbar infusion with pressure measurement and CSF flow studies most recently performed non-invasively with MRI.

In recent times, the emphasis has moved away from being able to accurately diagnose NPH, and rather focus on identifying patients who will benefit from receiving a CSF shunt. This move occurred because it became clear that only a proportion of patients with classical NPH would benefit from a shunt, and at the same time a number of patients who had far from typical NPH benefited very well from shunting. With this knowledge there seemed little point in spending effort naming the condition; a more useful approach being to categorise people as 'high probability' and 'low probability' of shunt response. Two methods in addition to clinical assessment and CT/MR imaging are currently in use at the Medical College of Virginia for prediction of shunt response - namely a bolus technique for assessing CSF pressure dynamics, and a 72 hour prolonged CSF drainage technique. These protocols are described more fully under "Evaluation".

Briefly, the CSF pressure dynamics study provides information about the pressure-volume index (PVI) within the CSF, which is a measure of tightness, or elastance of the CNS, and also the CSF outflow resistance, which increase in NPH (one of the postulated pathophysiological mechanisms). This test therefore provides additional diagnostic information. The CSF dynamics study also provides information about what type of CSF shunt should be used (i.e. low, medium or high pressure). A normal CSF dynamic study however, should never take precedent over a strong clinical indication for the presence of NPH. The 72 hour prolonged CSF drainage technique is a very sensitive measure for predicting those who will benefit from operative intervention.

The tests are relatively easy to perform. CSF dynamics can be done in an out-patient setting, requiring only a lumbar-puncture under local anesthesia. The external lumbar drainage procedure is done as an in-patient. The interpretation of the results, and appropriate calculations from the measurements are critical to the utility of this test. The tests need to be performed or evaluated by an experienced practitioner in order to get the maximum benefit.

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Maintained by: Andrew Beaumont MD

Department of Neurosurgery
Updated August 2003, Rev 3.0