Which patients will benefit from shunting?
Supplemental prognostic tests have been developed to help decide which patients are most likely to benefit from a ventriculoperitoneal shunt. Complicating comparisons between the various tests is the lack of a standard set of measures of function in gait, cognition, and urination; nor is there agreement on how long after shunting the clinician should make these measurements.
A systematic review4 of the most commonly used prognostic tests identified a response to a large-volume (40–50 mL) CSF tap test as having a positive predictive value (PPV) between 73% and 100% but a negative predictive value (NPV) of only 23% to 42%. Thus, observing an improvement of function after such a test is a good predictor of improvement after shunting, but many patients who do not respond to the test respond to shunting.
A variation of the CSF tap test is the extended lumbar drainage test, which involves placing a lumbar intrathecal catheter and allowing the drainage of 10 mL of CSF/hour for 72 hours. The PPV for this test ranges from 80% to 100%, and NPV from 66% to 100%.
A third possible test is the measurement of resistance to an infusion of saline into the lumbar subarachnoid space (CSF Ro test). This test has multiple variations of technique. Reported values for PPV are 75% to 92%, and for NPV of 27% to 92%.
Other tests, such as radionuclide cisternography or magnetic resonance imaging CSF flow void, have predictive values too low or have too few studies to be recommended.4
Recommendations from others
A recently published expert consensus statement proposes that the diagnosis of INPH be made using the history, clinical examination, and neuroimaging.4 Cases of probable INPH can proceed directly to ventriculoperitoneal shunt, or supplemental testing can be used to improve the certainty of a positive shunt response. A positive CSF tap test should lead to shunting.
Follow up negative tap tests with the extended lumbar drainage test or the CSF Ro test (or both). A positive response to any of the tests should lead to shunting; negative responses to all the tests indicates a low chance (<10%) of responding to a ventriculoperitoneal shunt.4