How is external lumbar drainage (ELD) used to predict response to shunt surgery for normal pressure hydrocephalus (NPH)?

Updated: Oct 19, 2018
  • Author: Michael J Schneck, MD, MBA; Chief Editor: Selim R Benbadis, MD  more...
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Answer

While large volume lumbar puncture was the earliest invasive diagnostic test in predicting response to shunt surgery, external lumbar drainage (ELD) is being used with increased frequency. In this method, clinicians use an indwelling CSF catheter in lieu of repeated lumbar punctures. The drainage catheter is generally left in place for 3 days, allowing sufficient time for return of neuronal function. [14] This method carries a higher risk of meningeal infection but may allow for a more accurate prognosis. [15]

In a prospective study of 151 patients with suspected idiopathic NPH, all patients underwent ELD. Patients with clinical improvement after ELD were offered shunt surgery, 90% of whom improved. [16] Others have confirmed the positive predictive value of improvement after ELD. [14, 17] Less clear, however, is the negative predictive value of ELD. In one study, 64% of patients who underwent shunt surgery had improvement, despite a negative ELD result. [18] Thus, given the dramatic improvement in quality of life for shunt responders, some have advocated for less reliance on predictive testing. [19, 20] Given the potential morbidity and mortality of shunt surgery, however, this has not been widely adopted.

An alternative method of predicting response to shunt surgery is CSF infusion testing. In this test, 2 lumbar drains are placed. One drain is used for continuous pressure monitoring while the other drain is used to continuously infuse solution into the CSF space. Elevated pressures during infusion are specific for shunt-responsive NPH. However, due to a lower sensitivity and potential morbidity, this is infrequently used.

Patients with a good response to predictive testing should be considered for ventriculoperitoneal or ventriculoatrial shunting. The best results are reported in patients who have no adverse risk factors; have responded favorably to a large-volume lumbar puncture; and have definite evidence of dementia and ataxia, CT scan or MRI evidence of chronic hydrocephalus, and a normal CSF at lumbar puncture. Some evidence indicates that patients with gait disturbance, mild or no incontinence, and mild dementia fare best among shunt surgery patients. [19, 21]


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