**13. External lumbar drainage**

In this test, CSF is drained (10 to 15 cc per hour) for 72 hours and patient is assessed before and after the drainage (positive predictive value 90% and negative predictive value 78%). Positive ELD indicates good benefit with shunt. Negative ELD indicates low risk-benefit ratio. Neuropsychological testing before and after external lumbar drainage may also be helpful. Most publications have cited 72 hours of CSF drainage, although some centers drain CSF for shorter periods [19, 20]. This test has the risk of headache, lumbar radiculopathy, and risk of meningitis.

## **14. CSF infusion testing**

Infusion testing for assessment of CSF hydrodynamics is commonly used in Europe to diagnose NPH, but is rarely used in the United States or Canada. In CSF infusion test, Ringer lactate is infused via one spinal needle and a second needle simultaneously records CSF pressure. One of the most consistent findings in NPH research is that patients have an increased resistance to outflow.

#### **15. ICP monitoring**

The recordings in NPH reveal wave-form abnormalities similar to those originally described for brain tumor or acute injury, (i.e., B waves and A waves). The presence of unstable ICP (predominantly B waves) in NPH is well known, and the correlation with NPH shunt responsiveness ranges from 50 to 90%. Recently, analysis of the amplitudes of the ICP pulse pressure has been pro-posed as a predictive test in NPH.

### **16. Practice guidelines**

If the CSF pressure is high, the patient should be investigated for other causes of obstructive hydrocephalus. If there is improvement of the patient after a 40 to 50-mL (high-volume) lumbar tap that the patient will likely respond well to shunting. An external ventricular drainage may be used in patients who fail to respond to a high-volume tap. Currently, there is no substantial evidence to support predictiveness to MRI CSF flow studies [19, 20].

#### **17. Treatment**

Treatment includes conservative measures and surgery for patients with favorable risk benefit ratio. Temporizing measures include acetazolamide and high volume tap. As per practice guidelines, surgery is considered for patients

with favorable risk benefit ratio. Age alone is not an exclusionary criterion unless there are other surgical risk factors. Surgical options for the management of INPH include ventriculoperitoneal shunt and endoscopic third ventriculostomy. Literature favors low pressure programmable ventriculo peritoneal shunt as both over and under drainage can be managed in non-invasive manner. Endoscopic third ventriculostomy is indicated in patients with relative aqueduct stenosis and when there is triventricular hydrocephalus. Gangemi et al. reported 72% improvement with 4% complications rate [24].
