Objective: To study the sensitivity and specificity of CSF tap test in predicting outcomes following shunt surgery

Background: Idiopathic Normal pressure hydrocephalus (iNPH) is a condition characterized by a specific triad of gait disturbance, cognitive impairment, and urinary incontinence. CSF tap test is thought to simulate the effect of shunt surgery. There are controversial opinions regarding its predicting power and validity. Usually, 70-85% of patients show improvement after shunting. However, the extent of change in gait score after tap test to predict the change after shunt intervention is not yet known.

Method: Ambispective cohort study. Patients suspected to have NPH based on clinico-radiologic parameters underwent a standard CSF drainage. MoCA, iNPH scale, Boon gait scale and modified rankin scales were assessed before and after a 30-50 mL CSF drainage. The patients underwent ventriculoperitoneal shunt insertion based on the clinico-radiologic picture and subjective improvement on tap test. Diagnostic accuracy measures were calculated.

Results: We screened 58 patients with clinical features of gait dysfunction, cognitive and urinary dysfunction and identified 40 patients who fulfilled the consensus guidelines criteria for Probable iNPH. 24 patients underwent VP shunt insertion. The mean age was 64 yeas (SD 9.5) and median duration of symptoms was 19 months (11-84). None of the patients who were unable to walk independently before tap test could walk independently after the tap test. We found that 1 point improvement on modified rankin scale following CSF tapping was 53% sensitive and 67% specific for predicting improvement in post surgical mRS by one point. Whereas, improvement in iNPH score by 1 point following CSF tap test was 60% sensitive and 50% specific. The ROC analysis for change in total gait score (PreCSF-PostCSF) showed a AUC of 0.65 to predict atleast one point reduction in the mRS at follow up as compared to baseline. At least 4-point decrease in gait score post CSF it has a sensitivity of 70.5% and specificity of 57.1% in predicting decrease in mRS post-surgery.

Conclusion: In a population of patients with high clinico-radiologic likelihood of idiopathic NPH, the role of CSF tap test is limited. We need better markers to help select patients for surgery and prognosticate them regarding the extent of improvement.

ROC curve to predict post op mRS change@6 months

Change in gait parameters following CSF tap test

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MDS Abstracts - https://www.mdsabstracts.org/abstract/diagnostic-accuracy-of-csf-tap-test-parameters-in-normal-pressure-hydrocephalus-an-ambispective-cohort-study/