Objective: To analyze the positive predictive values of specific imaging findings for CSF-TT responsiveness and shunt responsiveness

To determine whether composite diagnostic models incorporating CSF-TT and CSF opening pressure would perform better at predicting shunt responsiveness

Background: Idiopathic Normal Pressure Hydrocephalus (iNPH) is a condition characterized by a triad of gait disturbance, urinary disturbance, and cognitive impairment, and is treated by ventriculoperitoneal shunting. In the SINPHONI2 randomized trial, only 65% of patients with clinico-radiologic iNPH showed improvement after shunt surgery. A recent meta-analysis found that the diagnostic accuracy of CSF-TT was suboptimal and not predictive of postoperative outcomes. It is not known which baseline parameter, score, or MRI finding correlates best with CSF-TT responsiveness. This suggests that currently available tools are not accurate enough to select patients who would benefit from surgery.

Method: This is an Ambispective cohort study. Baseline MRI parameters, gait features, iNPH score, and CSF opening pressure were analyzed in probable iNPH patients. Functional outcome was assessed using the modified Rankin scale (mRS) at baseline, 24 hours after CSF-TT, and 24 weeks after VP shunt surgery. CSF-TT responders were defined as at least a 1-point improvement in mRS 24 hours after CSF-TT.

Results: Forty patients underwent CSF-TT. There were no significant differences between CSF-TT responders and non-responders in the baseline clinical gait parameters, the iNPH scale, and MRI findings. Turning disturbance, wide-based stride, and reduced foot clearance showed significant improvement after CSF-TT. Individual MRI parameters and CSF-TT parameters showed limited value in predicting shunt responsiveness. Composite diagnostic criteria combining CSF-TT and CSF opening pressure >18cm H2O showed sensitivity of 62.5% and specificity of 71.4%, with the highest Youden index indicating modest diagnostic accuracy in predicting shunt responsiveness.

Conclusion: Shunt surgery provided significant functional benefit in iNPH. Neither the CSF tap test nor conventional MRI markers alone reliably predicted shunt responsiveness. A multimodal assessment combining imaging, clinical evaluation, and CSF dynamics is required to optimize patient selection.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/gait-parameters-imaging-features-and-csf-tap-test-in-idiopathic-normal-pressure-hydrocephalus-inph-is-composite-testing-the-way-to-go/