Gait parameters, Imaging features, and CSF tap test in idiopathic Normal Pressure Hydrocephalus (iNPH). Is composite testing the way to go?

IntroductionIdiopathic normal pressure hydrocephalus is characterized by gait disturbance, cognitive decline, and urinary dysfunction which may improve with ventriculo-peritoneal shunting. This study evaluated the role of conventional MRI features and the CSF tap test (CSF-TT) in predicting shunt responsiveness in iNPH. MethodsThis is an Ambispective cohort study of 40 patients with probable iNPH evaluated between 2019 and 2024. Baseline MRI parameters, gait features, iNPH score, CSF opening pressure were analyzed. 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. The diagnostic performance of individual MRI parameters and composite diagnostic parameters were evaluated. ResultsForty 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 H20 showed sensitivity of 62.5 % and specificity of 71.4% with the highest Youden index indicating modest diagnostic accuracy in predicting shunt responsiveness. ConclusionShunt 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.