Evaluating the Cerebrospinal Fluid Tap Test With the Hellström iNPH Scale for Patients With Idiopathic Normal Pressure Hydrocephalus – a Retrospective Cohort Study of 132 Patients

Abstract

Background The cerebrospinal fluid tap test (CSF TT) is used for selecting shunt surgery candidates in idiopathic normal pressure hydrocephalus (iNPH). Variations in performance, and different outcome measures and cut-off levels in previous research on the CSF TT make comparison of accuracy difficult between studies. We aimed to evaluate the CSF TT, by using the Hellström iNPH scale for shunted iNPH patients with a standardized method. Methods One hundred thirty-two shunt operated iNPH patients were retrospectively included in this study. The gait and balance domains in the iNPH scale were used as outcome measures for the CSF TT and the total iNPH scale score as postoperatively outcome. To identify responders a cut-off level ≥ 5 points was used. Differences between responders and non-responders to the CSF TT, as well as the sensitivity, specificity, positive and negative predictive values, accuracy and correlations between outcomes of the CSF TT and postoperatively were calculated. Results In the gait domain, there were 62.9% responders and correspondingly 42.7 % in the balance domain of the CSF TT. CSF TT responders had significantly better outcomes in both the gait and balance domains but not in the neuropsychology or continence domains postoperatively. The sensitivity and specificity of the CSF TT and the outcome of the total iNPH scale score postoperatively were 67.6% and 53.3% for gait and 47.5% and 73.3% for balance. For age ≥ 80 years, the sensitivity and specificity for gait were 52.2% and 60.0%, and for age ≤ 80 years 72.2% and 50.0%. Gait as an outcome measure for both the CSF TT and postoperatively had the highest sensitivity, (73.2%) and specificity (65.7%) for all ages. Conclusions The CSF TT, with Hellström´s iNPH scale as the outcome measure, has clear limitations in predicting postoperative results. The gait domain may be used to detect changes of outcomes in gait, but the balance domain is too insensitive to use as an assessment for the CSF TT. The value of the CFS TT for patients over 80 years of age appears to be even lower. Differential diagnostic considerations together with radiological assessments remain cornerstones in selecting eligible shunt responders.