Lumbar puncture tap test in iNPH: Does extracting different volumes of CSF change the clinical response?

Introduction: Although the Lumbar Tap Test (LTT) typically involves removing 30-50 ml of cerebrospinal fluid (CSF), the optimal amount for a valid test is unclear. This study investigates the relationship between the volume of CSF removed and the extent of gait improvement in idiopathic normal pressure hydrocephalus (iNPH).

Methods: Seventy-six iNPH patients with gait improvement after LTT were divided into two groups: high CSF volume (> 40 ml) and low CSF volume (< 40 ml). Spearman's r correlations and non-parametric t-tests were used to analyze the relationship between CSF volume removed and gait improvement.

Results: Gait improvement after LTT showed a moderate positive correlation (r = 0.372, p < 0.001) with CSF volume. Those in the high-volume group had significantly greater improvement (p < 0.01). Improvement was also correlated with baseline gait parameters: pre-LTT gait speed (r = -4.14, p = 0.006), steps to complete a walking test (r = 0.440, p < 0.001), and a 360° turn (r = 0.563, p < 0.001).

Conclusions: Larger CSF removal during LTT positively affects gait improvement in iNPH patients. Gait improvement is also greater in those with more severe initial gait impairments independently from the CSF volume extracted.