The CSF tap test in normal pressure hydrocephalus: evaluation time, reliability and the influence of pain

Background: The cerebrospinal fluid tap test (TT) is a diagnostic tool used to select patients with idiopathic normal pressure hydrocephalus (iNPH) for shunt surgery. The procedure and the evaluation of the TT vary between centres. We aimed to describe the evaluation time after the TT, to assess the variability between repeated measurements, the interrater agreement of the gait tests chosen and finally to investigate whether pain affects the gait performance post-TT. Methods: Forty patients (21 men and 19 women) under evaluation for iNPH underwent a TT. Standardized gait analyses were performed before and 2, 4, 6, 8 and 24 h after the TT and repeated twice on every occasion. Independent of each other, two investigators evaluated the quality of gait. At each assessment time, the patients graded headache and back pain on a visual analogue scale. Results: Twenty-seven patients (15 men and 12 women) responded to TT. Improvements in gait speed and number of steps were significant at every assessment time post-TT. The variability between two measurements was low (Intra class correlation coefficient = 0.97), and the inter-rater agreement was good with a j = 0.74. Pain correlated negatively with improvement in gait speed (r = -0.40, P < 0.05). Conclusions: We suggest that the TT can be evaluated at any time within the first 24 h and should be repeated if the patient does not initially improve. Gait analysis appears reliable between two evaluators. Further, it is indicated that post-lumbar puncture pain negatively affects the gait and should be minimized.