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Table 1 Use and Interpretation of prognostic or diagnostic tests in KUH iNPH protocol

From: The Kuopio idiopathic normal pressure hydrocephalus protocol: initial outcome of 175 patients

Prognostic or diagnostic test Performance Interpretation Action
Tap test Gait task: Walking 10 meters, rotating and returning to the starting point (20 m in total). Repeated twice prior and twice after the CSF removal by lumbar puncture
CSF drainage: 20–40 ml of CSF is removed by lumbar puncture in a sitting position. Patient rests 1 h in supine position before the repetition of the gait task
Evaluation: Examining the gait in a standardized manner. The average gait speed (meters/second), the number and the length of steps prior to and after CSF removal are calculated
Positivea if there is at least 20% improvement in average gait speed. Negative if less If positive, patient is referred for CSF shunt treatment, if the patient is willing, and if there are no contraindications
Negative test does not exclude favorable CSF shunt treatment outcome. Such patients are referred to the infusion test if willing
Infusion test CSF outflow resistance via lumbar catheter by measuring changes in ICP caused by continuous or pulsatile infusion of Ringer solution Positiveb if: Outflow resistance is ≥ 12 mmHg/(ml/min). Negative if not If positive, patient is likely to suffer from iNPH, and thus may benefit from CSF shunt treatment. If test is negative, patient is unlikely to have iNPH, but some iNPH patients may have normal findings
Continuous measurement of ICP 24 h, intraventricular measurement of ICP Positive if: (a) a basal intracranial pressure is above 10 mmHg or (b) the presence of any A waves or (c) more than 30% B waves during the monitoring If positive, patient is likely to suffer from iNPH, and thus may benefit from CSF shunt treatment. If test is negative, patient is unlikely to have iNPH, but some iNPH patients may have normal findings
  1. CSF Cerebrospinal fluid, iNPH idiopathic normal pressure hydrocephalus, KUH Kuopio University Hospital, ICP intracranial pressure, ml milliliter, min minute, mmHg millimeter of mercury
  2. aThere are no uniform guidelines how to measure and what is the minimal clinically significant gait improvement after CSF removal
  3. bStricter outflow resistance limits exist (13, 19, 20)