Assessment of idiopathic normal pressure patients in neurological practice: the role of lumbar infusion testing for referral of patients to neurosurgery

Background and purpose: In neurological practice patients with tentative idiopathic normal pressure hydrocephalus (iNPH) usually are referred to neurosurgery based on clinical and radiological findings. Hydrodynamic assessment using lumbar infusion testing might be helpful in selecting patients. To retrospectively analyse lumbar infusion tests done in neurological practice in iNPH patients to see how infusion test results relate to the clinical course and shunt response. Materials and methods: Sixty-three consecutive patients with Possible/Probable iNPH were tested during a 1-year period. The pre-operative lumbar infusion tests were assessed according to two strategies: (i) Determining the resistance to cerebrospinal fluid (CSF) outflow (R-out). (ii) Quantification of the CSF pressure (CSFP) pulsatility during lumbar infusion (Q(pulse)). The results were related to the prospectively followed clinical course and shunt response after 12 months. Results: The lumbar infusion-derived parameters R-out and Q(pulse) related weakly. Shunt response after 12 months was not related to R-out, but was highly related to the Q(pulse). False negative results of lumbar infusion testing were observed in 16% of the patients. Discussion: In neurological practice lumbar infusion testing may be useful for determining which patients to refer to neurosurgery. Our data favour determination of CSFP pulsatility (Q(pulse)) rather than R-out for prediction of shunt response.