Invasive preoperative diagnosis of idiopathic normal pressure hydrocephalus

Introduction. Until now, the most informative methods for selecting patients with idiopathic normal pressure (iNPH) for neurosurgical treatment were invasive diagnostic methods: tap test, lumbar infusion test, external lumbar drainage. Nevertheless, choosing the sequence of using these diagnostic tools and the assessment of their results cause number of questions for doctors in everyday practice.

The study objective is to assess the informational content of invasive tests for differential diagnosis of iNPH and to create an algorithm of applying mentioned methods for clinical purposes.

Materials and methods. At least one of the invasive diagnostic methods was used for 374 patients, who were treated in the period from 2006 to 2018 in the neurosurgical clinic of S. M. Kirov Military Medical Academy. The patients with final diagnosis of iNPH (n = 231), aged 58–87 years old, were selected for shunt surgery. The informativeness measures were calculated for each method on the basis of revealed data.

Results. Sensitivity and specificity of tap test were 57.5 and 86.4 %, respectively, positive predictive value – 92.5 %, negative predictive value – 41.3 %, accuracy – 64.9 %. For lumbar infusion test sensitivity was 39.1 %, specificity – 63.6 %, but we calculated low negative predictive value (20.0 %) and accuracy (43.9 %) of the method despite of relatively high positive predictive value (81.8 %). External lumbar drainage revealed the highest significance of positive predictive value (92.9 %).

Conclusion. Excluding of lumbar infusion test from the pre-operative diagnostic algorithm of iNPH and recommendation for sequential using of tap-test and external lumbar drainage after questionable result of the last one are an advisable option for practitioners.

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