Improved lumbar infusion test analysis for normal pressure hydrocephalus diagnosis

Constant infusion lumbar infusion test (LIT) is an important way to find which patients, of those with signs and symptoms corresponding to normal pressure hydrocephalus (NPH) who will improve from shunt operation. LIT is a stress test on the ability for cerebrospinal fluid re-absorbtion. The aim of this study is to show how the information from LIT can be improved by quantitative analysis and avoidance of methodological pitfalls.

The potential pitfalls, and the analysis method, are described in detail. The analysis was applied on pre-operative constant infusion LIT from 31 patients operated for NPH, with known outcome. The pre- and post-operative walking speed was used to grade pathology progression or improvement.

The maximal, plateau, intra-spinal pressure at constant infusion LIT is an ambivalent indicator for NPH: while low maximal pressure indicates no cerebrospinal fluid (CSF) absorbtion pathology, too high pressure (≥47 mmHg) may mean no diagnosis, because of stenosis of the Sylvian aqueduct. When subjects with too high intra-spinal pressure were excluded, the new analysis gave a couple of diagnostic volume parameters, of which one appears to be an optimal LIT parameter for identifying NPH patients with 14% better accuracy than plateau pressure.

By avoiding methodological pitfalls, and optimal analysis of the results from lumbar infusion test, the number of NPH patients who do not have a successful outcome after shunt operation may be further decreased.