Predictive value of lumbar infusion test in normal pressure hydrocephalus

Abstract

Introduction: To detect the ability of the lumbar infusion test to predict the outcome of shunt surgery in patients with suspected normal pressure hydrocephalus. Methods: Twenty patients with suspected normal pressure hydrocephalus were studied. Preoperative CT and/ or MRI of the brain was done in all cases. The absence of preceding history indicated idiopathic disease. All patients were assessed with walking and psychometric tests before lumbar infusion test and tap test assessments. Tap test was done in all cases because it is the standard test used in these cases. The lumbar infusion test was done using a constant infusion rate (0.80 ml/min) using a syringe pump and regarded as positive if the steady state CSF plateau pressure reached levels of > 22 mm Hg (16 cm H2O). The tap test was regarded as positive if two or more of three different test items improved after CSF removal. Walking and psychometric tests were used to assess patients postoperatively. Results: The results of the CSF tap test and the lumbar infusion test agreed in only 40% of cases. Of all cases in the study, 18 (90%) had positive test results and were operated on; 16 (80%) of patients reported subjective improvement, and postoperative assessments verified the improvements in 15 patients (75%). Improvements were highly significant in walking and memory. Most of the patients improved by surgery (90%) were selected by a positive lumbar infusion test, and only 67% by a positive tap test. Conclusions: Both the lumbar infusion test and the tap test can predict a positive outcome of shunt operations in patients with suspected normal pressure hydrocephalus. Lumbar infusion test has a higher predictive value than the CSF tab test. The two tests are complementary and should be used together for a better patient selection.

KeyWords: Normal pressure hydrocephalus - Lumbar infusion test - Tap test"