Idiopathic normal pressure hydrocephalus in neurological practice

Background: We have previously seen that idiopathic normal pressure hydrocephalus (iNPH) patients havingelevated intracranial pressure (ICP) pulse amplitude consistently respond to shunt surgery. In this study weexplored how the cerebrospinal fluid pressure (CSFP) pulse amplitude determined during lumbar infusion testing,correlates with ICP pulse amplitude determined during over-night ICP monitoring and with response to shuntsurgery. Our goal was to establish a more reliable screening procedure for selecting iNPH patients for shuntsurgery using lumbar intrathecal infusion. Methods: The study population consisted of all iNPH patients undergoing both diagnostic lumbar infusion testingand continuous over-night ICP monitoring during the period 2002-2007. The severity of iNPH was assessed usingour NPH grading scale before surgery and 12 months after shunting. The CSFP pulse was characterized from theamplitude of single pressure waves. Results: Totally 62 iNPH patients were included, 45 of them underwent shunt surgery, in whom 78% were shuntresponders. Among the 45 shunted patients, resistance to CSF outflow(Rout) was elevated (≥ 12 mmHg/ml/min) in44. The ICP pulse amplitude recorded over-night was elevated (i.e. mean ICP wave amplitude ≥ 4 mmHg) in 68%of patients; 92% of these were shunt responders. In those with elevated overnight ICP pulse amplitude, we foundalso elevated CSFP pulse amplitude recorded during lumbar infusion testing, both during the opening phasefollowing lumbar puncture and during a standardized period of lumbar infusion (15 ml Ringer over 10 min). Theclinical response to shunting after 1 year strongly associated with the over-night ICP pulse amplitude, and alsowith the pulsatile CSFP during the period of lumbar infusion. Elevated CSFP pulse amplitude during lumbarinfusion thus predicted shunt response with sensitivity of 88 and specificity of 60 (positive and negative predictivevalues of 89 and 60, respectively). Conclusions: In iNPH patients, shunt response can be anticipated in 9/10 patients with elevated overnight ICPpulse amplitude, while in only 1/10 with low ICP pulse amplitude. Additionally, the CSFP pulse amplitude duringlumbar infusion testing was elevated in patients with elevated over-night ICP pulse amplitude. In particular,measurement of CSFP pulse amplitude during a standardized infusion of 15 ml Ringer over 10 min was useful inpredicting response to shunt surgery and can be used as a screening procedure for selection of iNPH patients forshunting. * Correspondence: [email protected] of Neurosurgery, Rikshospitalet University Hospital, N-0027Oslo, NorwayEide and Brean Cerebrospinal Fluid Research 2010, 7:5http://www.cerebrospinalfluidresearch.com/content/7/1/5CEREBROSPINAL FLUID RESEARCH © 2010 Eide and Brean; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the CreativeCommons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andreproduction in any medium, provided the original work is properly cited. BackgroundThe clinical condition normal pressure hydrocephalus(NPH) incorporates gait disturbance, mental deteriora-tion and urinary incontinence, combined with enlargedcerebral ventricles and a normal lumbar cerebrospinalfluid pressure (CSFP) [1]. Usually no cause is identified,in which case the condition is denoted idiopathic NPH(iNPH). Although the pathophysiology of iNPH is dis-puted [2], previous studies have shown that shunt sur-gery can be effective, and that clinical improvement canbe sustained for years [3-5].Hydrodynamic tests, in particular the lumbar infu-sion test, have been used for selecting patients for sur-gery, although the literature is very divergentconcerning its role in iNPH [6]. During lumbar infu-sion testing, the static CSFP can either be monitoredduring constant flow infusion, constant pressure infu-sion or during bolus infusion to the thecal sac. In ourpractice, we have for many years used a modificationof the constant rate infusion test originally describedby Katzman [7] for determination of resistance to CSFoutflow (Rout). However, the utility of Rout in selectingiNPH patients for surgery is controversial [8-13]. Onthe other hand, we have found that the ICP pulse (thatis the amplitude of the single cardiac-beat induced ICPwaves) during over-night ICP monitoring is very usefulfor predicting shunt response in iNPH [14]. Thus, inour previous series of 130 shunted iNPH patients,shunt response was seen in 9 of 10 patients with ele-vated ICP wave amplitudes but only in 1 of 10 withlow ICP wave amplitudes [15].With regard to lumbar infusion testing, the variousapproaches (e.g. constant flow, constant pressure orbolus infusion methods) consistently assess the staticand not the pulsatile CSFP. Others [16] and our group[8,11,17] have reported experiences from assessing thepulsatile CSFP during lumbar infusion testing. Based onthese experiences, it could be anticipated that determin-ing the CSFP pulse during lumbar infusion testingmight better characterize the pressure-volume reservecapacity than the static CSFP. Moreover, successfulassessment of the pulsatile CSFP during lumbar punc-ture might represent an advantage, given that lumbarpuncture is a low-risk procedure, and more useful in aclinical neurological setting than continuous ICP moni-toring. The pulsatile CSFP can be measured during theopening phase of lumbar puncture, as well as duringlumbar infusion. Thus, our goal with the present studywas to establish a more reliable screening procedure forselection of iNPH patients for shunt surgery, based ondetermining the CSFP pulse amplitude during lumbarinfusion testing. For this purpose, in the present studywe explored how measurement of the pulsatile CSFPduring lumbar infusion testing correlated with the ICPpulse monitored over-night and with the response toshunting. To do this we retrieved all lumbar infusiontests done during diagnostic work-up for iNPH in thisdepartment during the time period 2002-2007. Theseinfusion tests were stored as continuous CSFP raw data(originally sampled at 100-200 Hz). In the present study,these raw data files were re-analyzed; the CSFP pulseamplitude was determined during the opening phaseafter lumbar puncture and also during a period of lum-bar infusion (standardized as 15 ml infusion over 10min). All patients had their ICP monitored over-night;therefore the infusion test results could be related to thepulsatile ICP recorded over-night, and with the clinicalresponse to shunting. MethodsPatient materialThe patient material consisted of all patients beingassessed for iNPH at the Department of Neurosurgery,Rikshospitalet University Hospital, during the 6-yearsperiod 2002-2007, in whom both over-night ICP moni-toring and lumbar infusion testing had been done dur-ing the diagnostic pre-operative work-up. The patientswere referred from local neurological departments basedon their symptoms of gait disturbance, incontinence,and dementia, combined with radiologicalventriculomegaly.For diagnostic work-up the patients were hospitalizedfor 3 days. Following clinical and radiological assessmenton day 1 (day of admittance), ICP monitoring was donefrom day 2 to day 3. The lumbar infusion test was doneon day 3. After discharge from the department on day3, they returned 1-3 weeks later for surgical treatmentprovided this was advocated.This study was approved by the hospital authority ofRikshospitalet University Hospital and by the NorwegianSocial Science Data Services. The Regional Committeefor Research Ethics was informed in writing, and had noobjections to the study. Clinical and radiological assessmentOur diagnostic work-up for iNPH patients has pre-viously been described [14,15]. In short, based on find-ings at neurological examination, the severity of clinicaliNPH was graded using our NPH grading scale (scoresranging from 3-15), which assesses the combined sever-ity of gait disturbance, urinary incontinence and demen-tia. The size of the ventricles was assessed using thelinear measure Evan’s index [14]. Diagnostic ICP monitoring and lumbar infusion testingDiagnostic continuous ICP monitoring was donethrough a frontal burr hole prepared under localEide and Brean Cerebrospinal Fluid Research 2010, 7:5http://www.cerebrospinalfluidresearch.com/content/7/1/5Page 2 of 11