Prevalence of probable idiopathic normal pressure hydrocephalus in a Norwegian population

Abstract

Aims:The aims of this thesis are to estimate the epidemiology of iNPH in a Norwegian population compared to the incidence of surgery for the condition, to assess whether lumbar measurements of cerebrospinal fluid pressure (CSFP) concurs with intracranial pressure (ICP), and with the clinical response to shunting, and finally to assess which of the lumbar hydrodynamic measurements that best can predict the clinical response to shunting. Methods:The thesis consists of six publications. Publication Iassesses the prevalence of iNPH in a Norwegian population. Publication IIassesses the five year incidence of surgery for iNPH in Norway. Publication III compareslumbarCSFP waves versus ICPwaves in iNPH. Publication IV compares ICPmeasured simultaneously within the brain parenchyma and cerebral ventricles.Publication Vassesses the role of lumbar infusion testing for referral of iNPH patients to neurosurgery. Publication VI assesses whether CSFP waveamplitude during lumbar infusion in iNPH can predict response to shunting. Results: We found a prevalence of probable iNPH of 21.9/100.000 inhabitants,and an incidence of 5.5/100.000/year. The total rate of surgery for iNPH was 1.09/100.000/year. The lumbar CSFP wave amplitude during lumbar infusion could be used to predict the ICP wave amplitude during over-night monitoring of the intracranial pressure. There is no pressure gradient between pressure wave amplitudes derived from brain parenchyma and ventricular CSF. Resistance to outflow (Rout) and CSFP wave amplitude derived from lumbar infusion related only weakly, while shunt response related highly to the quantitative distribution of CSFP wave amplitudes during infusion, giving false negative results in 16% of the patients. Elevated CSFP wave amplitudes during lumbar infusion predictedshunt response with asensitivity of 88 and aspecificity of 60. Conclusions:Our data suggest that too few patients are being offered surgical treatment for iNPH in Norway. Lumbar CSFP wave amplitudes concur to a great extent with ICP wave amplitudes and with clinical response to shunting. Lumbar CSFP wave amplitudes predict clinical response to shunting better than Rout, but further studies are advocated to address the problem of false negative results from lumbar hydrodynamic measurements