Intracranial pressure parameters in idiopathic normal pressure hydrocephalus patients treated with ventriculo-peritoneal shunts

Background. Although the mean intracranial pressure (ICP) is normal in patients with idiopathic normal pressure hydrocephalus (iNPH), there could possibly be alterations in their single ICP waves. Method. Thirty-nine consecutive patients treated for iNPH with ventriculo-peritoneal shunts were followed prospectively with regard to clinical and radiological findings. Changes in clinical state 12 months after shunt surgery were assessed as change on a 15-3 score NPH Grading Scale, while the changes in ventricular size were assessed by linear measures. The ICP recordings were performed as part of routine pre-operative assessment, stored as raw data files, and analyzed retrospectively. The mean ICP as well as single ICP wave amplitudes were computed and analysed in consecutive 6 second time windows. Findings. Twelve months after shunt surgery, changes in NPH score of 5 or more (very significant improvement) were observed in 12 patients (31%), of 3 to 4 (significant improvement) in 6 patients (15%), of 1 to 2 (slight improvement) in 9 patients (23%) and of -4 to 0 (non-responders) in 12 patients (31%). The ventricular size did not change in any of the outcome categories. While the pre-operative mean ICP was similar between outcome groups, the mean ICP wave amplitude was significantly higher in patients improving clinically as compared to the non-responders. Conclusions. While pre-operative mean ICP was similar, the mean ICP wave amplitudes were significantly higher in iNPH patients improving clinically after shunt treatment as compared to the non-responders.