Object
This study was performed in patients with idiopathic normal-pressure hydrocephalus (iNPH) to monitor cerebral metabolism with microdialysis (MD) and intracranial pressure (ICP) readings, and relate to the clinical responses to extended lumbar drainage (ELD) and shunt surgery.
Methods
The baseline levels of MD metabolites and ICP were monitored overnight in 40 consecutive patients with iNPH. In a subset of 28 patients, monitoring was continued during 3 days of ELD. Thirty-one patients received a ventriculoperitoneal shunt. The clinical severity of iNPH was determined before and then 3 and 6–12 months after shunt surgery.
Results
Altered levels of MD markers (lactate, pyruvate, lactate/pyruvate ratio, glutamate, and/or glycerol) were seen in all patients at baseline; these improved during ELD. Despite normal static ICP (mean ICP), the pulsatile ICP (the ICP wave amplitude) was increased in 24 patients (60%). Only the level of the ICP wave amplitude differentiated the ELD and/or shunt responders from nonresponders.
Conclusions
The MD monitoring indicated low-grade cerebral ischemia in patients with iNPH; during ELD, cerebral metabolism improved. The pulsatile ICP (the ICP wave amplitude) was the only variable differentiating the clinical responders from the nonresponders. The authors suggest that the pulsatile ICP reflects the intracranial compliance and that CSF diversion improves the biophysical milieu of the nerve cells, which subsequently may improve their biochemical milieu.
Absence of Disproportionately Enlarged Subarachnoid Space Hydrocephalus, a Sharp Callosal Angle, or Other Morphologic MRI Markers Should Not Be Used to Exclude Patients with Idiopathic Normal Pressure Hydrocephalus from Shunt Surgery
