Cerebrospinal fluid osmolality cannot predict development or surgical outcome of idiopathic normal pressure hydrocephalus

Abstract

Background The etiology of idiopathic normal pressure hydrocephalus (iNPH) is currently unknown. With no visible obstructions, altered cerebrospinal fluid (CSF) dynamics may explain the accumulation of ventricular fluid. We hypothesized that elevated osmolality in the CSF of iNPH patients could potentiate formation of ventricular fluid and thereby cause the disease progression and/or predict the surgical outcome. To address this hypothesis, we determined the lumbar and ventricular CSF osmolality of iNPH patients at different disease stages and compared with lumbar CSF samples obtained from control subjects. Methods The osmolality of CSF was determined on a total of 35 iNPH patients at diagnosis and at the subsequent treatment with shunt surgery (n = 20) and compared with the CSF osmolality from 20 control subjects. Simultaneously collected lumbar and ventricular CSF samples from experimental pigs were used to evaluate the compatibility between CSF from different compartments. Results We found no evidence of increased osmolality in the CSF of iNPH patients upon diagnosis or at the time of shunt treatment months after the diagnosis, compared with control individuals. CSF tapped from the lumbar space could be used as a read-out for ventricular CSF osmolality, as these were similar in both the patient group and in experimental pigs. We further observed no correlation between the CSF osmolality in iNPH patients and their responsiveness to shunt surgeries. Conclusions The osmolality of lumbar CSF is a reliable reflection of the ventricular CSF osmolality, and is not elevated in iNPH patients. iNPH therefore does not appear to arise as a function of osmotic imbalances in the CSF system and CSF osmolality cannot serve as a biomarker for iNPH or as a predictive tool for shunt responsiveness.

Posthemorrhagic Hydrocephalus in Patients with Subarachnoid Hemorrhage Occurs Independently of CSF Osmolality

“…We here observed undisturbed osmolality in CSF samples obtained during the placement of EVD in patients with SAH compared to CSF obtained from the basal cisterns in healthy subjects undergoing preventive clipping of an unruptured aneurysm. The differential sampling site is ethically dictated and represents a limitation to the study, but whether the CSF content of the two compartments is compatible remains unclear, as CSF comparison studies remain largely limited to ventricular versus lumbar CSF [37,49], which, however, are of similar osmolality [49]. The CSF Na + (and Ca 2+ ) concentration was, likewise, similar in the two SAH patient groups, suggesting no overall electrolyte disturbance, which aligns with the gross similarity of the ionic content of blood entering during the hemorrhagic event and the resident CSF.…”