Osmolality of Cerebrospinal Fluid from Patients with Idiopathic Intracranial Hypertension (IIH)

Abstract

IntroductionIdiopathic intracranial hypertension (IIH) is a disorder of increased intracranial fluid pressure (ICP) of unknown etiology. This study aims to investigate osmolality of cerebrospinal fluid (CSF) from patients with IIH.MethodsWe prospectively collected CSF from individuals referred on suspicion of IIH from 2011–2013. Subjects included as patients fulfilled Friedman and Jacobson’s diagnostic criteria for IIH. Individuals in whom intracranial hypertension was refuted were included as controls. Lumbar puncture with ICP measurement was performed at inclusion and repeated for patients after three months of treatment. Osmolality was measured with a Vapor Pressure Osmometer.ResultsWe collected 90 CSF samples from 38 newly diagnosed patients and 28 controls. At baseline 27 IIH-samples and at 3 months follow-up 35 IIH-samples were collected from patients. We found no significant differences in osmolality between 1) patients at baseline and controls (p = 0. 86), 2) patients at baseline and after 3 months treatment (p = 0.97), and 3) patients with normalized pressure after 3 months and their baseline values (p = 0.79). Osmolality in individuals with normal ICP from 6–25 cmH2O (n = 41) did not differ significantly from patients with moderately elevated ICP from 26–45 cmH2O (n = 21) (p = 0.86) and patients with high ICP from 46–70 cmH2O (n = 4) (p = 0.32), respectively. There was no correlation between osmolality and ICP, BMI, age and body height, respectively. Mean CSF osmolality was 270 mmol/kg (± 1 SE, 95% confidence interval 267–272) for both patients and controls.ConclusionsCSF osmolality was normal in patients with IIH, and there was no relation to treatment, ICP, BMI, age and body height. Mean CSF osmolality was 270 mmol/kg and constitutes a reference for future studies. Changes in CSF osmolality are not responsible for development of IIH. Other underlying pathophysiological mechanisms must be searched.

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

“…The ventriculomegaly observed in iNPH patients therefore does not seem to arise as a consequence of elevated CSF osmolality and their CSF osmolality cannot be employed as a biomarker to detect iNPH development. A similar finding was earlier reported for idiopathic intracranial hypertension patients, the CSF osmolality of which resembled that of control individuals [39]. We cannot rule out that small elevations in CSF osmolality, which may have gone undetected in the present study, could suffice to cause a slight hypersecretion, which over time could promote the ventriculomegaly characteristic of iNPH.…”

Acute brain slice elastic modulus decreases over time

“…By contrast, human CSF values average closer to 260 mOsm/l 32,33 ; around 15% lower. Arti cial cerebrospinal uid recipes, which are largely developed for electrophysiological work and optimised to produce "healthy" action potentials in neurons (not to produce an environment in which brain tissue has stable mechanical properties), call for an osmolality of 280-338 mOsm/l depending on protocol and species 26,27,34 .…”

Acute brain slice elastic modulus decreases over time

“…The CSF osmolality of rats has been measured as ~ 307 mOsm/l 31 – 33 , suggesting that the two species are similar in this regard. By contrast, human CSF values average closer to 260 mOsm/l 34 , 35 ; around 15% lower. Artificial cerebrospinal fluid recipes, which are largely developed for electrophysiological work and optimised to produce “healthy” action potentials in neurons (not to produce an environment in which brain tissue has stable mechanical properties), call for an osmolality of 280–338 mOsm/l depending on protocol and species 18 , 29 , 36 .…”