normal pressure hydrocephalus

CSF dynamic analysis of a predictive pulsatility-based infusion test for normal pressure hydrocephalus

Authors: Qvarlander S, Malm J, Eklund A.

Disturbed cerebrospinal fluid (CSF) dynamics are part of the pathophysiology of normal pressure hydrocephalus (NPH) and can be modified and treated with shunt surgery. This study investigated the contribution of established CSF dynamic parameters to AMPmean, a prognostic variable defined as mean amplitude of cardiac-related intracranial pressure pulsations during 10 min of lumbar constant infusion, with the aim of clarifying the physiological interpretation of the variable. AMPmean and CSF dynamic parameters were determined from infusion tests performed on 18 patients with suspected NPH. Using a mathematical model of CSF dynamics, an expression for AMPmean was derived and the influence of the different parameters was assessed. There was high correlation between modelled and measured AMPmean (r = 0.98, p < 0.01). Outflow resistance and three parameters relating to compliance were identified from the model. Correlation analysis of patient data confirmed the effect of the parameters on AMPmean (Spearman's ρ = 0.58-0.88, p < 0.05). Simulated variations of ±1 standard deviation (SD) of the parameters resulted in AMPmean changes of 0.6-2.9 SD, with the elastance coefficient showing the strongest influence. Parameters relating to compliance showed the largest contribution to AMPmean, which supports the importance of the compliance aspect of CSF dynamics for the understanding of the pathophysiology of NPH.

Does the treatment of normal pressure hydrocephalus put the retinal ganglion cells at risk? A brief literature review and novel hypothesis

Authors: Bokhari RF, Baeesa SS.

Normal pressure hydrocephalus (NPH) is a poorly understood entity as well as a source of continuous controversy in the neuroscientific community. The surgical management of this disease requires that intracranial pressure (ICP), also referred to as the cerebrospinal fluid pressure (CSFP), be lowered using a cerebrospinal fluid (CSF) diversion procedure. Numerous complications are linked with this procedure; we believe that new evidence suggests that the induction or acceleration of glaucomatous optic neuropathy are possible sequelae that warrant further investigation. We also suggest potential solutions derived from the increased understanding of the disease's pathophysiology and new advances in imaging of the optic nerve head complex. The recent inclusion of the translaminar gradient (TLG) (the difference between the intraocular pressure (IOP) and the ICP/CSFP across the thickness of the lamina cribrosa in the optic nerve head complex) in the pathogenesis of normal tension glaucoma (NTG) suggests that the disease may be a complication encountered during the treatment of NPH with CSF diversion procedures. The significant decrease in CSFP required to treat NPH increases this gradient. In addition, there have been recent observations of an increased prevalence of NTG, as well as other forms of glaucoma, among patients with NPH, thought to be due to inherently fragile neurons in these patients. This new data suggest that patients who undergo ICP lowering therapy for their NPH may be at a higher risk of developing or accelerating already present NTG. We present the clinical and theoretical basis for our hypothesis after reviewing the relevant literature linking the two entities. We also propose a possible solution, as we believe that treatment guidelines for NPH should take the TLG into account. Indeed, recent advances in the imaging of the optic nerve head complex may provide an opportunity to detect the mechanical sequelae of an increased TLG in the preclinical stage, i.e., prior to optic nerve damage. If we are able to determine safe parameters for the TLG in this population, we may be able to recommend the initiation of prophylactic glaucoma therapy for selected patients.

Diagnosis of normal pressure hydrocephalus in elderly patients: a review

Authors: Verny M, Berrut G.

The definition of normal pressure hydrocephalus (NPH), in adults, associates clinical signs (Adams and Hakim triad) involving gait disorders, urinary incontinence and dementia, associated with aspects on brain imaging that are consistent with this hypothesis and also normal or slightly increased intracranial pressure. The aim of this study was to clarify the techniques and methods facilitating the diagnosis of NPH. The literature review has been conducted from the Medline database without date limitation including the keywords "normal pressure hydrocephalus" and "diagnosis." They should appear in the article title. From the 43 initially sorted, only 13 have been selected using exclusion criteria. The proposed methods are very sparse and focused on the improvement after surgical shunt. This focus is independent from the diagnosis criteria proposed in 2005. This introduces an ambiguity in the interpretation of the results. In practice, the diagnosis of NPH is more difficult in the elderly population where differential diagnoses are frequent, particularly vascular lesions (notably microangiopathy) and Alzheimer's disease. The more invasive techniques as continuous spinal drainage (usually during 3 days) or some features of CSF dynamics (R(out), compliance) seem to be the best predictors of after shunt improvement. However, these techniques are difficult to use in routine in the elderly. The combination of Evans index and corpus callosum angle on MRI is very useful to improve the differential diagnosis with cerebral atrophy. Spinal tap test (lumbar puncture with the removal of 40 mL of CSF) can be repeated two or three times for consecutive days to improve the predictive value before shunting. Gait and balance often improve after shunt, more than cognition and bladder disorders. In the elderly population, the prognosis after 3 years is non conclusive despite initial improvement. Poor prognosis seems to be due to associated pathologies in particular neurodegenerative diseases. This should be considered in decision-making of CSF shunt.

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