Cerebral oxygen metabolism in idiopathic-normal pressure hydrocephalus

Increasing brain N-acetylneuraminic acid alleviates hydrocephalus-induced neurological deficits

AIMS

This metabolomic study aimed to evaluate the role of N-acetylneuraminic acid (Neu5Ac) in the neurological deficits of normal pressure hydrocephalus (NPH) and its potential therapeutic effect.

METHODS

We analyzed the metabolic profiles of NPH using cerebrospinal fluid with multivariate and univariate statistical analyses in a set of 42 NPH patients and 38 controls. We further correlated the levels of differential metabolites with severity-related clinical parameters, including the normal pressure hydrocephalus grading scale (NPHGS). We then established kaolin-induced hydrocephalus in mice and treated them using N-acetylmannosamine (ManNAc), a precursor of Neu5Ac. We examined brain Neu5Ac, astrocyte polarization, demyelination, and neurobehavioral outcomes to explore its therapeutic effect.

RESULTS

Three metabolites were significantly altered in NPH patients. Only decreased Neu5Ac levels were correlated with NPHGS scores. Decreased brain Neu5Ac levels have been observed in hydrocephalic mice. Increasing brain Neu5Ac by ManNAc suppressed the activation of astrocytes and promoted their transition from A1 to A2 polarization. ManNAc also attenuated the periventricular white matter demyelination and improved neurobehavioral outcomes in hydrocephalic mice.

CONCLUSION

Increasing brain Neu5Ac improved the neurological outcomes associated with the regulation of astrocyte polarization and the suppression of demyelination in hydrocephalic mice, which may be a potential therapeutic strategy for NPH.

Cerebral oxygen extraction fraction declines with ventricular enlargement in patients with normal pressure hydrocephalus

OBJECTIVE

Normal pressure hydrocephalus (NPH) is a neurodegenerative disease that is potentially reversible by shunt surgery in approximately 60% of patients. Imaging may provide a means to investigate brain tissue viability and oxygen metabolism in NPH patients.

METHODS

Oxygen extraction fraction (OEF) mapping was generated from 3D multi-echo gradient echo MRI (mGRE) data using QQ-CCTV algorithm and cerebral blood flow (CBF) using 3D arterial spin labeling (ASL) MRI data, thereby calculating the cerebral metabolic rate of oxygen (CMRO2 = CBF × OEF × [H]a) in 16 NPH patients. Regression analyses using cortical gray matter and deep gray matter regions were conducted with age, gender, CSF stroke volume and normalized ventricular volume as independent variables.

RESULTS

OEF showed significant negative correlations with normalized brain ventricular volumes in the whole brain (p = 0.004, q = 0.01), cortical gray matter (p = 0.004, q = 0.01), caudate (p = 0.02, q = 0.04), and pallidum (p = 0.03, q = 0.04), but no significant correlation with CSF stroke volume (q > 0.05). There was no significant finding with CBF or CMRO2.

CONCLUSION

In NPH patients, low OEF in several regions was significantly correlated with large ventricular volumes, indicating decreased tissue oxygen metabolism with increased NPH severity. OEF mapping may provide a functional understanding of neurodegeneration in NPH and may improve monitoring of disease course and treatment outcomes.

The PUMCH Evaluation System of Idiopathic Normal Pressure Hydrocephalus and Clinical Practice

OBJECTIVE

Differentiating idiopathic normal pressure hydrocephalus (iNPH) from other neurodegenerative diseases is challenging. Only a portion of the patients clinically suspected of iNPH would respond to surgical intervention. A cerebrospinal fluid (CSF) tap test is usually used to predict surgery outcomes and hence aid clinical decision-making, but the workup varies. We introduce the CSF tap test conducted at our center and examine its power by analyzing data from a series of iNPH cases that underwent shunt placement. We analyze common features in the past medical history of our patients and investigate whether they are related to the etiology of iNPH.

METHODS

Data from 20 patients who were positive in the tap tests preoperatively and received ventriculoperitoneal shunting (VPS) were retrospectively analyzed. Preoperative and postoperative performance data were analyzed. History of any underlying medical conditions was taken into consideration. Patients with negative tap test results of the same period were also followed up.

RESULTS

We performed VPS placement in 20 NPH patients from October 2019 to February 2022. Of these, 90% exhibited improvement in at least 1 of the clinical triad, proving the predictive power of the Peking Union Medical College Hospital test workflow. The underlying conditions like hypertension, diabetes and insufficiency in cerebral blood supply were also found to be associated with the onset of NPH.

CONCLUSION

Our evaluation system is a valid tool for NPH assessment and can guide clinical decision-making. Comorbidities should be taken into consideration as they contribute to the pathogenesis and progression of NPH. Better identification of potential iNPH patients will lower the burden exerted on the family and the aging society.

Shunt Surgery Efficacy Is Correlated With Baseline Cerebrum Perfusion in Idiopathic Normal Pressure Hydrocephalus: A 3D Pulsed Arterial-Spin Labeling Study

This study investigated the relationship between preoperative cerebral blood flow (CBF) in patients with idiopathic normal pressure hydrocephalus (INPH) and preoperative clinical symptoms and changes of clinical symptoms after shunt surgery. A total of 32 patients with diagnosed INPH and 18 age-matched healthy controls (HCs) were involved in this study. All subjects underwent magnetic resonance imaging (MRI), including 3D pulsed arterial-spin labeling (PASL) for non-invasive perfusion imaging, and clinical symptom evaluation at baseline, and all patients with INPH were reexamined with clinical tests 1 month postoperatively. Patients with INPH had significantly lower whole-brain CBF than HCs, with the most significant differences in the high convexity, temporal lobe, precuneus, and thalamus. At baseline, there was a significant correlation between the CBF in the middle frontal gyrus, calcarine, inferior and middle temporal gyrus, thalamus, and posterior cingulate gyrus and poor gait manifestation. After shunting, improvements were negatively correlated with preoperative perfusion in the inferior parietal gyrus, inferior occipital gyrus, and middle temporal gyrus. Preoperative CBF in the middle frontal gyrus was positively correlated with the severity of preoperative cognitive impairment and negatively correlated with the change of postoperative MMSE score. There was a moderate positive correlation between anterior cingulate hypoperfusion and improved postoperative urination. Our study revealed that widely distributed and intercorrelated cortical and subcortical pathways are involved in the development of INPH symptoms, and preoperative CBF may be correlative to short-term shunt outcomes.

Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH), the most common type of adult‐onset hydrocephalus, is a potentially reversible neuropsychiatric entity characterized by dilated ventricles, cognitive deficit, gait apraxia, and urinary incontinence. Despite its relatively typical imaging features and clinical symptoms, the pathogenesis and pathophysiology of iNPH remain unclear. In this review, we summarize current pathogenetic conceptions of iNPH and its pathophysiological features that lead to neurological deficits. The common consensus is that ventriculomegaly resulting from cerebrospinal fluid (CSF) dynamics could initiate a vicious cycle of neurological damages in iNPH. Pathophysiological factors including hypoperfusion, glymphatic impairment, disturbance of metabolism, astrogliosis, neuroinflammation, and blood‐brain barrier disruption jointly cause white matter and gray matter lesions, and eventually lead to various iNPH symptoms. Also, we review the current treatment options and discuss the prospective treatment strategies for iNPH. CSF diversion with ventriculoperitoneal or lumboperitonealshunts remains as the standard therapy, while its complications prompt attempts to refine shunt insertion and develop new therapeutic procedures. Recent progress on advanced biomaterials and improved understanding of pathogenesis offers new avenues to treat iNPH.

The applause sign in elderly patients with idiopathic normal pressure hydrocephalus

Applause sign (AS) was shown to be an indicator of frontal subcortical dysfunction in many neurodegenerative diseases. Idiopathic normal pressure hydrocephalus (INPH) is one of those in which frontosubcortical disconnection can be displayed. We aimed to examine the presence of AS in the elderly patients with INPH and its possible diagnostic role in the frontal dysfunction commonly seen in the disease. Sixty-six patients diagnosed with probable INPH, 32 with behavioral variant of frontotemporal dementia (bvFTD) and 325 healthy elderly subjects were included in this cross-sectional and retrospective study. AS was evaluated with the clapping test. Patients with INPH were further assessed with frontal assessment battery (FAB), Stroop test, verbal fluency test and clock drawing test (CDT). The concentration of total amyloid-β 42 (Aβ42), Aβ40, total (t) tau and phosphorylated (p)-tau proteins were also measured in the cerebrospinal fluid (CSF). AS was observed in all groups (40% in bvFTD, 28.8% in INPH, 1.2% in controls, respectively). It was significantly more frequent in patients with bvFTD and INPH as compared to the controls (p < 0.001, for each). The frequency was similar in the patients with bvFTD and INPH (p = 0.802). Significant differences were found between the AS(+) and (-) INPH patients with regards to FAB, Stroop test-errors and verbal fluency test, except for the CSF proteins. AS can be used as a simple, useful and rapid clinical test that investigates executive dysfunction in elderly patients with INPH in both inpatient and outpatient settings.

Usefulness of Brain Positron Emission Tomography with Different Tracers in the Evaluation of Patients with Idiopathic Normal Pressure Hydrocephalous

Idiopathic normal pressure hydrocephalus (iNPH) is the only form of dementia that can be cured by surgery. Its diagnosis relies on clinical and radiological criteria. Identifying patients who can benefit from surgery is challenging, as other neurological diseases can be concomitant or mimic iNPH. We performed a systematic review on the role of positron emission tomography (PET) in iNPH. We retrieved 35 papers evaluating four main functional aspects with different PET radiotracers: (1) PET with amyloid tracers, revealing Alzheimer's disease (AD) pathology in 20-57% of suspected iNPH patients, could be useful in predictions of surgical outcome. (2) PET with radiolabeled water as perfusion tracer showed a global decreased cerebral blood flow (CBF) and regional reduction of CBF in basal ganglia in iNPH; preoperative perfusion parameters could predict surgical outcome. (3) PET with 2-Deoxy-2-[18F]fluoroglucose ([18F]FDG ) showed a global reduction of glucose metabolism without a specific cortical pattern and a hypometabolism in basal ganglia; [18F]FDG PET may identify a coexisting neurodegenerative disease, helping in patient selection for surgery; postsurgery increase in glucose metabolism was associated with clinical improvement. (4) Dopaminergic PET imaging showed a postsynaptic D2 receptor reduction and striatal upregulation of D2 receptor after treatment, associated with clinical improvement. Overall, PET imaging could be a useful tool in iNPH diagnoses and treatment response.

Current concepts on the pathophysiology of idiopathic chronic adult hydrocephalus: Are we facing another neurodegenerative disease?

INTRODUCTION

Since its description five decades ago, the pathophysiology of idiopathic chronic adult hydrocephalus (iCAH) has been traditionally related to the effect that ventricular dilatation exerts on the structures surrounding the ventricular system. However, altered cerebral blood flow, especially a reduction in the CSF turnover rate, are starting to be considered the main pathophysiological elements of this disease.

DEVELOPMENT

Compression of the pyramidal tract, the frontostriatal and frontoreticular circuits, and the paraventricular fibres of the superior longitudinal fasciculus have all been reported in iCAH. At the level of the corpus callosum, gliosis replaces a number of commissural tracts. Cerebral blood flow is also altered, showing a periventricular watershed region limited by the subependymal arteries and the perforating branches of the major arteries of the anterior cerebral circulation. The CSF turnover rate is decreased by 75%, leading to the reduced clearance of neurotoxins and the interruption of neuroendocrine and paracrine signalling in the CSF.

CONCLUSIONS

iCAH presents as a complex nosological entity, in which the effects of subcortical microangiopathy and reduced CSF turnover play a key role. According to its pathophysiology, it is simpler to think of iCAH more as a neurodegenerative disease, such as Alzheimer disease or Binswanger disease than as the classical concept of hydrocephalus.

A multicenter brain perfusion SPECT study evaluating idiopathic normal-pressure hydrocephalus on neurological improvement

PURPOSE

This study was designed to investigate the specific cerebral blood flow (CBF) pattern in patients with idiopathic normal-pressure hydrocephalus (iNPH) and a predictive value for shunt responsiveness in a multicenter study (Study of Idiopathic Normal-Pressure Hydrocephalus on Neurological Improvement: SINPHONI).

METHODS

Eighty-four iNPH patients underwent shunt operations using MRI selection criteria from the SINPHONI and were subjected to CBF single photon emission computed tomography (SPECT). The perfusion patterns on SPECT were classified: anterior-dominant CBF reduction type (A type), posterior-dominant CBF reduction type (P type), and mixed or diffuse CBF reduction type (M type). The predictive value of the CBF pattern for favorable shunt outcome was evaluated.

RESULTS

Favorable outcomes were obtained in 76% (64/84) of patients, and shunt responsiveness was achieved in 85% (71/84) of patients. Areas of severely reduced relative CBF were demonstrated around the corpus callosum and in the sylvian fissure area, which included the effects of dilatations of the ventricles and sylvian fissures and relatively increased perfusion in the medial and lateral frontal, parietal, and occipital areas at high convexity. Forty-nine (58%) cases were A type, 25 (30%) cases were M type, and 10 (12%) cases were P type. A, M, and P type cases exhibited 83, 84, and 90% positive predictive values for shunt responsiveness, respectively. Mean modified Rankin scale and Mini-Mental State Examination scores of the A type group were significantly better than those of other groups.

CONCLUSION

The iNPH patients showed various patterns of CBF reduction, but there was no significant difference in the predictive value among the three patterns, though CBF reduction patterns may suggest a severe condition of iNPH.

Global cerebral hypoperfusion in preclinical stage of idiopathic normal pressure hydrocephalus

In patients with idiopathic normal pressure hydrocephalus (iNPH), ventriculomegaly and narrowed subarachnoid spaces at the high convexity appear in magnetic resonance (MR) images before the occurrence of objective symptoms. In addition, quantitative regional cerebral blood flow (rCBF) has been reported to be reduced in iNPH patients with objective symptoms. To determine whether reduced rCBF is responsible for the appearance of symptoms, we compared rCBF in patients with suspected iNPH with no objective triad symptoms (NOS), iNPH patients with apparent objective triad symptoms (AOS) and normal control subjects (NC). Regional CBF was quantified in 35 Regions-of-interest (ROIs) by 123I-IMP single photon emission computed tomography (SPECT) using the autoradiography (ARG) method. Multiple comparisons showed that, in all brain regions examined except for in the frontal white matter, rCBF in the NOS group was significantly lower than that in the NC group, but in all brain regions, not significantly different from that of the AOS group. These results suggest that factors other than rCBF in the resting state are responsible for the occurrence of objective symptoms of iNPH.

Ongoing search for diagnostic biomarkers in idiopathic normal pressure hydrocephalus

Idiopathic normal pressure hydrocephalus is a syndrome, which typically has a clinical presentation of gait/balance disturbance, often accompanied by cognitive decline and/or urinary incontinence. Its diagnosis is based on relevant history and clinical examination, appropriate imaging findings and physiological testing. The clinical picture of idiopathic normal pressure hydrocephalus may occasionally be difficult to distinguish from that of Alzheimer’s dementia, subcortical ischemic vascular dementia and Parkinson’s disease. The aim of this article is to systematically review the literature from the last 29 years in order to identify cerebrospinal fluid (CSF) or imaging biomarkers that may aid in the diagnosis of the syndrome. The authors concluded that no CSF or imaging biomarker is currently fulfilling the criteria required to aid in the diagnosis of the condition. However, a few studies have revealed promising CSF and imaging markers that need to be verified by independent groups. The reasons that the progress in this field has been slow so far is also commented on, as well as steps required to apply the current evidence in the design of future studies within the field.

Normal pressure hydrocephalus

Normal Pressure Hydrocephalus first became recognized as a treatable, reversible disorder in the 1960s. The classic triad of magnetic apraxia, urinary incontinence, and dementia remain relevant into the 21(st) century as being the basis for symptomatic diagnosis and predicting potential benefit from ventriculoperitoneal shunting, though they have been greatly augmented by the addition of modern neuroimaging, particularly MRI. Modern criteria recognize a wider range of diagnostic criteria, and new positive and negative prognostic indicators for treatment benefit have been discovered, though the mainstay remains initial drainage of a large volume of cerebrospinal fluid and monitoring for clinical improvement. Even with our advances in understanding both primary and secondary normal pressure hydrocephalus, diagnosis, management, and counseling remain challenging in this disorder.

Brain metabolism in adult chronic hydrocephalus

Normal pressure hydrocephalus (NPH) is the most frequent form of chronic hydrocephalus in adults. NPH remains underdiagnosed although between 5% and 10% of all demented patients may suffer from this disorder. As dementia is an increasing demographic problem, treatable forms such as in NPH have become a central issue in neurology. Despite the traditional perception of hydrocephalus being a disorder of disturbed CSF dynamics, in NPH metabolic impairment seems at least as important. So far, the only valid animal model of NPH is chronic adult kaolin hydrocephalus. In this model, opening of alternative CSF outflow pathways leads to normal or near-normal intracranial pressure and CSF outflow resistance. Yet, various metabolic disturbances cause ongoing ventricular enlargement and characteristic symptoms including cognitive decline and gait ataxia. Delayed hippocampal neuronal death, accumulation of beta-amyloid and disturbed cholinergic neurotransmission may contribute to memory dysfunction. Compromised periventricular blood flow, decreased dopamine levels in the substantia nigra and damaged striatal GABAergic interneurons may reflect basal ganglia symptoms. At least in human hydrocephalus cerebrovascular co-morbidity of the white matter plays an important role as well. It seems that in hydrocephalus from a certain 'point of no return' metabolic impairment becomes decoupled from CSF dynamics and, at least partly, self-sustained. This is probably the reason why despite restored CSF circulation by shunting many patients with chronic hydrocephalus still suffer from severe neurological deficits. The present paper offers a comprehensive review of the experimental and clinical data suggesting metabolic disturbances in chronic hydrocephalus.

Shunting for normal pressure hydrocephalus (NPH)

BACKGROUND

Since the condition was first described in 1965, the syndrome of normal pressure hydrocephalus (NPH) has conventionally been managed by placement of a cerebrospinal fluid (CSF) shunt.

OBJECTIVES

To determine the effectiveness of shunting procedures in promoting stability or improvement in the neurological symptoms and signs of NPH.

SEARCH STRATEGY

The trials were identified from a search of the Specialized Register of the Cochrane Dementia and Cognitive Improvement Group on 26 June 2001 using the terms 'shunt*' and 'normal pressure hydrocephalus'.

SELECTION CRITERIA

Studies included for analysis were those involving the placement of a CSF shunt for the treatment of NPH as part of a randomized controlled trial.

DATA COLLECTION AND ANALYSIS

No data matching the selection criteria were found.

MAIN RESULTS

No randomized controlled trials of shunt placement versus no shunt were found.

REVIEWER'S CONCLUSIONS

There is no evidence to indicate whether placement of a shunt is effective in the management of NPH.