Altered white matter microstructure mediates the relationship between hemoglobin levels and cognitive control deficits in end-stage renal disease patients

Nomogram to Estimate the Risk of Chronic Kidney Disease-Associated Pruritus in Patients with End-Stage Renal Disease Undergoing Peritoneal Dialysis: Model Development and Validation Study

INTRODUCTION

Chronic kidney disease-associated pruritus (CKD-aP) frequently occurs in patients with end-stage renal disease (ESRD) undergoing peritoneal dialysis (PD) and presents a therapeutic challenge to physicians owing to the diversity of its pathogenesis. Herein, we developed and validated a nomogram model for individualized risk estimation of CKD-aP and investigated the possible causes of CKD-aP in PD patients.

METHODS

We retrospectively screened patients with CKD-aP who underwent PD between 2021 and 2023 at the First Affiliated Hospital of Xi'an Jiaotong University Peritoneal Dialysis Center. Nomograms for each outcome were computed from multivariate logistic regression models with the least absolute shrinkage and selection operator regression and univariate logistic regression for variable selection. The discriminative ability was estimated by Harrell's C-index, and the accuracy was assessed graphically with a calibration curve plot. Models were validated internally using bootstrapping and externally by calculating their performance on a validation cohort. Decision curve analysis was used to assess the model's clinical usefulness.

RESULTS

In all, a total of 487 patients were entered in the analysis, including 325 in the development cohort and 162 in the validation cohort. The final nomogram incorporated five variables: age, interleukin-6, hemoglobin, residual urine volume, and renal Kt/V. The C-index of the model was 0.733 (95% CI: 0.679-0.787), and the calibration curve was a straight line with a slope close to 1. Both internal and external validations confirmed the model's good performance, with C-index of 0.725 (95% CI: 0.662-0.774) and 0.706 (95% CI: 0.623-0.789), respectively. Decision curve analysis showed that the nomogram had good clinical benefits.

CONCLUSION

Our study proposes a nomogram model for CKD-aP risk assessment in ESRD patients with PD. This nomogram might help in clinical decision-making and evidence-based selection of therapy.

Assessing Cognition in CKD Using the National Institutes of Health Toolbox

Key Points

Participants with CKD had detectable cognitive deficits in fluid cognition, dexterity, and total cognition. Sex differences in cognition exist in people with CKD.

Background

CKD is largely an age-related clinical disorder with accelerated cognitive and cardiovascular aging. Cognitive impairment is a well-documented occurrence in midlife and older adults with CKD and affects multiple domains. We examined cognition function and potential sex differences in cognition in adults with CKD.

Methods

We included 105 individuals (49.5% women) with CKD stage 3b–4 (eGFR, 15–44 ml/min) from the Bicarbonate Administration in CKD Trial (NCT02915601 ). We measured cognitive function using the National Institutes of Health Toolbox Cognition Battery, which assesses cognitive and motor measures, such as executive function, attention, memory, and dexterity. All study measures were collected and analyzed at the study baseline.

Results

The mean (SD) age and eGFR were 61±12 years and 34.9±9.8 ml/min per 1.73 m2. Overall, when compared with the National Institutes of Health Toolbox reference population, participants scored, on average, below the 50th percentile across all cognitive domain tests and the dexterity test. Total cognition scores were also below the 50th percentile. Participants with stage 4 CKD had significantly lower fluid cognition scores compared with those with CKD stage 3b (β -estimate −5.4 [95% confidence interval, −9.8 to −0.9]; P = 0.03). Female participants with CKD performed significantly better on the episodic memory tests and dexterity tests (dominant and nondominant pegboard tests) and had higher crystallized cognition scores, on average, compared with male participants.

Conclusions

Participants with CKD had detectable cognitive deficits in fluid cognition, dexterity, and total cognition. In addition, sex differences in cognitive measures were found among people with CKD.

Risk factors for neurocognitive impairment and the relation with structural brain abnormality in children and young adults with severe chronic kidney disease

BACKGROUND

Severe chronic kidney disease (CKD) in children and young adults has shown to be associated with abnormal brain development, which may contribute to neurocognitive impairments. We aimed to investigate risk factors for neurocognitive impairment and investigate the relation with structural brain abnormalities in young severe CKD patients.

METHODS

This cross-sectional study includes 28 patients with severe CKD (eGFR < 30), aged 8-30 years (median 18.5 years), on different treatment modalities (pre-dialysis [n = 8], dialysis [n = 8], transplanted [n = 12]). We assessed neurocognitive functioning using a comprehensive test battery and brain structure by magnetic resonance imaging metrics of brain volume and white matter integrity (fractional anisotropy [FA] and mean diffusivity [MD] measured with diffusion tensor imaging). Multivariate regression and mediation analyses were performed between clinical CKD parameters, brain structure, and neurocognitive outcome.

RESULTS

A combination of risk factors (e.g., longer time since kidney transplantation, longer dialysis duration and late CKD onset) was significantly associated with lower intelligence and/or worse processing speed and working memory. Lower FA in a cluster of white matter tracts was associated with lower intelligence and mediated the relation between clinical risk factors and lower intelligence.

CONCLUSIONS

Young severe CKD patients with a prolonged duration of kidney replacement therapy, either dialysis or transplantation are at particular risk for impairments in intelligence, processing speed, and working memory. Disrupted white matter integrity may importantly contribute to these neurocognitive impairments. Prospective, longitudinal studies are needed to elucidate the mechanisms involved in CKD and treatment that affect white matter integrity and neurocognitive outcome in young patients. A higher resolution version of the Graphical abstract is available as Supplementary information.

Brain Micro-Structural and Functional Alterations for Cognitive Function Prediction in the End-Stage Renal Disease Patients Undergoing Maintenance Hemodialysis

RATIONALE AND OBJECTIVES

The goal of this study was to investigate the relationship between altered brain micro-structure and function, and cognitive function in patients with end-stage renal disease (ESRD) undergoing maintenance hemodialysis. Specially, diffusion kurtosis imaging (DKI), the resting-state functional connectivity (FC) algorithm, and the least squares support vector regression machine (LSSVRM) were utilized to conduct our study.

MATERIALS AND METHODS

A total of 50 patients and 36 matched healthy controls were prospectively enrolled in our study. All subjects completed the Montreal cognitive assessment scale (MoCA) test. DKI and resting-state functional magnetic resonance imaging were measured. Relationship between DKI parameters, FC, and MoCA scores was evaluated. LSSVRM combined with the whale optimization algorithm (WOA) was used to predict cognitive function scores.

RESULTS

In ESRD patients, altered DKI metrics were identified in 12 brain regions. Furthermore, we observed changes in FC values based on regions of interest (ROIs) in nine brain regions, involved in default mode network (DMN), frontoparietal network (FPN), and the limbic system. Significant correlations among DKI values, FC values, and MoCA scores were found. To some extent, altered FC showed significant correlations with changed DKI parameters. Furthermore, optimized prediction models were applied to more accurately predict the cognitive function associated with ESRD patients.

CONCLUSION

Micro-structural and functional brain changes were found in ESRD patients, which may account for the onset of cognitive impairment in affected patients. These quantitative parameters combined with our optimized prediction model may be helpful to establish more reliable imaging markers to detect and monitor cognitive impairment associated with ESRD.

Fiber connectivity density mapping in end-stage renal disease patients: a preliminary study

Abnormal brain structural connectivity of end-stage renal disease(ESRD) is associated with cognitive impairment. However, the characteristics of cortical structural connectivity have not been investigated in ESRD patients. Here, we study structural connectivity of the entire cerebral cortex using a fiber connectivity density(FiCD) mapping method derived from diffusion tensor imaging(DTI) data of 25 ESRD patients and 20 healthy controls, and between-group differences were compared in a vertexwise manner. We also investigated the associations between these abnormal cortical connectivities and the clinical variables using Pearson correlation analysis and multifactor linear regression analysis. Our results demonstrated that the mean global FiCD value was significantly decreased in ESRD patients. Notably, FiCD values were significantly changed(decreased or increased) in certain cortical regions, which mainly involved the bilateral dorsolateral prefrontal cortex(DLPFC), inferior parietal cortex, lateral temporal cortex and middle occipital cortex. In ESRD patients, we found a trend of negative correlation between the increased FiCD values of bilateral middle frontal gyrus and serum creatinine, urea, parathyroid hormone(PTH) levels and dialysis duration. Only the white matter hyperintensity(WMH) scores were significantly negatively correlated with the global FiCD value in multifactor regression analysis. Our results suggested that ESRD patients exhibited extensive impaired cortical structural connectivity, which was related to the severity of WMHs. A compensation mechanism of cortical structural recombination may play a role in how the brain adapts to maintain optimal network function. Additionally, the serum creatinine, urea and PTH levels may be risk factors for brain structural network decompensation in ESRD patients.

Structural brain abnormalities in children and young adults with severe chronic kidney disease

BACKGROUND

The pathophysiology of neurological dysfunction in severe chronic kidney disease (CKD) in children and young adults is largely unknown. We aimed to investigate brain volumes and white matter integrity in this population and explore brain structure under different treatment modalities.

METHODS

This cross-sectional study includes 24 patients with severe CKD (eGFR < 30) aged 8-30 years (median = 18.5, range = 9.1-30.5) on different therapy modalities (pre-dialysis, n = 7; dialysis, n = 7; transplanted, n = 10) and 21 healthy controls matched for age, sex, and parental educational level. Neuroimaging targeted brain volume using volumetric analysis on T1 scans and white matter integrity with tract-based spatial statistics and voxel-wise regression on diffusion tensor imaging (DTI) data.

RESULTS

CKD patients had lower white matter integrity in a widespread cluster of primarily distal white matter tracts compared to healthy controls. Furthermore, CKD patients had smaller volume of the nucleus accumbens relative to healthy controls, while no evidence was found for abnormal volumes of gray and white matter or other subcortical structures. Longer time since successful transplantation was related to lower white matter integrity. Exploratory analyses comparing treatment subgroups suggest lower white matter integrity and smaller volume of the nucleus accumbens in dialysis and transplanted patients relative to healthy controls.

CONCLUSIONS

Young CKD patients seem at risk for widespread disruption of white matter integrity and to some extent smaller subcortical volume (i.e., nucleus accumbens). Especially patients on dialysis therapy and patients who received a kidney transplant may be at risk for disruption of white matter integrity and smaller volume of the nucleus accumbens.

Fixel-based Analysis of Diffusion MRI: Methods, Applications, Challenges and Opportunities

Diffusion MRI has provided the neuroimaging community with a powerful tool to acquire in-vivo data sensitive to microstructural features of white matter, up to 3 orders of magnitude smaller than typical voxel sizes. The key to extracting such valuable information lies in complex modelling techniques, which form the link between the rich diffusion MRI data and various metrics related to the microstructural organization. Over time, increasingly advanced techniques have been developed, up to the point where some diffusion MRI models can now provide access to properties specific to individual fibre populations in each voxel in the presence of multiple "crossing" fibre pathways. While highly valuable, such fibre-specific information poses unique challenges for typical image processing pipelines and statistical analysis. In this work, we review the "Fixel-Based Analysis" (FBA) framework, which implements bespoke solutions to this end. It has recently seen a stark increase in adoption for studies of both typical (healthy) populations as well as a wide range of clinical populations. We describe the main concepts related to Fixel-Based Analyses, as well as the methods and specific steps involved in a state-of-the-art FBA pipeline, with a focus on providing researchers with practical advice on how to interpret results. We also include an overview of the scope of all current FBA studies, categorized across a broad range of neuro-scientific domains, listing key design choices and summarizing their main results and conclusions. Finally, we critically discuss several aspects and challenges involved with the FBA framework, and outline some directions and future opportunities.

Neurological effects of hemodialysis on white matter microstructure in end-stage renal disease

OBJECTIVES

To detect the effects of hemodialysis (HD) on the central nervous system (CNS), the present study forces the memory storage capacity and the difference in white matter (WM) microstructure characteristics among end-stage renal disease (ESRD) participants before HD initiation (ESRD-BHD), ESRD participants with maintenance HD (ESRD-MHD), and healthy participants (HCs).

METHODS

Between 2016 and 2018, 56 ESRD-BHD, 39 ESRD-MHD, and 56 HCs were recruited for this study. The fractional anisotropy (FA) of tractography streamlines within the working memory network was investigated using a novel along-tracts analysis method. The relationship between WM microstructure and working memory scores, measured from an n-back task, were detected by multiple correlation analysis.

RESULTS

As compared with HCs, a significantly lower FA was found along part of the WM in the working memory network in ESRD-BHD. In the group-difference location of ESRD-BHD and HCs, the FA of ESRD-MHD was reversed to normal levels in HCs. However, the FA in a new location was differentially reduced across groups: highest in HCs, intermediate in ESRD-BHD, and lowest in ESRD-MHD. Correlation analysis showed that a longer reaction time correlated to a lower FA, according to the following pattern: ESRD-BHD > ESRD-MHD > HCs.

CONCLUSION

Despite the persisting abnormal brain structure, our findings suggest HD has a neuroprotective effect in ESRD patients.

CENTRAL NERVOUS SYSTEM RESPONSE TO CHRONIC KIDNEY DISEASE

Due to the aging of the human population, the prevalence of chronic diseases such as chronic kidney disease (CKD) is increasing every year. Chronic kidney disease is a general term that refers to heterogeneous disorders that affect kidney structure and function. Decrease in glomerular filtration can be defined as chronic and progressive deterioration in fluid-solute balance, metabolic and endocrine functions of the kidney. CKD often affects the elderly. With the advancement of age, some structural and functional changes occur in the kidneys. Therefore, the number of patients suffering from mild and moderate CKD is expected to increase in the future.CKD leads to the deep metabolic and hemodynamic changes that damage other organs, such as the heart and brain. CNS abnormalities and cognitive deficits progress with the severity of CBS and occurs mostly among hemodialysis patients. It also has great socio-economic effects on individuals. Since symptoms of CKD are not often found in patients, early recognition of risk factors is the main point. For this reason, it is necessary to identify possible protective and preventive treatments to be applied in at-risk groups and to examine these mechanisms for the treatment of the disease. This review provides available information on the relevant mechanisms.

Visual Dysfunction Predicts Cognitive Impairment and White Matter Degeneration in Parkinson's Disease

BACKGROUND

Visual dysfunction predicts dementia in Parkinson's disease (PD), but whether this translates to structural change is not known. The objectives of this study were to identify longitudinal white matter changes in patients with Parkinson's disease and low visual function and also in those who developed mild cognitive impairment.

METHODS

We used fixel-based analysis to examine longitudinal white matter change in PD. Diffusion MRI and clinical assessments were performed in 77 patients at baseline (22 low visual function/55 intact vision and 13 PD-mild cognitive impairment/51 normal cognition) and 25 controls and again after 18 months. We compared microstructural changes in fiber density, macrostructural changes in fiber bundle cross-section and combined fiber density and cross-section, across white matter, adjusting for age, sex, and intracranial volume.

RESULTS

Patients with PD and visual dysfunction showed worse cognitive performance at follow-up and were more likely to develop mild cognitive impairment compared with those with normal vision (P = 0.008). Parkinson's with poor visual function showed diffuse microstructural and macrostructural changes at baseline, whereas those with mild cognitive impairment showed fewer baseline changes. At follow-up, Parkinson's with low visual function showed widespread macrostructural changes, involving the fronto-occipital fasciculi, external capsules, and middle cerebellar peduncles bilaterally. No longitudinal change was seen in those with mild cognitive impairment at baseline or converters, even when the 2 groups were combined.

CONCLUSION

Parkinson's patients with poor visual function show increased white matter damage over time, providing further evidence for visual function as a marker of imminent cognitive decline. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

How Do You Feel Now? The Salience Network Functional Connectivity in End-Stage Renal Disease

Objective

The network connectivity basis of cognitive declines in end-stage renal disease (ESRD) remains unclear. A triple-network model of the salience (SN), executive control, and default mode networks has been suggested to be critical for efficient cognition. Here, we aimed to test the hypothesis that SN may play a role in cognitive impairment in patients with ESRD.

Materials and Methods

We investigated functional connectivity (FC) alterations within the SN between 43 ESRD patients (19 females/24 males, 46 ± 10 years) and 43 healthy controls (HC) (19 females/24 males, 47 ± 10 years), and performed linear support vector machine (LSVM) analysis on significant FC pairs within the SN to discriminate the two groups, and tested the accuracy of the classifier. Association and mediation analyses were conducted among the significant FC pairs within the SN nodes, clinical indicators, and neuropsychological tests scores.

Results

We identified significant between-group FC pairs within the SN and fairly good classification efficiency with significant accuracy (72.09%, p < 0.001). We found that FC between the right supramarginal gyrus and right anterior insula (AISL) was positively correlated with MoCA (r = 0.4010, p = 0.008); FC between the dorsal anterior cingulate cortex (dACC) and left AISL was positively correlated with the level of hemoglobin (r = 0.4979, p < 0.001). Mediation analysis found that the indirect effect of hemoglobin on forward digit span test scores via the FC between the dACC and right AISL (p < 0.05).

Conclusion

Disrupted SN connectivity may help explain cognitive declines in ESRD patients and act as a potential early biomarker. Moreover, the SN connectivity may interact with anemia to promote cognitive impairment.

Dentatorubrothalamic tract reduction using fixel-based analysis in corticobasal syndrome

PURPOSE

The word "fixel" refers to the specific fiber population within each voxel, and fixel-based analysis (FBA) is a recently developed technique that facilitates fiber tract-specific statistical analysis. The aim of the paper is to apply FBA to detect impaired fibers for corticobasal syndrome (CBS) especially in regions that contain multiple crossed fibers.

METHODS

FBA was performed in cohorts of participants clinically diagnosed with CBS (n = 10) and Parkinson's disease (n = 15) or in healthy controls (n = 9). The parameters of the diffusion weighted image were echo time, 83 ms; time, 8123.6 ms; flip angle, 90°; section thickness, 2 mm; b = 1000 s/mm²; and 32 axes. Diffusion tensor analysis was conducted using tract-based spatial statistics (TBSS), and white matter volume was estimated via voxel-based morphometry.

RESULTS

A comparison of PD or HC to CBS revealed a significant difference in the dentatorubrothalamic tract of the brainstem in FBA in addition to the affected regions in voxel-based morphometry and TBSS (family-wise error-corrected p < 0.05). Reduction of the white matter fibers crossing the brainstem could not be detected via microstructural changes identified using TBSS, but it was detected using FBA.

CONCLUSION

FBA has some advantages in determining the distribution of corticobasal syndrome lesions.

Fixel Based Analysis Reveals Atypical White Matter Micro- and Macrostructure in Adults With Autism Spectrum Disorder: An Investigation of the Role of Biological Sex

Atypical white matter (WM) microstructure is commonly implicated in the neuropathophysiology of autism spectrum disorder (ASD). Fixel based analysis (FBA), at the cutting-edge of diffusion-weighted imaging, can account for crossing WM fibers and can provide indices of both WM micro- and macrostructure. We applied FBA to investigate WM structure between 25 (12 males, 13 females) adults with ASD and 24 (12 males, 12 females) matched controls. As the role of biological sex on the neuropathophysiology of ASD is of increasing interest, this was also explored. There were no significant differences in WM micro- or macrostructure between adults with ASD and matched healthy controls. When data were stratified by sex, females with ASD had reduced fiber density and cross-section (FDC), a combined metric comprised of micro- and macrostructural measures, in the corpus callosum, a finding not detected between the male sub-groups. We conclude that micro- and macrostructural WM aberrations are present in ASD, and may be influenced by biological sex.

Vasogenic Brain Edema During Maintenance Hemodialysis : Preliminary Results from Tract-based Spatial Statistics and Voxel-based Morphometry

BACKGROUND

Hemodialysis (HD), especially when first initiated, can cause neurological deterioration. Presumably this is due to transient cerebral edema, which has been observed using diffusion weighted magnetic resonance imaging (MRI) in experimental and human studies; however, this has not been investigated under maintenance hemodialysis (mHD). Moreover, there are no studies to date investigating regional effects of mHD on grey and white matter volumes.

METHODS

In this study eight patients with end stage renal disease (ESRD) were examined immediately before and after mHD sessions with multimodal MRI, including diffusion tensor imaging (DTI) and high-resolution structural imaging. Additionally, eight healthy, age-matched and sex-matched controls were examined for comparison. Data were analyzed using tract-based spatial statistics and voxel-based morphometry.

RESULTS

At baseline, ESRD patients had significantly reduced values of fractional anisotropy (FA) and axial diffusivity as well as bilaterally reduced grey matter volume in the insula, compared with controls. After the mHD session, FA further decreased while axial, radial, and mean diffusivity significantly increased ubiquitously throughout the white matter. Voxel-based morphometry revealed a corresponding significant increase in white matter volume in the central right hemisphere and splenium, as well as in cortical grey matter in the anterior medial frontal and cingulate cortex. None of the patients showed neurological deterioration.

CONCLUSION

In this study ESRD patients showed white matter changes indicative of chronic microstructural damage when compared with healthy controls, as previously reported. In addition, patients showed signs of a transient extracellular cerebral edema, which has not yet been observed in the absence of neurological symptoms.

Altered white matter microstructure mediates the relationship between hemoglobin levels and cognitive control deficits in end-stage renal disease patients

The brain-kidney crosstalk theory suggested that the brain and kidneys may be considered end organs on parallel trajectories and subject to shared risk factors, which are receiving increasing attention. Cognitive control deficits were frequently presented in patients with end-stage renal disease (ESRD). Whether or not cognitive control impairment is concerned with brain-kidney crosstalk is in need of further research. To detect the relationship between ESRD and cognitive control impairment, diffusion tensor imaging was collected in 64 healthy controls (HCs) and 64 patients with ESRD. Tract-based spatial statistics and fixel-based analysis were used to detect the difference of white matter (WM) microstructure and morphology between ESRD patients and HCs in the whole brain. Tractography atlas-based analysis was also used to investigate the difference of diffusional characteristics along fiber bundles of interest between the two groups. For the whole-brain analysis, ESRD patients showed WM microstructural alteration and fiber density variation in the cingulum. In addition, ESRD patients exhibited higher MD and RD than HCs along the anterior cingulum. Among all of the blood biochemistry tests that represent kidney disease to a degree, the stepwise regression analysis showed that only hemoglobin significantly contributed to the cognitive control deficits in ESRD patients. Mediation analysis proved that the relationship between hemoglobin and cognitive control deficits of ESRD patients was mediated by WM microstructural alteration of the cingulum. Our results indicated that the anterior cingulum was correlated with cognitive control deficits and mediated the impact of hemoglobin on cognitive control.