Silent infarcts in sickle cell disease occur in the border zone region and are associated with low cerebral blood flow

The influence of voxelotor on cerebral blood flow and oxygen extraction in pediatric sickle cell disease

ABSTRACT

Voxelotor is an inhibitor of sickle hemoglobin polymerization that is used to treat sickle cell disease. Although voxelotor has been shown to improve anemia, the clinical benefit on the brain remains to be determined. This study quantified the cerebral hemodynamic effects of voxelotor in children with sickle cell anemia (SCA) using noninvasive diffuse optical spectroscopies. Specifically, frequency-domain near-infrared spectroscopy combined with diffuse correlation spectroscopy were used to noninvasively assess regional oxygen extraction fraction (OEF), cerebral blood volume, and an index of cerebral blood flow (CBFi). Estimates of CBFi were first validated against arterial spin-labeled magnetic resonance imaging (ASL-MRI) in 8 children with SCA aged 8 to 18 years. CBFi was significantly positively correlated with ASL-MRI-measured blood flow (R2 = 0.651; P = .015). Next, a single-center, open-label pilot study was completed in 8 children with SCA aged 4 to 17 years on voxelotor, monitored before treatment initiation and at 4, 8, and 12 weeks (NCT05018728). By 4 weeks, both OEF and CBFi significantly decreased, and these decreases persisted to 12 weeks (both P < .05). Decreases in CBFi were significantly correlated with increases in blood hemoglobin (Hb) concentration (P = .025), whereas the correlation between decreases in OEF and increases in Hb trended toward significance (P = .12). Given that previous work has shown that oxygen extraction and blood flow are elevated in pediatric SCA compared with controls, these results suggest that voxelotor may reduce cerebral hemodynamic impairments. This trial was registered at www.ClinicalTrials.gov as #NCT05018728.

Distribution of Silent Cerebral Infarcts in Adults With Sickle Cell Disease

BACKGROUND AND OBJECTIVES

Previously we demonstrated that 90% of infarcts in children with sickle cell anemia occur in the border zone regions of cerebral blood flow (CBF). We tested the hypothesis that adults with sickle cell disease (SCD) have silent cerebral infarcts (SCIs) in the border zone regions, with a secondary hypothesis that older age and traditional stroke risk factors would be associated with infarct occurrence in regions outside the border zones.

METHODS

Adults with SCD 18-50 years of age were enrolled in a cross-sectional study at 2 centers and completed a 3T brain MRI. Participants with a history of overt stroke were excluded. Infarct masks were manually delineated on T2-fluid-attenuated inversion-recovery MRI and registered to the Montreal Neurological Institute 152 brain atlas to generate an infarct heatmap. Border zone regions between anterior, middle, and posterior cerebral arteries (ACA, MCA, and PCA) were quantified using the Digital 3D Brain MRI Arterial Territories Atlas, and logistic regression was applied to identify relationships between infarct distribution, demographics, and stroke risk factors.

RESULTS

Of 113 participants with SCD (median age 26.1 years, interquartile range [IQR] 21.6-31.4 years, 51% male), 56 (49.6%) had SCIs. Participants had a median of 5.5 infarcts (IQR 3.2-13.8). Analysis of infarct distribution showed that 350 of 644 infarcts (54.3%) were in 4 border zones of CBF and 294 (45.6%) were in non-border zone territories. More than 90% of infarcts were in 3 regions: the non-border zone ACA and MCA territories and the ACA-MCA border zone. Logistic regression showed that older participants have an increased chance of infarcts in the MCA territory (odds ratio [OR] 1.08; 95% CI 1.03-1.13; p = 0.001) and a decreased chance of infarcts in the ACA-MCA border zone (OR 0.94; 95% CI 0.90-0.97; p < 0.001). The presence of at least 1 stroke risk factor did not predict SCI location in any model.

DISCUSSION

When compared with children with SCD, in adults with SCD, older age is associated with expanded zones of tissue infarction that stretch beyond the traditional border zones of CBF, with more than 45% of infarcts in non-border zone regions.

Montreal cognitive assessment in Brazilian adults with sickle cell disease: The burdens of poor sociocultural background

Sickle cell disease (SCD) patients are at higher risk of developing silent cerebral infarcts and overt stroke, which may reflect cognitive impairment, functional limitations, and worse quality of life. The cognitive function of Brazilian adult SCD patients (n = 124; 19-70 years; 56 men; 79 SS, 28 SC, 10 S/β0, 7 S/β+) was screened through Montreal Cognitive Assessment (MoCA) and correlated the results with possible predictive factors for test performance, including sociocultural, clinical, laboratory data and brain imaging. The Median MoCA score was 23 (8-30); 70% had a 25-or-less score, suggesting some level of cognitive impairment. There were no significant associations between MoCA results and any clinical or laboratory data in SS and SC patients; however, a significant correlation (P = 0.03) with stroke was found in HbS/β-thalassemic patients. Correlations were further detected according to sociodemographic conditions, such as age (r = -0.316; P < 0.001), age at first job (r = 0.221; P = 0.018), personal (r = 0.23; P = 0.012) and per capita familiar incomes (r = 0.303; P = 0.001), personal (r = 0.61; P = 0), maternal (r = 0.536; P = 0), and paternal educational status (r = 0.441; P = 0). We further sought independent predictors of performance using multivariable regressions and increased education was an independent predictor of better scores in MoCA (0.8099, 95% confidence interval [CI]: 0.509-1.111). Brain imaging analysis showed significant and progressive atrophy in important cerebral areas related to memory, learning, and executive function. These data point to the high prevalence and impact of cognitive decline in adult SCD patients, mirrored in brain atrophic areas. It is also possible to observe the influence of sociodemographic conditions on patients' cognitive performances and the need for creating focused therapeutic plans that address these deficiencies. Moreover, the absence of a significant correlation of MoCA values with stroke in the SS and SC groups may be related to the worst sociocultural and economic conditions of the Brazilian African descent population, in which the impact of low educational stimulation on cognitive function can outweigh even the anatomical damage caused by the disease.

Comparison of cerebral oxygen extraction fraction using ASE and TRUST methods in patients with sickle cell disease and healthy controls

Abnormal oxygen extraction fraction (OEF), a putative biomarker of cerebral metabolic stress, may indicate compromised oxygen delivery and ischemic vulnerability in patients with sickle cell disease (SCD). Elevated OEF was observed at the tissue level across the brain using an asymmetric spin echo (ASE) MR method, while variable global OEFs were found from the superior sagittal sinus (SSS) using a T2-relaxation-under-spin-tagging (TRUST) MRI method with different calibration models. In this study, we aimed to compare the average ASE-OEF in the SSS drainage territory and TRUST-OEF in the SSS from the same SCD patients and healthy controls. 74 participants (SCD: N = 49; controls: N = 25) underwent brain MRI. TRUST-OEF was quantified using the Lu-bovine, Bush-HbA and Li-Bush-HbS models. ASE-OEF and TRUST-OEF were significantly associated in healthy controls after controlling for hematocrit using the Lu-bovine or the Bush-HbA model. However, no association was found between ASE-OEF and TRUST-OEF in patients with SCD using either the Bush-HbA or the Li-Bush-HbS model. Plausible explanations include a discordance between spatially volume-averaged oxygenation brain tissue and flow-weighted volume-averaged oxygenation in SSS or sub-optimal calibration in SCD. Further work is needed to refine and validate non-invasive MR OEF measurements in SCD.

Cerebral hemodynamic changes after haploidentical hematopoietic stem cell transplant in adults with sickle cell disease

ABSTRACT

Preliminary evidence from a series of 4 adults with sickle cell disease (SCD) suggests that hematopoietic stem cell transplant (HSCT) improves cerebral hemodynamics. HSCT largely normalizes cerebral hemodynamics in children with SCD. We tested the hypothesis in adults with SCD that cerebral blood flow (CBF), oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO2) measured using magnetic resonance imaging, normalized to healthy values, comparing measurements from ∼1 month before to 12 to 24 months after HSCT (n = 11; age, 33.3 ± 8.9 years; 389 ± 150 days after HSCT) with age-, race- and sex-matched values from healthy adults without sickle trait (n = 28; age, 30.2 ± 5.6 years). Before transplant, 7 patients had neurological indications for transplant (eg, overt stroke) and 4 had nonneurological reasons for haploidentical bone marrow transplant (haplo-BMT). All received haplo-BMT from first-degree relatives (parent, sibling, or child donor) with reduced-intensity preparation and maintained engraftment. Before transplant, CBF was elevated (CBF, 69.11 ± 24.7 mL/100 g/min) compared with that of controls (P = .004). Mean CBF declined significantly after haplo-BMT (posttransplant CBF, 48.2 ± 13.9 mL/100 g/min; P = .003). OEF was not different from that of controls at baseline and did not change significantly after haplo-BMT (pretransplant, 43.1 ± 6.7%; posttransplant, 39.6 ± 7.0%; P = .34). After transplant, CBF and OEF were not significantly different from controls (CBF, 48.2 ± 13.4 mL/100 g/min; P = .78; and OEF, 39.6 ± 7.0%; P > .99). CMRO2 did not change significantly after haplo-BMT (pretransplant, 3.18 ± 0.87 mL O2/100 g/min; posttransplant, 2.95 ± 0.83; P = .56). Major complications of haplo-BMT included 1 infection-related death and 1 severe chronic graft-versus-host disease. Haplo-BMT in adults with SCD reduces CBF to that of control values and maintains OEF and CMRO2 on average at levels observed in healthy adult controls. The trial was registered at www.clinicaltrials.gov as #NCT01850108.

Neurocognitive Impairment in Ugandan Children with Sickle Cell Anemia Compared to Sibling Controls: A cross-sectional study

Introduction

Neurocognitive function in Ugandan children aged 1-12 years with sickle cell anemia (SCA) were compared to their non-SCA siblings to identify risk factors for disease-associated impairment.

Methods

This cross-sectional neurocognitive function study of children with SCA (N=242) and non-SCA siblings (N=127) used age- and linguistically-appropriate standardized tests of cognition, executive function and attention for children ages 1-4 and 5-12 years. Test scores were converted to locally derived age-normalized z-scores. The SCA group underwent standardized stroke examination for prior stroke and transcranial doppler ultrasound (TCD) to determine stroke risk by arterial flow velocity.

Results

The SCA group was younger than siblings (mean ages 5.46±3.0 versus 7.11±3.51 years, respectively; p <.001), with lower hemoglobin concentration (7.32±1.02 vs. 12.06±1.42, p <.001). Overall cognitive SCA z-scores were lower: -0.73 ±0.98 vs. siblings -0.25 ±1.12 (p<.001), with comparable findings for executive function of -1.09±0.94 versus -0.84±1.26 (p=0.045), respectively. Attention z-scores for ages 5-12 for the SCA group and controls were similar: -0.37±1.4 vs. -0.11±0.17 (p=.09). Overall differences by SCA status were largely driven by the older age group, as z-scores in the younger sub-sample did not differ from controls. Analyses revealed the strongest predictors of poor neurocognitive outcomes among the SCA sample to be the disease, age and prior stroke (each p<.001). Impact from anemia and SCA were indistinguishable.

Discussion

Neurocognitive testing in children with SCA compared to non-SCA siblings revealed poorer SCA-associated functioning in children older than age 4. Results indicate need for trials assessing impact from disease modification for children with SCA.

From Stress to Sick(le) and Back Again-Oxidative/Antioxidant Mechanisms, Genetic Modulation, and Cerebrovascular Disease in Children with Sickle Cell Anemia

Sickle cell anemia (SCA) is a genetic disease caused by the homozygosity of the HBB:c.20A>T mutation, which results in the production of hemoglobin S (HbS). In hypoxic conditions, HbS suffers autoxidation and polymerizes inside red blood cells, altering their morphology into a sickle shape, with increased rigidity and fragility. This triggers complex pathophysiological mechanisms, including inflammation, cell adhesion, oxidative stress, and vaso-occlusion, along with metabolic alterations and endocrine complications. SCA is phenotypically heterogeneous due to the modulation of both environmental and genetic factors. Pediatric cerebrovascular disease (CVD), namely ischemic stroke and silent cerebral infarctions, is one of the most impactful manifestations. In this review, we highlight the role of oxidative stress in the pathophysiology of pediatric CVD. Since oxidative stress is an interdependent mechanism in vasculopathy, occurring alongside (or as result of) endothelial dysfunction, cell adhesion, inflammation, chronic hemolysis, ischemia-reperfusion injury, and vaso-occlusion, a brief overview of the main mechanisms involved is included. Moreover, the genetic modulation of CVD in SCA is discussed. The knowledge of the intricate network of altered mechanisms in SCA, and how it is affected by different genetic factors, is fundamental for the identification of potential therapeutic targets, drug development, and patient-specific treatment alternatives.

Silent Cerebral Infarcts in Iraqi Patients with Sickle Cell Disease

Silent ischemic infarcts have been reported to be the most frequent neurological abnormalities in sickle cell disease (SCD) in several studies worldwide. However, no previous studies investigated this neurological disorder in Iraqi SCD patients. To address this issue, a total of 52 patients with a median age of 20 years (range 10-46) and including 46.2% males were enrolled. Patients were clinically evaluated and their records were reviewed. They had full blood and reticulocyte counts, hemoglobin F estimation, serum lactic dehydrogenase and bilirubin assayed, as well as brain magnetic resonance imaging (MRI) to screen for silent cerebral infarcts. Six out of the 52 patients (11.5%) had silent cerebral infarcts, all of which were in the deep white matter, ranging from 6 to 10 mm in their largest diameters. There were no significant differences in age, sex, or sickle cell genotype between those with silent cerebral infarcts and those without it. Those with silent cerebral infarcts had lower median hemoglobin, higher reticulocytes and lower pain frequencies than those without it, yet again this was not significant. Follow up MRI in four out of the six silent infarct patients showed no additional lesions and no increase in size of the original ones after six to eight months. In conclusion, it appears that the frequency of silent cerebral infarcts in Iraqi SCD patients is lower than the bulk of the literature from other populations. Further studies to screen for genetic polymorphisms that may explain this lower rate may be informative.

Molecular and environmental contributors to neurological complications in sickle cell disease

Sickle cell disease (SCD) is an inherited hemoglobinopathy in which affected hemoglobin polymerizes under hypoxic conditions resulting in red cell distortion and chronic hemolytic anemia. SCD affects millions of people worldwide, primarily in Sub-Saharan Africa and the Indian subcontinent. Due to vaso-occlusion of sickled red cells within the microvasculature, SCD affects virtually every organ system and causes significant morbidity and early mortality. The neurological complications of SCD are particularly devastating and diverse, ranging from overt stroke to covert cerebral injury, including silent cerebral infarctions and blood vessel tortuosity. However, even individuals without evidence of neuroanatomical changes in brain imaging have evidence of cognitive deficits compared to matched healthy controls likely due to chronic cerebral hypoxemia and neuroinflammation. In this review, we first examined the biological contributors to SCD-related neurological complications and then discussed the equally important socioenvironmental contributors. We then discuss the evidence for neuroprotection from the two primary disease-modifying therapies, chronic monthly blood transfusions and hydroxyurea, and end with several experimental therapies designed to specifically target these complications.

Toward Automated Detection of Silent Cerebral Infarcts in Children and Young Adults With Sickle Cell Anemia

BACKGROUND

Silent cerebral infarcts (SCI) in sickle cell anemia (SCA) are associated with future strokes and cognitive impairment, warranting early diagnosis and treatment. Detection of SCI, however, is limited by their small size, especially when neuroradiologists are unavailable. We hypothesized that deep learning may permit automated SCI detection in children and young adults with SCA as a tool to identify the presence and extent of SCI in clinical and research settings.

METHODS

We utilized UNet-a deep learning model-for fully automated SCI segmentation. We trained and optimized UNet using brain magnetic resonance imaging from the SIT trial (Silent Infarct Transfusion). Neuroradiologists provided the ground truth for SCI diagnosis, while a vascular neurologist manually delineated SCI on fluid-attenuated inversion recovery and provided the ground truth for SCI segmentation. UNet was optimized for the highest spatial overlap between automatic and manual delineation (dice similarity coefficient). The optimized UNet was externally validated using an independent single-center prospective cohort of SCA participants. Model performance was evaluated through sensitivity and accuracy (%correct cases) for SCI diagnosis, dice similarity coefficient, intraclass correlation coefficient (metric of volumetric agreement), and Spearman correlation.

RESULTS

The SIT trial (n=926; 31% with SCI; median age, 8.9 years) and external validation (n=80; 50% with SCI; age, 11.5 years) cohorts had small median lesion volumes of 0.40 and 0.25 mL, respectively. Compared with the neuroradiology diagnosis, UNet predicted SCI presence with 100% sensitivity and 74% accuracy. In magnetic resonance imaging with SCI, UNet reached a moderate spatial agreement (dice similarity coefficient, 0.48) and high volumetric agreement (intraclass correlation coefficient, 0.76; ρ=0.72; P<0.001) between automatic and manual segmentations.

CONCLUSIONS

UNet, trained using a large pediatric SCA magnetic resonance imaging data set, sensitively detected small SCI in children and young adults with SCA. While additional training is needed, UNet may be integrated into the clinical workflow as a screening tool, aiding in SCI diagnosis.

Brain BOLD and NIRS response to hyperoxic challenge in sickle cell disease and chronic anemias

PURPOSE

Congenital anemias, including sickle cell anemia and thalassemia, are associated with cerebral tissue hypoxia and heightened stroke risks. Recent works in sickle cell disease mouse models have suggested that hyperoxia respiratory challenges can identify regions of the brain having chronic tissue hypoxia. Therefore, this work investigated differences in hyperoxic response and regional cerebral oxygenation between anemic and healthy subjects.

METHODS

A cohort of 38 sickle cell disease subjects (age 22 ± 8 years, female 39%), 25 non-sickle anemic subjects (age 25 ± 11 years, female 52%), and 31 healthy controls (age 25 ± 10 years, female 68%) were examined. A hyperoxic gas challenge was performed with concurrent acquisition of blood oxygen level-dependent (BOLD) MRI and near-infrared spectroscopy (NIRS). In addition to hyperoxia-induced changes in BOLD and NIRS, global measurements of cerebral blood flow, oxygen delivery, and cerebral metabolic rate of oxygen were obtained and compared between the three groups.

RESULTS

Regional BOLD changes were not able to identify brain regions of flow limitation in chronically anemic patients. Higher blood oxygen content and tissue oxygenation were observed during hyperoxia gas challenge. Both control and anemic groups demonstrated lower blood flow, oxygen delivery, and metabolic rate compared to baseline, but the oxygen metabolism in anemic subjects were abnormally low during hyperoxic exposure.

CONCLUSION

These results indicated that hyperoxic respiratory challenge could not be used to identify chronically ischemic brain. Furthermore, the low hyperoxia-induced metabolic rate suggested potential negative effects of prolonged oxygen therapy and required further studies to evaluate the risk for hyperoxia-induced oxygen toxicity and cerebral dysfunction.

Silent infarction in sickle cell disease is associated with brain volume loss in excess of infarct volume

Introduction

Sickle cell disease (SCD) increases cerebral infarct risk, but reported effects on brain volume have varied. More detailed information using larger cohorts and contemporary methods could motivate the use of longitudinal brain volume assessment in SCD as an automated marker of disease stability or future progression. The purpose of this study was to rigorously evaluate whether children and young adults with SCD have reduced gray matter volume (GMV) and white matter volume (WMV) compared to healthy controls using high-resolution MRI. We tested the hypotheses that (i) elevated CBF, a marker of cerebral hemodynamic compensation in SCD, is associated with global and regional brain atrophy, and (ii) silent cerebral infarct burden is associated with brain atrophy in excess of infarct volume.

Methods

Healthy controls (n = 49) and SCD participants without overt stroke (n = 88) aged 7-32 years completed 3 T brain MRI; pseudocontinuous arterial spin labeling measured CBF. Multivariable linear regressions assessed associations of independent variables with GMV, WMV, and volumes of cortical/subcortical regions.

Results

Reduced hemoglobin was associated with reductions in both GMV (p = 0.032) and WMV (p = 0.005); reduced arterial oxygen content (CaO2) was also associated with reductions in GMV (p = 0.035) and WMV (p = 0.006). Elevated gray matter CBF was associated with reduced WMV (p = 0.018). Infarct burden was associated with reductions in WMV 30-fold greater than the infarct volume itself (p = 0.005). Increased GM CBF correlated with volumetric reductions of the insula and left and right caudate nuclei (p = 0.017, 0.017, 0.036, respectively). Infarct burden was associated with reduced left and right nucleus accumbens, right thalamus, and anterior corpus callosum volumes (p = 0.002, 0.002, 0.009, 0.002, respectively).

Discussion

We demonstrate that anemia and decreased CaO2 are associated with reductions in GMV and WMV in SCD. Increased CBF and infarct burden were also associated with reduced volume in subcortical structures. Global WMV deficits associated with infarct burden far exceed infarct volume itself. Hemodynamic compensation via increased cerebral blood flow in SCD seems inadequate to prevent brain volume loss. Our work highlights that silent cerebral infarcts are just a portion of the brain injury that occurs in SCD; brain volume is another potential biomarker of brain injury in SCD.

Insulin-like Growth Factor-1 Prevents Hypoxia/Reoxygenation-Induced White Matter Injury in Sickle Cell Mice

Occlusion of cerebral blood vessels causes acute cerebral hypoxia—an important trigger of ischemic white matter injury and stroke in sickle cell disease (SCD). While chronic hypoxia triggers compensatory neuroprotection via insulin-like growth factor-1 (IGF-1) and hypoxia inducible factor-1α (HIF-1α), severe bouts of acute hypoxia and subsequent restoration of blood flow (hypoxia/reoxygenation, H/R) overwhelm compensatory mechanisms and cause neuroaxonal damage–identified as white matter lesions–in the brain. The neuroprotective role of IGF-1 in the pathogenesis of white matter injury in SCD has not been investigated; however, it is known that systemic IGF-1 is reduced in individuals with SCD. We hypothesized that IGF-1 supplementation may prevent H/R-induced white matter injury in SCD. Transgenic sickle mice homozygous for human hemoglobin S and exposed to H/R developed white matter injury identified by elevated expression of non-phosphorylated neurofilament H (SMI32) with a concomitant decrease in myelin basic protein (MBP) resulting in an increased SMI32/MBP ratio. H/R-challenge also lowered plasma and brain IGF-1 expression. Human recombinant IGF-1 prophylaxis significantly induced HIF-1α and averted H/R-induced white matter injury in the sickle mice compared to vehicle-treated mice. The expression of the IGF-1 binding proteins IGFBP-1 and IGFBP-3 was elevated in the IGF-1-treated brain tissue indicating their potential role in mediating neuroprotective HIF-1α signaling. This study provides proof-of-concept for IGF-1-mediated neuroprotection in SCD.

Working memory and school readiness in preschool children with sickle cell disease compared to demographically matched controls

Children diagnosed with sickle cell disease (SCD) are at risk of the development of neurobehavioural problems early in life. Specific impairments in executive function skills, including working memory, have been documented in school-aged children with SCD. These executive skills are known to strongly contribute to early academic skills and preparedness for entering kindergarten. This study examined working memory and school readiness in preschool children with SCD compared to a healthy control group matched for race, sex and parent education. A total of 84 patients diagnosed with SCD (61.9% haemoglobin [Hb]SS/HbSβ0 -thalassaemia) and 168 controls completed testing. The mean (SD) ages of patients and controls at testing were 4.53 (0.38) and 4.44 (0.65) years respectively. The SCD group performed worse than controls on measures of executive function, working memory and school readiness (p < 0.01; Cohen's D range: 0.32-0.39). Measures of working memory were associated with school readiness after accounting for early adaptive development. Multiple linear regression models among patients diagnosed with SCD revealed that college education of the primary caregiver was positively associated with school readiness (p < 0.001) after controlling for sex, genotype, age and early adaptive development. These results highlight the need to implement school readiness interventions in young children diagnosed with SCD emphasising executive function skills.

Measurement of Cerebral Oxygen Extraction Fraction Using Quantitative BOLD Approach: A Review

Quantification of brain oxygenation and metabolism, both of which are indicators of the level of brain activity, plays a vital role in understanding the cerebral perfusion and the pathophysiology of brain disorders. Magnetic resonance imaging (MRI), a widely used clinical imaging technique, which is very sensitive to magnetic susceptibility, has the possibility of substituting positron emission tomography (PET) in measuring oxygen metabolism. This review mainly focuses on the quantitative blood oxygenation level-dependent (qBOLD) method for the evaluation of oxygen extraction fraction (OEF) in the brain. Here, we review the theoretic basis of qBOLD, as well as existing acquisition and quantification methods. Some published clinical studies are also presented, and the pros and cons of qBOLD method are discussed as well.

Normalization of cerebral hemodynamics after hematopoietic stem cell transplant in children with sickle cell disease

Children with sickle cell disease (SCD) demonstrate cerebral hemodynamic stress and are at high risk of strokes. We hypothesized that curative hematopoietic stem cell transplant (HSCT) normalizes cerebral hemodynamics in children with SCD compared with pre-transplant baseline. Whole-brain cerebral blood flow (CBF) and oxygen extraction fraction (OEF) were measured by magnetic resonance imaging 1 to 3 months before and 12 to 24 months after HSCT in 10 children with SCD. Three children had prior overt strokes, 5 children had prior silent strokes, and 1 child had abnormal transcranial Doppler ultrasound velocities. CBF and OEF of HSCT recipients were compared with non-SCD control participants and with SCD participants receiving chronic red blood cell transfusion therapy (CRTT) before and after a scheduled transfusion. Seven participants received matched sibling donor HSCT, and 3 participants received 8 out of 8 matched unrelated donor HSCT. All received reduced-intensity preparation and maintained engraftment, free of hemolytic anemia and SCD symptoms. Pre-transplant, CBF (93.5 mL/100 g/min) and OEF (36.8%) were elevated compared with non-SCD control participants, declining significantly 1 to 2 years after HSCT (CBF, 72.7 mL/100 g per minute; P = .004; OEF, 27.0%; P = .002), with post-HSCT CBF and OEF similar to non-SCD control participants. Furthermore, HSCT recipients demonstrated greater reduction in CBF (-19.4 mL/100 g/min) and OEF (-8.1%) after HSCT than children with SCD receiving CRTT after a scheduled transfusion (CBF, -0.9 mL/100 g/min; P = .024; OEF, -3.3%; P = .001). Curative HSCT normalizes whole-brain hemodynamics in children with SCD. This restoration of cerebral oxygen reserve may explain stroke protection after HSCT in this high-risk patient population.

The Development of Neuroimaging Biomarkers for Cognitive Decline in Sickle Cell Disease

Sickle cell disease (SCD) is complicated by neurologic complications including vasculopathy, hemorrhagic or ischemic overt stroke, silent cerebral infarcts and cognitive dysfunction. Patients with SCD, even in the absence of vasculopathy or stroke, have experience cognitive dysfunction that progresses with age. Transcranial Doppler ultrasound and structural brain MRI are currently used for primary and secondary stroke prevention, but laboratory or imaging biomarkers do not currently exist that are specific to the risk of cognitive dysfunction in patients with SCD. Recent investigations have used advanced MR sequences assessing cerebral hemodynamics, white matter microstructure and functional connectivity to better understand the pathophysiology of cognitive decline in SCD, with the long-term goal of developing neuroimaging biomarkers to be used in risk prediction algorithms and to assess the efficacy of treatment options for patients with SCD.

Neurodevelopmental Outcomes in Preterm Children with Sickle Cell Disease

OBJECTIVES

To explore the combined effect of pediatric sickle cell disease (SCD) and preterm birth on cognitive functioning.

METHODS

Cognitive functioning was examined in children ages 6-8 with high risk SCD genotypes born preterm (n = 20) and full-term (n = 59) and lower risk SCD genotypes/no SCD born preterm (n = 11) and full-term (n = 99) using tests previously shown to be sensitive to SCD-related neurocognitive deficits. Factorial ANOVAs and log linear analyses were conducted to examine the relationship between SCD risk, preterm birth status, and cognitive outcomes. Continuous scores were examined for specific tests. Children were categorized as having an abnormal screening outcome if at least one cognitive score was ≥1.5 standard deviations below the population mean.

RESULTS

Children with elevated risk due to high risk SCD and preterm birth performed worse than other groups on a test of expressive language but not on tests that emphasize processing speed and working memory. There was a three-way interaction between preterm status, SCD risk, and abnormal screening outcome, which was largely driven by the increased likelihood of abnormal cognitive scores for children with high risk SCD born preterm.

CONCLUSIONS

The combination of SCD and preterm birth may confer increased risk for language deficits and elevated rates of abnormal cognitive screenings. This suggests that neurodevelopmental risk imparted by comorbid SCD and preterm birth may manifest as heterogenous, rather than specific, patterns of cognitive deficits. Future studies are needed to clarify the domains of cognitive functioning most susceptible to disease-related effects of comorbid SCD and preterm birth.

Quantitative susceptibility mapping (QSM) and R2* of silent cerebral infarcts in sickle cell anemia

Silent cerebral infarction (SCI) is the most commonly reported radiological abnormality in patients with sickle cell anemia (SCA) and is associated with future clinical stroke risk. To date, there have been few histological and quantitative MRI studies of SCI and multiple radiological definitions exist. As a result, the tissue characteristics and composition of SCI remain elusive. The objective of this work was therefore to investigate the composition of segmented SCI lesions using quantitative MRI for R2 * and quantitative magnetic susceptibility mapping (QSM). 211 SCI lesions were segmented from 32 participants with SCA and 6 controls. SCI were segmented according to two definitions (FLAIR+/-T1w-based threshold) using a semi-automated pipeline. Magnetic susceptibility (χ) and R2 * maps were calculated from a multi-echo gradient echo sequence and mean SCI values were compared to an equivalent region of interest in normal appearing white matter (NAWM). SCI χ and R2 * were investigated as a function of SCI definition, patient demographics, anatomical location, and cognition. Compared to NAWM, SCI were significantly less diamagnetic (χ = -0.0067 ppm vs. -0.0153 ppm, p < 0.001) and had significantly lower R2 * (16.7 s-1 vs. 19.2 s-1, p < 0.001). SCI definition had a significant effect on the mean SCI χ and R2 * , with lesions becoming significantly less diamagnetic and having significantly lower R2 * after the application of a more stringent T1w-based threshold. SCI-NAWM R2 * decrease was significantly greater in patients with SCA compared with controls (-2.84 s-1 vs. -0.64 s-1, p < 0.0001). No significant association was observed between mean SCI-NAWM χ or R2* differences and subject age, lesion anatomical location, or cognition. The increased χ and decreased R2 * in SCI relative to NAWM observed in both patients and controls is indicative of lower myelin or increased water content within the segmented lesions. The significant SCI-NAWM R2 * differences observed between SCI in patients with SCA and controls suggests there may be differences in tissue composition relative to NAWM in SCI in the two populations. Quantitative MRI techniques such as QSM and R2 * mapping can be used to enhance our understanding of the pathophysiology and composition of SCI in patients with SCA as well as controls.

Effect of Blood Transfusion on Cerebral Hemodynamics and Vascular Topology Described by Computational Fluid Dynamics in Sickle Cell Disease Patients

The main objective of this study was to demonstrate that computational fluid dynamics (CFD) modeling can be used to study the contribution of covert and overt vascular architecture to the risk for cerebrovascular disease in sickle cell disease (SCD) and to determine the mechanisms of response to therapy such as chronic red blood cell (cRBC) transfusions. We analyzed baseline (screening), pre-randomization and study exit magnetic resonance angiogram (MRA) images from 10 (5 each from the transfusion and observation arms) pediatric sickle SCD participants in the silent cerebral infarct transfusion (SIT) trial using CFD modeling. We reconstructed the intracranial portion of the internal carotid artery and branches and extracted the geometry using 3D Slicer. We cut specific portions of the large intracranial artery to include segments of the internal carotid, middle, anterior, and posterior cerebral arteries such that the vessel segment analyzed extended from the intracranial beginning of the internal carotid artery up to immediately after (~0.25 inches) the middle cerebral artery branching point. Cut models were imported into Ansys 2021R2/2022R1 and laminar and time-dependent flow simulation was performed. Change in time averaged mean velocity, wall shear stress, and vessel tortuosity were compared between the observation and cRBC arms. We did not observe a correlation between time averaged mean velocity (TAMV) and mean transcranial Doppler (TCD) velocity at study entry. There was also no difference in change in time average mean velocity, wall shear stress (WSS), and vessel tortuosity between the observation and cRBC transfusion arms. WSS and TAMV were abnormal for 2 (developed TIA) out of the 3 participants (one participant had silent cerebral infarctions) that developed neurovascular outcomes. CFD approaches allow for the evaluation of vascular topology and hemodynamics in SCD using MRA images. In this proof of principle study, we show that CFD could be a useful tool and we intend to carry out future studies with a larger sample to enable more robust conclusions.

Sickle cell cerebrovascular reactivity to a CO2 stimulus: Too little, too slow

Background: Despite increased cerebral blood flow (CBF), cerebral infarcts occur in patients with sickle cell disease (SCD). This suggests increased CBF does not meet metabolic demand possibly due to compromised cerebral vasodilatory response. Hypothesis: In adult SCD patients, cerebrovascular reactivity (CVR) and speed of vasodilatory response (tau) to a standardized vasodilatory stimulus, are reduced compared to normal subjects.

Methods: Functional brain imaging performed as part of routine care in adult SCD patients without known large vessel cerebral vasculopathy was reviewed retrospectively. CVR was calculated as the change in CBF measured as the blood-oxygenation-level-dependent (BOLD)-magnetic resonance imaging signal, in response to a standard vasoactive stimulus of carbon dioxide (CO₂). The tau corresponding to the best fit between the convolved end-tidal partial pressures of CO₂ and BOLD signal was defined as the speed of vascular response. CVR and tau were normalized using a previously generated atlas of 42 healthy controls.

Results: Fifteen patients were included. CVR was reduced in grey and white matter (mean Z-score for CVR −0.5 [−1.8 to 0.3] and −0.6 [−2.3 to 0.7], respectively). Tau Z-scores were lengthened in grey and white matter (+0.9 [−0.5 to 3.3] and +0.8 [−0.7 to 2.7], respectively). Hematocrit was the only significant independent predictor of CVR on multivariable regression.

Conclusion: Both measures of cerebrovascular health (CVR and tau) in SCD patients were attenuated compared to normal controls. These findings show that CVR represents a promising tool to assess disease state, stroke risk, and therapeutic efficacy of treatments in SCD and merits further investigation.

Chronic anemia: The effects on the connectivity of white matter

Chronic anemia is commonly observed in patients with hemoglobinopathies, mainly represented by disorders of altered hemoglobin (Hb) structure (sickle cell disease, SCD) and impaired Hb synthesis (e.g. thalassemia syndromes, non-SCD anemia). Both hemoglobinopathies have been associated with white matter (WM) alterations. Novel structural MRI research in our laboratory demonstrated that WM volume was diffusely lower in deep, watershed areas proportional to anemia severity. Furthermore, diffusion tensor imaging analysis has provided evidence that WM microstructure is disrupted proportionally to Hb level and oxygen saturation. SCD patients have been widely studied and demonstrate lower fractional anisotropy (FA) in the corticospinal tract and cerebellum across the internal capsule and corpus callosum. In the present study, we compared 19 SCD and 15 non-SCD anemia patients with a wide range of Hb values allowing the characterization of the effects of chronic anemia in isolation of sickle Hb. We performed a tensor analysis to quantify FA changes in WM connectivity in chronic anemic patients. We calculated the volumetric mean of FA along the pathway of tracks connecting two regions of interest defined by BrainSuite's BCI-DNI atlas. In general, we found lower FA values in anemic patients; indicating the loss of coherence in the main diffusion direction that potentially indicates WM injury. We saw a positive correlation between FA and hemoglobin in these same regions, suggesting that decreased WM microstructural integrity FA is highly driven by chronic hypoxia. The only connection that did not follow this pattern was the connectivity within the left middle-inferior temporal gyrus. Interestingly, more reductions in FA were observed in non-SCD patients (mainly along with intrahemispheric WM bundles and watershed areas) than the SCD patients (mainly interhemispheric).

Quantification of Silent Cerebral Infarction on High-Resolution FLAIR and Cognition in Sickle Cell Anemia

Research in sickle cell anemia (SCA) has used, with limited race-matched control data, binary categorization of patients according to the presence or absence of silent cerebral infarction (SCI). SCI have primarily been identified using low-resolution MRI, with radiological definitions varying in lesion length and the requirement for abnormality on both fluid attenuated inversion recovery (FLAIR) and T1-weighted images. We aimed to assess the effect of published SCI definitions on global, regional, and lobar lesion metrics and their value in predicting cognition. One hundred and six patients with SCA and 48 controls aged 8-30 years underwent 3T MRI with a high-resolution FLAIR sequence and Wechsler cognitive assessment. Prevalence, number, and volume of lesions were calculated using a semi-automated pipeline for SCI defined as: (1) Liberal: any length (L-SCI); (2) Traditional: >3 mm in greatest dimension (T-SCI); (3) Restrictive; >3 mm in greatest dimension with a corresponding T1-weighted hypo-intensity (R-SCI). Globally, as hypothesized, there were large effects of SCI definition on lesion metrics in patients and controls, with prevalence varying from 24-42% in patients, and 4-23% in controls. However, contrary to hypotheses, there was no effect of any global metric on cognition. Regionally, there was a consistent distribution of SCI in frontal and parietal deep and juxta-cortical regions across definitions and metrics in patients, but no consistent distribution in controls. Effects of regional SCI metrics on cognitive performance were of small magnitude; some were paradoxical. These findings expose the challenges associated with the widespread use of SCI presence as a biomarker of white-matter injury and cognitive dysfunction in cross-sectional high-resolution MRI studies in patients with SCA. The findings indicate that with high-resolution MRI: (1) radiological definitions have a large effect on resulting lesion groups, numbers, and volumes; (2) there is a non-negligible prevalence of lesions in young healthy controls; and (3) at the group-level, there is no cross-sectional association between global lesion metrics and general cognitive impairment irrespective of lesion definition and metric. With high-resolution multi-modal MRI, the dichotomy of presence or absence of SCI does not appear to be a sensitive biomarker for the detection of functionally significant pathology; the search for appropriate endpoints for clinical treatment trials should continue.

Sluggish Cognitive Tempo in Pediatric Sickle Cell Disease

Background

Sickle cell disease (SCD) imparts risk for a range of neurodevelopmental and neurocognitive disorders. Sluggish cognitive tempo (SCT) is a distinct syndrome that often co-occurs with attention-deficit/hyperactivity disorder (ADHD) but has not been described in SCD. We investigated the reliability and validity of a SCT measure in SCD and examined associations with biopsychosocial risk factors and functional outcomes.

Materials and Methods

Caregivers (n = 85) of children with SCD ages 7-16 reported on socio-demographics and the Kiddie-Sluggish Cognitive Tempo (K-SCT) measure, Behavior Rating Inventory of Executive Function, and Conners 3. Disease-related characteristics were extracted from health records.

Results

The K-SCT demonstrated excellent internal consistency (α = 0.92) and test-retest reliability (r = 0.82, p < 0.001). K-SCT scores were correlated with ADHD-Inattention (r = 0.64, p < 0.001) and ADHD-Hyperactive/Impulsive (r = 0.46, p < 0.001) scores, as well as functional outcomes, including learning problems (r = 0.69, p < 0.001). In multivariate analyses controlling for ADHD symptoms, SCT accounted for unique variance in learning (b = 9.67, p < 0.01) and executive functioning (b = 5.93, p < 0.01). Nearly all participants (93%) with elevated levels of co-occurring SCT and ADHD-Inattention symptoms had significant learning problems.

Conclusion

The K-SCT is a reliable and valid measure of SCT in SCD. SCT symptoms are associated with learning difficulties even after controlling for ADHD symptoms. Further research is needed to understand the biopsychosocial factors that lead to SCT symptoms in SCD and examine long-term implications of SCT.

Venous cerebral blood flow quantification and cognition in patients with sickle cell anemia

Prior studies have described high venous signal qualitatively using arterial spin labelling (ASL) in patients with sickle cell anemia (SCA), consistent with arteriovenous shunting. We aimed to quantify the effect and explored cross-sectional associations with arterial oxygen content (CaO2), disease-modifying treatments, silent cerebral infarction (SCI), and cognitive performance. 94 patients with SCA and 42 controls underwent cognitive assessment and MRI with single- and multi- inflow time (TI) ASL sequences. Cerebral blood flow (CBF) and bolus arrival time (BAT) were examined across gray and white matter and high-signal regions of the sagittal sinus. Across gray and white matter, increases in CBF and reductions in BAT were observed in association with reduced CaO2 in patients, irrespective of sequence. Across high-signal sagittal sinus regions, CBF was also increased in association with reduced CaO2 using both sequences. However, BAT was increased rather than reduced in patients across these regions, with no association with CaO2. Using the multiTI sequence in patients, increases in CBF across white matter and high-signal sagittal sinus regions were associated with poorer cognitive performance. These novel findings highlight the utility of multiTI ASL in illuminating, and identifying objectively quantifiable and functionally significant markers of, regional hemodynamic stress in patients with SCA.

Cerebral oxygen metabolic stress is increased in children with sickle cell anemia compared to anemic controls

Patients with sickle cell anemia (SCA) experience cerebral metabolic stress with an increase in oxygen extraction fraction (OEF) to compensate for reduced oxygen carrying capacity due to anemia. It remains unclear if anemia alone drives this metabolic stress. Using MRI, we collected voxel-wise OEF measurements to test our hypothesis that OEF would be elevated in anemic controls without SCA (AC) compared to healthy controls (HC), but OEF would be even higher in SCA compared to AC. Brain MRIs (N = 159) were obtained in 120 participants (34 HC, 27 AC, 59 SCA). While hemoglobin was lower in AC versus HC (p < 0.001), hemoglobin was not different between AC and SCA cohorts (p = 0.459). Whole brain OEF was higher in AC compared to HC (p < 0.001), but lower compared to SCA (p = 0.001). Whole brain OEF remained significantly higher in SCA compared to HC (p = 0.001) while there was no longer a difference between AC versus HC (p = 0.935) in a multivariate model controlling for age and hemoglobin. OEF peaked within the border zone regions of the brain in both SCA and AC cohorts, but the volume of white matter with regionally elevated OEF in AC was smaller (1.8%) than SCA (58.0%). While infarcts colocalized within regions of elevated OEF, more SCA participants had infarcts than AC (p < 0.001). We conclude that children with SCA experience elevated OEF compared to AC and HC after controlling for the impact of anemia, suggesting that there are other pathophysiologic factors besides anemia contributing to cerebral metabolic stress in children with SCA.

Cerebral Vasculopathy in Children With Sickle Cell Disease in an Amazonian Population

Introduction: Sickle cell disease is the most prevalent hereditary disease in the country. The aim of this study was to use transcranial Doppler as a screening method for identifying cerebral vasculopathy in children with sickle cell disease. Methods: An epidemiologic, descriptive, and cross-sectional study was conducted. Patients aged 2-16 years with sickle cell disease and followed at a neurology referral service between January 2014 and March 2020 underwent transcranial Doppler and complementary examinations to screen for cerebral vasculopathy. Results: Screening and confirmatory examinations diagnosed 14 of 164 patients (8.5%) with cerebral vasculopathy. Regarding stroke risk, as measured by cerebral blood flow velocity, 2 of 14 patients (14.2%) were classified as conditional risk (170-199 cm/s) and 12 of 14 (85.7%) as high risk of stroke. Conclusion: Complementary examinations should be performed in all patients with changes on transcranial Doppler to confirm cerebral vasculopathy. Further studies, particularly genetic, are needed to better understand the relationship between sickle cell disease and cerebral vasculopathy.

Assessment of functional shunting in patients with sickle cell disease

Silent cerebral infarcts (SCI) are common in patients with sickle cell disease (SCD) and are thought to be caused by a mismatch between oxygen delivery and consumption. Functional cerebrovascular shunting is defined as reduced oxygen offloading due to the rapid transit of blood through the capillaries caused by increased flow and has been suggested as a potential mechanism underlying reduced oxygenation and SCI. We investigated the venous arterial spin labeling signal (VS) in the sagittal sinus as a proxy biomarker of cerebral functional shunting, and its association with hemodynamic imaging and hematological laboratory parameters. We included 28 children and 38 adults with SCD, and ten healthy racematched adult controls. VS, cerebral blood flow (CBF), velocity in the brain feeding arteries, oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2) were measured before and after acetazolamide administration. VS was higher in patients with SCD compared to controls (P<0.01) and was increased after acetazolamide administration in all groups (P<0.01). VS was primarily predicted by CBF (P<0.01), but CBF-corrected VS was also associated with decreased CMRO2 (P<0.01). Additionally, higher disease severity defined by low hemoglobin and increased hemolysis was associated with higher CBF-corrected VS. Finally, CMRO2 was negatively correlated with fetal hemoglobin, and positively correlated with lactate dehydrogenase, which could be explained by changes in oxygen affinity. These findings provide evidence for cerebral functional shunting and encourage future studies investigating the potential link to aberrant capillary exchange in SCD.

Individual Watershed Areas in Sickle Cell Anemia: An Arterial Spin Labeling Study

Previous studies have pointed to a role for regional cerebral hemodynamic stress in neurological complications in patients with sickle cell anemia (SCA), with watershed regions identified as particularly at risk of ischemic tissue injury. Using single- and multi-inflow time (TI) arterial spin labeling sequences (ASL) in 94 patients with SCA and 42 controls, the present study sought to investigate cerebral blood flow (CBF) and bolus arrival times (BAT) across gray matter, white matter with early arrival times, and in individual watershed areas (iWSAs). In iWSAs, associations between hemodynamic parameters, lesion burden, white matter integrity, and general cognitive performance were also explored. In patients, increases in CBF and reductions in BAT were observed in association with reduced arterial oxygen content across gray matter and white matter with early arrival times using both sequences (all p < 0.001, d = -1.55--2.21). Across iWSAs, there was a discrepancy between sequences, with estimates based on the single-TI sequence indicating higher CBF in association with reduced arterial oxygen content in SCA patients, and estimates based on the multi-TI sequence indicating no significant between-group differences or associations with arterial oxygen content. Lesion burden was similar between white matter with early arrival times and iWSAs in both patients and controls, and using both sequences, only trend-level associations between iWSA CBF and iWSA lesion burden were observed in patients. Further, using the multi-TI sequence in patients, increased iWSA CBF was associated with reduced iWSA microstructural tissue integrity and slower processing speed. Taken together, the results highlight the need for researchers to consider BAT when estimating CBF using single-TI sequences. Moreover, the findings demonstrate the feasibility of multi-TI ASL for objective delineation of iWSAs and for detection of regional hemodynamic stress that is associated with reduced microstructural tissue integrity and slower processing speed. This technique may hold promise for future studies and treatment trials.

Retinal atrophy and markers of systemic and cerebrovascular severity in homozygous sickle cell disease

Introduction

While paramacular retinal atrophy (PRA) is known to be found in 48% of eyes of adults and 42% of eyes of children with homozygous SCD (SS-SCD), the aim of this study is to assess the association between PRA and red blood cell (RBC) deformability, hematological markers and brain imaging abnormalities in SS-SCD.

Methods

This study is a subset of DREAM2, a prospective observational study performed between August 2015 and August 2016. Children (5–17 years) with SS-SCD and no history of large vessel vasculopathy, were included. Ophthalmological characteristics including visual acuity, fundus examination, OCT of central and temporal retina (with several retinal thickness measurements) were explored in relation with RBC deformability (ektacytometry), hematological and biochemical (hemolysis parameters), and neurological (cerebral oxygenation estimated by Near Infrared Spectroscopy, brain magnetic resonance imaging) investigations.

Results

17 children (5 boys; mean age: 13 years) with complete ophthalmological investigations were included in the analysis; 8 exhibited PRA. RBC deformability was found to be significantly lower in children with PRA for measurements made at 1.69 Pa (0.16 a.u ± 0.02 vs 0.21 a.u ± 0.03, p = 0.02) and above, as well as cerebral oxygenation (59.25% ± 9.9 vs 71.53% ± 4.9, p = 0.02). A significant positive correlation was found between temporal retinal thickness and hemoglobin level (ρ = 0.65, p = 0.007), hematocrit (ρ = 0.53, p = 0.04) and RBC deformability at 3 Pa (ρ = 0.75, p = 0.005) and above.

Conclusions

These results suggest that PRA could be an early marker of systemic severity and cerebral oxygenation in SCD. Whether it could help predicting cerebral vasculopathy requires further investigations.

EVALUATION OF MACULAR FLOW VOIDS ON OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY AS POTENTIAL BIOMARKERS FOR SILENT CEREBRAL INFARCTION IN SICKLE CELL DISEASE

PURPOSE

To determine the relationship between macular microvascular abnormalities on optical coherence tomography angiography and silent cerebral infarctions (SCIs) on cerebral magnetic resonance imaging in sickle cell disease.

METHODS

Patients (age <18 years old) from our previous pediatric sickle cell disease study cohort who had prior optical coherence tomography angiography and brain magnetic resonance imaging were identified. Brain magnetic resonance imaging images were compared with macular optical coherence tomography angiography scans to identify macular vascular density differences between patients with SCI and without SCI.

RESULTS

Sixty-eight eyes from 34 patients who underwent optical coherence tomography angiography were evaluated, of whom 28 eyes from 14 patients met the inclusion criteria for this study. Eight patients (57%) with SCI and 6 patients (43%) without SCI were identified. The mean age (17 years in SCI and 16.3 years in non-SCI) was comparable between groups. There was no statistically significant difference in systemic complications. Deep capillary plexus vessel density was lower in the temporal quadrant in patients with SCI (49.3% vs. 53.7%, P = 0.014).

CONCLUSION

Patients with SCI were found to have lower vessel density in the deep capillary plexus compared with those without SCI. This finding suggests that deep capillary plexus vessel density may have utility as an imaging biomarker to predict the presence of SCI.

Morbidities and Mortality in Patients with Hereditary Thrombotic Thrombocytopenic Purpura

More women (117) than men (85) were diagnosed with hTTP. The difference was caused by 34 women who were diagnosed during pregnancy.

Half of patients with hTTP who were older than age 40 years had had stroke, kidney injury requiring dialysis, and/or severe cardiac injury.

Hereditary thrombotic thrombocytopenic purpura (hTTP) is a rare disorder caused by severe ADAMTS13 deficiency. Major morbidities and death at a young age are common. Although replacement of ADAMTS13 can prevent morbidities and death, current regimens of plasma prophylaxis are insufficient. We identified 226 patients with hTTP in 96 reports published from 2001 through 2020. Age at diagnosis was reported for 202 patients; 117 were female and 85 were male. The difference was caused by diagnosis of 34 women during pregnancy, suggesting that many men and nulliparous women are not diagnosed. Eighty-three patients had severe jaundice at birth; hTTP was suspected and effectively treated in only 3 infants. Of the 217 patients who survived infancy, 73 (34%) had major morbidities defined as stroke, kidney injury, or cardiac injury that occurred at a median age of 21 years. Sixty-two patients had stroke; 13 strokes occurred in children age 10 years or younger. Of the 54 patients who survived their initial major morbidity and were subsequently observed, 37 (69%) had sustained or subsequent major morbidities. Of the 39 patients who were observed after age 40 years, 20 (51%) had experienced a major morbidity. Compared with an age- and sex-matched US population, probability of survival was lower at all ages beginning at birth. Prophylaxis was initiated in 45 patients with a major morbidity; in 11 (28%), a major morbidity recurred after prophylaxis had begun. Increased recognition of hTTP and more effective prophylaxis started at a younger age are required to improve health outcomes.

Hematopoietic stem cell transplantation reverses white matter injury measured by diffusion-tensor imaging (DTI) in sickle cell disease patients

Brain injury in sickle cell disease (SCD) comprises a wide spectrum of neurological damage. Neurocognitive deficits have been described even without established neurological lesions. DTI is a rapid, noninvasive, and non-contrast method that enables detection of normal-appearing white matter lesions not detected by conventional magnetic resonance imaging (MRI). The aim of the study was to evaluate if stem cell transplantation can revert white matter lesions in patients with SCD. Twenty-eight SCD patients were evaluated with MRI and DTI before and after allogeneic hematopoietic stem cell transplantation (HSCT), compared with 26 healthy controls (HC). DTI metrics included fractional anisotropy (FA), mean diffusivity (MD), radial (RD), and axial (AD) diffusivity maps, global efficiency, path length, and clustering coefficients. Compared to HC, SCD patients had a lower FA (p = 0.0086) before HSCT. After HSCT, FA increased and was not different from healthy controls (p = 0.1769). Mean MD, RD, and AD decreased after HSCT (p = 0.0049; p = 0.0029; p = 0.0408, respectively). We confirm previous data of white matter lesions in SCD and present evidence that HSCT promotes recovery of brain injury with potential improvement of brain structural connectivity.

Blood-brain barrier permeability in survivors of immune-mediated thrombotic thrombocytopenic purpura: a pilot study

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare, life-threatening disorder of systemic microthrombosis and organ ischemia. The etiology of chronic cerebrovascular outcomes in iTTP survivors is largely unknown. In this pilot study, we measured blood-brain barrier (BBB) permeability in patients with iTTP at the start of remission and 6 months later. This prospective pilot study included 7 adult patients with incident iTTP. Eligibility criteria included ADAMTS13 activity < 10% and detectable inhibitor at diagnosis. Patients were recruited from London Health Sciences Centre in Canada (2017-2019) within 3 days of hospital admission and followed for 6 months after remission (defined as normalization of platelet count and lactate dehydrogenase with no clinical signs or symptoms of microvascular injury for more than 30 days after the last plasma exchange). All patients had cerebral computed tomography perfusion scans with BBB permeability surface product measurements. Patients (5 women, 2 men) had a mean age of 48 years (range, 21-77 years). At diagnosis, patients had a mean platelet count of 22 (standard deviation [SD], 25) × 109/L. At the start of remission, mean BBB permeability surface product was 0.91 (0.30) mL/min/100 g. Six months later, the mean permeability surface product was 0.56 (0.22) mL/min/100 g, with a mean difference of -0.312 mL/min/100 g (95% confidence interval: -0.4729 to -0.1510; P = .0032). In this pilot study of patients with iTTP, pathologically increased BBB permeability was evident, and although there was some improvement, this persisted 6 months after remission. Future work will explore the chronicity of these findings and their clinical implications.

Effects of hydroxyurea on brain function in children with sickle cell anemia

INTRODUCTION

Sickle cell anemia (SCA) results in numerous adverse effects on the brain, including neurocognitive dysfunction. Hydroxyurea has been utilized extensively for management of SCA, but its effects on brain function have not been established.

METHODS

We examined prospectively the effects of 1 year of treatment with hydroxyurea on brain function in children with SCA (HbSS/HbSβ⁰ -thalassemia) by baseline and exit evaluations, including comprehensive neurocognitive testing, transcranial Doppler ultrasound (TCD), and brain MRI (silent cerebral infarcts [SCI], gray matter cerebral blood flow [GM-CBF], and blood oxygen level-dependent [BOLD] signal from visual stimulation).

RESULTS

Nineteen patients with SCA, mean age 12.4 years (range 7.2-17.8), were evaluated. At baseline, subjects had these mean values: full-scale IQ (FSIQ) 82.8, TCD velocity 133 cm/s, GM-CBF 64.4 ml/100 g/min, BOLD signal 2.34% increase, and frequency of SCI 47%. After 1 year of hydroxyurea, there were increases in FSIQ (+2, p = .059) and reading passage comprehension (+4, p = .033), a significant decrease in TCD velocity (-11 cm/s, p = .007), and no significant changes in GM-CBF, BOLD, or SCI frequency. Hemoglobin F (HbF) was associated with passage comprehension, hemoglobin with lower TCD velocity, and lower GM-CBF with greater working memory. Higher BOLD signal was associated with higher processing speed and lower TCD velocity with higher math fluency.

DISCUSSION

Improvements in neurocognition and decreased TCD velocity following 1 year of treatment support hydroxyurea use for improving neurocognitive outcomes in SCA. Understanding the mechanisms of benefit, as indicated by relationships of neurocognitive function with HbF, hemoglobin, and CBF, requires further evaluation.

Cerebrovascular Complications of Anemia

PURPOSE OF THE REVIEW

Anemia has been called the fifth cardiovascular risk factor. It is one of the most prevalent pathologies worldwide. In this article, we aimed to perform a narrative review of the main cerebrovascular complications of anemia and its influence on stroke prognosis.

RECENT FINDINGS

Both hypoproliferative anemia (thalassemia, iron deficiency anemia, etc.) and hyperproliferative anemia (sickle cell disease, paroxysmal nocturnal hemoglobinuria, hereditary spherocytosis, etc.) are associated to cerebrovascular disease ranging from transient ischemic attack to ischemic stroke and hemorrhagic stroke with both intraparenchymal hemorrhage and subarachnoid hemorrhage or cerebral venous thrombosis. Anemia is associated to a worse prognosis in patients with cerebrovascular disease In some cases, like sickle cell disease, pathophysiological mechanisms and therapeutic guidelines are well established, while in others, due to their rarity, there are still lack of robust data. More studies are needed to clarify how the prognosis of stroke patients with anemia could be improved.

Neurologic and Cognitive Outcomes in Sickle Cell Disease from Infancy through Adolescence

Children with sickle cell disease (SCD) are at risk for neurologic and cognitive complications beginning in early childhood. Current treatment for SCD focuses on primary prevention of complications, such as hydroxyurea for prevention of pain and acute chest syndrome, and chronic transfusion therapy for children who are at high risk for strokes. In this article, the prevalence, pathophysiology, and available interventions to prevent and treat neurologic and cognitive complications of SCD will be reviewed.

Reduced global cerebral oxygen metabolic rate in sickle cell disease and chronic anemias

Anemia is the most common blood disorder in the world. In patients with chronic anemia, such as sickle cell disease or major thalassemia, cerebral blood flow increases to compensate for decreased oxygen content. However, the effects of chronic anemia on oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO₂ ) are less well understood. In this study, we examined 47 sickle-cell anemia subjects (age 21.7 ± 7.1, female 45%), 27 non-sickle anemic subjects (age 25.0 ± 10.4, female 52%) and 44 healthy controls (age 26.4 ± 10.6, female 71%) using MRI metrics of brain oxygenation and flow. Phase contrast MRI was used to measure resting cerebral blood flow, while T₂ -relaxation-under-spin-tagging (TRUST) MRI with disease appropriate calibrations were used to measure OEF and CMRO₂ . We observed that patients with sickle cell disease and other chronic anemias have decreased OEF and CMRO₂ (respectively 27.4 ± 4.1% and 3.39 ± 0.71 ml O₂ /100 g/min in sickle cell disease, 30.8 ± 5.2% and 3.53 ± 0.64 ml O₂ /100 g/min in other anemias) compared to controls (36.7 ± 6.0% and 4.00 ± 0.65 ml O₂ /100 g/min). Impaired CMRO₂ was proportional to the degree of anemia severity. We further demonstrate striking concordance of the present work with pooled historical data from patients having broad etiologies for their anemia. The reduced cerebral oxygen extraction and metabolism are consistent with emerging data demonstrating increased non-nutritive flow, or physiological shunting, in sickle cell disease patients.

Co-Occurrence of Neurodevelopmental Disorders in Pediatric Sickle Cell Disease

OBJECTIVE

The objective of this study is to retrospectively determine the co-occurrence, associated characteristics, and risk factors for neurodevelopmental disorders (NDD) in a pediatric sickle cell disease (SCD) clinic population.

METHOD

We investigated the co-occurrence and features of NDD in pediatric SCD through a retrospective cohort study conducted between July 2017 and January 2019. The participants were patients with SCD younger than 18 years of age identified from our institutions' clinic rosters and medical records databases.

RESULTS

A total of 276 participants were eligible for study inclusion, and 65 participants were found to have various NDD. Children with SCD and NDD were more likely to have a history of multiple SCD-related complications in comparison to children with SCD without NDD. Children with SCD and NDD were more likely to use disease-modifying therapies in comparison to children with SCD without NDD (χ2 27.2, p < 0.001).

CONCLUSION

Children with SCD and NDD have higher odds of having certain disease-related complications and higher use of disease-modifying treatments than children with SCD who do not have NDD. Screening and diagnoses of NDD may be relevant to clinical management of pediatric SCD.

Cerebral Oxygen Metabolic Stress, Microstructural Injury, and Infarction in Adults With Sickle Cell Disease

OBJECTIVE

To determine the patient- and tissue-based relationships between cerebral hemodynamic and oxygen metabolic stress, microstructural injury, and infarct location in adults with sickle cell disease (SCD).

METHODS

Control and SCD participants underwent brain MRI to quantify cerebral blood flow (CBF), oxygen extraction fraction (OEF), mean diffusivity (MD), and fractional anisotropy (FA) within normal-appearing white matter (NAWM), and infarcts on FLAIR. Multivariable linear regression examined the patient- and voxel-based associations between hemodynamic and metabolic stress (defined as elevated CBF and OEF, respectively), white matter microstructure, and infarct location.

RESULTS

Of 83 control and SCD participants, adults with SCD demonstrated increased CBF (50.9 vs 38.8 mL/min/100g, p<0.001), increased OEF (0.35 vs 0.25, p<0.001), increased MD (0.76 vs 0.72 x 10^-3mm² s^-1, p=0.005), and decreased FA (0.40 vs 0.42, p=0.021) within NAWM compared to controls. In multivariable analysis, increased OEF (β=0.19, p=0.035), but not CBF (β=0.00, p=0.340), independently predicted increased MD in the SCD cohort, while neither were predictors in controls. On voxel-wise regression, the SCD cohort demonstrated widespread OEF elevation, encompassing deep white matter regions of elevated MD and reduced FA, which spatially extended beyond high density infarct locations from the SCD cohort.

CONCLUSION

Elevated OEF, a putative index of cerebral oxygen metabolic stress, may provide a metric of ischemic vulnerability which could enable individualization of therapeutic strategies in SCD. The patient- and tissue-based relationships between elevated OEF, elevated MD, and cerebral infarcts suggest that oxygen metabolic stress may underlie microstructural injury prior to the development of cerebral infarcts in SCD.

PHACES Syndrome and Associated Anomalies: Risk Associated With Small and Large Facial Hemangiomas

OBJECTIVE. PHACES syndrome includes posterior fossa malformations, hemangioma, arterial anomalies, coarctation of the aorta and cardiac defects, eye abnormalities, and sternal defect with or without supraumbilical raphe. Usually, brain imaging is performed when facial hemangiomas are larger than 5 cm. Data on associated anomalies regardless of hemangioma size are sparse. The objective of this study was to determine, first, the prevalence of PHACES-like associated anomalies in a large sample of infants with all sizes of segmental facial or periorbital focal infantile hemangioma and, second, whether the cutaneous localization of the hemangioma correlates with the type of anomalies present. MATERIALS AND METHODS. The records of all patients of a vascular anomalies practice who had a diagnosis of segmental facial or periorbital focal infantile hemangioma and who had clinical photographs and brain MRI available were reviewed. The clinical photographs were reviewed to determine the localization by segment and lateralization. MRI was reviewed by two experienced pediatric radiologists. If present, cardiovascular anomalies, sternal defects, and eye anomalies were recorded. The criteria for definite and possible PHACES were used. RESULTS. The study included 122 children (90 girls, 32 boys; mean age, 16.6 months). Forty-five (36.9%) children had a facial infantile hemangioma larger than 5 cm. Twenty-two patients (18.0%) had PHACES or possible PHACES syndrome. Cerebrovascular structural anomalies were seen in 14 of 22 and brain anomalies in 6 of 22 patients with PHACES syndrome but in none and one of the patients in the group without PHACES (p < .001). Cardiovascular anomalies were seen in six patients and ocular anomalies in eight patients. All but one of them had PHACES syndrome. CONCLUSION. Clinical concern about associated extracutaneous anomalies is warranted for all children with facial segmental or periorbital focal infantile hemangiomas, including those with small hemangiomas. Further studies are needed to correlate cerebrovascular anomalies with the clinical evolution of hemangiomas and their effects on cerebral perfusion.

American Society of Hematology 2020 guidelines for sickle cell disease: prevention, diagnosis, and treatment of cerebrovascular disease in children and adults

BACKGROUND

Central nervous system (CNS) complications are among the most common, devastating sequelae of sickle cell disease (SCD) occurring throughout the lifespan.

OBJECTIVE

These evidence-based guidelines of the American Society of Hematology are intended to support the SCD community in decisions about prevention, diagnosis, and treatment of the most common neurological morbidities in SCD.

METHODS

The Mayo Evidence-Based Practice Research Program supported the guideline development process, including updating or performing systematic evidence reviews. The panel used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach, including GRADE evidence-to-decision frameworks, to assess evidence and make recommendations.

RESULTS

The panel placed a higher value on maintaining cognitive function than on being alive with significantly less than baseline cognitive function. The panel developed 19 recommendations with evidence-based strategies to prevent, diagnose, and treat CNS complications of SCD in low-middle- and high-income settings.

CONCLUSIONS

Three of 19 recommendations immediately impact clinical care. These recommendations include: use of transcranial Doppler ultrasound screening and hydroxyurea for primary stroke prevention in children with hemoglobin SS (HbSS) and hemoglobin Sβ0 (HbSβ0) thalassemia living in low-middle-income settings; surveillance for developmental delay, cognitive impairments, and neurodevelopmental disorders in children; and use of magnetic resonance imaging of the brain without sedation to detect silent cerebral infarcts at least once in early-school-age children and once in adults with HbSS or HbSβ0 thalassemia. Individuals with SCD, their family members, and clinicians should become aware of and implement these recommendations to reduce the burden of CNS complications in children and adults with SCD.

Advances in neuroimaging to improve care in sickle cell disease

Sickle cell disease is associated with progressive and increased neurological morbidity throughout the lifespan. In people with sickle cell anaemia (the most common and severe type of sickle cell disease), silent cerebral infarcts are found in more than a third of adolescents by age 18 years and roughly half of young adults by age 30 years, many of whom have cognitive impairment despite having few or no conventional stroke risk factors. Common anatomical neuroimaging in individuals with sickle disease can assess structural brain injury, such as stroke and silent cerebral infarcts; however, emerging advanced neuroimaging methods can provide novel insights into the pathophysiology of sickle cell disease, including insights into the cerebral haemodynamic and metabolic contributors of neurological injury. Advanced neuroimaging methods, particularly methods that report on aberrant cerebral blood flow and oxygen delivery, have potential for triaging patients for appropriate disease-modifying or curative therapies before they have irreversible neurological injury, and for confirming the benefit of new therapies on brain health in clinical trials.

Hydroyxurea improves cerebral oxygen saturation in children with sickle cell anemia

Neurologic complications are common in patients with sickle cell anemia (SCA), but conventional tools such as MRI and transcranial Doppler ultrasonography (TCD) do not fully assess cerebrovascular pathology. Cerebral tissue oximetry measures mixed oxygen saturation in the frontal lobes (S_CT O₂ ) and provides early prognostic information about tissue at risk of ischemic injury. Untreated patients with SCA have significantly lower S_CT O₂ than healthy controls that declines with age. Hydroxyurea is effective in preventing many SCA-related complications, but the degree to which it preserves normal neurophysiology is unclear. We analyzed participants enrolled in the Therapeutic Response Evaluation and Adherence Trial (TREAT, NCT02286154), which enrolled participants initiating hydroxyurea using individualized dosing (new cohort) and those previously taking hydroxyurea (old cohort) and was designed to monitor the long-term benefits of hydroxyurea. Cerebral oximetry was performed at baseline and annually. For the new cohort (median starting age = 12 months, n = 55), mean baseline S_CT O₂ was normal before starting hydroxyurea (mean 65%, 95% CI 58-72%) and significantly increased after 2 years (mean 72%, 95% CI 65-79%, p < .001). The S_CT O₂ for patients receiving long-term hydroxyurea (median age = 9.6 years) was normal at study entry (mean 66%, 95% CI 58-74%) and remained stable across 2 years. Both cohorts had significantly higher S_CT O₂ than published data from predominantly untreated SCA patients. Cerebral oximetry is a non-invasive method to assess cerebrovascular pathology that complements conventional imaging. Our results indicate that hydroxyurea suggests protection against neurophysiologic changes seen in untreated SCA.

Impairment of Cerebrovascular Hemodynamics in Patients With Severe and Milder Forms of Sickle Cell Disease

In patients with sickle cell disease (SCD), cerebral blood flow (CBF) is elevated to counteract anemia and maintain oxygen supply to the brain. This may exhaust the vasodilating capacity of the vessels, possibly increasing the risk of silent cerebral infarctions (SCI). To further investigate cerebrovascular hemodynamics in SCD patients, we assessed CBF, arterial transit time (ATT), cerebrovascular reactivity of CBF and ATT (CVR_CBF and CVR_ATT) and oxygen delivery in patients with different forms of SCD and matched healthy controls. We analyzed data of 52 patients with severe SCD (HbSS and HbSβ⁰-thal), 20 patients with mild SCD (HbSC and HbSβ⁺-thal) and 10 healthy matched controls (HbAA and HbAS). Time-encoded arterial spin labeling (ASL) scans were performed before and after a vasodilatory challenge using acetazolamide (ACZ). To identify predictors of CBF and ATT after vasodilation, regression analyses were performed. Oxygen delivery was calculated and associated with hemoglobin and fetal hemoglobin (HbF) levels. At baseline, severe SCD patients showed significantly higher CBF and lower ATT compared to both the mild SCD patients and healthy controls. As CBF_postACZ was linearly related to CBF_preACZ, CVR_CBF decreased with disease severity. CVR_ATT was also significantly affected in severe SCD patients compared to mild SCD patients and healthy controls. Considering all groups, women showed higher CBF_postACZ than men (p < 0.01) independent of baseline CBF. Subsequently, post ACZ oxygen delivery was also higher in women (p < 0.05). Baseline, but not post ACZ, GM oxygen delivery increased with HbF levels. Our data showed that baseline CBF and ATT and CVR_CBF and CVR_ATT are most affected in severe SCD patients and to a lesser extent in patients with milder forms of SCD compared to healthy controls. Cerebrovascular vasoreactivity was mainly determined by baseline CBF, sex and HbF levels. The higher vascular reactivity observed in women could be related to their lower SCI prevalence, which remains an area of future work. Beneficial effects of HbF on oxygen delivery reflect changes in oxygen dissociation affinity from hemoglobin and were limited to baseline conditions suggesting that high HbF levels do not protect the brain upon a hemodynamic challenge, despite its positive effect on hemolysis.

Reduced oxygen extraction efficiency in sickle cell anemia patients with evidence of cerebral capillary shunting

Arterial spin labeling (ASL) magnetic resonance imaging (MRI) utilizes arterial blood water as an endogenous contrast agent to provide a quantitative measure of cerebral blood flow (CBF). Recently, hyperintense signal within dural venous sinuses in ASL images of sickle cell anemia (SCA) patients has been shown to be consistent with elevated flow velocities and may indicate capillary shunting and reduced oxygen extraction. Here, we performed oxygen extraction fraction (OEF) and CBF measurements in adults (cumulative n = 114) with (n = 69) and without (n = 45) SCA to test the hypothesis that hyperintense venous ASL signal is associated with reduced OEF. Higher categorical scores of shunting on ASL MRI were associated with lower OEF in participants with silent cerebral infarcts or white matter hyperintensities (p = 0.003), but not in those without lesions (p = 0.551). These findings indicate that venous hyperintense signal in ASL images in SCA patients may represent a marker of capillary-level disturbances in oxygen exchange efficiency and small vessel pathology.

Tract-specific analysis and neurocognitive functioning in sickle cell patients without history of overt stroke

INTRODUCTION

Sickle cell disease (SCD) is a hereditary blood disorder in which the oxygen-carrying hemoglobin molecule in red blood cells is abnormal. SCD patients are at increased risks for strokes and neurocognitive deficit, even though neurovascular screening and treatments have lowered the rate of overt strokes. Tract-specific analysis (TSA) is a statistical method to evaluate microstructural WM damage in neurodegenerative disorders, using diffusion tensor imaging (DTI).

METHODS

We utilized TSA and compared 11 major brain WM tracts between SCD patients with no history of overt stroke, anemic controls, and healthy controls. We additionally examined the relationship between the most commonly used DTI metric of WM tracts and neurocognitive performance in the SCD patients and healthy controls.

RESULTS

Disruption of WM microstructure orientation-dependent metrics for the SCD patients was found in the genu of the corpus callosum (CC), cortico-spinal tract, inferior fronto-occipital fasciculus, right inferior longitudinal fasciculus, superior longitudinal fasciculus, and left uncinate fasciculus. Neurocognitive performance indicated slower processing speed and lower response inhibition skills in SCD patients compared to controls. TSA abnormalities in the CC were significantly associated with measures of processing speed, working memory, and executive functions.

CONCLUSION

Decreased DTI-derived metrics were observed on six tracts in chronically anemic patients, regardless of anemia subtype, while two tracks with decreased measures were unique to SCD patients. Patients with WMHs had more significant FA abnormalities. Decreased FA values in the CC significantly correlated with all nine neurocognitive tests, suggesting a critical importance for CC in core neurocognitive processes.