Reversibility of Cognitive Deficits and Functional Connectivity With Transfusion in Children With Sickle Cell Disease

BACKGROUND AND OBJECTIVES

People with sickle cell disease (SCD) are at risk of cognitive dysfunction independent of stroke. Diminished functional connectivity in select large-scale networks and white matter integrity reflect the neurologic consequences of SCD. Because chronic transfusion therapy is neuroprotective in preventing stroke and strengthening executive function abilities in people with SCD, we hypothesized that red blood cell (RBC) transfusion facilitates the acute reversal of disruptions in functional connectivity while white matter integrity remains unaffected.

METHODS

Children with SCD receiving chronic transfusion therapy underwent a brain MRI measuring white matter integrity with diffusion tensor imaging and resting-state functional connectivity within 3 days before and after transfusion of RBCs. Cognitive assessments with the NIH Toolbox were acquired after transfusion and then immediately before the following transfusion cycle.

RESULTS

Sixteen children with a median age of 12.5 years were included. Global assessments of functional connectivity using homotopy (p = 0.234) or modularity (p = 0.796) did not differ with transfusion. Functional connectivity within the frontoparietal network significantly strengthened after transfusion (median intranetwork Z-score 0.21 [0.17-0.30] before transfusion, 0.29 [0.20-0.36] after transfusion, p < 0.001), while there was not a significant change seen within the sensory motor, visual, auditory, default mode, dorsal attention, or cingulo-opercular networks. Corresponding to the change within the frontoparietal network, there was a significant improvement in executive function abilities after transfusion (median executive function composite score 87.7 [81.3-90.7] before transfusion, 90.3 [84.3-93.7] after transfusion, p = 0.021). Participants with stronger connectivity in the frontoparietal network before transfusion had a significantly greater improvement in the executive function composite score with transfusion (r = 0.565, 95% CI 0.020-0.851, p = 0.044). While functional connectivity and executive abilities strengthened with transfusion, there was not a significant change in white matter integrity as assessed by fractional anisotropy and mean diffusivity within 16 white matter tracts or globally with tract-based spatial statistics.

DISCUSSION

Strengthening of functional connectivity with concomitant improvement in executive function abilities with transfusion suggests that functional connectivity MRI could be used as a biomarker for acutely reversible neurocognitive injury as novel therapeutics are developed for people with SCD.

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.

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.

Abstract 63: Age-related Changes In Gray Matter Cerebral Metabolism And Vascular Reactivity In Children

Introduction: Metabolic demand changes throughout childhood as the brain develops, peaking in the 2 nd decade of life. Cerebral blood flow (CBF) is dynamic throughout childhood, likely in response to the increased metabolic demand of brain development. Cerebrovascular reactivity (CVR) reflects the ability to further increase CBF in response to a stimulus, such as carbon dioxide (CO 2 ). We hypothesized that gray matter oxygen metabolism (GM CMRO 2 ) is increased in younger children, corresponding to higher GM CBF and lower GM CVR.

Methods: CVR was calculated as the proportional change of a subject’s MRI-measured blood oxygen level dependent signal in response to an increase in end-tidal CO 2 administered by the RespirAct® RA-MR™ device. GM CMRO 2 was calculated voxel-by-voxel as the product of GM CBF (arterial spin labeling), GM oxygen extraction fraction (asymmetric spin echo), and arterial oxygen content (= Hb х (oxygen saturation)х1.34). Univariate relationships were tested using Spearman’s correlation coefficient, and corrected for multiple comparisons.

Results: GM CVR, CBF, and CMRO 2 were calculated for 15 healthy participants (ages 8-19, 7 male). GM CMRO 2 was highest in young children and decreased with age (ρ=-0.68, P=0.005), as did CBF (ρ =-0.67, P=0.006). CVR was lower in young children, increasing with age (ρ=0.58, P=0.02). However, while GM CVR correlated with CBF (ρ=-0.64, P=0.01) it did not significantly associate with CMRO 2 (ρ=-0.43, P=0.114).

Conclusion: Although GM CMRO 2 and CVR both have age-related changes, CVR does not directly correlate with CMRO 2 . Rather, their relationship may be moderated through other influences on CBF, as further study will investigate.

Figure: Linear fits and 95% confidence intervals of subject data, including age, GM CBF, and GM CMRO 2 , versus GM CVR. P-values are from Spearman’s test for monotonic correlation.

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.

Silent Infarcts, White Matter Integrity, and Oxygen Metabolic Stress in Young Adults With and Without Sickle Cell Trait

BACKGROUND

Individuals with sickle cell anemia have heightened risk of stroke and cognitive dysfunction. Given its high prevalence globally, whether sickle cell trait (SCT) is a risk factor for neurological injury has been of interest; however, data have been limited. We hypothesized that young, healthy adults with SCT would show normal cerebrovascular structure and hemodynamic function.

METHODS

As a case-control study, young adults with (N=25, cases) and without SCT (N=24, controls) underwent brain magnetic resonance imaging to quantify brain volume, microstructural integrity (fractional anisotropy), silent cerebral infarcts (SCI), intracranial stenosis, and aneurysms. Pseudocontinuous arterial spin labeling and asymmetric spin echo sequences measured cerebral blood flow and oxygen extraction fraction, respectively, from which cerebral metabolic oxygen demand was calculated. Imaging metrics were compared between SCT cases and controls. SCI volume was correlated with baseline characteristics.

RESULTS

Compared with controls, adults with SCT demonstrated similar normalized brain volumes (SCT 0.80 versus control 0.81, P=0.41), white matter fractional anisotropy (SCT 0.41 versus control 0.43, P=0.37), cerebral blood flow (SCT 62.04 versus control, 61.16 mL/min/100 g, P=0.67), oxygen extraction fraction (SCT 0.27 versus control 0.27, P=0.31), and cerebral metabolic oxygen demand (SCT 2.71 versus control 2.70 mL/min/100 g, P=0.96). One per cohort had an intracranial aneurysm. None had intracranial stenosis. The SCT cases and controls showed similar prevalence and volume of SCIs; however, in the subset of participants with SCIs, the SCT cases had greater SCI volume versus controls (0.29 versus 0.07 mL, P=0.008). Of baseline characteristics, creatinine was mildly elevated in the SCT cohort (0.9 versus 0.8 mg/dL, P=0.053) and correlated with SCI volume (ρ=0.49, P=0.032). In the SCT cohort, SCI distribution was similar to that of young adults with sickle cell anemia.

CONCLUSIONS

Adults with SCT showed normal cerebrovascular structure and hemodynamic function. These findings suggest that healthy individuals with SCT are unlikely to be at increased risk for early or accelerated ischemic brain injury.

GRAPES: Trivia game increases sickle cell disease knowledge in patients and providers and mitigates healthcare biases

BACKGROUND

Patients with sickle cell disease (SCD) endure healthcare biases that are partially due to a lack of disease-specific education among healthcare providers. Furthermore, there is a paucity of age-appropriate health education materials for patients with SCD. To address this gap, we created the GRAPES tool (Game to Raise Awareness for Patient/Provider/Public Education of SCD; www.tinyurl.com/GRAPESgame) and hypothesized that utilization of the GRAPES tool will improve patient and provider SCD knowledge and mitigate healthcare bias.

PROCEDURE

The GRAPES tool is an online, single-player trivia game. A feasibility study was conducted in pediatric patients with SCD at age 10 years or older and registered nurses. All participants were assessed for change in SCD-relevant knowledge and satisfaction post-gameplay. Providers were assessed for change in attitudes toward patients with SCD post-gameplay.

RESULTS

Twenty-five patients and 25 providers were enrolled. All participants (P < 0.001), and specifically within the patient (P = 0.019) and provider (P < 0.001) cohorts, showed increased SCD knowledge post-gameplay. Both patients and providers reported high satisfaction with GRAPES. Provider negative attitudes were reduced (P = 0.007) post-gameplay without change in positive attitudes (P = 0.959). Providers demonstrated post-gameplay reduced (P = 0.001) belief that patients' changing behavior around providers indicates inappropriate drug-seeking behavior.

CONCLUSIONS

This study demonstrates the feasibility and acceptability of the GRAPES tool as a potential digital, behavioral intervention to provide educational materials for patients and their providers in different clinical settings, improve knowledge about SCD, and decrease stigma against patients with SCD in the healthcare setting.

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.

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.

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.

Functional Connectivity Decreases with Metabolic Stress in Sickle Cell Disease

OBJECTIVE

Children with sickle cell disease (SCD) experience cognitive deficits even when unaffected by stroke. Using functional connectivity magnetic resonance imaging (MRI) as a potential biomarker of cognitive function, we tested our hypothesis that children with SCD would have decreased functional connectivity, and that children experiencing the greatest metabolic stress, indicated by elevated oxygen extraction fraction, would have the lowest connectivity.

METHODS

We prospectively obtained brain MRIs and cognitive testing in healthy controls and children with SCD.

RESULTS

We analyzed data from 60 participants (20 controls and 40 with sickle cell disease). There was no difference in global cognition or cognitive subdomains between cohorts. However, we found decreased functional connectivity within the sensory-motor, lateral sensory-motor, auditory, salience, and subcortical networks in participants with SCD compared with controls. Further, as white matter oxygen extraction fraction increased, connectivity within the visual (p = 0.008, parameter estimate = -0.760 [95% CI = -1.297, -0.224]), default mode (p = 0.012, parameter estimate = -0.417 [95% CI = -0.731, -0.104]), and cingulo-opercular (p = 0.009, parameter estimate = -0.883 [95% CI = -1.517, -0.250]) networks decreased.

INTERPRETATION

We conclude that there is diminished functional connectivity within these anatomically contiguous networks in children with SCD compared with controls, even when differences are not seen with cognitive testing. Increased white matter oxygen extraction fraction was associated with decreased connectivity in select networks. These data suggest that elevated oxygen extraction fraction and disrupted functional connectivity are potentially presymptomatic neuroimaging biomarkers for cognitive decline in SCD. ANN NEUROL 2020;88:995-1008.

Higher executive abilities following a blood transfusion in children and young adults with sickle cell disease

Individuals with sickle cell disease (SCD) experience cognitive deficits; however, it remains unclear whether medical treatments for SCD improve cognition. Given that executive abilities are typically impaired in individuals with SCD, they were the focus of the current study. Our primary hypothesis was that executive abilities would be higher acutely soon after a blood transfusion in children and young adults with SCD. We used tests from the NIH Toolbox to assess executive abilities in 27 participants with SCD receiving chronic transfusion in comparison to 34 participants with SCD receiving hydroxyurea (HU) and 41 non-SCD demographically matched controls, all of whom were tested at two time points. Participants in the transfusion group completed cognitive testing within 3 days after a transfusion (soon after transfusion) and then within 3 days before their next transfusion (long after transfusion) over an interval of 3-7 weeks. We found that executive abilities were significantly poorer for the transfusion and HU groups than for the control group. In support of our primary hypothesis, executive abilities for the transfusion group were significantly better soon after a transfusion compared to long after a transfusion, χ² (1) = 17.8, P < .0001. Our results demonstrate that executive abilities were higher acutely following a blood transfusion. These findings have implications for daily functioning, medical decision making, and academic achievement in children and young adults with SCD.

Abstract 51: Aging and Metabolic Stress Are Associated With Disrupted White Matter Integrity in Children and Young Adults With Sickle Cell Disease

Introduction: Silent cerebral infarcts (SCIs) in sickle cell disease (SCD) begin in early childhood and increase with age, affecting 50% by age 30. SCIs often occur in the watershed area, where cerebral blood flow (CBF) is low, and oxygen extraction fraction (OEF) is high. Diffusion tensor imaging (DTI) measures white matter integrity; lower fractional anisotropy (FA) and higher mean diffusivity (MD) may precede the appearance of SCIs. We hypothesized that age and oxygen metabolic stress, defined by elevated watershed OEF, are associated with disruption of white matter integrity as measured by FA and MD.

Methods: Children and young adults with and without SCD were recruited for brain MRI (T1, FLAIR, pseudocontinuous arterial spin label (CBF), asymmetric spin echo (OEF) and DTI). We averaged CBF maps of non-SCD participants and created a watershed region of interest (ROI), defined as CBF <30% of mean gray matter CBF, which was applied to individual maps. All SCIs were outlined and excluded. We evaluated age and SCD as predictors of FA and MD. Within the watershed ROI, we evaluated OEF and age as predictors of FA and MD.

Results: Fifty SCD and 53 control participants, age 6-39 years, underwent MRI. Within all normal appearing white matter, FA decreased (p<0.001) and MD increased (p<0.001) with advancing age. MD, but not FA, changed at a faster rate with advancing age in SCD compared to controls (p=0.02). Within the watershed region, OEF significantly predicted FA (p=0.002) and MD (p <0.001), after adjusting for age.

Conclusion: Disruption of white matter integrity worsens with early life aging, particularly in SCD. Oxygen metabolic stress within the watershed region, a region at high risk for SCIs, is associated with lower FA and higher MD, suggesting OEF may provide an early tissue marker of ischemic vulnerability in SCD, prior to developing SCIs.

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

Silent cerebral infarcts (SCIs) are associated with cognitive impairment in sickle cell anemia (SCA). SCI risk factors include low hemoglobin and elevated systolic blood pressure; however, mechanisms underlying their development are unclear. Using the largest prospective study evaluating SCIs in pediatric SCA, we identified brain regions with increased SCI density. We tested the hypothesis that infarct density is greatest within regions in which cerebral blood flow is lowest, further restricting cerebral oxygen delivery in the setting of chronic anemia. Neuroradiology and neurology committees reached a consensus of SCIs in 286 children in the Silent Infarct Transfusion (SIT) Trial. Each infarct was outlined and coregistered to a brain atlas to create an infarct density map. To evaluate cerebral blood flow as a function of infarct density, pseudocontinuous arterial spin labeling was performed in an independent pediatric SCA cohort. Blood flow maps were aligned to the SIT Trial infarct density map. Mean blood flow within low, moderate, and high infarct density regions from the SIT Trial were compared. Logistic regression evaluated clinical and imaging predictors of overt stroke at 3-year follow-up. The SIT Trial infarct density map revealed increased SCI density in the deep white matter of the frontal and parietal lobes. A relatively small region, measuring 5.6% of brain volume, encompassed SCIs from 90% of children. Cerebral blood flow was lowest in the region of highest infarct density (P < .001). Baseline infarct volume and reticulocyte count predicted overt stroke. In pediatric SCA, SCIs are symmetrically located in the deep white matter where minimum cerebral blood flow occurs.

Regional oxygen extraction predicts border zone vulnerability to stroke in sickle cell disease

OBJECTIVE

To determine mechanisms underlying regional vulnerability to infarction in sickle cell disease (SCD) by measuring voxel-wise cerebral blood flow (CBF), oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen utilization (CMRO2) in children with SCD.

METHODS

Participants underwent brain MRIs to measure voxel-based CBF, OEF, and CMRO2. An infarct heat map was created from an independent pediatric SCD cohort with silent infarcts and compared to prospectively obtained OEF maps.

RESULTS

Fifty-six participants, 36 children with SCD and 20 controls, completed the study evaluation. Whole-brain CBF (99.2 vs 66.3 mL/100 g/min, p < 0.001), OEF (42.7% vs 28.8%, p < 0.001), and CMRO2 (3.7 vs 2.5 mL/100 g/min, p < 0.001) were higher in the SCD cohort compared to controls. A region of peak OEF was identified in the deep white matter in the SCD cohort, delineated by a ratio map of average SCD to control OEF voxels. CMRO2 in this region, which encompassed the CBF nadir, was low relative to all white matter (p < 0.001). Furthermore, this peak OEF region colocalized with regions of greatest infarct density derived from an independent SCD cohort.

CONCLUSIONS

Elevated OEF in the deep white matter identifies a signature of metabolically stressed brain tissue at increased stroke risk in pediatric patients with SCD. We propose that border zone physiology, exacerbated by chronic anemic hypoxia, explains the high risk in this region.

Red cell exchange transfusions lower cerebral blood flow and oxygen extraction fraction in pediatric sickle cell anemia

Blood transfusions are the mainstay of stroke prevention in pediatric sickle cell anemia (SCA), but the physiology conferring this benefit is unclear. Cerebral blood flow (CBF) and oxygen extraction fraction (OEF) are elevated in SCA, likely compensating for reduced arterial oxygen content (CaO2). We hypothesized that exchange transfusions would decrease CBF and OEF by increasing CaO2, thereby relieving cerebral oxygen metabolic stress. Twenty-one children with SCA receiving chronic transfusion therapy (CTT) underwent magnetic resonance imaging before and after exchange transfusions. Arterial spin labeling and asymmetric spin echo sequences measured CBF and OEF, respectively, which were compared pre- and posttransfusion. Volumes of tissue with OEF above successive thresholds (36%, 38%, and 40%), as a metric of regional metabolic stress, were compared pre- and posttransfusion. Transfusions increased hemoglobin (Hb; from 9.1 to 10.3 g/dL; P < .001) and decreased Hb S (from 39.7% to 24.3%; P < .001). Transfusions reduced CBF (from 88 to 82.4 mL/100 g per minute; P = .004) and OEF (from 34.4% to 31.2%; P < .001). At all thresholds, transfusions reduced the volume of peak OEF found in the deep white matter, a location at high infarct risk in SCA (P < .001). Reduction of elevated CBF and OEF, both globally and regionally, suggests that CTT mitigates infarct risk in pediatric SCA by relieving cerebral metabolic stress at patient- and tissue-specific levels.

Large-Vessel Vasculopathy in Children With Sickle Cell Disease: A Magnetic Resonance Imaging Study of Infarct Topography and Focal Atrophy

BACKGROUND

Large-vessel vasculopathy (LVV) increases stroke risk in pediatric sickle cell disease beyond the baseline elevated stroke risk in this vulnerable population. The mechanisms underlying this added risk and its unique impact on the developing brain are not established.

METHODS

We analyzed magnetic resonance imaging and angiography scans of 66 children with sickle cell disease and infarcts by infarct density heatmaps and Jacobian determinants, a metric utilized to delineate focal volume change, to investigate if infarct location, volume, frequency, and cerebral atrophy differed among hemispheres with and without LVV.

RESULTS

Infarct density heatmaps demonstrated infarct "hot spots" within the deep white matter internal border zone region in both LVV and non-LVV hemispheres, but with greater infarct density and larger infarct volumes in LVV hemispheres (2.2 mL versus 0.25 mL, P < 0.001). Additional scattered cortical infarcts in the internal carotid artery territory occurred in LVV hemispheres, but were rare in non-LVV hemispheres. Jacobian determinants revealed greater atrophy in gray and white matter of the parietal lobes of LVV compared with non-LVV hemispheres.

CONCLUSION

Large-vessel vasculopathy in sickle cell disease appears to increase ischemic vulnerability in the borderzone region, as demonstrated by the increased frequency and extent of infarction within deep white matter, and increased risk of focal atrophy. Scattered infarctions across the LVV-affected hemispheres suggest additional stroke etiologies of vasculopathy (i.e., thromboembolism) in addition to chronic hypoxia-ischemia.

Abstract 171: Cerebral Blood Flow and Oxygen Extraction Fraction are Age-dependent in Children and Young Adults with and without Sickle Cell Disease

Introduction: Children with sickle cell disease (SCD) are a high risk population for pediatric stroke. Young children with SCD have a higher stroke incidence than older children. Cerebral oxygen metabolism, the product of CBF, OEF and arterial oxygen content (CaO 2 , [oxygen saturation (SpO 2 ) x hemoglobin (Hb) x 1.36]) is age-dependent in healthy children, peaking at 5-9 years of age. CBF is age-dependent, but OEF variation across childhood is not well-studied. In non-SCD adults, elevated OEF confers higher stroke risk. Children with SCD have higher CBF and OEF than healthy controls, but also have lower CaO 2 . It is unknown if age independently influences CBF and OEF. We hypothesized that age, sex and CaO 2 influence components of cerebral oxygen metabolism, as measured by MRI.

Methods: Subjects with SCD and sibling/relative controls without SCD underwent brain MRI with measurement of CBF and OEF by pseudocontinuous arterial spin labeling and asymmetric spin echo sequences, respectively. Blood samples were obtained for Hb and hematocrit values. A fast inversion recovery sequence measured T1 values in the superior sagittal sinus. A multiple regression model determined significant factors influencing CBF and OEF (age, sex, CaO 2 ).

Results: We scanned 25 subjects without SCD (ages 6-27) and 56 subjects with SCD (ages 5-28). In multiple regression analysis, age (p=0.0009) and CaO 2 (p < 0.0001) were significantly predictive of CBF, controlling for sex. Age (p=0.027) and CaO 2 (p<0.0001), were also significantly predictive of OEF, controlling for sex.

Conclusion: Age is an independent predictor of CBF and OEF. Younger children have higher CBF and OEF, even after controlling for the lower CaO 2 associated with SCD. This may explain the increased stroke incidence in young children with SCD.

Abstract TMP57: Cerebral Oxygen Metabolism as a Biomarker to Stratify Stroke Risk in Young Adults with Sickle Cell Disease

Background: While imaging biomarkers guide stroke prevention strategies in children with sickle cell (SC) disease, none have been adequately studied in adults. High oxygen extraction (OEF) predicts stroke in non-SC adults with carotid occlusion, while low oxygen metabolism (CMRO 2 ) predicts tissue at imminent risk in acute ischemic stroke. We hypothesized that metrics of cerebral metabolism: (1) differ between SC adults with and without stroke and (2) correlate with infarct burden.

Methods: A prospective MRI study enrolled 37 adults (28 ± 8 yr) from SC clinic into 4 groups: (1) 9 age/race matched healthy controls, (2) 6 SC adults without infarcts, (3) 15 SC adults with infarcts (infarct volume 7.4 ± 17.5 ml), and (4) 7 SC adults on chronic transfusions (Tx) (infarct volume 3.6 ± 6.6 ml). Arterial spin labelling and asymmetric spin echo measured voxel-wise cerebral blood flow (CBF) and OEF. CMRO 2 = CBF x OEF x blood oxygen content. Infarcts were delineated on FLAIR. OEF, CBF, and CMRO 2 (excluding infarcted tissue) were compared: between groups 1-3 (Kruskal-Wallis) and in group 4 between pre- and post-tx scans (Signed Rank). An ROI defined by high OEF within the deep white matter (a region at high stroke risk in SC) was applied to group 3. OEF, CBF, and CMRO 2 within the ROI were correlated with hemispheric infarct volume (IV) (Spearman’s ρ ).

Results: Whole brain OEF showed a stepwise increase from controls, to SC adults without stroke, to SC adults with stroke (P<.001). SC adults on chronic Tx had intermediate OEF, with lowering of OEF post-Tx (Fig A). CBF and CMRO 2 were similar for SC adults with and without stroke (Fig B, C). High OEF and low CBF/CMRO 2 in the ROI correlated with hemispheric infarct burden: IV vs. OEF ( ρ =.40, P=.043); IV vs. CBF ( ρ =-.61, P=.002); and IV vs. CMRO 2 ( ρ =-.50, P=.016).

Conclusion: Global OEF holds promise to stratify stroke risk in SC disease. Regional metrics of cerebral oxygen metabolism may indicate tissue-specific metabolic stress at imminent risk of infarction.

A pilot study of parent education intervention improves early childhood development among toddlers with sickle cell disease

BACKGROUND

Young children with sickle cell disease (SCD) are at risk for cognitive delay. In addition to biologic risk factors associated with SCD, environmental factors contribute to cognitive dysfunction within this cohort.

METHODS

We completed a single-arm, prospective cohort study. Children with SCD between the ages of 3 and 36 months and their caregivers were followed between October 2010 and December 2013. The aim was to describe the role of a home visitation model, the home environment, and socioeconomic status in the development of young children with SCD. Primary outcome measures were the Bayley Scales of Infant and Toddler Development, Third Edition (BSID-III) and the Home Observation for Measurement of the Environment (HOME). We hypothesized that the home visitation model, Parents as Teachers^® (PAT), would encourage positive parent-child interactions and improve cognitive outcomes.

RESULTS

Thirty-five participants had at least two PAT visits and BSID-III assessments. Mean scores within all five subtests of the BSID-III improved between enrollment and exit, with significant changes within cognitive (P = 0.016) and expressive language (EL) domains (P = 0.002). Multivariate modeling found the HOME score associated with the exit results of the cognitive domain.

CONCLUSION

We report longitudinal results of the first home visitation program within the early childhood SCD population and show significant improvement in cognitive and EL development. Additionally, home environment was a significant predictor of cognitive development. Randomized controlled trials to test the impact of interventions targeting the home environment are warranted for this vulnerable population.

Abstract 35: Transfusion Relieves Cerebral Metabolic Stress in Children with Sickle Cell Disease

Introduction: Transfusions (Tx) are the mainstay of stroke prevention in children with sickle cell disease (SCD), but the pathophysiology conferring this neuroprotection is not well understood.

Hypothesis: Tx relieves cerebral metabolic stress by improving arterial oxygen content, thereby lowering chronically-elevated cerebral blood flow (CBF) and oxygen extraction fraction (OEF) in children with SCD at risk for stroke.

Methods: Children with SCD on chronic Tx therapy underwent two brain MRIs with measurement of CBF via pseudocontinuuous arterial spin labeling and OEF via asymmetric spin echo sequence within 24 hours of exchange Tx. To determine how Tx may reduce regions of elevated OEF, we set absolute OEF thresholds (45, 47.5, 50%) and compared tissue volumes above each threshold pre- and post-Tx using nonparametric paired statistics.

Results: Twelve children with SCD (6-21 yrs) underwent MRIs. Tx raised Hb and lowered CBF and OEF (Figure), suggesting that elevated CBF and OEF may be markers of metabolic stress relieved by Tx. While CBF correlates with age in healthy children, pre-Tx CBF correlation with age was lost (τ= -0.42, p=0.07), but regained post-Tx (τ= -0.76, p=0.001). Also, absolute change in OEF diminished with increasing age (τ=. -0.75, p=0.003). Regions with very high OEF were found in the periventricular white matter, a common area of infarcts in SCD (Figure, average OEF maps pre- and post-Tx). Tx reduced the volume of these brain regions defined by all three OEF thresholds (Table), suggesting that Tx reduces brain regions at high risk for stroke.

Conclusion: Tx in SCD children improves arterial oxygen content by increasing Hb, allowing CBF and OEF to fall, thus relieving metabolic stress globally and regionally. The absolute change in OEF correlates with age, suggesting that the efficacy of Tx may be age-dependent.

Red blood cell storage duration is not associated with clinical outcomes for acute chest syndrome in children with sickle cell disease

BACKGROUND

Providers commonly transfuse sickle cell disease (SCD) patients with fresh red blood cells (RBCs) as treatment for acute chest syndrome (ACS). The objective of this study was to determine if there is an association between the storage duration of RBCs and length of hospitalization and oxygen requirement after transfusion in pediatric SCD patients with ACS.

STUDY DESIGN AND METHODS

This is a retrospective cohort study of pediatric SCD patients with ACS treated with a simple RBC transfusion over 8.5 years at a single institution. Multivariate generalized estimation equation analysis was used to identify associations between storage duration of RBCs and outcome measures.

RESULTS

A total of 234 ACS episodes in 131 subjects were included. The median storage duration of the oldest unit of transfused RBCs was 17 days (interquartile range, 11-26). The majority of ACS episodes, 77.4%, were treated with 1 unit of transfused RBCs; 20.9% received 2 units; and 1.7% received 3 or more units of RBCs. There was no association between the storage duration of the oldest unit of transfused RBCs and either duration of hospitalization or supplemental oxygen requirement after transfusion in multivariate analyses.

CONCLUSION

This retrospective study is one of the first to investigate the role of the storage lesion in children with SCD and does not support the preferential transfusion of fresh RBCs for ACS. Ultimately, a randomized controlled trial is necessary to determine whether the storage age of RBCs affects outcomes for patients with SCD and ACS.

Abstract 21: Infarct Distributions Differ in Pediatric Sickle Cell Patients With or Without Large Vessel Vasculopathy

Introduction: Children with sickle cell disease (SCD) have a high risk of ischemic strokes in diverse spatial distributions, but mechanisms responsible for these different patterns are unclear.

Methods: MRIs and MRAs from 2006-2014 were retrospectively collected on SCD children with an overt stroke history. Hemispheres were categorized based on presence or absence of large vessel vasculopathy (Vsc) on MRA. Manually delineated infarcts on FLAIR were individually co-registered to the corresponding T1 MPRAGE maps, and then co-registered onto a common space. Left and right hemispheres were separated with a mask in the common space. Hemispheres were flipped so all with Vsc were oriented as right hemispheres, and those without Vsc as left. Co-registered infarct maps were warped into the final anatomic space and averaged to create a lesion density map. A cerebral blood flow (CBF) map was created from average pseudocontinuous arterial spin labeled measurements prospectively collected on 7 children with SCD and no Vsc.

Results: Of 22 children with SCD and overt stroke history (median 15.5y, 41% male), 14 had Vsc (median 16 y, 50% male) in 19/44 hemispheres. Both non-Vsc and Vsc hemispheres had infarct hot-spots in a predominantly deep white matter watershed distribution, but Vsc hemisphere infarcts were more numerous, more extensive and encompassed more gray matter (Figure). Hot-spots overlapped with regions of lowest flow within the deep white matter on the CBF map. Vsc hemispheres also had infarcts in classic large artery territories, not seen in non-Vsc hemispheres.

Conclusions: The etiology of ischemia in SCD is likely multifactorial, involving reduced oxygen delivery (anemia), impaired CBF (Vsc), and possible associated thrombosis (Vsc with low/turbulent flow distal to stenosis). Differential patterns of infarction reflect these different layers of compromise.

The 13-kD FK506 binding protein, FKBP13, interacts with a novel homologue of the erythrocyte membrane cytoskeletal protein 4.1

We have identified a novel generally expressed homologue of the erythrocyte membrane cytoskeletal protein 4.1, named 4.1G, based on the interaction of its COOH-terminal domain (CTD) with the immunophilin FKBP13. The 129-amino acid peptide, designated 4.1G-CTD, is the first known physiologic binding target of FKBP13. FKBP13 is a 13-kD protein originally identified by its high affinity binding to the immunosuppressant drugs FK506 and rapamycin (Jin, Y., M.W. Albers, W.S. Lane, B.E. Bierer, and S.J. Burakoff. 1991. Proc. Natl. Acad. Sci. USA. 88:6677- 6681); it is a membrane-associated protein thought to function as an ER chaperone (Bush, K.T., B.A. Henrickson, and S.K. Nigam. 1994. Biochem. J. [Tokyo]. 303:705-708). We report the specific association of FKBP13 with 4.1G-CTD based on yeast two-hybrid, in vitro binding and coimmunoprecipitation experiments. The histidyl-proline moiety of 4.1G-CTD is required for FKBP13 binding, as indicated by yeast experiments with truncated and mutated 4.1G-CTD constructs. In situ hybridization studies reveal cellular colocalizations for FKBP13 and 4.1G-CTD throughout the body during development, supporting a physiologic role for the interaction. Interestingly, FKBP13 cofractionates with the red blood cell homologue of 4.1 (4.1R) in ghosts, inside-out vesicles, and Triton shell preparations. The identification of FKBP13 in erythrocytes, which lack ER, suggests that FKBP13 may additionally function as a component of membrane cytoskeletal scaffolds.