Neuropsychologic effects of stroke in children with sickle cell anemia

Neuroimaging and Cognitive Function in Sickle Cell Disease: A Systematic Review

Sickle cell disease (SCD) is the most common inherited single-gene disease. Complications include chronic anaemia, reduced oxygen-carrying capability, and cerebral vasculopathy, resulting in silent cerebral infarction, stroke, and cognitive dysfunction with impairments in measures of executive function, attention, reasoning, language, memory, and IQ. This systematic review aims to investigate the association between neuroimaging findings and cognition in children with SCD. Searches of PubMed and Embase were conducted in March 2022. Studies were included if participants were <18 years, if original data were published in English between 1960 and 2022, if any genotype of SCD was included, and if the relationship between cognition and neuroimaging was examined. Exclusion criteria included case studies, editorials, and reviews. Quality was assessed using the Critical Appraisal Skills Programme Case Control Checklist. A total of 303 articles were retrieved; 33 met the eligibility criteria. The presence of overt or silent strokes, elevated blood flow velocities, abnormal functional connectivity, and decreased fMRI activation were associated with neuropsychological deficits in children with SCD when compared to controls. There is a critical need to address the disease manifestations of SCD early, as damage appears to begin at a young age. Most studies were cross-sectional, restricting the interpretation of the directionality of relationships. Future research employing longitudinal neuroimaging and neuropsychological assessments could improve our understanding of the cumulative consequences of SCD on the developing brain.

Hypoxia-Induced Neurite Outgrowth Involves Regulation Through TRPM7

Transient receptor potential melastatin 7 (TRPM7) is a ubiquitously expressed divalent cation channel that plays a key role in cell functions such as ion homeostasis, cell proliferation, survival, and cytoskeletal dynamics and mediates cells death in hypoxic and ischemic conditions. Previously, TRPM7 was found to play a role in the neurite outgrowth and maturation of primary hippocampal neurons. Either knockdown of TRPM7 with target-specific shRNA or blocking channel conductance by a specific blocker waixenicin A enhanced axonal outgrowth in the primary neuronal culture. In this study, we investigated whether and how TPRM7 is involved in hypoxia-altered neurite outgrowth patterns in E16 hippocampal neuron cultures. We demonstrate that short-term hypoxia activated the MEK/ERK and PI3K/Akt pathways, reduced TRPM7 activity, and enhanced axonal outgrowth of neuronal cultures. On the other hand, long-term hypoxia caused a progressive retraction of axons and dendrites that could be attenuated by the TRPM7-specific inhibitor waixenicin A. Further, we demonstrate that in the presence of astrocytes, axonal retraction in long-term hypoxic conditions was enhanced, and TRPM7 block by waixenicin A prevented this retraction. Our data demonstrate the effect of hypoxia on TRPM7 activity and axonal outgrowth/retraction in cultures with or without astrocytes present.

Blood Transfusion Vs. Hydroxyurea for Stroke Prevention in Children With Sickle Cell Anemia: A Systematic Review and Meta-Analysis

Sickle cell anemia (SCA) is a hereditary condition that can lead to severe complications in children such as acute coronary syndrome, splenic sequestration, renal failure, and stroke. Blood transfusion and hydroxyurea (HU) therapy are used to prevent stroke in children with sickle cell disease (SCD). Preliminary data show considerable variation and inconsistency in the use of these two therapeutic interventions. Therefore, this systematic review was carried out to compare the effects of blood transfusion to HU therapy in preventing stroke for children with sickle cell disease. There was an extensive literature search in reliable and authentic databases like PubMed, Medline, Scopus, Cochrane, and Science Direct to obtain relevant articles. This study used the standards and guidelines from the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). During the systematic review, data were obtained focusing on the following parameters: the size of the sample in the study, the age of the subjects involved in the study, the type of Intervention, and the outcome. After an initial search of 163 papers, 25 studies were included. The results of the research give the first evidence that HU is effective in the treatment of cerebrovascular problems in children with SCD. However, it is unclear under what circumstances HU may prevent a second stroke. It can be concluded that children with SCA can effectively avoid primary strokes through chronic blood transfusions and HU.

Considerations for Selecting Cognitive Endpoints and Psychological Patient-Reported Outcomes for Clinical Trials in Pediatric Patients With Sickle Cell Disease

Pediatric patients with sickle cell disease (SCD) experience a range of medical complications that result in significant morbidity and mortality. Recent advances in prophylactic and curative treatment approaches have highlighted the need for sensitive and clinically-meaningful trial endpoints. The detrimental effects of cognitive and psychological difficulties on social and economic mobility are well described. Although numerous reviews have assessed cognitive outcomes in other rare genetic disorders, SCD has not received the same focus. This review describes the cognitive (i.e., executive function and processing speed) and psychological domains (i.e., depression and anxiety) that are consistently associated with SCD pathology and, therefore, may be of particular interest as clinical trial endpoints. We then discuss corresponding well-validated and reliable cognitive tests and patient-reported outcomes (PROs) that may be appropriate for clinical trials given their robust psychometric properties, ease of administration, and previous use in the SCD population. Further, we provide a discussion of potential pitfalls and considerations to guide endpoint selection. In line with the move toward patient-centered medicine, we identify specific tests (e.g., NIH Toolbox Cognition Module, Wechsler Cancellation Test) and psychological PROs (e.g., PROMIS depression and anxiety scales) that are sensitive to SCD morbidity and have the potential to capture changes that are clinically meaningful in the context of patients' day to day lives. In particularly vulnerable cognitive domains, such as executive function, we highlight the advantages of composite over single-test scores within the context of trials. We also identify general (i.e., practice effects, disease heterogeneity) and SCD-specific considerations (i.e., genotype, treatment course, and disease course, including degree of neurologic, pain, and sleep morbidity) for trial measures. Executive function composites hold particular promise as trial endpoints that are clinically meaningful, amenable to change, relatively easy to collect, and can be incorporated into the routine care of patients with SCD in various settings and countries.

Vascular Instability and Neurological Morbidity in Sickle Cell Disease: An Integrative Framework

It is well-established that patients with sickle cell disease (SCD) are at substantial risk of neurological complications, including overt and silent stroke, microstructural injury, and cognitive difficulties. Yet the underlying mechanisms remain poorly understood, partly because findings have largely been considered in isolation. Here, we review mechanistic pathways for which there is accumulating evidence and propose an integrative systems-biology framework for understanding neurological risk. Drawing upon work from other vascular beds in SCD, as well as the wider stroke literature, we propose that macro-circulatory hyper-perfusion, regions of relative micro-circulatory hypo-perfusion, and an exhaustion of cerebral reserve mechanisms, together lead to a state of cerebral vascular instability. We suggest that in this state, tissue oxygen supply is fragile and easily perturbed by changes in clinical condition, with the potential for stroke and/or microstructural injury if metabolic demand exceeds tissue oxygenation. This framework brings together recent developments in the field, highlights outstanding questions, and offers a first step toward a linking pathophysiological explanation of neurological risk that may help inform future screening and treatment strategies.

Integrated psychology support and comprehensive cognitive evaluation improves access to special education services for children with sickle cell disease

BACKGROUND

Children with sickle cell disease (SCD) are at risk for cognitive deficits. Limited data describe whether comprehensive cognitive evaluation improves education resources and whether caregivers perceive the assessment as beneficial. We tested our two hypotheses: (a) an integrated comprehensive cognitive evaluation program in children with SCD results in increased special education services allocation; and (b) caregivers will value comprehensive cognitive evaluation services provided.

PROCEDURE

In a tertiary care medical facility, as part of quality improvement project, in a before-and-after evaluation between March 2011 and July 2014, we examined the impact of targeted comprehensive cognitive evaluation on change in special education services. We also evaluated the caregiver's perception regarding the utility of the provided services.

RESULTS

A total of 21% (42 of 196) students (median age 11 years, range 3-18) with SCD were referred for cognitive assessment due to overt stroke (n = 11), silent stroke (n = 14), or concerns about cognitive or academic functioning without evidence of strokes (n = 17). At baseline, 45.2% received special education services and after the comprehensive cognitive evaluation 86.7% received special education services (P < 0.001). Among 33 caregivers who completed the survey, 97% reported that the assessment was helpful and 60% indicated that assessment led to beneficial changes for their children at school.

CONCLUSION

Education advocacy coupled with comprehensive cognitive assessment in students with SCD improved access to special education services, and caregivers uniformly endorse this service as having added value.

Sickle Cell Disease and Stroke

Cerebral infarction is a common complication of sickle cell disease and may manifest as overt stroke or cognitive impairment associated with "silent" cerebral infarction on magnetic resonance imaging. Vasculopathy may be diagnosed on transcranial Doppler or magnetic resonance angiography. The risk factors in sickle cell disease for cognitive impairment, overt ischemic stroke, silent cerebral infarction, overt hemorrhagic stroke, and vasculopathy defined by transcranial Doppler or magnetic resonance angiography overlap, with severe acute and chronic anemia, acute chest crisis, reticulocytosis, and low oxygen saturation reported with the majority. However, there are differences reported in different cohorts, which may reflect age, geographic location, or neuroimaging techniques, for example, magnetic resonance imaging field strength. Regular blood transfusion reduces, but does not abolish, the risk of neurological complications in children with sickle cell disease and either previous overt stroke or silent cerebral infarction or abnormal transcranial Doppler. There are relatively few data on the use of hydroxyurea or other management strategies. Early assessment of the risk of neurocognitive complications is likely to become increasingly important in the management of sickle cell disease.

Transcranial Doppler Screening in 50 Patients With Sickle Cell Hemoglobinopathies in Iran

BACKGROUND

As previous studies had discordant results with regard to the correlation of transcranial Doppler (TCD) screening and brain MRI, the aim of this study was to find the correlation between TCD values and silent ischemia in sickle cell disease (SCD) patients.

METHOD AND MATERIALS

In this cross-sectional study, 50 patients with proven diagnosis of sickle cell hemoglobinopathies based on their hemoglobin electrophoresis were included. Demographic data, their physical exam, information with regard to crises history, and their laboratory data were recorded. Brain MRI and TCD were requested for all patients.

RESULTS

The mean age of the patients was 10.2±5.8 years. Only 3 patients (6%) showed evidence of ischemia on brain MRI. Normal and ischemic patients were not significantly different with respect to TCD values, sex, splenomegaly, aplastic crisis, and laboratory test results (P-value >0.05). Only platelet count was significantly higher in the ischemic group compared with that in the normal group (P=0.002). The pain crisis was significantly associated with the mean velocity values of RMCA, LMCA, RV, and LV arteries (P-value <0.05).

CONCLUSION

On the basis of our results, there was no significant difference in the mean velocity TCD values between patients with and without evidence of ischemic brain damage in brain MRI. The frequency of silent ischemia was much lower than expected. Further studies with larger sample sizes are needed to elucidate the positive predictive value of abnormal TCD in the prediction of silent ischemia in patients with sickle hemoglobinopathy in certain ethnic groups.

Hypoxia and inflammation in children with sickle cell disease: implications for hippocampal functioning and episodic memory

Children with sickle cell disease (SCD) suffer from systemic processes (e.g., chronic anemia, recurrent hypoxic-ischemic events, chronic inflammation) that have been associated with neurocognitive impairment in a range of clinical populations, but which have been largely understudied in relation to specific domains of cognitive functioning in children with SCD. This review focuses on episodic memory, as the hippocampus may be especially vulnerable to the systemic processes associated with SCD. The first part of the paper outlines the pathophysiology of SCD and briefly reviews the extant literature on academic and cognitive functioning in children with SCD, emphasizing the dearth of research on episodic memory. Next, the complex systemic processes of hypoxia and inflammation associated with SCD are reviewed, along with research that has associated these processes with hippocampal damage and memory impairment. The paper concludes with suggestions for future research that are informed, in part, by the literature on developmental amnesia.

Intellectual function evaluation of first generation immigrant children with sickle cell disease: the role of language and sociodemographic factors

Background

Sickle Cell Disease (SCD) is the most common genetic disease worldwide. Neurological events are among the most worrisome clinical complications of SCD and are frequently accompanied by cognitive impairment. Intellectual function in SCD may vary according to genetic and environmental factors. Immigrant children with SCD are increasing at a global level and display specific health care needs. The aim of our multicenter study was to describe the intellectual function of first generation African immigrants with SCD and the influence of sociodemographic factors on its characteristics.

Methods

The Wechsler Intelligence Scales were administered to evaluate broad intellectual functions in children with SCD and in age-matched healthy siblings. Patients’ clinical, socio-demographic, Magnetic Resonance Imaging (MRI) and Angiography (MRA) data were correlated to intellectual function scores.

Results

68 children, mean age 8.95 years were evaluated. 72% spoke three languages, 21% two. FSIQ was <75 in 25% of the children. Mean VIQ was lower than PIQ in 75%. Mean verbal subtest scores were lower than performance scores. Female gender, number of languages spoken at home and mother’s employment were associated with single subtest performances (p < 0.05). MRA was abnormal in 73.4% and MRI in 35.9%. No significant correlation was established between silent lesions and intellectual function, even if patients with lesions performed worse. Fifteen siblings performed better than patients on cognitive domains, including language (p < 0.05).

Conclusions

Immigrant bilingual children with SCD seem to display a rate of cognitive impairment similar to their monolingual counterparts but a more pronounced and precocious onset of language difficulties. Adjunctive tests need to be considered in this group of patients to better define their specific deficits.

Psychiatric problems in children and adolescents with sickle cell disease, based on parent and teacher reports

OBJECTIVE

This study aimed to investigate the occurrence of psychiatric problems in children and adolescents withsickle cell disease (SCD).

MATERIAL AND METHODS

The Child Behavior Checklist for ages 4-18 years (CBCL/4-18), Conners' Parent RatingScale (CPRS), Conners' Teacher Rating Scale (CTRS-R), and The Turgay DSM-IV Based Child and Adolescent BehaviorDisorders Screening and Rating Scale, clinician and parent forms (T-DSM-IV-S) were given to the caregivers and teachersof 31 children with SCD aged between 7-18 years and the caregivers and teachers of 34 age matched controls with irondeficiencyanemia.

RESULTS

The SCD patients had higher scores on all 4 of scales. Among the subscales, internalizing problems, andattention problems were more prominent in the SCD patients.

CONCLUSION

Children and adolescents with SCD appear to have an increased risk for psychiatric problems. Regularpsychological evaluation and referral to child and adolescent psychiatry clinics may facilitate timely diagnosis andeffective treatment of at-risk children and adolescents.

Pathology of sickle cell disease

Sickle cell disease (SCD) is a hereditary chronic hemolytic anemia with numerous clinical consequences. Intravascular sickling of red blood cells leads to multiorgan dysfunction. Although the pathophysiology of SCD has been well studied, there remains a lack of effective treatment. Refinements in overall care have improved quality of life; however, premature death is still not uncommon. SCD usually presents in childhood and is common in areas where malaria is (or was) common. The association with malaria is apparently of benefit to the individual because these individuals tend to contract a milder form of the disease. This review highlights the spectrum of pathology seen in people with SCD, with an emphasis on the pathogenesis of sudden death.

Advantages of isovolemic hemodilution-red cell exchange therapy to prevent recurrent stroke in sickle cell anemia patients

Chronic simple hypertransfusion (every 3 to 4 weeks) effectively prevents secondary stroke in children with sickle cell anemia but leads to iron overload despite chelation therapy. Conventional red blood cell exchange (C-RBCx) has advantages over simple transfusion: no net iron gain and less frequent hospital visits. However, C-RBCx requires more red blood cell units, an apheresis instrument and skilled personnel; it is also more expensive. We developed a modified procedure where isovolemic hemodilution precedes RBCx (IHD-RBCx) to decrease RBC units required and to increase the interval between procedures. Twenty patients underwent IHD-RBCx over a period of 7 years. IHD-RBCx required 11% fewer RBC units and increased inter-procedure interval from 37 to 53 days compared to C-RBCx. The median number of annual procedures decreased from 9.8 to 7.0 per patient, resulting in estimated savings of more than $4.5 million over 10 years for 20 patients while providing improved care. Five patients have discontinued chelation therapy; three while on C-RBCx and two while on IHD-RBCx. No adverse events occurred related to the isovolemic hemodilution phase and no patients had recurrent stroke. IHD-RBCx is a safe, efficient, and cost effective therapy for secondary prevention of stroke in patients with sickle cell anemia.

Neurocognitive deficits in children with sickle cell disease: a comprehensive profile

BACKGROUND

Sickle cell disease (SCD) can lead to profound cerebral damage, associated with neurocognitive deficits. The aim of the current study was to evaluate a broad range of neurocognitive functions in children with SCD compared to a SES-matched control group, in order to gain more insight into the specific deficits of these patients.

METHODS

Forty-one children with homozygous SCD (HbSS or HbS-β0-thalassemia) and 38 controls were assessed on a comprehensive set of well-defined and validated measures of neurocognitive functioning. Besides general intelligence, we evaluated executive functioning extensively (including response inhibition, sustained attention, planning, visuo-spatial working memory, and verbal working memory) as well as visuo-motor functioning.

RESULTS

SCD was clearly associated with lower IQ scores. More than one in three children with SCD had a Full-scale IQ below 75. Furthermore, children with SCD showed deficits in visuo-motor functioning. Some evidence was found for executive dysfunction: Children with SCD displayed poor visuo-spatial working memory, as well as subtle deficits in sustained attention and planning. No significant differences were found between children with SCD and controls in terms of response inhibition and verbal working memory.

CONCLUSIONS

Children with SCD are at increased risk of lower intelligence, visuo-motor impairments, and executive dysfunction. These neurocognitive deficits may underlie high rates of scholastic impairments in these children. The present findings further illuminate the importance of regular neurocognitive evaluations and future neurocognitive rehabilitation programs for children with SCD.

Event-based prospective memory in children with sickle cell disease: effect of cue distinctiveness

Event-based prospective memory (EB-PM) is the formation of an intention and remembering to perform it in response to a specific event. Currently, EB-PM performance in children with sickle cell disease (SCD) is unknown. In this study, we designed a computer-based task of EB-PM; No-Stroke, Silent-Infarct, and Overt-Stroke groups performed significantly below the demographically similar control group without SCD. Cue distinctiveness was varied to determine if EB-PM could be improved. All groups, with the exception of the Overt-Stroke group, performed significantly better with a perceptually distinctive cue. Overall, these results suggest that EB-PM can be improved significantly in many children with SCD.

Design of the silent cerebral infarct transfusion (SIT) trial

BACKGROUND

Silent cerebral infarct (SCI) is the most common cause of serious neurological disease in sickle cell anemia (SCA), affecting approximately 22% of children. The goal of this trial is to determine whether blood transfusion therapy will reduce further neurological morbidity in children with SCI, and if so, the magnitude of this benefit.

PROCEDURE

The Silent Cerebral Infarct Transfusion (SIT) Trial includes 29 clinical sites and 3 subsites, a Clinical Coordinating Center, and a Statistical and Data Coordinating Center, to test the following hypothesis: prophylactic blood transfusion therapy in children with SCI will result in at least an 86% reduction in the rate of subsequent overt strokes or new or progressive cerebral infarcts as defined by magnetic resonance imaging (MRI) of the brain. The intervention is blood transfusion versus observation. Two hundred and four participants (102 in each treatment assignment) will ensure 85% power to detect the effect necessary to recommend transfusion therapy (86% reduction), after accounting for 10% drop out and 19% crossover rates. MRI examination of the brain is done at screening, immediately before randomization and study exit. Each randomly assigned participant receives a cognitive test battery at study entry, 12-18 months later, and study exit and an annual neurological examination. Blood is obtained from all screened participants for a biologic repository containing serum and a renewable source of DNA.

CONCLUSION

The SIT Trial could lead to a change in standard care practices for children affected with SCA and SCI, with a consequent reduction in neurological morbidity.

Behavioral and emotional problems in children with sickle cell disease and healthy siblings: Multiple informants, multiple measures

BACKGROUND

Behavioral and emotional problems in children with sickle cell disease (SCD) may be related to disease factors, or to socio-demographic factors. The aim of this study was to investigate the prevalence of behavioral and emotional problems in children with SCD living in a Western European country, compared to healthy siblings (who were comparable in age, gender, ethnicity, and socio-economic status-SES), and to a Dutch norm population.

METHODS

The Child Behavior Checklist (CBCL), Teacher Report Form (TRF) and Disruptive Behavior Disorders rating scale (DBD) were distributed among caregivers and teachers of 119 children with SCD aged 6-18 years and among caregivers and teachers of 38 healthy siblings.

RESULTS

Questionnaires were returned by caregivers and/or teachers of 106 children with SCD and 37 healthy siblings. According to caregivers and teachers, children with SCD had more severe internalizing problems than healthy siblings and the norm population. According to teachers, subgroups of both children with SCD and healthy siblings had more severe externalizing problems than the norm population. Children with SCD had more difficulties than healthy siblings in terms of school functioning, showed less competent social behavior and tended to have more attention deficits.

CONCLUSIONS

Children with SCD are at increased risk of developing internalizing problems as a result of their disease. Subgroups of children with SCD are at increased risk of developing severe externalizing problems, which may either be related to socio-demographic factors, or to disease factors, such as neurocognitive deficits associated with cerebral infarction.

Brain morphometry and intelligence quotient measurements in children with sickle cell disease

OBJECTIVE

To verify the hypothesis that volume of regional gray matter accounts substantially for variability in intelligence quotient (IQ) score among children with sickle cell disease, who have no magnetic resonance visible infarcts.

METHODS

We studied 31 children with sickle cell disease, homozygous for hemoglobin S, with no history of stroke, no magnetic resonance signal-intensity abnormality, and transcranial Doppler velocities <170 cm/sec, with a T1-weighted magnetic resonance sequence and the Kaufman Brief Intelligence Test. On the basis of Kaufman Brief Intelligence Test, we classified these children into 2 groups: high and low IQ based on a median split. We then used an automated and novel Bayesian voxel-based morphometry technique, called Graphical-Model-Based Multivariate Analysis (GAMMA), to assess the probabilistic association between IQ score and regional gray matter volume.

RESULTS

GAMMA found 1 region linking low IQ with smaller cortical gray matter volume. In comparison with the children in the high-IQ group, children in the low-IQ group had smaller regional gray matter volume in both frontal lobes, both temporal lobes, and both parietal lobes.

CONCLUSIONS

In children with sickle cell disease, we found a linear association between IQ and regional gray matter volume. This finding suggests that some variance in intellectual ability in children with sickle cell disease is accounted for by regional variability of gray matter volume, which is independent of neuroradiological evidence of infarct.

Neurocognitive sequelae of pediatric sickle cell disease: a review of the literature

This literature review summarizes all studies relating neuropsychological performance to neuroimaging findings in pediatric sickle cell disease (N=28; published 1991-2005). Although inconsistencies exist within and across domains, deficits in intelligence (IQ), attention and executive functions, memory, language, visuomotor abilities, and academic achievement have been identified. Overall neurocognitive compromise was revealed to be related to the level of neurological injury and the location of silent infarct. Attentional and executive dysfunction is prevalent and related to frontal lobe abnormalities.

The association of oral hydroxyurea therapy with improved cognitive functioning in sickle cell disease

This study examined potential cognitive benefits of oral hydroxyurea therapy for children with sickle cell disease (SCD). Cognitive abilities of 15 children with SCD on hydroxyurea were compared to 50 other children with SCD, controlling for demographics and hematocrit. Children on hydroxyurea scored significantly higher on tests of verbal comprehension, fluid reasoning, and general cognitive ability than children not on the drug. The data therefore provide preliminary evidence of cognitive benefits of hydroxyurea. Mechanisms for this effect may be improved blood/oxygen supply to the brain or reduced fatigue and illness.

Overt and Incomplete (Silent) Cerebral Infarction in Sickle Cell Anemia: Diagnosis and Management

Cerebral vasculopathy in sickle cell anemia (HbSS) is manifest clinically as cerebral infarction and intracranial hemorrhage. The type of stroke, ischemic or hemorrhagic, is age specific with distinct differences in outcomes. Cerebral infarction with or without clinical stroke begins during early childhood and rarely causes death immediately.

Sickle cell disease as a neurodevelopmental disorder

Sickle cell disease (SCD) is a blood disorder; however, the central nervous system (CNS) is one of the organs frequently affected by the disease. Brain disease can begin early in life and often leads to neurocognitive dysfunction. Approximately one-fourth to one-third of children with SCD have some form of CNS effects from the disease, which typically manifest as deficits in specific cognitive domains and academic difficulties. We discuss SCD as a neurodevelopmental disorder by reviewing the mechanisms of neurological morbidity in SCD, the timing of these mechanisms, the types of cognitive and behavioral morbidity that is typical, and the interaction of social-environmental context with disease processes. The impact of the disease on families shares many features similar to other neurodevelopmental disorders; however, social-environmental factors related to low socioeconomic status, worry and concerns about social stigma, and recurrent, unpredictable medical complications can be sources of relatively higher stress in SCD. Greater public awareness of the neurocognitive effects of SCD and their impact on child outcomes is a critical step toward improved treatment, adaptation to illness, and quality of life.

Physiological correlates of intellectual function in children with sickle cell disease: hypoxaemia, hyperaemia and brain infarction

Lowered intelligence relative to controls is evident by mid-childhood in children with sickle cell disease. There is consensus that brain infarct contributes to this deficit, but the subtle lowering of IQ in children with normal MRI scans might be accounted for by chronic systemic complications leading to insufficient oxygen delivery to the brain. We investigated the relationship between daytime oxyhaemoglobin saturation (SpO2), cerebral blood flow velocity (CBFV) and intellectual function (IQ) using path-analysis in 30 adolescents with sickle cell disease (mean age 17.4 years, SD 4.2). Initial analyses revealed that the association between SpO2 and Full Scale IQ (FSIQ) was fully mediated by increased CBFV, whereby SpO2 was negatively correlated with CBFV and CBFV was negatively correlated with FSIQ, i.e. decreases in oxygen saturation are associated with increases in velocity, and increased velocity is associated with lowered IQ scores. The mediated relationship suggests that lowered IQ may be a function of abnormal oxygen delivery to the brain. Further analyses showed that the association between CBFV and IQ was significant for verbal but not for performance IQ. The pathophysiology characteristic of SCD can interfere with brain function and constrain intellectual development, even in the absence of an infarct. This supports the hypothesis that lowered intellectual function is partly explained by chronic hypoxia, and has wider implications for our understanding of SCD pathophysiology.

Detecting white matter injury in sickle cell disease using voxel-based morphometry

OBJECTIVE

Sickle cell disease (SCD) is associated with cerebrovascular disease, cerebral infarction, and cognitive dysfunction. This study aimed to detect the presence and extent of white matter abnormalities in individuals with SCD using voxel-based morphometry (VBM).

METHODS

Thirty-six children and adolescents with SCD (age range, 9-24 years) and 31 controls (8-25 years) underwent magnetic resonance investigations using T1- and T2-weighted protocols. White and gray matter density maps were obtained from three-dimensional magnetic resonance imaging (MRI) data sets. Using VBM, we compared the maps between controls and SCD individuals with silent white matter infarct lesions (SCD+L; n = 16), and those without visible abnormality (SCD-L; n = 20).

RESULTS

In comparison with controls, intelligence quotients (IQs) were lower in both SCD groups irrespective of presence of visible lesions. VBM showed widespread bilateral white matter abnormalities in the SCD+L group, extending beyond the regions of focal infarction in the deep anterior and posterior white matter borderzones. Bilateral white matter abnormalities were also observed in the SCD-L group, in locations similar to those in the SCD+L group.

INTERPRETATION

VBM is sensitive to detection of widespread white matter injury in SCD patients in borderzones between arterial territories even in the absence of evidence of infarction. Those changes may contribute to cognitive deficits in this population.

Radiographic predictors of neurocognitive functioning in pediatric Sickle Cell disease

We compared magnetic resonance imaging (MRI), magnetic resonance angiography, and transcranial Doppler ultrasonography as predictors of specific neurocognitive functions in children with sickle cell disease. Participants were 27 children with sickle cell anemia (hemoglobin SS) who were participants in the Stroke Prevention Trial in Sickle Cell Anemia (STOP) and had no documented history of stroke. Children's MRIs were classified as normal or silent infarct, and their magnetic resonance angiograms were classified as normal or abnormal. The highest time-averaged mean flow velocity on transcranial Doppler ultrasonographic examination of the major cerebral arteries was analyzed. Age and hematocrit also were analyzed as predictor variables. The battery of neurocognitive tests included measures of intellectual functioning, academic achievement, attention, memory, visual-motor integration, and executive functions. MRI, magnetic resonance angiography, transcranial Doppler ultrasonography, age, and hematocrit were analyzed as predictors of participants' performance on the various measures of neurocognitive functioning. Age and hematocrit were robust predictors of a number of global and specific neurocognitive functions. When age and hematocrit were controlled, transcranial Doppler ultrasonography was a significantly unique predictor of verbal memory. We found an association between low hemoglobin and neurocognitive impairment. We also found that abnormalities on transcranial Doppler ultrasonography can herald subtle neurocognitive deficits. (J Child Neurol 2006;21:37-44).

Decreased corpus callosum size in sickle cell disease: relationship with cerebral infarcts and cognitive functioning

We assessed midsagittal corpus callosum size in sickle cell disease (SCD) and its relationship to lesion volume, lesion location, and cognitive functioning. Twenty-eight children with SCD and 16 demographic controls completed magnetic resonance imaging (MRI) and neuropsychological testing. Corpus callosum (CC) size was smaller for children with silent infarcts (n = 8) or overt stroke (n = 8) than for those without visible infarcts (n = 12) or control participants. Lesion volume was a robust predictor of IQ and other cognitive scores; total CC size did not typically add explanatory power for these measures. The size of the rostral body of the CC, however, independently predicted measures of distractibility, speeded production, and working memory. Posterior CC size was also decreased among many of the children with SCD, even in the absence of visible infarcts in this region. Brain morphology appears to provide additional information about SCD-related effects on the brain above and beyond visible infarcts.

A multidisciplinary health care team's efforts to improve educational attainment in children with sickle-cell anemia and cerebral infarcts

The primary objective of this study was to improve the educational success of children with sickle-cell disease (SCD) and cerebral infarcts. A prospective intervention trial was conducted; a multidisciplinary team was created to maximize educational resources for children with SCD and cerebral infarcts. Students were evaluated systematically before and after the intervention. A baseline evaluation was completed assessing the presence of an Individualized Education Plan (IEP), grade retention in school, and days absent from school in the year preceding the intervention. A postintervention assessment occurred 2 years later for these same measurements. At baseline, 74% (17 of 23) of the students were receiving IEPs. Two years later, 87% (20 of 23) students received IEPs (p = .34). Despite the intervention, the rate of children retained in their school grade increased from 0.6 per 100 years in school at baseline to 1.7 per 100 years, 95% CI (-3.86, 1.49). The school absenteeism rate did not significantly change after the intervention; the average days absent per student rose from 15.5 to 22.5, (p = .05). The multidisciplinary team effort alone was insufficient to decrease grade retention and absenteeism rate. Further support, from either the parents or school administration, is needed to increase education attainment of students with cerebral infarcts.

Overt and Incomplete (Silent) Cerebral Infarction in Sickle Cell Anemia: Diagnosis and Management

Regional complete infarctions in children with sickle cell anemia (HbSS) are often associated with stenosis of the large intracranial arteries and result in lifetime disability. Incomplete infarction occurs more frequently than previously recognized and has far-reaching effects on neurocognitive development and the risk for overt secondary strokes into adulthood. Clinical and neuroimaging modalities have been highlighted in an algorithmic approach, with the studies giving the highest yield in results and most likely to be available listed in sequential order. The recognition of an emerging "second peak" incidence in the third decade of life is worrisome and warrants more intense scrutiny and diagnosis of subtle findings of stroke in this young adult population.

Psychological complications in sickle cell disease

This review examines the evidence for some of the common psychological complications found across the life span of patients with sickle cell disease (SCD), which are likely to be encountered by haematologists responsible for their medical management. Electronic searches of medical and psychological databases were conducted with a focus on three main areas: psychological coping, quality of life and neuropsychology. Psychological complications were identified in both children and adults with SCD, and included inappropriate pain coping strategies; reduced quality of life owing to restrictions in daily functioning, anxiety and depression; and neurocognitive impairment. There were wide variations in design and consistency of the studies, therefore, some caution needs to be observed in the findings. Moreover, interventional studies were lacking in some areas such as neuropsychology. Utilization of psychological interventions including patient education, cognitive behavioural therapy, and special educational support to help improve the quality of life of patients are recommended.

Coexisting Systemic Lupus Erythematosus and Sickle Cell Disease

Systemic lupus erythematosus (SLE) and sickle cell disease (SCD) are relatively common disorders with comparable prevalence among blacks. The coexistence of these 2 conditions in the same individual appears to be rare. We report 4 cases of coexisting SLE and SCD. These patients displayed a broad spectrum of musculoskeletal, central nervous system, and renal complications that may be associated with either SCD or SLE. Because of a substantial overlap between the clinical manifestations of these 2 disorders, the diagnosis of SLE in patients with SCD may be difficult to establish and is often delayed. Up to 23% of patients with SCD may have antinuclear antibodies. All patients in this series had antecedent SCD but new important complications from SLE.

Arginine supplementation improves rotorod performance in sickle transgenic mice

Patients with sickle cell disease (SCD) have been shown to have impaired visual-motor speed and coordination. Sensorimotor deficits in mice can be investigated by motor coordination tests that require whole body movements such as the rotorod. A sickle transgenic mouse model (S+S-Antilles) that expresses human alpha, human beta(S) and human beta(S-Antilles), is homozygous for the mouse beta(major) deletion, and has low plasma arginine was compared to control C57BL/6J mice and S+S-Antilles mice supplemented with 5% arginine on the rotorod. The rotorod consists of a 2.5 cm diameter, grooved rod turning at constant acceleration, requiring postural adjustments on the part of the mice to maintain equilibrium. C57BL mice on Purina mouse chow had an average latency to fall of S+S-Antilles mice on Purina mouse chow had an average of 127+/-56 s S+S-Antilles mice after 5% arginine supplementation had a mean latency of Arginine may improve rotorod performance in sickle transgenic mice by increasing NO synthesis thereby improving vasodilatation and blood flow with reversal of ischemia in brain and/or muscle. In conclusion, impaired rotorod performance in sickle transgenic mice presents an opportunity to apply this simple task to provide an efficient method to screen some types of therapeutic regimens for efficacy in SCD.

Stroke and elevated blood flow velocity in the anterior cerebral artery in sickle cell disease

Transcranial Doppler ultrasonography provides a noninvasive method of predicting stroke risk in children with sickle cell disease. Elevated cerebral blood flow velocity in the terminal internal carotid or middle cerebral artery is associated with an increased stroke risk, but the clinical significance of elevated velocities in the other large intracranial vessels is unknown. The authors report stroke in two children with sickle cell disease and high blood flow velocity limited to the anterior cerebral artery. This suggests that elevated velocity in this vessel may be associated with an increased risk of stroke.

Asymmetries in Visual-Spatial Processing Following Childhood Stroke

The authors compared hemisphere-based and cognitive-domain-based hypotheses for visual-spatial deficits in children with stroke (n = 33) and children without stroke (n = 43). Children with unilateral left (n = 14) or right (n = 7) injury showed less efficient search for the visual field contralateral to their injury. Right-hemisphere injury was associated with deficient global-level processing and coordinate spatial judgments. Left-hemisphere injury resulted in relatively intact local versus global processing and categorical versus coordinate judgments. Bilateral injury (n = 12) resulted in disruption of visual search across visual fields and relative deficits in global-level processing and coordinate spatial judgments. Recovery of visual-spatial processing in children following childhood stroke is task specific. Certain visual-spatial functions typically mediated by the left hemisphere appear less vulnerable to disruption.

Sickle Cell Disease

Much progress has been made during the past several decades in gaining understanding about the natural history of sickle cell disease and management approaches aimed at treating or even preventing certain disease complications. The characterization of the human genome now offers the opportunity to understand relationships regarding how gene polymorphisms as well as how environmental factors affect the sickle cell disease phenotype, i.e., the individual patient’s overall clinical severity as well as their specific organ function. This chapter explores some of these recent advances in knowledge.

In Section I, Dr. Michael DeBaun characterizes the problem of silent stroke in sickle cell disease, comparing and contrasting its clinical and neuroimaging features with overt stroke. Combined, these events affect virtually 40% of children with sickle cell anemia. New understanding of risk factors, associated clinical findings, and imaging technologies are impacting substantially on treatment options. The appreciable cognitive dysfunction and other sequelae of silent infarct demand more effective treatments and ultimate prevention.

In Section II, Dr. Charles Quinn addresses the conundrum of why some patients with sickle cell disease do well whereas others fare poorly. Some risk factors have been known for years, based upon careful study of hundreds of patients by the Cooperative Study for Sickle Cell Disease and investigators studying the Jamaican newborn cohort. Other prognostic measures have only recently been defined. Dr. Quinn devotes special attention to stroke and chest syndrome as organ-related complications but also describes attempts to measure overall disease severity and to predict survival. Recently, investigators have attempted to predict factors responsible for early mortality in children and following onset of pulmonary hypertension in adults.

In Section III, Dr. Martin Steinberg reviews pharmacologic approaches to sickle cell disease and the rationale for their use. In addition to the inhibition of hemoglobin S polymerization, newer targets have been defined during the past one to two decades. These include the erythrocyte membrane, changes in the red cell intracellular content (especially loss of water), endothelial injury, and free radical production. Hydroxyurea treatment attracted the greatest interest, but many uncertainties remain about its long-term benefits and toxicities. Newer “anti-sickling” agents such as decitabine and short-chain fatty acids also receive attention. Prevention of red cell dehydration, “anti-endothelial” therapy, and marshaling the potentially beneficial effects of nitric oxide are other new and exciting approaches.

Patterns of verbal long-term and working memory performance reveal deficits in strategic processing in children with frontal infarcts related to sickle cell disease

Frontal brain regions are thought to mediate strategic processes that facilitate memory. We hypothesized that children with frontal cerebral infarcts related to sickle cell disease (SCD) would exhibit impairments in long-term and working memory as a result of disruptions in strategic processing. Word-list learning and digit span tasks were used to assess verbal memory and strategic processing in 21 children with SCD without infarcts (controls) and in 10 children with SCD with frontal infarcts. On the word-list learning task, children with frontal infarcts performed more poorly in terms of learning and free recall, although recognition and cued recall were adequate; this pattern suggested intact encoding and storage with impaired retrieval. Children with frontal infarcts performed more poorly on backward digit span, although forward digit span was adequate; this pattern suggested intact maintenance with impaired manipulation of information in working memory. Overall, these findings support the notion that disruptions in strategic processing contribute to memory impairments in children with frontal infarcts.

Transcranial Doppler ultrasonography and neurocognitive functioning in children with sickle cell disease

OBJECTIVE

We examined the relationship between cerebral blood flow velocity, measured by transcranial Doppler (TCD) ultrasonography, and neurocognitive functioning.

METHODS

Participants were 60 children who had sickle cell disease (HbSS) and had no documented history of stroke. Children were classified according to Stroke Prevention Trial in Sickle Cell Anemia criteria (normal, conditional, and abnormal), and their performance was compared on measures of intellectual abilities, academic achievement, sustained attention/concentration, executive function, and parent and teacher ratings of executive function.

RESULTS

Children with abnormal TCD values performed more poorly than children with conditional TCD values on measures of verbal intelligence and executive function. Children with conditional TCD values performed more poorly than children with normal TCD values on measures of sustained attention/concentration and executive function. TCD values also were a significant predictor of auditory working memory in exploratory analyses.

CONCLUSIONS

Our findings support the hypothesis that neurocognitive functions subserved by the frontal systems (eg, sustained attention/concentration and executive function) seem to be the most useful indices of progressive cerebrovasculopathy in children with HbSS disease.

Sickle cell disease and stroke in a pediatric population

Cerebrovascular complications are common in SCD and constitute a major source of concern to the pediatric hematologist. These complications can be either clinically overt or covert. The authors' review of the diagnostic tests does not offer absolute indications for neuroimaging because most of the evidence is based on studies that are not randomized controlled trials. Imaging guidelines for children have emerged based on the available level 2 and 3 literature, however, CT and MR imaging remain the initial tests of choice for stroke assessment, and TCD is the imaging tool of choice for stroke prevention. Based on guidelines handed down from the NIH, TCD has become a part of routine continuing care of children with SCD.

Attention deficits in children with sickle cell disease

Previous research has suggested that children with sickle cell disease may exhibit cognitive deficits even in the absence of direct cerebrovascular involvement (stroke). This study was designed to assess specific attentional deficits in children with sickle cell disease. 12 children with sickle cell disease (Hb SS) with a prior history of stroke, 14 children with sickle cell disease (Hb SS) without evidence of stroke, and 13 similar aged siblings (Hb AA or Hb AS) were compared on measures of attention, intellectual functioning, achievement, and adaptive functioning. Significant differences were found between children with sickle cell disease (with or without stroke) and healthy controls on a timed test of visual scanning, the Coding subtest of the Wechsler Intelligence Scale for Children-Revised, and subtests of Reading, Arithmetic, and Spelling from the Wide Range Achievement Test-Revised. The differences between children with sickle cell disease and their healthy siblings appear to be the result of strokes rather than sickle cell disease itself as children with sickle cell disease without strokes did not significantly differ from controls. Implications for the effects of sickle cell disease and stroke on academic performance are discussed.

Sickle cell and the brain

Sickle cell disease affects many organ systems, but one of the major morbidities is brain disease, especially stroke. In this paper, the etiology, diagnosis, treatment, and prevention of clinical stroke, as well as so-called "silent stroke," are examined. Risk factors, diagnostic tools, and data from prevention and treatment studies as well as issues pertaining to neuropsychological function, especially in younger patients, are discussed and current best options for treatment considered.

Sickle cell disease: the neurological complications

The genetic cause of sickle cell disease has been known for decades, yet the reasons for its clinical variability are not fully understood. The neurological complications result from one point mutation that causes vasculopathy of both large and small vessels. Anemia and the resultant cerebral hyperemia produce conditions of hemodynamic insufficiency. Sickled cells adhere to the endothelium, contributing to a cascade of activated inflammatory cells and clotting factors, which result in a nidus for thrombus formation. Because the cerebrovascular reserve becomes exhausted, the capacity for compensatory cerebral mechanisms is severely limited. There is evidence of small-vessel sludging, and a relative deficiency of nitric oxide in these vessels further reduces compensatory vasodilatation. Both clinical strokes and silent infarcts occur, affecting motor and cognitive function. New data suggest that, in addition to sickle cell disease, other factors, both environmental (eg, hypoxia and inflammation) and genetic (eg, mutations resulting in thrombogenesis), may contribute to a patient's stroke risk. The stroke risk is polygenic, and sickle cell disease can be considered a model for all cerebrovascular disease. This complex disease underscores the potential intellectual and practical distance between the determination of molecular genetics and effective clinical application and therapeutics.

Stroke in children with sickle cell anaemia: aetiology and treatment

Cerebral infarction is a frequent, severe complication of sickle cell anaemia. During childhood, most strokes are due to infarction with the majority resulting from occlusion of the large cerebral arteries. Risk factors include transient ischaemic attacks, acute chest syndrome, severe anaemia and elevated blood pressure. Less certain is the association with leucocytosis, or protection provided by alpha-thalassaemia or fetal haemoglobin. Children who have one stroke are at significant risk for having subsequent events that can be substantially reduced by maintaining haemoglobin S below 30%. It has not yet been possible to identify individuals for whom transfusion can be safely stopped. Haemosiderosis is a consequence of intensive and long term transfusion therapy, which requires chelation with deferoxamine. Iron accumulation can be minimised using erythrocytapheresis but this is technically difficult in children, expensive and results in increased donor exposure. In addition to lesions associated with strokes, an additional 17% of patients can be shown to have clinically silent cerebral infarcts. Although these are termed 'silent', those affected have mild neuropsychological deficits. Their relationship to stroke or risk for recurrence is unknown. Transfusion therapy has been shown to provide primary stroke prevention for children who have elevated cerebral artery velocity. Finally, intracranial haemorrhages, more commonly found in adults, also affect children. Subarachnoid haemorrhage is frequently found to result from cerebral artery aneurysms. A condition that mimics the moyamoya syndrome radiographically, as well as for its risk of haemorrhage, can be found in children with partly occluded cerebral arteries either as a result of stroke or silent infarct.

Neuropsychological aspects of pediatric sickle cell disease

Sickle cell disease (SCD), a class of genetic disorders characterized by abnormal, sickled red blood cells, is a chronic illness that results in progressive cerebrovascular disease. Neurocognitive sequelae of clinically apparent cerebrovascular accidents in children with SCD are characterized by pervasive impairments, including decrements in general intellectual functioning, language and verbal abilities, visual-motor and visual-spatial processing, memory, academic achievement, and processing of subtle prosodic information. In contrast, subtle neurocognitive deficits in the areas of attention and concentration, executive function, and visual-motor speed and coordination appear to be associated with silent infarcts that are not necessarily detected on physical examination. Investigation of the disease course and associated neurocognitive sequelae suggest a disease-specific model of neuropsychological impairment. Recommendations are made for clinical and research efforts in the field of pediatric neuropsychology.

Neuropsychologic performance in school-aged children with sickle cell disease: a report from the Cooperative Study of Sickle Cell Disease

OBJECTIVES

To compare the results of serial neuropsychologic testing in children with sickle cell disease with the results of serial magnetic resonance imaging (MRI) examinations, particularly to evaluate neuropsychologic function in the absence of overt stroke.

STUDY DESIGN

In the Cooperative Study of Sickle Cell Disease, serial neuropsychologic and MRI tests were performed in 373 patients (255 with hemoglobin SS and 118 with hemoglobin SC), 6 to 18 years of age. MRI of the brain and a neuropsychologic battery that included the Wechsler Intelligence Scale for Children (WISC-R or WISC-III) and the Woodcock-Johnson Math and Reading Achievement Tests were performed concurrently and repeated every 2 to 3 years. A silent infarct was defined as an MRI finding of increased signal intensity on T(2) imaging in a patient without a history of stroke.

RESULTS

Twenty-seven patients, all with hemoglobin SS, had overt strokes and 62 had silent infarcts (52 with hemoglobin SS). Patients with hemoglobin SS and silent infarcts had significantly lower scores for math and reading achievement, Full-Scale IQ, Verbal IQ, and Performance IQ, when compared with those with normal MRI findings. In children with hemoglobin SS and normal MRI findings, the scores for Verbal IQ, math achievement, and coding (a subscale of Performance IQ) declined with increasing age.

CONCLUSIONS

School-aged children with sickle cell disease had compromised neuropsychologic function in the presence of silent infarcts. In addition, they had declines in performance in certain areas of function over time. Therapeutic interventions that prevent or lessen cognitive impairment are needed before school entry for children with sickle cell disease.

Correlation of abnormal intracranial vessel velocity, measured by transcranial Doppler ultrasonography, with abnormal conjunctival vessel velocity, measured by computer-assisted intravital microscopy, in sickle cell disease

The Stroke Prevention Trial has confirmed that utilization of transcranial Doppler ultrasonography (TCD), which examines blood flow in large intracranial vessels, can identify children with sickle cell disease (SCD) who are at high risk of developing a premature stroke. It is not known to what extent the vasculopathy in SCD involves small vessels and whether the abnormalities, if present, correlate with large-vessel vasculopathy. Eighteen children with SCD were examined with TCD to determine middle cerebral artery (MCA) velocity and computer-assisted intravital microscopy (CAIM) to determine bulbar conjunctival vessel velocity during the same visit for vasculopathy correlation. High MCA velocity (≥ 200 cm/sec) was found by TCD in 4 patients who also showed abnormal conjunctival velocity (&lt; 0.2 mm/sec or intermittent trickle flow) by CAIM. Three patients had conditional (≥ 170 cm/sec and &lt; 200 cm/sec) MCA velocity: 2 showed abnormal (trickle) and 1 showed normal conjunctival velocity (1.9 mm/sec). One patient with unmeasurable MCA velocity had abnormal (trickle) conjunctival velocity. Of the remaining 10 patients who had normal MCA velocity, 2 showed abnormal (0.05 mm/sec and 0.1 mm/sec) and 8 showed normal conjunctival velocities (1.1-2.4 mm/sec). The MCA velocities correlated significantly with bulbar conjunctival flow velocities (P ≤ .008, Fisher exact test). A correlation exists between MCA (large-vessel) and conjunctival (small-vessel) flow velocities. CAIM is a noninvasive quantitative technique that might contribute to the identification of SCD patients at high risk of stroke. Small-vessel vasculopathy might be an important pathological indicator and should be further explored in a large-scale study.