Cerebral infarction in sickle cell anemia: mechanism based on CT and MRI

White-matter abnormalities and cognitive dysfunction are linked to astrocyte activation in sickle mice

White-matter injury in sickle-cell disease (SCD) includes silent cerebral infarction diagnosed by diffusion tensor imaging (DTI), a complication associated with cognitive dysfunction in children with SCD. The link between white-matter injury and cognitive dysfunction has not been fully elucidated. The goal of this study was to define whether cerebrovascular lesions and cognitive function in SCD are linked to neuroaxonal damage and astrocyte activation in humanized Townes' SCD mice homozygous for human sickle hemoglobin S (SS) and control mice homozygous for human normal hemoglobin A (AA). Mice underwent MRI with DTI and cognitive testing, and histology sections from their brains were stained to assess microstructural tissue damage, neuroaxonal damage, and astrocyte activation. Fractional anisotropy, showing microstructural cerebrovascular abnormalities identified by DTI in the white matter, was significantly associated with neuronal demyelination in the SS mouse brain. SS mice had reduced learning and memory function with a significantly lower discrimination index compared with AA control mice in the novel object recognition tests. Neuroaxonal damage in the SS mice was synchronously correlated with impaired neurocognitive function and activation of astrocytes. The interplay between astrocyte function and neurons may modulate cognitive performance in SCD.

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

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

Renal and extrarenal effects of fibroblast growth factor 23

Fibroblast growth factor 23 (FGF23) is a hormone with a central role in the regulation of phosphate homeostasis. This regulation is accomplished by the coordinated modulation of renal phosphate handling, vitamin D metabolism and parathyroid hormone secretion. Patients with kidney disease have increased circulating levels of FGF23 and in other patient populations and in healthy individuals, FGF23 levels also rise following an increase in dietary phosphate intake. Maladaptive increases in FGF23 have a detrimental effect on several organs and tissues and, importantly, these pathological changes most likely contribute to increased morbidity and mortality. For example, in the context of heart disease, FGF23 is involved in the development of pathological hypertrophy that can lead to congestive heart failure. Increased FGF23 concentrations can also lead to microcirculatory changes, in particular reduced vasodilatory capacity, and collectively these cardiovascular changes can compromise tissue perfusion. In addition, FGF23 is associated with inflammation and an increased risk of infection; other potentially detrimental effects of FGF23 are likely to emerge in the future. Most importantly, recent insights demonstrate that FGF23 can be therapeutically targeted, which holds promise for the treatment of many patients in a variety of clinical settings.

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.

Transcranial Doppler and Magnetic Resonance in Tanzanian Children With Sickle Cell Disease

Supplemental Digital Content is available in the text.

Background and Purpose—

We determined prevalences of neurological complications, vascular abnormality, and infarction in Tanzanian children with sickle cell disease.

Methods—

Children with sickle cell disease were consecutively enrolled for transcranial Doppler; those with slightly elevated (>150 cm/s), low (<50 cm/s) or absent cerebral blood flow velocity (CBFv) were invited for brain magnetic resonance imaging and magnetic resonance angiography.

Results—

Of 200 children (median age 9; range 6–13 years; 105 [2.5%] boys), 21 (11%) and 15 (8%) had previous seizures and unilateral weakness, respectively. Twenty-eight (14%) had elevated and 39 (20%) had low/absent CBFv, all associated with lower hemoglobin level, but not higher indirect bilirubin level. On multivariable analysis, CBFv>150 cm/s was associated with frequent painful crises and low hemoglobin level. Absent/low CBFv was associated with low hemoglobin level and history of unilateral weakness. In 49 out of 67 children with low/absent/elevated transcranial Doppler undergoing magnetic resonance imaging, 43% had infarction, whereas 24 out of 48 (50%) magnetic resonance angiographies were abnormal. One had hemorrhagic infarction; none had microbleeds. Posterior circulation infarcts occurred in 14%. Of 11 children with previous seizure undergoing magnetic resonance imaging, 10 (91%) had infarction (5 silent) compared with 11 out of 38 (29%) of the remainder (P=0.003). Of 7 children with clinical stroke, 2 had recurrent stroke and 3 died; 4 out of 5 had absent CBFv. Of 193 without stroke, 1 died and 1 had a stroke; both had absent CBFv.

Conclusions—

In one-third of Tanzanian children with sickle cell disease, CBFv is outside the normal range, associated with frequent painful crises and low hemoglobin level, but not hemolysis. Half have abnormal magnetic resonance angiography. African children with sickle cell disease should be evaluated with transcranial Doppler; those with low/absent/elevated CBFv should undergo magnetic resonance imaging/magnetic resonance angiography.

Pathophysiology of Sickle Cell Disease

Since the discovery of sickle cell disease (SCD) in 1910, enormous strides have been made in the elucidation of the pathogenesis of its protean complications, which has inspired recent advances in targeted molecular therapies. In SCD, a single amino acid substitution in the β-globin chain leads to polymerization of mutant hemoglobin S, impairing erythrocyte rheology and survival. Clinically, erythrocyte abnormalities in SCD manifest in hemolytic anemia and cycles of microvascular vaso-occlusion leading to end-organ ischemia-reperfusion injury and infarction. Vaso-occlusive events and intravascular hemolysis promote inflammation and redox instability that lead to progressive small- and large-vessel vasculopathy. Based on current evidence, the pathobiology of SCD is considered to be a vicious cycle of four major processes, all the subject of active study and novel therapeutic targeting: ( a) hemoglobin S polymerization, ( b) impaired biorheology and increased adhesion-mediated vaso-occlusion, ( c) hemolysis-mediated endothelial dysfunction, and ( d) concerted activation of sterile inflammation (Toll-like receptor 4- and inflammasome-dependent innate immune pathways). These molecular, cellular, and biophysical processes synergize to promote acute and chronic pain and end-organ injury and failure in SCD. This review provides an exhaustive overview of the current understanding of the molecular pathophysiology of SCD, how this pathophysiology contributes to complications of the central nervous and cardiopulmonary systems, and how this knowledge is being harnessed to develop current and potential therapies.

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.

Other cerebrovascular occlusive disease

In this chapter we review the optimal imaging modalities for subacute and chronic stroke. We discuss the utility of computed tomography (CT) and multimodal CT imaging. Further, we analyze the importance of specific magnetic resonance imaging sequences, such as diffusion-weighted imaging for acute ischemic stroke, T2/fluid-attenuated inversion recovery for subacute and chronic stroke, and susceptibility imaging for detection of intracranial hemorrhages. Different ischemic stroke mechanisms are reviewed, and how these imaging modalities may aid in the determination of such. Further, we analyze how topographic patterns in ischemic stroke may provide important clues to the diagnosis, in addition to the temporal evolution of the stroke. Lastly, specific cerebrovascular occlusive diseases are reviewed, with emphasis on the optimal imaging modalities and their findings in each condition.

Intelligence quotient in paediatric sickle cell disease: a systematic review and meta-analysis

AIM

Sickle cell disease (SCD) is the commonest cause of childhood stroke worldwide. Magnetic resonance imaging (MRI) is routinely used to detect additional silent cerebral infarction (SCI), as IQ is lower in SCI as well as stroke. This review assesses the effect of infarction on IQ, and specifically whether, compared to healthy controls, IQ differences are seen in children with SCI with no apparent MRI abnormality.

METHOD

A systematic review was conducted to include articles with an SCD paediatric population, MRI information, and Wechsler IQ. A meta-analysis of 19 articles was performed to compare IQ in three groups: stroke vs SCI; SCI vs no SCI; and no SCI vs healthy controls.

RESULTS

Mean differences in IQ between all three groups were significant: stroke patients had lower IQ than patients with SCI by 10 points (six studies); patients with SCI had lower IQ than no patients with SCI by 6 points (17 studies); and no patients with SCI had lower IQ than healthy controls by 7 points (seven studies).

INTERPRETATION

Children with SCD and no apparent MRI abnormality have significantly lower IQ than healthy controls. In this chronic condition, other biological, socioeconomic, and environmental factors must play a significant role in cognition.

Guidelines for the prevention of stroke in patients with stroke and transient ischemic attack: a guideline for healthcare professionals from the American Heart Association/American Stroke Association

The aim of this updated guideline is to provide comprehensive and timely evidence-based recommendations on the prevention of future stroke among survivors of ischemic stroke or transient ischemic attack. The guideline is addressed to all clinicians who manage secondary prevention for these patients. Evidence-based recommendations are provided for control of risk factors, intervention for vascular obstruction, antithrombotic therapy for cardioembolism, and antiplatelet therapy for noncardioembolic stroke. Recommendations are also provided for the prevention of recurrent stroke in a variety of specific circumstances, including aortic arch atherosclerosis, arterial dissection, patent foramen ovale, hyperhomocysteinemia, hypercoagulable states, antiphospholipid antibody syndrome, sickle cell disease, cerebral venous sinus thrombosis, and pregnancy. Special sections address use of antithrombotic and anticoagulation therapy after an intracranial hemorrhage and implementation of guidelines.

Sickle-cell disease stroke throughout life: a retrospective study in an adult referral center

Strokes are one of the most severe complications of sickle-cell disease. Most studies have been restricted to children with sickle-cell disease. To better understand the characteristics and follow-up of strokes occurring from childhood to adulthood, we undertook a retrospective cohort study of 69 stroke patients among the 2,875 patients consulting at the French Adult Sickle-Cell Disease Referral Center. Between 1970 and 2008, they had experienced 104 strokes: 80 ischemic, 22 hemorrhagic, and 2 intracranial sinus thromboses. Coma and/or fatal outcomes underscored the severity of strokes in sickle-cell disease patients.Hemorrhagic strokes occurred mostly in adults and carried a higher risk of death than ischemic stroke. The mechanisms underlying sickle-cell disease associated strokes were reevaluated and etiologies were determined for first stroke and recurrences, in childhood and adulthood. Sickle-cell disease vasculopathy concerned only SS patients and remains their most frequent stroke etiology. Cardioembolism, vaso-occlusive crisis and triggering factors were other etiologies identified in adults. Recurrences occurred in 19 SS patients only after a first ischemic stroke. SC patients' strokes occurred in adulthood and were associated with cardiovascular risk factors. Our findings provide novel information about cerebrovascular pathologies throughout the lives of sickle-cell disease patients and suggest the need for different diagnostic and therapeutic management approaches in those different settings.

Sickle cell anemia: intracranial stenosis and silent cerebral infarcts in children with low risk of stroke

PURPOSE

Children with sickle cell anemia (SCA), who have mean blood flow velocities <170 cm/s in the terminal internal carotid (tICA) or middle cerebral (MCA) arteries on transcranial Doppler ultrasonography (TCD), are considered to be at low risk of stroke. The prevalence of intracranial stenosis, which raises the risk of stroke, is not known in these children. Here, we estimated the prevalence of stenosis and explored its association with silent cerebral infarcts determined based on Magnetic Resonance (MR) scans.

PATIENTS/METHODS

We studied prospectively a cohort of 67 children with SCA without prior clinically overt stroke or TIA (median age 8.8 years; range limits 2.3-13.1 years; 33 females) and with TCD mean velocity <170 cm/s. They underwent MR imaging of the brain and MR angiography of intracranial arteries.

RESULTS

In 7 children (10.5%, 95% CI: 4.9-20.3%) we found 10 stenoses, including 4 with isolated left tICA stenosis and 3 with multiple stenoses. We found silent infarcts in 26 children (37.7%, 95% CI: 27.2-49.5%). The median number of infarcts in an affected child was 2 (range limits: 1-9), median volume of infarcts was 171 mm(3) (range limits: 7-1060 mm(3)), and median infarct volume in relation to total brain volume was 0.020% (range limits: 0.001-0.101%). The number and volume of infarcts were significantly higher in children with arterial stenosis (both p=0.023).

CONCLUSIONS

The prevalence of intracranial arterial stenosis in children with SCA classified as at low risk of stroke by TCD mean velocity <170 cm/s is high. Children with stenosis are at higher risk of brain parenchymal injury as they have more silent cerebral infarcts.

Sickle cell disease in children: accuracy of imaging transcranial Doppler ultrasonography in detection of intracranial arterial stenosis

This study aimed to determine the accuracy of imaging transcranial Doppler sonography in detection of intracranial arterial stenosis in children with sickle cell disease using three-dimensional MR angiography as a reference standard. Sixty-one children (mean age 102±39 months, 30 males), who had no history of overt stroke, and were classified as at lowest risk of stroke by mean flow velocity criterion <170 cm/s, underwent conventional and imaging transcranial Doppler ultrasonographic examinations. We employed the area under the receiver operating characteristic curve (AUC) to determine the accuracy of flow velocity measurements obtained with imaging ultrasonography with and without correction for the angle of insonation as well as with conventional ultrasonography. We also established the most efficacious velocity thresholds for detection of the stenosis. We found ten intracranial stenoses in six patients on MR angiography, but we calculated AUC only for detection of stenosis (n=6) of the left intracranial internal carotid artery. The accuracy of flow velocity with angle correction was lower than the accuracy of velocity without angle correction (AUC=0.73, 95% CI, 0.53-0.93 versus AUC=0.87, 95% CI, 0.74-1.00; p=0.017). The accuracy of flow velocity obtained with conventional ultrasonography (AUC=0.82, 95% CI, 0.67-0.97) was not different from the accuracy of flow velocities obtained with imaging ultrasonography. We found that the threshold of 165 cm/s of mean velocity without angle correction is associated with highest efficiency for imaging (92%) and conventional ultrasonography (90%). Velocity measurements without angle-correction provide good accuracy in detection of stenosis of the terminal internal carotid artery, whereas angle-corrected velocities have lower accuracy.

Stenosis or hyperperfusion in sickle cell disease--ultrasound assessment of cerebral blood flow volume

Increased blood flow velocity (BFV) in basal cerebral arteries measured by transcranial color-coded sonography (TCCS) is a stroke risk factor in sickle cell disease (SCD). Raised BFV may be caused by vessel narrowing or by hyperperfusion. In 44 SCD patients and 14 controls, intracranial arterial BFVs and global cerebral blood flow (CBF) were analyzed by TCCS and extracranial duplex ultrasound, respectively. Magnetic resonance imaging and magnetic resonance angiography were performed in all patients with pathologic intracranial BFV rise. Intracranial BFVs and CBF in SCD were significantly higher than in controls. CBF in SCD correlated with BFV in all intracranial arteries and correlated inversely with age and hemoglobin values. Magnetic resonance angiography failed to demonstrate any stenosis in our SCD patients, thus raised intracranial BFVs must be interpreted as an anemia-dependent cerebral hyperperfusion. These findings suggest that the pathomechanism of stenosis-derived arterio-arterial embolism might be less relevant in SCD-related ischemic stroke, and other factors like small vessel disease or sickle cell-induced microvascular blood clotting have to be considered.

Symptomatic intracranial arterial disease: incidence, natural history, diagnosis, and management

Symptomatic intracranial arterial disease is associated with a high rate of recurrent ischemic events. The management of this condition is controversial, with some advocating medical therapy as a sole means of treatment and others recommending endovascular therapy in addition to best medical management. In rare cases, surgical intervention is considered. A thorough review of the available literature was performed, and treatment recommendations based on these data are provided.

Guidelines for the prevention of stroke in patients with stroke or transient ischemic attack: a guideline for healthcare professionals from the american heart association/american stroke association

The aim of this updated statement is to provide comprehensive and timely evidence-based recommendations on the prevention of ischemic stroke among survivors of ischemic stroke or transient ischemic attack. Evidence-based recommendations are included for the control of risk factors, interventional approaches for atherosclerotic disease, antithrombotic treatments for cardioembolism, and the use of antiplatelet agents for noncardioembolic stroke. Further recommendations are provided for the prevention of recurrent stroke in a variety of other specific circumstances, including arterial dissections; patent foramen ovale; hyperhomocysteinemia; hypercoagulable states; sickle cell disease; cerebral venous sinus thrombosis; stroke among women, particularly with regard to pregnancy and the use of postmenopausal hormones; the use of anticoagulation after cerebral hemorrhage; and special approaches to the implementation of guidelines and their use in high-risk populations.

Epidemiology of intracranial stenosis

Intracranial stenosis is a common etiology for ischemic stroke. Due to limitations of imaging studies, there are limited data on the prevalence of symptomatic and asymptomatic intracranial stenosis. Intracranial stenosis is more prevalent in Asian, Hispanic, and African-American populations. The reported proportion of patients with symptomatic intracranial stenosis among those hospitalized for ischemic cerebral events varies from 1% in non-Hispanic whites to as high as 50% in Asian populations. In population-based studies, the estimated prevalence of symptomatic intracranial disease varies from 1 in 100,000 for whites to 15 in 100,000 in African Americans. A Chinese population-based study reported intracranial stenosis in 7% of the population aged more than 40 years. Autopsy studies have noted intracranial atherosclerotic disease in about 23% of population in the 6th decade and 80% of population in the 9th decade of life. Angiotensin-converting enzyme polymorphisms, plasma endostatin/vascular endothelial growth factor ratio, glutathione S-transferase omega-1 gene polymorphism, and plasma homocysteine levels are non-modifiable risk factors noted to be associated with intracranial stenosis. Hypertension and serum lipid profile are major modifiable risk factors, whereas sickle cell disease is an uncommon risk factor that can be managed to reduce risk. Associations of intracranial atherosclerosis with diabetes mellitus, metabolic syndrome, Alzheimer's disease, aortic plaques, radiotherapy, and meningitis are less well documented.

Intracranial atherosclerotic disease: an update

The consensus conference on intracranial atherosclerosis provides a comprehensive review of the existing literature relevant to the epidemiology, diagnosis, prevention, and treatment of intracranial atherosclerosis, and identifies principles of management and research priorities. Patients who have suffered a stroke or transient ischemic attack attributed to stenosis (50-99%) of a major intracranial artery face a 12 to 14% risk for subsequent stroke during the 2-year period after the initial ischemic event, despite treatment with antithrombotic medications. The annual risk for subsequent stroke may exceed 20% in high-risk groups. In patients with intracranial atherosclerotic disease, short-term and long-term anticoagulation is not superior to antiplatelet treatment. Overall, the subgroup analyses from randomized trials provide evidence about benefit of aggressive atherogenic risk factor management. Intracranial angioplasty with or without stent placement has evolved as a therapeutic option for patients with symptomatic intracranial atherosclerotic disease, particularly those with high-grade stenosis with recurrent ischemic symptoms, medication failure, or both. A multicenter randomized trial is currently under way to compare stent placement with intense medical management for patients with high-grade symptomatic intracranial atherosclerotic disease.

Neuroimaging in assessment of risk of stroke in children with sickle cell disease

PURPOSE

Stroke and subclinical "silent infarcts" are major causes of morbidity in children with Sickle Cell Disease (SCD). Ischemic strokes are more common in younger children while hemorrhagic strokes are more frequent in adults. The goal of neuroimaging in acute stroke is to document whether the stroke is ischemic or hemorrhagic, to assess the extent of parenchymal abnormalities and to determine the presence of other cerebrovascular lesions. Computed Tomography (CT) is the primary modality for the assessment of acute stroke patients because of its 24/7 availability and ability to exclude hemorrhagic causes. Magnetic resonance imaging (MRI) and MR angiography (MRA) are recommended to determine precisely extent of infarction and detect cerebrovascular abnormalities. The goal of neuroimaging in patients with hemorrhagic stroke is to identify an arteriovenous malformation or aneurysm(s) amenable to surgery or catheter intervention.The risk of first stroke is very high in asymptomatic children with intracranial arterial mean velocities over 200 cm/s on transcranial Doppler (TCD) examination. The risk can be substantially reduced if chronic blood transfusions are timely implemented. Large cerebral vessel disease detected by TCD can be confirmed or excluded by MRI/MRA. Those with evidence of parenchymal and/or cerebrovascular lesions should be followed by preventive therapy. In patients with neurologic symptoms and negative MRI/MRA findings Positron Emission Tomography or single photon emission CT is recommended. There are no specific neuroimaging findings that suggest that blood transfusions can be safely halted in children with SCD.

Therapy Insight: stroke risk and its management in patients with sickle cell disease

Children with sickle cell disease, a chronic hemolytic anemia, present with a wide variety of neurological syndromes, including ischemic and hemorrhagic stroke, transient ischemic attacks, 'soft neurological signs', seizures, headache, coma, visual loss, altered mental status, cognitive difficulties, and covert or 'silent' infarction. Those with ischemic stroke usually have stenosis or occlusion of the distal internal carotid and proximal middle cerebral arteries. Indefinite transfusion prevents recurrence in most patients who have had a stroke, and can prevent first stroke in those with high transcranial Doppler velocities. High white cell count, low hemoglobin and oxyhemoglobin desaturation predict neurological complications. Other risk factors for overt ischemic stroke include hypertension, previous transient ischemic attack, covert infarction and chest crisis. For hemorrhagic stroke, aneurysms are common in adults but not children, who often present with hypertension after transfusion or corticosteroids. Seizures are particularly common in patients with cerebrovascular disease and covert infarction; the latter is also associated with hyposplenism and infrequent pain. Factors associated with cognitive difficulties include thrombocytosis, infarction, large-vessel disease, and perfusion abnormality on neuroimaging. As well as investigating the role of genes and the possibility that hydroxyurea or blood pressure control reduce neurological complications, we should explore the modifiable effects of poor nutrition, chronic infection, hemolysis and oxyhemoglobin desaturation on stroke risk.

The pathophysiology, prevention, and treatment of stroke in sickle cell disease

PURPOSE OF REVIEW

Stroke is one of the most devastating complications of sickle cell disease, but current research has led to improved understanding of its pathogenesis and to new approaches in the prevention of both primary and secondary stroke. This review focuses on advances reported in the past 2 years.

RECENT FINDINGS

New concepts in the pathophysiology of central nervous system events in sickle cell disease have centered around hemolytic anemia and nitric oxide metabolism. Genetic risk factors are now being explored. Major improvement in primary stroke prevention has occurred through transcranial Doppler ultrasonography screening, but utilization of this technique is far from optimal. Hydroxyurea is now being tested as an alternative approach to chronic transfusion for secondary stroke prevention through a multicenter trial. Other studies are addressing the management of silent infarcts and nocturnal hypoxemia.

SUMMARY

Increased understanding of the etiology and pathogenesis of stroke in sickle cell disease should eventually lead to improved management of all central nervous system complications. Alternative secondary stroke prevention with hydroxyurea may allow patients to avoid dependence on life-long chronic transfusion. Primary stroke prevention through transcranial Doppler ultrasonography screening may ultimately yield a dramatic reduction in the incidence of stroke in sickle cell disease.

Treatment and prevention of stroke in children with sickle cell disease

Stroke is one of the major complications in children with sickle cell disease (SCD). Ischemic stroke is associated with small asymptomatic subcortical infarcts to large territorial lesions causing major disability. Intracranial hemorrhages may be caused by aneurysm rupture or by leakage from moyamoya vessels or venous sources. There have been no acute stroke treatment studies in SCD, but hydration and exchange transfusion are often recommended. However, there is an evidence base for primary and to some extent secondary stroke prevention. Primary prevention of stroke was demonstrated in the Stroke Prevention Trial in Sickle Cell Anemia (STOP), in which children with transcranial Doppler (TCD) mean blood flow velocities of 200 cm/second (previously shown to indicate high stroke risk) or higher were randomized to either regular blood transfusions or no transfusion. The study showed a very significant 90% reduction in first stroke with transfusion. In STOP2, discontinuing transfusions after 30 months or more (even with normal TCD) resulted in a high rate of reversion to abnormal TCD values and stroke. TCD screening of all children with SCD, and initiation and maintenance of chronic transfusion to maintain hemoglobin S below 30% in the high-risk group, is the only proven prevention strategy for stroke in SCD. Hydroxyurea is being studied as secondary stroke prevention at this time. No recommendation specific to SCD regarding the use of antiplatelet agents or anticoagulants in ischemic stroke can be made. Bone marrow transplantation can be curative for SCD, and limited data support its use to prevent stroke in SCD.

Hypoxic adaptation during development: relation to pattern of neurological presentation and cognitive disability

Children with acute hypoxic-ischaemic events (e.g. stroke) and chronic neurological conditions associated with hypoxia frequently present to paediatric neurologists. Failure to adapt to hypoxia may be a common pathophysiological pathway linking a number of other conditions of childhood with cognitive deficit. There is evidence that congenital cardiac disease, asthma and sleep disordered breathing, for example, are associated with cognitive deficit, but little is known about the mechanism and whether there is any structural change. This review describes what is known about how the brain reacts and adapts to hypoxia, focusing on epilepsy and sickle cell disease (SCD). We prospectively recorded overnight oxyhaemoglobin saturation (SpO2) in 18 children with intractable epilepsy, six of whom were currently or recently in minor status (MS). Children with MS were more likely to have an abnormal sleep study defined as either mean baseline SpO2 <94% or >4 dips of >4% in SpO2/hour (p = .04). In our series of prospectively followed patients with SCD who subsequently developed acute neurological symptoms and signs, mean overnight SpO2 was lower in those with cerebrovascular disease on magnetic resonance angiography (Mann-Whitney, p = .01). Acute, intermittent and chronic hypoxia may have detrimental effects on the brain, the clinical manifestations perhaps depending on rapidity of presentation and prior exposure.

Stroke in Black Americans

Black Americans bear a disproportionate stroke burden in the United States compared with other racial and ethnic groups. Poor stroke awareness, higher vascular risk factor burden, limited access to care, mistrust of the medical system, and inequities in diagnostic testing and treatment usage may account for some of the disparity. In addition, blacks have historically been under-represented in observational studies and clinical trials of stroke prevention and treatment. Therefore, our knowledge regarding stroke in black Americans is somewhat limited. This article provides an update on developments in our understanding regarding stroke in this at-risk population.

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.

Pathophysiology and treatment of stroke in sickle-cell disease: present and future

Sickle-cell anaemia is the most common cause of stroke in children, and stroke is one of the most devastating complications of sickle-cell disease. Overt strokes are typically due to large-artery vasculopathy affecting the intracranial internal carotid arteries and proximal middle cerebral arteries, whereas silent strokes typically occur in the territory of penetrating arteries. The sickled red blood cell can contribute to the pathogenesis of stroke via abnormal adherence to the vascular endothelium and by haemolysis, which results in endothelial cell activation, a hypercoaguable state, and alterations in vasomotor tone. Red-blood-cell transfusion, the most common preventive measure for stroke in sickle-cell disease, is associated with iron overload in chronic disease. Therefore, interventions directed towards the potential mechanisms that promote vasculopathy and occlusion in sickle-cell anaemia should be investigated. Here we review the epidemiology, clinical spectrum, and pathophysiology of stroke in sickle-cell disease to identify potential therapeutic targets.

Stroke in sickle cell disease in Africa: case report

Stroke, including asymptomatic cerebrovascular events, is a significant cause of morbidity and mortality in sickle cell disease, occurring with an incidence of 10 to 25%. Extensive research has established that cerebral stenosis, involving the circle of Willis, is the most common mechanism in children. We report a child with sickle cell disease who presented with cortical blindness and right-sided hemiplegia. Computerised tomography of the brain revealed an infarct involving the left parietal region and extending to the occipital region. Stroke in SCD is multifactorial, but high-risk individuals can be identified by simple well-established strategies such as transcranial doppler ultrasonography. There are approaches for both primary and secondary interventions, which have been shown to be effective and need to be incorporated into management guidelines for SCD patients. Before schemes are recommended into health care policies, research in the appropriate setting is required.

HLA-DRB1 alleles in Hb SS patients with avascular necrosis of the femoral head

Strong associations have been established between various HLA alleles and different complications of sickle cell disease (SCD). Recently, the HLA-DRB1*03 allele was shown to be associated with susceptibility to stroke while the HLA-DRB1*02 allele may be protective. While stroke and silent brain infarcts (SBI) are unusual in Kuwaiti children with SCD, avascular necrosis of the femoral head (AVNFH) is quite common. The modulatory association factors must still be elucidated. An investigation of HLA-DRB1 alleles was carried out in a group of 68 Kuwaiti SS patients, of age 7-44 years, of whom 20 (29.4%) had AVNFH, confirmed by magnetic resonance imaging. A group of 167 apparently healthy age- and sex-matched individuals served as controls. Comparison of the HLA alleles between the whole SS group and the controls showed a significant over-representation of DRB1*01 (P < 0.01) and DRB1*10 (P < 0.05) in the patient group. No significant differences in the allele frequencies in the SS patients with or without AVNFH were observed. It therefore appears that the HLA-DRB1 locus does not play a significant role in the pathogenesis of AVNFH Kuwaiti patients.

Stroke in children with sickle cell disease

Children with sickle disease are at high risk for ischemic stroke and transient ischemic attacks, usually secondary to intracranial arteriopathy involving the terminal internal carotid and proximal middle cerebral and anterior cerebral arteries, which may be diagnosed using transcranial Doppler ultrasound or magnetic resonance angiography (MRA). Other central nervous system (CNS) complications include seizures and coma, which may be secondary to ischemic stroke, sinovenous thrombosis, reversible posterior leukoencephalopathy, or acute demyelination. The immediate priority after an acute CNS event is to improve cerebral oxygenation with oxygen supplementation to maintain peripheral saturation measured using pulse oximetry between 96% and 99%, and a simple transfusion of packed cells within an hour of presentation if the patient's hemoglobin is less than 10 g/dL. The patient then should have erythrocytapheresis or manual exchange to reduce the hemoglobin S percentage to below 30%. Computed tomography to exclude hemorrhage is mandatory and MR T2-weighted imaging with MRA, fat-saturated imaging of the neck (dissection), MR venography (sinovenous thrombosis), and diffusion-weighted imaging usually distinguishes between arterial ischemic stroke and the differential diagnoses. Comatose patients with widespread focal or global cerebral edema may have good functional outcome after surgical decompression. Anticoagulation may be indicated for dissection or sinovenous thrombosis and steroids for demyelination. Blood pressure should be reduced slowly if raised in patients with reversible posterior leukoencephalopathy. Seizures should be treated aggressively and electroencephalogram monitoring should be done to exclude subclinical seizures if the patient is unconscious. Hemorrhagic stroke may require craniectomy and drainage and/or management of vasospasm. Interventional neuroradiology with coils is an alternative to surgical clipping for aneurysms. For secondary prevention, regular blood transfusion to hemoglobin S of less than 30% reduces the risk of recurrent stroke from approximately 67% to approximately 10%. Hydroxyurea and phlebotomy may be used in patients who are alloimmunized. Moyamoya syndrome is a risk factor for recurrence despite prophylactic blood transfusion. Revascularization may prevent additional stroke. Bone marrow transplantation may be offered to patients with human leukocyte antigen-compatible siblings. Blood transfusion prevents stroke in patients with velocities greater than 200 cm per second on TCD; a phase III trial studying the prevention of the progression of silent infarction is being done. Emerging primary prophylaxis regimens being tested include citrulline and arginine, aspirin, and overnight oxygen supplementation. Physicians caring for children with sickle cell disease also should ensure adequate nutrition, including five servings of fruit and vegetables a day. The role of vitamin supplementation is controversial, particularly when patients must take daily penicillin prophylaxis.

Prevention of secondary stroke and resolution of transfusional iron overload in children with sickle cell anemia using hydroxyurea and phlebotomy

OBJECTIVE

Transfusions prevent secondary stroke in children with sickle cell anemia (SCA) but also cause iron overload. Alternatives for stroke prophylaxis with effective therapy to reduce iron burden are needed.

STUDY DESIGN

For 35 children with SCA and stroke, transfusions were prospectively discontinued. Hydroxyurea was prescribed for stroke prophylaxis, and phlebotomy removed excess iron. Initial patients discontinued transfusions before hydroxyurea therapy, but later patients overlapped transfusions with hydroxyurea until tolerating full-dose therapy.

RESULTS

Children received hydroxyurea for 42 +/- 30 months (range, 3-104 months). Hydroxyurea (26.7 +/- 4.8 mg/kg per day) led to mild neutropenia (3.9 +/- 2.3 x 10(9)/L) with significant increases in hemoglobin concentration, mean corpuscular volume, and fetal hemoglobin. Stroke recurrence rate was 5.7 events per 100 patient-years, but children receiving overlapping hydroxyurea therapy had only 3.6 events per 100 patient-years. For 26 children with >6 months of phlebotomy, 14,311 +/- 12,459 mL blood (315 +/- 214 mL/kg) was removed, with serum ferritin decreasing from a median of 2722 to 298 ng/mL. Among patients completing phlebotomy, liver biopsy documented normal histology and no excess iron deposition.

CONCLUSIONS

For children with SCA and stroke, hydroxyurea effectively prevents secondary stroke and serial phlebotomy leads to complete resolution of transfusional iron overload.

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.

Silent brain infarcts in adult Kuwaiti sickle cell disease patients

Although overt stroke is a common complication of sickle cell disease (SCD), its incidence is very low in Kuwaiti patients. On the other hand, the prevalence of silent brain infarcts, which is reported to be about 17-20% in American patients, has not been documented in adult Kuwaiti patients. This is a 1-year study of consecutive, asymptomatic SCD patients seen in the hematology clinic of Mubarak Al-Kabeer Hospital. Patients with a past history of seizure or any other neurological abnormality were excluded. The patients' charts were reviewed for frequency of hospitalizations, any documented complications, and steady-state CBC. MRI was done with a 1.5-Tesla unit with super-conducting magnet. T1- and T2-weighted sagittal and axial sections and proton-density axial images were obtained in 5-mm-thick sections. Thirty-five patients were studied, made up of 25 SS and 10 Sbeta(0)Thal, aged between 17 and 44 years, with a mean age of 26.9 +/- 9.3 years. MRI findings consistent with infarcts were found in 7 (20.0%) patients-6 SS and 1 Sbeta(0)thal-with a mean age of 31.8 +/- 8.2 years, which was significantly higher (P < 0.05) than the mean age of the unaffected group (25.1 - 9.0 years). There were also no differences in the mean Hb, Hb F, or any other hematological parameter in the two groups. Among the affected 6 SS, 2 had co-existent alpha-thal trait. It is interesting that, while silent infarcts are prevalent in young American patients, it is in the older age group that they occur in Kuwaiti patients. Further studies are needed to investigate the factors modulating this heterogeneity.

Sickle cell disease: continuous arterial spin-labeling perfusion MR imaging in children

Cerebral blood flow (CBF) was measured with continuous arterial spin-labeling perfusion magnetic resonance (MR) imaging in 14 children with sickle cell disease and seven control subjects. Mean CBF values were higher in patients (P <.005) than in control subjects in all cerebral artery territories. Three patients had decreased CBF in right anterior and middle cerebral artery territories compared with CBF on the left, and one patient had a profound decrease in CBF in all three territories in the right hemisphere. Baseline CBF was significantly decreased in territories seen as unaffected on conventional MR images and MR angiograms in four children with sickle cell 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.

Moyamoya syndrome in childhood sickle cell disease: a predictive factor for recurrent cerebrovascular events

We conducted a retrospective study to determine whether the presence of moyamoya collaterals influenced the risk of recurrence of cerebrovascular events (CVEs: stroke or transient ischemic attack) in patients with sickle cell disease placed on chronic transfusions after a stroke. Forty-three patients with homozygous sickle cell anemia (HbSS) and 1 with HbSO(Arab) (16 females, 28 males) who had suffered strokes while under the age of 18 were studied. All patients had been on transfusions aimed at maintaining the sickle hemoglobin (HbS) level below 30%. They were followed for a mean of 6.6 years (2.2 to 20.4 years). The presence of collaterals was diagnosed based on either magnetic resonance angiography or conventional angiography. Eighteen (41%) of the 44 patients suffered recurrent CVEs. Nineteen (43%) (6 females, 13 males) patients had moyamoya collaterals. Eleven (58%) of these 19 experienced 21 total recurrent CVEs, including 4 strokes in 4 patients (21%). In comparison, 7 (28%) of 25 patients without moyamoya collaterals experienced 9 recurrent CVEs (P <.05) with only 1 recurrent stroke (4%). Moyamoya patients were also more likely to have 2 recurrent CVEs (42% vs 8%, P <.05) as well as poorer neuropsychological testing results. A proportional hazards regression analysis indicated that patients with moyamoya were more than twice as likely to incur a subsequent CVE (hazard ratio, 2.40; 95% confidence interval, 0.85, 6.75). We conclude that up to 41% of patients with sickle cell disease experience recurrent CVEs after an initial stroke despite chronic transfusions and that the risk of recurrence is significantly higher for those who have moyamoya collaterals.

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.

Hydroxyurea as an Alternative to Blood Transfusions for the Prevention of Recurrent Stroke in Children With Sickle Cell Disease

Children with sickle cell disease (SCD) and stroke receive chronic transfusions to prevent stroke recurrence. Transfusion risks including infection, erythrocyte allosensitization, and iron overload suggest a need for alternative therapies. We previously used hydroxyurea (HU) and phlebotomy in two young adults with SCD and stroke as an alternative to transfusions. We have now prospectively discontinued transfusions in 16 pediatric patients with SCD and stroke. Reasons to discontinue transfusions included erythrocyte alloantibodies or autoantibodies, recurrent stroke on transfusions, iron overload, noncompliance, and deferoxamine allergy. HU was started at 15 mg/kg/d and escalated to 30 mg/kg/d based on hematologic toxicity. Patients with iron overload underwent phlebotomy. The children have been off transfusions 22 months, (range, 3 to 52 months). Their average HU dose is 24.9 ± 4.2 mg/kg/d, hemoglobin concentration is 9.4 ± 1.3 g/dL, and mean corpuscular volume (MCV) is 112 ± 9 fL. Maximum percentage fetal hemoglobin (%HbF) is 20.6% ± 8.0% and percentage HbF-containing erythrocytes (%F cells) is 79.3% ± 14.7%. Fourteen patients underwent phlebotomy with an average of 8,993 mL (267 mL/kg) removed. Serum ferritin has decreased from 2,630 to 424 ng/mL, and 4 children have normal ferritin values. Three patients (19%) had neurological events considered recurrent stroke, each 3 to 4 months after discontinuing transfusions, but before maximal HU effects. These preliminary data suggest some children with SCD and stroke may discontinue chronic transfusions and use HU therapy to prevent stroke recurrence. Phlebotomy is well-tolerated and significantly reduces iron overload. Modifications in HU therapy to raise HbF more rapidly might increase protection against stroke recurrence.

Hydroxyurea as an Alternative to Blood Transfusions for the Prevention of Recurrent Stroke in Children With Sickle Cell Disease

Children with sickle cell disease (SCD) and stroke receive chronic transfusions to prevent stroke recurrence. Transfusion risks including infection, erythrocyte allosensitization, and iron overload suggest a need for alternative therapies. We previously used hydroxyurea (HU) and phlebotomy in two young adults with SCD and stroke as an alternative to transfusions. We have now prospectively discontinued transfusions in 16 pediatric patients with SCD and stroke. Reasons to discontinue transfusions included erythrocyte alloantibodies or autoantibodies, recurrent stroke on transfusions, iron overload, noncompliance, and deferoxamine allergy. HU was started at 15 mg/kg/d and escalated to 30 mg/kg/d based on hematologic toxicity. Patients with iron overload underwent phlebotomy. The children have been off transfusions 22 months, (range, 3 to 52 months). Their average HU dose is 24.9 ± 4.2 mg/kg/d, hemoglobin concentration is 9.4 ± 1.3 g/dL, and mean corpuscular volume (MCV) is 112 ± 9 fL. Maximum percentage fetal hemoglobin (%HbF) is 20.6% ± 8.0% and percentage HbF-containing erythrocytes (%F cells) is 79.3% ± 14.7%. Fourteen patients underwent phlebotomy with an average of 8,993 mL (267 mL/kg) removed. Serum ferritin has decreased from 2,630 to 424 ng/mL, and 4 children have normal ferritin values. Three patients (19%) had neurological events considered recurrent stroke, each 3 to 4 months after discontinuing transfusions, but before maximal HU effects. These preliminary data suggest some children with SCD and stroke may discontinue chronic transfusions and use HU therapy to prevent stroke recurrence. Phlebotomy is well-tolerated and significantly reduces iron overload. Modifications in HU therapy to raise HbF more rapidly might increase protection against stroke recurrence.

Prothrombotic changes in children with sickle cell disease: relationships to cerebrovascular disease and transfusion

Vascular occlusion has a central role in the pathophysiology of sickle cell disease (SCD) and, although there is little evidence that thrombosis alone is responsible, patients with sickle cell disease are known to have an ill-defined but increased thrombotic risk. The most serious complication of this in childhood is stroke which occurs in 7-10% of children and a further 14% have asymptomatic cerebrovascular disease (CVD) on imaging. We have performed a comprehensive profile of coagulation inhibitors and markers of thrombin generation in 96 children (83 nontransfused [NTx] and 13 transfused [Tx]) with steady-state SCD and 18 healthy sibling controls. The levels of protein S (free and total) and heparin cofactor II were reduced in both the NTx and Tx groups compared to controls and protein C and APC resistance ratios were reduced in the NTx group only. Antithrombin levels were not different from controls. Thrombin-antithrombin complexes and prothrombin fragment F1+2 were increased in both patient groups. In the NTx subgroups with or without CVD there were no differences for any of the parameters measured except for lower haemoglobin levels and higher white cell counts in those with asymptomatic CVD. We conclude that children with SCD have a reduction in levels of the majority of the coagulation inhibitors and increased thrombin generation in the steady-state and these are only partially reversed by transfusion. However, these abnormalities do not appear to play a primary role in the development of cerebrovascular disease.

Cognitive deficits associated with frontal-lobe infarction in children with sickle cell disease

This study examined the cognitive manifestations of frontal-lobe infarction in a population of children with sickle cell disease (SCD). Forty-one patients with SCD underwent MRI. Five patients with stroke symptoms had large infarcts encroaching on the tissue of the frontal lobes. Four patients without symptoms had smaller frontal-lobe infarcts. The patients with stroke were significantly impaired on measures of intelligence, memory, and frontal-lobe function (Wisconsin Card Sorting Test, WCST) compared with both the patients with normal MRI scans (N=30) and a group of sibling controls (N=15), who did not differ from each other. Patients with covert infarction obtained scores on the intelligence tests and the WCST that fell in between those of the stroke patients and the other two groups. This trend toward impairment suggests that patients with covert infarction are at similar risk for cognitive deficits to those with stroke.