Treatment and prevention of stroke in children with sickle cell disease

The Role of Antiplatelet in the Management of Sickle Cell Disease Patients

Sickle cell disease (SCD) is a genetic disorder characterized by abnormal hemoglobin, leading to red blood cell deformities and subsequent vaso-occlusive events. Platelet activation and adhesion play a significant role in the pathophysiology of SCD, contributing to the development of complications such as vaso-occlusive events, stroke, acute chest syndrome, and other manifestations. Antiplatelet therapy has emerged as a potential strategy to mitigate these complications by modulating the platelet function and reducing thrombotic events. This review article provides an overview of antiplatelet therapy's role in managing SCD patients. It discusses the pathophysiological abnormalities in the platelet function in SCD, the rationale for antiplatelet therapy, and the evidence supporting its use in various clinical scenarios. The article explores aspirin as the primary antiplatelet agent in SCD, including its mechanism of action, dosing considerations, and efficacy and safety data. Additionally, it highlights other antiplatelet agents, such as clopidogrel, prasugrel, ticagrelor, and emerging therapies under investigation. Clinical applications of antiplatelet therapy in primary and secondary prevention and the management of acute chest syndrome and other SCD complications are also discussed. Safety considerations are emphasized, including bleeding risk assessment, monitoring, and patient selection for antiplatelet therapy. Finally, the review highlights future research and clinical practice directions, including the development of novel antiplatelet agents, combination therapies, and the integration of antiplatelet therapy with other SCD treatments. Overall, this review provides a comprehensive understanding of the current role of antiplatelet therapy in SCD management, the challenges faced, and future directions for improving patient outcomes.

Pulmonary hypertension in sickle cell disease

PURPOSE OF REVIEW

This review highlights the prevalence of pulmonary hypertension as a chronic complication of sickle cell disease (SCD) and its importance in the prognosis.

RECENT FINDINGS

In recent years, the limitations of echocardiogram for the appropriate diagnosis of SCD-associated pulmonary hypertension have been demonstrated, emphasizing the need of invasive hemodynamics assessment before any specific treatment for pulmonary hypertension is considered. The hemodynamic profile observed in this clinical situation is characterized by elevated cardiac output and low pulmonary vascular resistance that differs considerably from what is seen in pulmonary arterial hypertension. Furthermore, both hemodynamic profiles, precapillary and postcapillary, can be equally found in this setting stressing the need for a better understanding of the multiple pathophysiological mechanisms involved in the development of pulmonary hypertension before considering those patients for targeted therapies. Nevertheless, the presence of any form of pulmonary hypertension clearly denotes worse prognosis in SCD.

SUMMARY

Pulmonary hypertension is an important and prevalent complication of SCD with multiple associated mechanisms. A more aggressive approach of the baseline condition might be necessary, although the data supporting this assumption and also the use of targeted pulmonary arterial hypertension therapy are still lacking.

Cellular, pharmacological, and biophysical evaluation of explanted lungs from a patient with sickle cell disease and severe pulmonary arterial hypertension

Pulmonary hypertension is recognized as a leading cause of morbidity and mortality in patients with sickle cell disease (SCD). We now report benchtop phenotyping from the explanted lungs of the first successful lung transplant in SCD. Pulmonary artery smooth muscle cells (PASMCs) cultured from the explanted lungs were analyzed for proliferate capacity, superoxide (O2 (•-)) production, and changes in key pulmonary arterial hypertension (PAH)-associated molecules and compared with non-PAH PASMCs. Upregulation of several pathologic processes persisted in culture in SCD lung PASMCs in spite of cell passage. SCD lung PASMCs showed growth factor- and serum-independent proliferation, upregulation of matrix genes, and increased O2 (•-) production compared with control cells. Histologic analysis of SCD-associated PAH arteries demonstrated increased and ectopically located extracellular matrix deposition and degradation of elastin fibers. Biomechanical analysis of these vessels confirmed increased arterial stiffening and loss of elasticity. Functional analysis of distal fifth-order pulmonary arteries from these lungs demonstrated increased vasoconstriction to an α1-adrenergic receptor agonist and concurrent loss of both endothelial-dependent and endothelial-independent vasodilation compared with normal pulmonary arteries. This is the first study to evaluate the molecular, cellular, functional, and mechanical changes in end-stage SCD-associated PAH.

Whole blood viscosity assessment issues II: Prevalence in endothelial dysfunction and hypercoagulation

Background:

Virchow's triad in cardiovascular disease comprises blood viscosity, plasma D-dimer and homocysteine as indices of three associated but separate vascular phenomena.

Aims:

This work investigates prevalence of hyperviscosity in hyperhomocysteinaemia and positive D-dimer; and differences or similarities in stasis status among sub-populations of hyperhomocysteinaemia vs. normohomocysteinaemia and negative vs. positive D-dimer.

Patients and Methods:

10-years de-identified archived clinical pathology data for the period of January 1999 to December 2008 were audited. All cases tested for D-dimer (n=6845) and homocysteine (n=1665), which were concomitantly tested for haematocrit and total proteins, were extracted.

Results:

The results show a very low prevalence of hyperviscosity associated with a positive D-dimer sub-population (1.48%), which is not statistically different in comparison with the negative D-dimer sub-population. The prevalence of hyperviscosity associated with hyperhomocysteinaemia (5.04%) was statistically significantly higher in comparison to the normohomocysteinaemia sub-population (p = 0.05). The prevalence of low viscosity is significantly higher in the positive D-dimer sub-population relative to the negative D-dimer sub-population (p < 0.00001), but not different between hyperhomocysteinaemia vs. normohomocysteinaemia. Normoviscosity is statistically significantly commoner in normoviscosity relative to hyper-homocysteinaemia as well as in negative compared with positive D-dimer (p < 0.00001).

Conclusion:

The findings reported here suggest putting into perspective the specificity of whole blood viscosity relative to stasis, not necessarily sensitivity to disease conditions where it is implicated.

Paediatric and adult vascular intracranial complications of sickle-cell disease

BACKGROUND

To enumerate possible intracranial vascular sequelae of sickle-cell disease, to identify risk factors and outline management strategies.

METHOD

Retrospective review of a single unit experience managing vascular intracranial complications of sickle-cell disease from 1995 until 2005. Information such as homozygosity/heterozygosity, duration of disease, disease control as indicated by haematology follow-up, concurrent sickle-cell disease (SCD)-related health problems and neurosurgical management was recorded. The pattern of vascular disease was analysed to reveal possible contributory/risk factors towards development of vascular intracranial complications.

SUBJECTS

All patients presenting with vascular intracranial complications of sickle-cell disease from 1995 to 2005 were evaluated.

OUTCOME MEASURES

Classification of vascular intracranial complications into one or more of the following categories: aneurysmal subarachnoid haemorrhage, non-aneurysmal subarachnoid/intraventricular haemorrhage and vasculitis.

FINDINGS

There were ten patients in the study. All symptomatic vascular intracranial complications of SCD requiring neurosurgical intervention were homozygous for SCD. Aneurysms were likely to be multiple. Ruptured aneursyms in SCD were small (average 4 mm). There was a propensity for aneurysms to occur in the posterior circulation, in particular the posterior cerebral artery was frequently involved. Patients with aneurysms and Moyamoya-type vasculitis were likely to have occlusive disease of the internal carotid arteries.

CONCLUSIONS

The vascular intracranial complications of sickle-cell disease have an aggressive natural history. Tight control of SCD may reduce the possibility of complications. Complications that arise should be managed in the context of the disease entity rather than in isolation. Consideration should be given to bypass procedures, parent vessel ligations and revascularization techniques. Transcranial Doppler may be used to identify SCD patients with cerebrovascular occlusive disease, who may have increased risk of aneurysmal rupture.

Hydroxyurea or chronic exchange transfusions in patients with sickle cell disease: role of transcranial Doppler ultrasound in stroke prophylaxis

Hydroxyurea is increasingly used in patients with sickle cell disease and acts by several underlying mechanisms. Its usage has been reported to eliminate transfusion needs in children with beta-thalassemia major. It has also been used in sickle cell disease patients on stroke prophylaxis with exchange transfusions who develop transfusional iron overload and is now being considered as a possible alternative to chronic transfusions for secondary stroke prophylaxis. Our case demonstrates a pitfall when using hydroxyurea without monitoring intracranial cerebral vessels for vasculopathic changes; presence of which can predict stroke risk and alert the need for chronic blood transfusions as primary stroke prophylaxis. Transcranial Doppler is a crucial investigation that can reveal elevated cerebral arterial flow velocities.

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.