Sickle cell disease and pulmonary hypertension in Africa: a global perspective and review of epidemiology, pathophysiology, and management.

Secondary pulmonary hypertension (PAH) has been shown to have a prevalence of 30% in patients with sickle cell disease (SCD) with mortality rates of 40% at 40 months after diagnosis in the United States. The burden of SCD is highest in sub-Saharan Africa, especially in Nigeria (West Africa), where approximately 6 million people are afflicted. The true global incidence, prevalence, and burden of SCD and its associated end organ complications however remain unknown. Chronic hemolysis represents a prominent mechanistic pathway in the pathogenesis of SCD-associated pulmonary hypertension via a nitric oxide (NO) scavenging and abrogation of NO salutatory effects on vascular function, including smooth muscle relaxation, downregulation of endothelial adhesion molecules and inhibition of platelet activation. Many known infectious risk factors for PAH are also hyperendemic in Africa, including Human Immunodeficiency Virus/Acquired Immune Deficiency Syndrome (HIV/AIDS), chronic hepatitis B and C, and possibly malaria. Interactions between these infectious complications and SCD-related hemolysis could yield an even higher prevalence of pulmonary hypertension and compound the existing global health systems challenges in managing SCD. Indeed, our preliminary analysis of African immigrants currently in the United States suggests that pulmonary hypertension represents a significant complication of SCD in the African subcontinent. There is clearly a need to include Africa and other parts of the world with high SCD prevalence in future comprehensive studies on the epidemiology and treatment of end organ complications of an aging SCD population world-wide.