The role of acute and chronic splenic dysfunctions in aetiopathogenesis of anaemia in sickle cell disease: narrative review of hyperhaemolytic implications of autosplenectomy, autoimmunity, infections, and splenomegaly
Short Title: Autosplenectomy, splenomegaly, and hyperhaemolysis in SCD
Keywords:Sickle cell disease, splenomegaly, sequestration crisis, hypersplenism, autosplenectomy, infection induced haemolysis, autoimmune haemolysis.
Background: Splenic dysfunction (SD) in SCD occurs due to one of two ‘diametrically opposed’ anatomical manifestations: splenomegaly or autosplenectomy. Literature on SD-associated hyperhaemolysis is predominated by splenomegaly, acute splenic sequestration crisis (ASSC) and chronic hypersplenism (CH). However, autosplenectomy predisposes to haemolytic erythrocytopathic infections (HECI) and autoimmune haemolysis (AIH). This narrative review highlighted the aetiopathogenesis, management, and prevention of hyperhaemolysis due to both splenomegaly and autosplenectomy in SCD.
Method: Online literature search using terms relevant to splenomegaly, autosplenectomy, and hyperhaemolysis in SCD. Only articles that examined aetiopathogenesis, management, and/or prevention of hyperhaemolysis due to SD vis-à-vis sequestration, hypersplenism, immune-suppression, infections, and autoimmunity in SCD were selected.
Findings: Literature search revealed three major categories of SD-associated hyperhaemolysis in SCD: 1) Autosplenectomy-associated impaired immune-response, leading to HECI; 2) Autosplenectomy-associated impaired immune-tolerance, leading to AIH; 3) Splenomegaly-associated sequestration, leading to ASSC/CH.
Conclusion: Autosplenectomy and splenomegaly are anatomically mutually exclusive but concordant in hyperhaemolysis in SCD. While autosplenectomy is an ‘indirect’ cause of hyperhaemolysis (HECI/AIH), splenomegaly is a ‘direct’ cause of hyperhaemolysis (ASSC/CH). Transfusion, chemotherapy, and/or immune modulation can treat HECI, AIH, ASSC or CH. Prevention against HECI is achievable through, chemoprophylaxis and immunization. The role of hydroxyurea in ‘preventing and reversing’ autosplenectomy must be considered cautiously by physicians, because hydroxyurea may ‘inadvertently’ cause splenomegaly (ASSC/CH). Surgical splenectomy should only be considered in recurrent ASSC or severe CH, and such patients should be offered peri-operative vaccinations and post-operative chemoprophylaxis.
Sickle cell disease, splenomegaly, sequestration crisis, hypersplenism, autosplenectomy, infection induced haemolysis, autoimmune haemolysis.
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