Sickle Cell Anemia
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Sickle cell anaemia is a hematological disorder caused by a single amino acid substitution in the beta globin chain, resulting in abnormal hemoglobin S. Homozygotes (SS) have only HbS and experience sickle cell disease, while heterozygotes (AS) have a mixture of HbA and HbS and are asymptomatic carriers. Clinical features include painful vaso-occlusive crises involving bones and organs due to sickled red blood cells blocking small vessels. Management focuses on prevention, treatment of crises, blood transfusions, and increasing fetal hemoglobin levels to inhibit HbS polymerization.
Sickle Cell Anemia
- 1. Sickle cell anaemia Dr Nikhil Bansal J.N.M.C.,Wardha
- 2. Introduction :- It is a haematological disorder which results due to the inheritance of an autosomal recessive trait. It results due to a single glutamic acid to valine substitution at the position 6 of the beta globin polypeptide chain.
- 3. Homozygotes (termed SS) produce only abnormal beta chains that make only haemoglobin S (HbS). This gives rise to sickle cell anaemia. Heterozygotes (termed AS) produce a mixture of normal and abnormal beta chains making HbA and HbS both. This gives rise to the clinically asymptomatic sickle trait.
- 4. Inheritance pattern :- AS AS AA AS AS SS (Normal) (Sickle cell disease) (Sickle cell trait) Possible genotype of the offspring of parents with the sickle cell trait
- 5. Epidemoilogy:- This disease is profound in the mainly central Africa, Madagascar, south-eastern coastal areas of India , the European nations along the Mediterranean coast like Italy, Spain, Portugal ,Arab nations like Oman, Saudi Arabia .
- 6. Pathogenesis :- The main role in pathogenesis is played by the HbS. Deoxygenation of HbS leads to formation of pseudocrystalline structures called ”TACTOIDS” These tactoids distort the red cell membrane,thus forming sickle shaped cells.
- 7. Now ,if reoxygenation occurs, this polymerisation is reversible. BUT,the distortion which has already occurred may become irreversible. This leads to the formation of “IRREVERSIBLY SICKLED” red cells. More the amount of HbS, more easily occurs the formation of TACTOIDS.
- 8. Influence of other abnormal haemoglobins on sickle cell polymerisation:- HbC participates more readily HbA participates but less readily HbF strongly inhibits the process
- 9. Clinical features :- Hypoxia Acidosis Dehydration Infection Plugging of blood vessels leading to “CRISES”
- 10. The “CRISES”
- 11. 1)Vaso – occlusive crisis :- Plugging of small vessels in the bone Severe bone pain Damage to areas producing bone marrow Tachycardia ,sweating and fever The most common crisis
- 12. 2)Sickle chest syndrome :- Follows on from a vaso–occlusive crisis Bone marrow infarction Fat emboli in lungs Further infarction Ventilatory failure DEATH
- 13. 3)Sequestration crisis :- Thrombosis of veinous outflow Massive splenic enlargement Hepatic sequestration with pain Circulatory collapse DEATH
- 14. 4)Aplastic crisis :- Adult sickle cell anaemia case Infection with parvovirus B19 Red cell aplasia (self limiting but severe) Very low Hb count Heart failure
- 15. Investigations :- Hb count as low as 6-8 g/dl Blood film Reticulocyte count Detection of the presence of HbS by exposing the RBC’s to sodium dithionite. Hb electrophoresis (definitive diagnosis)
- 16. Management :- Prophylaxis with daily folic acid, penicillin V for protection against pneumococcal infection. Vaccination against pneumococcus, haemophilus & hepatitis B. Vaso-occlusive crisis – aggressive rehydration, oxygen therapy, analgesics & antibiotics.
- 17. Sequestration & aplastic crises – transfusion of fully genotyped blood. Exchange transfusion of HbS with HbA. Administration of agents which induce increased synthesis of HbF viz hydroxycarbamide thus inhibiting polymerisation of HbS.