SN2
SHORT NOTE
5M
★ High-yield
Define Sickle Cell Disease. Describe its clinical features, investigations, management and types.
Definition
- Sickle cell disease is an autosomal recessive haemoglobinopathy caused by a point mutation (glutamate → valine at position 6 of the beta-globin chain) producing haemoglobin S (HbS).
- Under low-oxygen conditions HbS polymerises, deforming red cells into a rigid sickle shape → vaso-occlusion and chronic haemolysis.
Clinical Features
- Vaso-occlusive (painful) crises — bone/abdominal pain; dactylitis (painful hand-foot swelling) is often the first sign in infants.
- Acute chest syndrome, stroke, priapism.
- Splenic sequestration and aplastic crisis (parvovirus B19).
- Functional asplenia → susceptibility to encapsulated-organism infection; chronic haemolytic anaemia, jaundice and gallstones.
Investigations
- Sickling test (positive); haemoglobin HPLC/electrophoresis shows HbS (diagnostic).
- Blood film — sickle cells, target cells, Howell-Jolly bodies (hyposplenism).
Management
- Crisis — hydration, analgesia, oxygen, and treatment of any precipitant/infection.
- Preventive — penicillin prophylaxis and vaccination (pneumococcus etc.), folic acid, and hydroxyurea (raises HbF, reduces crises).
- Transfusion for severe complications; stem-cell transplant is curative in selected cases.
Types of Crises
| Crisis | Features |
|---|---|
| Vaso-occlusive | Pain (bones, abdomen), dactylitis |
| Sequestration | Sudden splenic pooling → shock, anaemia |
| Aplastic | Parvovirus B19 → marrow shutdown |
| Haemolytic | Increased haemolysis, worsening anaemia |
Prognosis
Prognosis has improved greatly with early diagnosis, penicillin prophylaxis, vaccination and hydroxyurea; complications such as stroke and acute chest syndrome remain important causes of morbidity and mortality.
Precipitants of Crisis
- Infection, dehydration, hypoxia, cold exposure, acidosis and physical/emotional stress.
- Avoiding these — plus good hydration, prompt infection treatment and vaccination — reduces crises.
Genotypes
- HbSS (sickle cell anaemia) — homozygous, most severe.
- HbSC disease and HbS/β-thalassaemia — variable severity.
- Sickle cell trait (HbAS) — asymptomatic carrier (protective against malaria).
Newborn Screening & Diagnosis
Early diagnosis (newborn screening/HPLC) allows penicillin prophylaxis and pneumococcal vaccination from infancy, which markedly reduce early mortality from overwhelming sepsis (functional asplenia).
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