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Sickle cell anaemia

Definition
  • 'Sickling' of red blood cells at low pO2 as a result of a defective haemoglobin beta chain (Glu-> Val)
Risk Factors
  • Hypoxia
  • Age
Differential diagnosis
  • Iron deficiency
  • Other causes of anaemia
  • Asthma / other causes of SOB
  • Drug abusers?
  • NB Pain is specific to sickle-cell anaemia
  • Spleen - painful/enlarged (splenomegaly) in sickle-cell

Epidemiology
  • Allele is more common in (West) African populations (85 % of cases)
  • Sickel cell trait:
                
  • Malaria
       
  • Due to increased RBC turnover with HbS even when heterozygous
Aetiology
  • The deoxygenated form of HbS is insoluble and polymerises
  • HbA is made faster/not degraded as fast c.f. HbS, therefore heterozygotes generally asymptomatic
Clinical features
  • Tiredness, breathlessness, lethargy, especially at low pO2 (after exercise, altitude etc)
  • Malaise, night sweats, sleeplessness
  • Splenomegaly
  • Dactylitis (esp. in infants)
  • Normocytic anaemia
  • Normal reticulocyte count
  • Ventricular hypertrophy ?
  • Developmental (delayed growth, puberty)
  • Occasional 'crises' with severe pain
    • Pain (anywhere)
Pathophysiology
  • 'Sickled' cells are inflexible and block small capillaries
  • Therefore ischaemia, necrosis
  • Necrotic tissue can be colonised by pathogens e.g. S. aureus 
  • Frequent autosplenectomy causing further problems
Investigations
  • TBC (RBC, MCH, MCHC, Reticulocytes)
    • Low MCH
    • High reticulocyte
  • Bone X-ray
  • Blood film
  • Genetic testing
  • Heel prick test for neonates
  • Hb solubility test
  • Electrophoresis / HPLC for Hb alleles
Management

a) conservative
  • Fluids, warmth, local massage
  • Avoid hypoxia
  • Education
b) medical
  • Prophylactic antibiotics vs. encapsulated bacteria (e.g. Streptococcus pneumoniae, Staphylococcus aureus)
  • Hydroxyurea to stimulate HbF production?
  • Gene therapy
  • Sub-cut. morphine for pain relief
  • Blood transfusion
  • Pre-implantation genetic diagnosis (PGD) for future children ?
c) surgical
  • Excision of ulcers
  • Bone marrow transplant
  • Hip replacement etc. to repair damaged bones / joints
Prognosis
  • Likely to worsen with age
  • Recurrent pain
  • Life-long blood transfusions
  • Mean life expectancy 60 yrs in Western countries
  • Much shorter without medical treatment
    • >50 % die before 1st birthday
    • Especially vulnerable to malaria
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