Pathology
- Normal haemoglobin has two alpha and two beta chains
- In sickle cell disease single amino acid substitution occurs on beta chain
- Valine substituted for glutamic acid at position 6
- The resulting Hb S is less soluble than Hb A
- Sickle haemoglobin gene is inherited as autosomal recessive
- Commonly seen in patients of Afro-Caribbean descent
- Sickle cell anaemia occurs in homozygotes
- Sickle cell trait occurs in heterozygotes
- When deoxygenated haemoglobin undergoes polymerisation and forms characteristic sickle cells
- Blockage of small vessels results in vaso-occlusive events
- Sickling may be precipitated by infection, fever, dehydration, cold, hypoxia
Clinical features
- Patients have chronic haemolytic anaemia with high reticulocyte counts
- At increased risk of infection by encapsulated bacteria
- Acute complications include
- Painful crises
- Worsening anaemia
- Acute chest symptoms
- Symptoms and signs of neurological or ocular events
- Priapism
- Diagnosis can be confirmed by:
- Sickle solubility test
- High performance liquid chromatography
Prevention of complications
- Patent and parent education is important
- Patients need to avoid the cold, dehydration, etc
- Antibiotic prophylaxis should be considered in children less than 5 years
- Usually phenoxymethylpenicillin is the antibiotic of choice
- Children should be vaccinated with the pneumococcal vaccine
Peri-operative precautions
- Patients at high risk of acute sickling complications under general anaesthesia
- Require careful pre and peri-operative management
- Transfusion may be required to ensure Hb of 9-10 g/dL
- Preoperative exchange transfusion is rarely required
- Need to:
- Avoid dehydration
- Avoid hypoxia
- Control intra and postoperative pain
Management of complications
- Patients with suspected complications require
- Intravenous fluids
- Adequate pain relief often with opiates
- Oxygen
- Early antibiotic therapy if suspected infection
Painful crises
- 60% of patients with sickle cell anaemia will have one episode per year
- Bony crises result from localised ischaemia
- Avascular necrosis may occur
- Treatment involves rest and analgesia
- Abdominal crises present with pain, vomiting, distension and features of peritonism
- 40% of adolescents with sickle cell anaemia will have gallstones
Anaemia
- Worsening anaemia often presents with tiredness and cardiac failure
- Results from acute splenic sequestration of aplastic crisis
- In both situations urgent transfusion may be required
Acute chest syndrome
- Presents with chest pain, cough, fever and tachypnoea
- Accompanied by clinical and radiological features of consolidation
- Chlamydia and Mycoplasma are important aetiological agents
- Require parenteral antibiotic therapy - usually erythromycin
Acute neurological events
- A stoke occurs in approximately 10% of patients before the age of 20 years
- All acute neurological symptoms require investigation
- Acute stroke requires urgent exchange transfusion
Priapism
- Occurs in about 20% of males before the age of 20 years
- If lasts for more than a few hours can result in erectile impotence
- Blood should be aspirated from corpora cavernosa
- Intra-cavernosal injection of alpha agonist (e.g. phenylephrine) may be of benefit
Bibliography
Davies S C, Oni L. Management of patients with sickle-cell disease. Br Med J
1997; 315: 656-660.
Fixler J, Styles L. Sickle-cell disease. Paediatr Clin North Am 2002;
49: 1193-1210
Serjeant G R. Sickle-cell disease. Lancet 1997; 350: 725-730.
Steinberg M H. Management of sickle cell disease. N Engl J Med 1999: 340: 1021-1030.
Vichinsky E. New therapies in sickle cell disease. Lancet 2002; 360: 629-631. |