Sickle Cell Disease Flashcards
What is sickle cell disease?
https://www.youtube.com/watch?v=1ql-X60CUNQ
Sickle-cell disease (SCD) is a group of blood disorders typically inherited from a person’s parents. The most common type is known as sickle-cell anaemia (SCA). It results in an abnormality in the oxygen-carrying protein haemoglobin (haemoglobin S) found in red blood cells. This leads to a rigid, sickle-like shape under certain circumstances
What is the pathophysiology of SCD?
Sickle cell haemoglobin (HbS) results from a single-base mutation of adenine to thymine, producing a substitution of valine for glutamic acid at the sixth codon of the β-globin chain. Deoxygenated HbS molecules are insoluble and polymerize. This process is initially reversible but, with repeated sickling, the cells eventually lose their membrane flexibility and become irreversibly sickled. Cells are fragile and prone to haemolysis, and cause small vessel occlusion
Which ethnicity is SCD most common in?
Those of african decent
Why does the disease not normally manifest until 6 months of age?
As the synthesis of HbF is normal, the disease usually does not manifest itself until the HbF decreases to adult levels at about 6 months of age
What does SC trait protect against?
Malaria
When can vaso-occlusive crises occur in those with SC trait?
Any hypoxic situations
- Unpressurised aircraft
- Anaesthesia
What gene is involved in SCD?
HbS gene
Why is the chronic haemolysis normally well tolerated by those with SC anaemia?
HbS releases its oxygen to the tissues more easily than does normal Hb, and patients therefore feel well despite being anaemic (except of course during crises or complications).
What are features of SCD?
- Jaundice
- Gallstones
- Mild anaemia
- Crisis syndromes - Bone, Chest, Stroke, Spleen, Liver
What is a vaso-occlusive crisis?
Vaso-occlusion of the small vessels. It often affects the marrow of bone
What can trigger vaso-occlusive crises?
- Cold
- Dehydration
- Hypoxia
- Infection
What is the most common site of pain for vaso-occlusive crises in children?
Hands and feet - dactylitis
Why might someone with SC anaemia present with an acute abdomen?
Mesenteric Ischaemia
Why can strokes, seizures or cognitive defects occur in those with sickle cell anaemia?
CNS ischaemia
How might someone with a sickle cell chest crisis present?
- SOB
- Wheeze
- Cough
- Chest Pain
- Fever
- Worsening hypoxia
Why might someone with SCD be at increased risk of infection?
Due to hyposplenism
Organs which are prone to vaso-occlusion are also prone to specific infection
What long-term complications can occur in SCD?
- Splenic infarction
- Poor growth
- Chronic renal failure
- Gallstones
- Retinal disease
- Pulmonary fibrosis and hypertension
- Avascular necrosis
- Leg ulcers
- Priapism
- Spontaneous abortion
- Cardiac problems
When are sequestration crises most likely to occur?
Childhood - splenic infarction has not occured at this point
What is the cause of aplastic crisis in Sickle Cell anaemia?
Parvovirus B19
What is acute chest crisis caused by?
- Infection
- Fat embolism - from necrotic bone marrow
- Pulmonary infarction - due to sequestration of sickle cells
What are the primary causes of acute chest crisis?
Fat embolism from infarcted bone marrow, or infection from chlamydia, mycoplasma or viruses
How would you test a child for suspected sickle cell disease?
- Bloods - FBC, U+E’s, LFTs, reticulocytes, serum bilirubin
- Coombs test
- Blood film
- Hb electrophoresis
- Sickle solubility test
- Genetic study - parents
What does a positive sickle solubility test not indicate?
Whether someone is homozygote or heterozygote
How would you manage sickle cell anaemia as a chronic disease?
- Hydroxycarbamide
- Prophylactic immunisation
- Folic acid
Why is hydroxycarbamide used to treat SCD?
Raises the conc of fetal Hb. This results in reduction in the episodes of pain, the acute chest syndrome, and the need for blood transfusions
Why is folic acid used to treat SCD?
Used in patients with severe anaemia
How would you manage and acute sickle cell crisis?
- IV opiates
- Rehydrate
- Consider O2 - if hypoxic/sats < 95%
- Antibiotics - if temp >38oC
- Give transfusion - if Hb or retic count fall dramatically
What are indications for an exchange transfusion?
- Severe chest crisis
- Suspecte CNS event
- Multiorgan failure
How would you manage an acute chest crisis?
- O2
- Analgesia
- Antibiotics
- Bronchodilators - those who are wheezy
- Consider ITU - if PaO2 <9.2 kPa
What is the average life expectancy of someone with Sickle Cell disease?
- Males - 42 yrs
- Females - 48 yrs
If someone had SCD, what would there reticulocyte count be?
Increased by 10-20%
What range does the Hb of someone with SCD normally sit in?
60-90 g/L
What might you see when looking at serum bilirubin in someone with SCD?
Increased bilirubin
What organisms does splenic atrophy increase the risk of being infected by?
- Pneumococcus
- Salmonella species
- Haemophilus
What are the most commonly affected sites of Avascular necrosis in adults?
- Ribs
- Spine
- Pelvis
