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Sickle Cell Anaemia Flashcards

1
Q

How is sickle cell anaemia inherited?

A

Autosomal recessive

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2
Q

What gene is affected in sick cell?

A

Beta-globin gene on chromosome 11

Responsible for the beta hb subunit

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3
Q

What does the HbS allele result from?

A

Single nucleic acid substitution

GAG to GTG

In the beta globin coding gene

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4
Q

What does a GAG to GTG result in?

A

Glutamic acid substitution to Valine

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5
Q

Why does sickling occur in the deoxygenated state?

A

HbS tetramers bind to each other, this leads to polymerisation

This causes growth into long fibres which distort the shape of the RBC

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6
Q

In SCD gene carriers what is the expected amount of different haemoglobins?

A

HbA 60%
HbS 40%

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7
Q

How is sickle cell related to malaria?

A

More common in patients from areas traditionally affected by malaria e.g. Africa, India, Middle East and Caribbean

Sickle cell trait reduced severity of malaria

Patients with sickle cell trait more likely to survive to pass genes on, therefore selective advantage in areas of malaria

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8
Q

What is the incidence of SCD in Black, Asian and White people?

A

Black
1/200 affected
1/10 carriers

Asian
1/6,000 affected
1/60 carriers

White
1/90,000 affected
1/600 carriers

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9
Q

How is sickle cell disease screened for?

A

New born blood spot

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10
Q

When is new born heel prick test done?

A

5 days of age

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11
Q

When are pregnant women offered sickle cell testing?

A

When they are at higher risk of being a carrier of the gene

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12
Q

Why is the burden of SCD set to increase?

A

Higher survival rates among infants

Increased HbS prevalence in high-income countries

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13
Q

What investigations are used for SCD?

A

Haemoglobin electrophoresis - detects HbA absence
Blood film
FBC and reticulocyte count
X-ray of long bones- confirm presence of bone infarctions
CXR - infiltrates

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14
Q

What are the complications of SCD?

A

Anaemia
Increased infection risk
CKD
Sickle cell crises
Acute chest syndrome
Stroke
Avascular necrosis
Pulmonary hypertension
Gallstones
Priapism

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15
Q

What joints are affected by avascular necrosis in SCD?

A

Large joints such as the hip

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16
Q

What happens in sickle cell crisis?

A

Acute exacerbation caused by SCD, range from mild to life-threatening

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17
Q

What causes a sickle cell crisis?

A

Spontaneous
Dehydration
Infection
Stress
Cold weather

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18
Q

How is sickle cell crisis managed?

A

Supportive management
- Low hospital admission threshold
- Treating infections that triggered crisis
- Keep warm
- Good hydration, may need IV fluids
- Analgesia, avoid NSAIDs in renal impairment

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19
Q

What is a vaso-occlusive crisis?

A

AKA painful crisis

Most common type of sickle cell crisis

Sickle cells clog capillaries causing distal ischaemia

20
Q

How does a vaso-occlusive crisis present?

A

Dactylitis (pain and swelling in hands or feet)

Can affect chest, back

Can be associated with fever

21
Q

What is present on examination of a patient with a vaso-occlusive crisis?

A

Pallor- anaemia
Jaundice- haemolysis
Fever
Tachycardia
Tachypnoea
Digital redness, swelling and pain - inflammation

22
Q

What are some differential diagnoses for a vaso-occlusive crisis?

A

Gout

Acute abdominal pain
- Pancreatitis
- Appendicitis
- Cholecystitis

23
Q

If a vaso-occlusive crisis lasts more than 7 days what should be considered?

A

Other causes of bone pain e.g.
Osteomyelitis
Avascular necrosis

24
Q

What usually causes vaso-occlusive crisis?

A

Strenuous exercise
Dehydration
Infection

25
Why does a vaso-occlusive crisis cause priapism?
Blood trapped in the penis, causes painful and persistent erection
26
How is priapism treated?
Urological emergency Treated by aspirating blood from penis
27
How can SCD lead to hyposplenism?
**Splenic sequestration crisis** RBCs block blood flow within spleen Causes an acute enlarged and painful spleen This can lead to splenic infarction leading to hyposplenism
28
What does blood pooling in the spleen due to splenic sequestration crisis lead to?
Severe anaemia Hypovolaemic shock
29
What infections are more likely in hyposplenism?
**Encapsulated bacteria** - Streptococcus pneumoniae - Haemophilus influenzae - Meningococcus
30
How are recurrent splenic sequestration crises prevented?
Splenectomy
31
What regular vaccinations should patients with a splenectomy receive?
- Seasonal flu vaccines - Pneumococcal vaccines - every 5 years - Meningococcal C vaccine - Haemophilus influenza B vaccine - Hepatitis B vaccine - if getting regular blood transfusions
32
What is an aplastic crisis?
Temporary absence of RBC production
33
What can trigger an aplastic crisis?
Parvovirus B19 infection
34
What does an aplastic crisis lead to?
Significant aplastic anaemia
35
How do you manage an aplastic crisis?
Supportive Blood transfusions if necessary Usually resolves within a week spontaneously
36
What is acute chest syndrome?
Vessels supplying lungs become clogged with RBCs
37
What causes acute chest syndrome?
Vaso-occlusive crisis Fat embolism Infection
38
How does acute chest syndrome present?
Fever Shortness of breath Chest pain Cough Hypoxia
39
What does a CXR show in acute chest syndrome?
Pulmonary infiltrates
40
How is acute chest syndrome managed?
Medical emergency with high mortality Supportive management and treat underlying cause - Analgesia - IV fluids - Antibiotics or antivirals for infections - Blood transfusions for anaemia - Incentive spirometry - Respiratory support, oxygen, NIV or MV
41
How is SCD managed generally?
**Specialist MDT** - Avoid triggers for crises e.g. dehydration - Up-to-date vaccinations - Antibiotic prophylaxis - Hydroxycarbamide - Crizanlizumab - Blood transfusions - Bone marrow transplant (can be curative)
42
What are blood transfusions used for prophylactically?
Maintain HbS < 30%
43
What is the typical antibiotic prophylaxis for infection?
Penicillin V
44
What does hydroxycarbamide do?
Stimulates HbF HbF does not lead to sickling of RBCs Reduces frequency of vaso-occlusive crises, improves anaemia and can extended lifespan
45
When can patients with SCD first present?
6 months old when HbF decreases
46
What is crizanlizumab?
Monoclonal antibody Targets P-selectin
47
What is P-selectin?
Adhesion molecule found on endothelial cells on the inside walls of blood vessels and platelets Prevents RBCs from sticking to blood vessel wall Reduces frequency of vaso-occlusive crises

Haematology (16 decks)

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