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Year 3 > Sickle cell disease (CH) > Flashcards

Sickle cell disease (CH) Flashcards

1
Q

Define sickle cell anaemia.

A

Caused by an autosomal recessive single gene defect in the beta chain of haemoglobin, resulting in the production of sickle cell haemoglobin (HbS)

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2
Q

What specific mutation happens in sickle cell anaemia?

A

Valine (non-polar) replaces glutamic acid (polar) at the 6th amino acid of the beta globin chain

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3
Q

How does the amino acid change in HbS explain the symptoms that occur in sickle cell anaemia?

A

Valine can fit into the hydrophobic pocket of another HbS molecule –> haemoglobin polymerises within the RBC –> long stiff fragile fibres of Hb tetramers

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4
Q

What is sickle cell trait vs sickle cell anaemia?

A
  • sickle cell trait - HbS is inherited from one parent and normal HbA from the other
  • sickle cell anaemia - sickle gene inherited from each parent
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5
Q

What are the different haemoglobins in normal vs sickle cell trait vs sickle cell anaemia?

A
  • normal: HbAA
  • carrier (sickle cell trait): HbAS
  • sickle cell anaemia: HbSS
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6
Q

What % of black people carry the sickle cell gene?

A

8%

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7
Q

When does sickle cell anaemia typically present?

A

Presents after 6 months of age as the production of HbF decreases and HbS levels increase

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8
Q

What is the typical presentation of sickle cell anaemia?

A

Hand-foot syndrome = swelling, pain (crying baby), erythema in hands and feet

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9
Q

In which regions of the world is there positive selection for the sickle cell gene mutation?

A

Endemic regions for malaria as sickle cell trait/disease offers a protective effect against malaria

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10
Q

What are RBCs containing HbS like?

A

Rigid and distorted into a crescent shape

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11
Q

What can sickle cells cause?

A

Can cause occlusion of small vessels or adhere to vascular endothelium –> reduced blood flow and hypoxia –> more sickling and occlusion

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12
Q

What are sickle cells prone to?

A

Haemolysis - reduced RBC survival (around 20 days)

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13
Q

How do sickle cells cause anaemia?

A

Obstructs blood flow + breaks down prematurely –> anaemia

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14
Q

What factors precipitate sickling (sickle cell anaemia)? (7)

A

HADICSS

  • hypoxia (HbAS sickle at pO2 2.5-4kPa, HbSS at pO2 5-6kPa)
  • acidosis
  • dehydration
  • infection
  • cold temperatures
  • strenuous exercise
  • stress
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15
Q

What are the clinical features of sickle cell anaemia? (10)

A
  • bone pain / persistent pain in bones, chest, abdomen
  • dactylitis (painful dorsa of hands and feet)
  • anaemia Sx - tiredness, SOB, pallor
  • high temperature
  • pneumonia-like syndrome (sickling in pulmonary vessels)
  • tachypnoea
  • tachycardia
  • jaundice
  • splenomegaly in early disease (atrophy in late disease)
  • visual floaters (sickling and occlusion of small retinal arterioles –> neovascularisation, cotton wool spots)
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16
Q

Are sickle cell carriers symptomatic?

A

Only if severely hypoxic

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17
Q

What crises are there in sickle cell anaemia? (4)

A
  • vaso-occlusive crisis (persistent pain in skeleton, chest or abdomen)
  • splenic sequestration (splenomegaly)
  • acute chest syndrome (most dangerous)
  • gallstones, chronic cholecystitis
18
Q

Why do vaso-occlusive crises (causing persistent pain in skeleton, chest or abdomen) occur in sickle cell anaemia?

A

Sickle cells are fragile and haemolyse, which block small blood vessels and cause infarction

19
Q

Why does splenic sequestration (–> splenomegaly) occur in sickle cell anaemia?

A

Sickle cells block blood vessels leading out of the spleen –> pooling of blood in the spleen (splenomegaly and low blood count) –> undergoes phagocytosis –> functional hyposplenism causing reduced immune function (increased risk of infections)

20
Q

What is acute chest syndrome (sickle cell crisis)?

A
  • pain, fever and respiratory symptoms e.g. dyspnoea, wheeze and cough
  • caused by pulmonary infiltrates which can be seen on CXR
21
Q

How do we manage acute chest syndrome (sickle cell anaemia)?

A

Attack On (A) Titan

  • Analgesia
  • Oxygen
  • Antibiotics
  • Transfusion
22
Q

How do we manage gallstones and chronic cholecystitis due to sickle cell anaemia?

A

Cholecystectomy

23
Q

What is the main risk factor for sickle cell anaemia?

A

Genetic - 25% chance of SCA if both parents are carriers

24
Q

Which presentation of sickle cell anaemia can be diagnosed clinically?

A

Acute painful vaso-occlusive crisis

25
Q

What is the gold-standard investigation for sickle cell anaemia?

A

Haemoglobin electrophoresis

26
Q

What would haemoglobin electrophoresis show in sickle cell anaemia? (3)

A
  • HbS
  • no HbA
  • raised HbF
27
Q

What would a blood film show in sickle cell anaemia? (4+2)

A
  • sickle cells
  • nucleated RBCs
  • anisocytosis
  • features of hyposplenism: Howell-Jolly bodies, target cells
28
Q

What would FBC show in sickle cell anaemia?

A
  • anaemia - haemolytic
  • elevated reticulocyte count in haemolytic (sequestration) crises
    • may be low in aplastic crises (parvovirus B19)
29
Q

What are sequestration crises characterised by? (2)

A
  • high reticulocytes (haemolytic anaemia)
  • splenomegaly
30
Q

Why would you request an iron study in sickle cell anaemia?

A

To distinguish haemolytic anaemia from IDA

31
Q

What does cellular acetate electrophoresis show in sickle cell anaemia vs sickle cell trait?

A
  • sickle cell anaemia: 75-95% HbS, absent HbA
  • sickle cell trait: 40% HbS, 60% HbA, <2% HbF
32
Q

What are some differential diagnoses for sickle cell anaemia? (10)

A
  • gout - can be seen in those with SCD
  • septic arthritis
  • connective tissue diseases
  • avascular necrosis - hip/shoulder, differentiated from vaso-occlusive crisis by chronicity
  • Perthe’s disease
  • acute abdomen
  • osteomyelitis
  • trauma
  • Parvovirus B19
  • IDA
33
Q

How do we manage an acute vaso-occlusive crisis (sickle cell anaemia)? (5)

A

F*ck Attack On (A) Titan:

  • Fluids
  • Analgesia (paracetamol, weak opioids +/- antihistamine if pruritus)
  • Oxygen
  • Antibiotics - if infection suspected
  • Transfusion - if Hb low (<20)
34
Q

What can we do if sickle cell crisis does not resolve, or if patient presents with stroke?

A

Exchange therapy - reduces sickle cells and increases normal cells

35
Q

How do we manage chronic sickle cell anaemia?

A
  • hydroxycarbamide / hydroxyurea - increases HbF which reduces frequency and duration of crises
  • repeated blood transfusions - maintain HbS<30%
  • infection prophylaxis (regular vaccinations) - particularly against encapsulated bacteria e.g. Pneumococcus due to hyposplenism
36
Q

What vaccine should patients with sickle cell anaemia receive?

A

Pneumococcal polysaccharide vaccine every 5 years

37
Q

What do we do for repeated splenic sequestration crises in sickle cell anaemia?

A

Splenectomy

38
Q

How do we manage acute chest syndrome (sickle cell anaemia)? (4)

A

Attack On (A) Titan:

  • Analgesia
  • Oxygen
  • Antibiotics
  • Transfusion
39
Q

What are some complications of sickle cell anaemia? (8)

A
  • aplastic crises
  • anaemia
  • liver complications and cholelithiasis
  • avascular necrosis
  • dactylitis
  • leg ulcers
  • cardiovascular manifestations
  • priapism (prolonged erection)
40
Q

What are aplastic crises (sickle cell anaemia)?

A

Aplastic crises due to infection with parvovirus B19 which can lead to temporary cessation of erythropoiesis –> sudden drop in Hb and reduced reticulocytes

41
Q

What is the median survival for sickle cell anaemia?

A

58 years

Year 3 (208 decks)

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