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MCD Haematology > Sickle cell anaemia > Flashcards

Sickle cell anaemia Flashcards

1
Q

What ethnicities are most affected by sickle cell anaemia?

A

10% of Caribbeans carry the sickle gene

25% of Africans carry

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2
Q

What does sickle cell match the distribution of?

A

Malaria

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3
Q

What is the beta s?

A

Point mutation at codon 6 of the gene for beta globin

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4
Q

What is sickle haemoglobin like compared to normal haemoglobin?

A

Sickle haemoglobin has two normal alpha chains and two variant beta chains

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5
Q

What is the difference in the beta chains compared to normal?

A

Glutamic acid is replaced by valine at position 6

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6
Q

What are the differences in character between glutamic acid and valine?

A

Glutamic acid- Polar and soluble

Valine- Non polar and insoluble

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7
Q

What effect do the characteristics of valine have on the haemoglobin?

A

The deoxyhaemoglobin is insoluble

HbS polymerises to form fibres called tactoids

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8
Q

What are the three stages in sickling of red cells?

A

Distortion- polymerisation
Dehydration
Increased adherence to vascular endothelium
(Also changes in red cell membrane)

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9
Q

What are the three typical characteristics of sickle cells?

A

Rigid
Adherent
Dehydrated

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10
Q

What accounts for the increased transit time of red blood cells which leads to the increased sickling?

A

The cells are more adherent so stick to vessel wall and increases transit time hence allows more time for the polymerisation to occur

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11
Q

What is the definition of sickle cell disease?

A

Generic term that encompasses sickle anaemia and all other conditions that can lead to a disease syndrome due to sickling

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12
Q

What is the most common and severe sickle cell disorder?

A

Sickle cell anaemia - homozygous SS

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13
Q

What happens when a red cell distorts?

A

It is removed from the body

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14
Q

What is the lifespan of a sickle cell?

A

20 days

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15
Q

The decreased lifespan leads to increased haemolysis, what are the effects of this?

A 
Anaemia- partly due to a reduced erythropoietic drive as haemoglobin S has a low affinity for oxygen so is more effective
Gallstones- increased bilirubin
Aplastic crisis (parvovirus B19)
Blockage of microvascular circulation
Tissue damage and necrosis
Pain
Dysfunction
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16
Q

What is parvovirus B19?

A

Common respiratory virus

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17
Q

Why does parvovirus B19 cause an aplastic crisis in sickle cell anaemia?

A

It infects the developing red cells in the bone marrow and block production, it isn’t a problem normally because erythrocytes last 120 days so it’ll just switch it off for a few days whilst the infection lasts but sickle cells have a shorter lifespan so it can cause severe anaemia

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18
Q

How do you treat gallstones?

A

Cholecystectomy

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19
Q

What is a genetic modifier that increases the incidence of gallstones in people with hereditary haemolytic anaemia?

A

Coinheritance of Gilbert’s syndrome- reduced activity of UGT (uridine glucuronyl transferase)

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20
Q

What are the majority of individuals with Gilbert’s homozygous for?

A

Variant in the promoter of the gene within the TATA block- normally has six TA repeats but in Gilbert’s, homozygous for variant allele that has an extra TA dinucleotide on each chromosome

21
Q

What is the effect of this different TATA block?

A

Increased risk of having gallstones 3-5 fold

22
Q

What is one of the first organs to be affected by tissue infarction?

A

Spleen

23
Q

What does damage to/loss of splenic function predispose individuals to?

A

Life-threatening infection from capsulated bacteria (mainly pneumococcal)

24
Q

What is the most common site of tissue infarction in terms of clinical presentation?

A

Bones and joints

25
Q

How do the bones and jones characteristically present?

A

Dactylitis- inflammation of a finger or toe caused by bone infection- painful

26
Q

In terms of bones and joints, what can chronic ischaemic damage lead to over time?

A

Avascular necrosis

Osteomyelitis

27
Q

What is avascular necrosis?

A

Death of bone tissue due to lack of blood supply

28
Q

What is osteomyelitis?

A

Inflammation of bone due to infection

29
Q

Where else is a common site that is affected by tissue infarction?

A

Skin- causing chronic ulcers

30
Q

What is the commonest cause of death in adults with sickle cell disease?

A

Acute chest syndrome

31
Q

What is acute chest syndrome?

A

Vaso-occlusive crisis of the pulmonary vasculature

32
Q

What are the long term effects of tissue infarction on lungs?

A

Pulmonary hypertension

Chronic sickle cell lung disease

33
Q

What effect does tissue infarction have on urinary tract?

A

Haematuria
Impaired concentration of urine
Renal failure
Priapism

34
Q

What is priapism?

A

Persistent and usually painful erection of penis that requires urgent decompression

35
Q

What effect does tissue infarction have on the brain?

A

Stroke

Cognitive impairment

36
Q

What effect does tissue infarction have on the eyes?

A

Proliferative retinopathy

37
Q

What correlates with how severe pulmonary hypertension is?

A

Severity of haemolysis

38
Q

How is pulmonary hypertension caused by tissue infarction?

A

Free plasma haemoglobin from intravascular haemolysis scavenges nitric oxide and depletes it, this takes away the vasodilatory effect hence causing vasoconstriction of certain vascular beds

39
Q

What percentage of patients with sickle cell disease are affected by strokes?

A

8%

40
Q

When does sickle cell disease present?

A

Symptoms are rare before 3-6 months when you get a switch to adult haemoglobin

41
Q

What are the early manifestations of sickle cell disease?

A

Dactylitis
Splenic sequestration- pooling of blood in spleen
Infection (pneumococcal)

42
Q

What triggers painful crises in sickle cell disease?

A 
Infection 
Exertion
Dehydration
Hypoxia 
Psychological stress
43
Q

What are the median survival ages for females and males with SCD?

A

Female- 48

Male- 42

44
Q

What is the general management of SCD?

A

Folic acid supplementation- high RBC production
Penicillin- reduce risk of pneumococcal infection
Vaccination- protect due to hyposplenism
Monitor spleen size- sequestration can cause death
Blood transfusion for acute anaemic events, acute chest syndrome and stroke
Pregnancy care
Painful crisis management- pain relief, hydration, keep warm, oxygen if hypoxic
Exchange transfusions
Haematopoietic stem cell transplantation- good in young
Induction to HbF- hydroxyurea

45
Q

What are the laboratory features of sickle cell disease?

A 
Hb low (6-8g/dL)
Reticulocytes high (except aplastic crisis)
Blood film:
Sickle cells
Boat cells
Target cells
Howell-Jolly bodies
46
Q

How can you diagnose sickle cell disease?

A

Solubility test

Electrophoresis/high performance liquid chromatography

47
Q

What is the solubility test?

A

In presence of reducing agent, oxyhemoglobin can be converted to deoxyhaemoglobin and solubility decreases
In presence of deoxyhaemoglobin S the solution becomes turbid instead

48
Q

What does the solubility test not differentiate between?

A

AS and SS

49
Q

What is someone with sickle cell trait like?

A

Normal life expectancy
Normal blood count
Usually symptomatic
Rarely painless haematuria

MCD Haematology (11 decks)

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