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Haematology > Sickle Cell Disease > Flashcards

Sickle Cell Disease Flashcards

1
Q

What is sickle cell disease.

A

Autosomal recessive genetic disease due to haemoglobin chain mutation.

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2
Q

What are the characterisitcs of sickle cell disease.

A

Abnormal haemoglobin (HbS) has a tendency to become rigid and sickle, causing occlusion of small vessels.

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3
Q

What can occlusion of small vessels in sickle cell disease lead to.

A

Sickle cell crisis.

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4
Q

What can a sickle cell crisis be precipitated by. (5)

A 
Infection. 
Dehydration. 
Hypoxia. 
Acidosis. 
Cold.
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5
Q

What are the clinical systems most affected by sickle cell disease. (6)

A 
Ocular. 
Pulmonary. 
Renal. 
Musculoskeletal. 
CNS. 
Cardiac.
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6
Q

What investigations should be carried out to diagnose sickle cell disease. (2)

A

Blood film.

Hb electrophoresis.

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7
Q

What kind of treatment is used for sickle cell disease.

A

Treatment is supportive.

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8
Q

What is involved in the supportive treatment of sickle cell disease. (3)

A

When needed:
Aggressive analgesia.
Antibiotics.
Fluids.

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9
Q

What are the complications of sickle cell disease. (10)

A 
Gallstones. 
Leg ulcers. 
Avascular necrosis of the femoral head. 
Pulmonary hypertension. 
Splenic infarction (in children). 
Poor growth. 
Retinal disease. 
Iron overload. 
Lung damage. 
Chronic renal disease.
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10
Q

What is the mutation involved in sickle cell disease.

A

A single glutamic acid to valine substitution at position 6 of the beta globin polypeptide chain

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11
Q

What do sickle cell homozygotes produce.

A

They only produce the abnormal beta chains that make HbS.

This results in the clinical syndrome of sickle cell disease.

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12
Q

What do sickle cell heterozygotes produce.

A

They produce a mixture of normal and abnormal beta chains that make both normal HbA and HbS.
This results in the clinically asymptomatic sickle cell trait.

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13
Q

What is the heterozygote frequency of sickle cell in tropical Africa.

A

20%.

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14
Q

What ethnic minority has the largest rate of sickle cell trait.

A

Black American population - at 8%.

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15
Q

What is sickle cell trait protective against.

A

It is protective against the lethal effects of falciparum malaria in early childhood.
You are not granted a greater resistance against malaria if you are a homozygote for sickle cells.

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16
Q

What gives HbS its characteristic ‘sickle’ shape.

A

When HbS is deoxygenated, the molecules of Hb polymerise to form pseudocrystalline structures known as ‘tactoids’.
These distort the RBC membrane.

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17
Q

What are the ocular clinical features of sickle cell disease. (3)

A

Background retinopathy.
Proliferative retinopathy.
Vitreous bleeds.

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18
Q

What are the pulmonary features of sickle cell disease. (3)

A

Sickle chest syndrome.
Infection.
Pulmonary hypertension.

19
Q

What are the cardiac features of sickle cell disease. (3)

A

Sickle myocardium.
Cardiomegaly.
Transfusional iron overload (eg splenic infarction).

20
Q

What are the CNS features of sickle cell disease. (2)

A

Subarachnoid bleed.

Fits.

21
Q

What are the renal features of sickle cell disease. (4)

A

Enuresis.
Haematuria.
Papillary necrosis.
Chronic renal failure.

22
Q

What are the musculoskeletal features of sickle cell disease. (6)

A 
Osteomyeitis. 
Dactylitis. 
Arthropathy. 
Vertebral collapse. 
Osteoporosis. 
Avascular necrosis of the femoral head.
23
Q

What other features are there of sickle cell disease. (4)

A

Leg ulcerations.
Priapism.
Hepatic sequestration.
Choleslithiasis.

24
Q

What is seen on the blood film of a patient with sickle cell disease. (2)

A

Sickle cells.

Nucleated red cells.

25
Q

What is the cause behind the sickle cell crises that can occur.

A

Irreversibly sickled cells have a shortened survival and plug vessels in the microcirculation.
This plugging results in a number of acute syndromes, leading to chronic organ damage.

26
Q

What is the most common form of sickle cell crisis.

A

Painful vaso-occlusive crisis.

27
Q

What usually accompanies the bone pain of a vaso-occlusive crisis. (3)

A

A systemic response with sweating, fever and tachycardia.

28
Q

What is significant about a sickle chest syndrome.

A

It may follow a vaso-occlusive crisis.

It is the most common cause of death in adult sickle cell disease.

29
Q

What is sickle chest syndrome.

A

Bone marrow infarction results in fat emboli to the lungs, which cause further sickling and infarction, leading to ventilatory failure if left untreated.

30
Q

What is involved in a painful vaso-occlusive crisis.

A

Plugging of small vessels in the bone produces acute severe bone pain.

31
Q

What is the most common symptom of a vaso-occlusive crisis in children.

A

Dactylitis.

32
Q

What is a sequestation crisis. (3)

A

Thrombosis of the venous outflow from an organ causes loss of function and acute painful enlargement.
In children, the spleen is the most common site.
In adults, the liver may undergo sequestration.

33
Q

What is an aplastic crisis.

A

Infection with human parovovirus B19 results in a severe but self-limiting red cell aplasia.
It produces a very low Hb, which may cause heart failure.
The reticulocyte count is low in this crisis.

34
Q

What are the types of sickle cell crisis. (4)

A

Painful vaso-occlusive crisis.
Sickle chest syndrome.
Sequestration crisis.
Aplastic crisis.

35
Q

What is the definitive investigation to diagnose sickle cell disease.

A

Electrophoresis to demonstrate the absence of HbA, HbF and the predominance of HbS.

36
Q

What is the treatment for sickle cell disease. (3)

A

All patients with sickle cell disease should receive prophylaxis with daily folic acid and penicillin V to protect against pneumococcal infection.
Hydroxycarbamide if frequent crises.
Treatment is otherwise supportive when needed.

37
Q

How are vaso-occlusive crises managed. (5)

A 
Aggressive rehydration. 
Oxygen therapy. 
Adequate analgesia. 
Antibiotics. 
If transfusions are necessary, they should be fully genotyped wherever possible.
38
Q

How many hospitlal admissions can a patient with relatively severe sickle cell disease,

A

Around 3 a year from painful vaso-occlusive crisis.

39
Q

In what percentage of patents with sickle cell disease is pulmonary hypertension also present.

A

30-40%.

40
Q

What do sickle cell homozygotes have.

A

Sickle cell anaemia.

41
Q

What do sickle cell heterozygotes have.

A

Sickle cell trait.

42
Q

What is the prevalence of sickle cell disease.

A

1 in 700 people of African heritage.

43
Q

What is the limitation of the sickle solubility test.

A

It does not distinguish between HbS and HbAS.

44
Q

What tests should be carried out in a patient with sickle cell. (4)

A

Blood film.
FBC.
Sickle solubility test.
Hb electrophoresis.

Haematology (17 decks)

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