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YR3: Haematology > Sickle Cell Disease > Flashcards

Sickle Cell Disease Flashcards

1
Q

What is Sickle Cell Anaemia?

A

Homozygosity for HbS

HbSS

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2
Q

What is Sickle Cell Disease?

A

Group of chronic conditions with sickling of RBCs caused by inheritance of haemoglobin S (HbS)

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3
Q

What is the genotype in Sickle Cell trait? How does this present?

A

HbAS

Asymptomatic except in conditions that favour sickling (hypoxia, dehydration)

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4
Q

What causes sickling of red blood cells?

A

Point mutation in B globin gene (Valine subs glutamic acid on position 6= non-polar so insoluble).
Results in formation of abnormal haemoglobin S

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5
Q

Describe the pathophysiology of sickling cells

A

HbS polymerises when deoxygenated, causing sickling of RBCs
Sickling makes RBC’s more fragile + inflexible
Triggered by any event associated with reduced O2 tension

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6
Q

Why are inflexible sickled cells pathological?

A

Lack elasticity + adhere to vascular endothelium

This disrupts microcirculation, causes vascular occlusion + subsequent tissue infarction.

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7
Q

List 4 triggers precipitating sickling of RBCs

A

Infection
Hypoxia
Acidosis
Dehydration

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8
Q

Describe the epidemiology of Sickle Cell disease

A

1 in 2000 births

African, Afro-Caribbean, Asian or Mediterranean

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9
Q

What deficiency may arise in sickle cell disease? Why? What is done to restore this?

A

Folate deficiency
Haemolysis + subsequent increased turnover of RBCs increases demand for folate
Give Folic Acid: If severe haemolysis or in pregnancy

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10
Q

Why is sickle cell disease more common in non UK populations?

A

Sickle cell trait confers resistance to Malaria, thus carrying HbS has a survival advantage

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11
Q

When do symptoms of sickle cell disease start to present?

A

Coincides with switch from HbF to HbA synthesis

~3-6 months

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12
Q

What are sickled red blood cells prone to?

A 
Sequestration + destruction, leading to decreased RBC survival (20 days)
through Extravascular (Spleen) + intravascular haemolysis
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13
Q

What are the acute manifestations of sickle cell anaemia?

A

Haemolytic crises
Infection
Vaso-occlusive events

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14
Q

What 2 acute haemolytic crises can occur in sickle cell disease?

A

Splenic sequestration crisis

Aplastic crisis

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15
Q

What is a splenic sequestration crisis?

A

Occlusion of blood flow out of spleen
Causes pooling of RBCs in spleen + splenomegaly
Results in anaemia + hypovolaemic shock

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16
Q

List 4 features of a splenic sequestration crisis

A

Acute LUQ pain
Anemia
Reticulocytosis
Intravascular volume depletion: hypotension

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17
Q

What 5 infections are those with sickle cell disease particularly susceptible to?

A 
Pneumococcus
Meningococcus
Haemophilus Influenza
Osteomyelitis: Salmonella, Staph aureus 
Sepsis: Strep. pneumoniae
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18
Q

What causes Aplastic Crises?

A

Infection by Parvovirus B19
infects developing red cells in BM + arrests maturation
With such reduced lifespan of RBC’s in SCD, results in dramatic fall in Hb

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19
Q

Why are people with sickle cell disease more susceptible to infection?

A

Recurrent crises causes atrophy or infarction of the spleen

Increases risk of infection with encapsulated organisms

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20
Q

List 5 vaso-occlusive crises in sickle cell disease

A 
Acute chest syndrome 
Priapism 
Stroke (common in children) 
Infarctions of nearly any organ (esp. spleen)
Avascular necrosis
21
Q

What are Vaso-occlusive crises ?

A

Ischaemia caused by obstruction of microcirculation by sickled RBCs

22
Q

List 6 symptoms of vaso-occlusive crises

A 
Swollen painful joints + bones
Abdo pain
Visual loss (proliferative retinopathy)
Loin pain
Neuro signs e.g. Hemiplegia (Stroke)
Tachypnoea
23
Q

Which bones are commonly affected in adults and children by vaso-occlusion?

A

Adults: Ribs, Spine, Pelvis, Long bones
Children: Small bones of hand= Dactylitis

24
Q

What symptom may indicate sequestration crises?

A

LUQ pain

25
Q

Give 2 signs of sequestration crises on examination

A

Splenomegaly

Hypotension

26
Q

Give 3 chronic features of sickle cell anaemia

A

Haemolytic anaemia: fatigue, weakness, pallor
Pain
Cholelithiasis (pigmented stones)

27
Q

What may provoke vaso-occlusive crises?

A

Cold
Infection
Exertion
Dehydration

28
Q

List 4 signs of vaso-occlusion and infarction

A

Joint or muscle tenderness or swelling (due to avascular necrosis)
Short digits: due to infarction in small bones of the hands
Retina: cotton wool spots due to retinal ischaemia
Jaundice (haemolysis)

29
Q

What causes priapism in sickle cell anaemia?

A

Microvascular occlusion of the penis so blood can’t leave, it remains painful + erected for a long time

30
Q

What characterises Acute Chest syndrome? What causes ACS?

A

New pulmonary infiltrate on CXR with:
fever, cough, chest pain, tachypnoea.
Vaso-occlusive crisis of the pulmonary vasculature

31
Q

What investigations are performed in sickle cell disease?

A

Bloods: Anaemia
Blood smear
Sickle solubility test
Haemoglobin electrophoresis / HPLC

32
Q

What other investigations may be used in sickle cell disease? Why?

A

MRI or CT Head: neuro complications
X-rays: identify avascular necrosis
Bacterial cultures: to confirm infection
CXR: if resp Sx

33
Q

What is seen on a blood smear in sickle cell anaemia?

A

Sickle cells: crescent-shaped RBCs
Target cells
Howell-Jolly bodies
Reticulocytosis

34
Q

What is a sickle solubility test?

A

Dithionate added to blood smear

SCD: increased turbidity (no difference between SCA or trait so need to do HPLC to confirm)

35
Q

What sign may be seen on skull x-ray in sickle cell anaemia?

A

“Hair on end”

36
Q

Which investigation gives a definitive diagnosis of sickle cell disease?

A

Hb Electrophoresis
Shows HbS
Absence of HbA (if homozygous HbS)
High HbF

37
Q

How does reticulocyte count vary in sickle cell disease?

A

HIGH: in splenic sequestration crises
LOW: in aplastic crises

38
Q

List 3 prophylactic measures used in management of sickle cell anaemia

A

Pneumococcal vaccines
Meningococcal vaccines
Daily penicillin

39
Q

Give 2 indications for treatment in sickle cell anaemia with hyroxyurea

A

Frequent, acute painful episodes or other vaso-occlusive events
Severe symptomatic anaemia

40
Q

Describe the mechanism of action of hydroxyurea in sickle cell anaemia. What adverse side effect may result from treatment with hydroxyurea?

A 
Stimulates erythropoiesis + increases HbF
HbS is proportionally reduced 
RBC polymerisation decreases
Fewer vaso-occlusive episodes
SE: Myelosuppression
41
Q

What is used to prevent repeated admission due to septicaemia in febrile children?

A

Ceftriaxone

42
Q

What drug can be used if patients are intolerant/ refractory to hydroxyurea?

A

L-glutamine

43
Q

What treatment may be used in severe anaemia?

A

Red cell transfusion

44
Q

When may an exchange transfusion be necessary in sickle cell patients?

A

Severe crises
Pre-op
Pregnancy

45
Q

What advice is given to sickle cell patients?

A

Avoid precipitating factors
Good hygiene + nutrition
Genetic counselling
Prenatal screening

46
Q

What surgical treatment may be used in some patients?

A

BM transplant

Joint replacement for avascular necrosis

47
Q

Describe the management of acute painful crises

A

Oxygen
IV fluids
Strong analgesia (IV opiates)
Abx

48
Q

List 9 complications of sickle cell anaemia

A 
Cardiovascular manifestations
Cholelithiasis
Liver complications e.g. hepatomegaly, jaundice
Leg ulcers 
Lung damage 
Poor growth in children
Chronic renal failure 
Retinal disease 
Iron overload from repeated transfusion
49
Q

What is the prognosis for those with sickle cell disease

A

Most survive to ~50 with good care

Major mortality results from pulmonary, neuro or infectious complications

YR3: Haematology (19 decks)

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