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eMCD - Hae > Haematology 5 (Sickle Cell Disease) > Flashcards

Haematology 5 (Sickle Cell Disease) Flashcards

1
Q

why/how does sickle cell disease occur?

A
  • missense mutation at codon 6 (of gene for beta globe chain)
  • Glu replaced by Val
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2
Q

describe the stages in the process of sickling of RBCs

A
  1. Distortion
    - initially = reversible polymerization w oxyHbS formation
  2. Dehydration
  3. increased adherence to vascular endothelium.
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3
Q

the reduction in life span of rbc leads to :

A

increased hemolysis

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4
Q

what are the 3 different consequences of hemolysis?

A
  1. anaemia
  2. gallstones
  3. aplastic crisis
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5
Q

Why does anaemia occur in hemolysis?

A
  • due to reduced erythropoietic drive
  • HbS has low affinity for O2
  • so hypoxia = doesn’t stimulate erythropoietin release as much (from kidney)
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6
Q

what are the 2 methods of pathogenesis of sickle cell disorders ?

A
  1. increased hemolysis

2. blockage of microvascular circulation (vaso-occlusion)

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7
Q

Why does gallstone occur in hemolysis?

A
  • increased hemolysis = increase Bilirubin release

- increased risk of gallstone formation

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8
Q

Why does aplastic crisis occur in hemolysis?

A
  • parvovirus B19 = respiratory virus
  • can cause aplastic crisis in people with sickle cell disease
  • infects developing RBCs in bone marrow
  • blocks production of RBC
  • with sickled cell: can lead to steep drop in hb –> anaemia
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9
Q

What are 3 possible consequences of blockage of microvascular circulation?

A
  • distorted RBCs get clumped together –> block vessels –> infarction
  • tissue damage,
  • pain,
  • dysfunction
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10
Q

Which three main organs/parts does tissue infarction affect?

A
  • Spleen
  • Bones / Joints
  • Skin
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11
Q

How does tissue infarction affect the spleen?

A
  • spleen = one of 1st affected organ
  • spleen = subject to repetitive vaso-occlusve damage from (early-life) infarction
  • -> loss of splenic function = predisposed to infection of capsulated bacteria
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12
Q

How does tissue infarction affect bones + joints?

A
  • Bone + joint = most common clinical presentation site of tissue infarction
  • presents with DACTYLITIS
  • over time –> can lead to avascular necrosis
  • -> these patients = susceptible to osteomyelitis
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13
Q

What is DACTYLITIS?

A
  • inflammation of finger or toe –> due to bone infection
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14
Q

What is avascular necrosis?

A
  • lack of blood supply –> death of bone tissue
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15
Q

What is osteomyelitis?

A
  • inflammation of the bone due to infection
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16
Q

How does Pulmonary hypertension correlate with the severity of hemolysis?

A
  • free plasma Hb –> from intravascular hemolysis
  • scavenges NO
  • causes vasoconstriction
    (associated with increased mortality)
17
Q

Clinical course _____ and _____ even within same family.

A

Clinical course VARIABLE and UNPREDICTABLE even within same family.

18
Q

Describe and give examples of early presentation of sickle cell disorders.

A
  • clinical problem = usually AFTER 3-6 months
  • onset occurs as HbF –> switches with adult Hb synthesis
  • early manifestation = dactylics, splenic sequestration, infection (S.pneumoniae)
19
Q

List Sickle emergencies:

A
  • septic shock
  • neurological signs/symptoms
  • SpO2 <92% on air
  • anaemia (symptoms) w Hb < 5
  • Priapism > 4hours
20
Q

Define Acute Chest Syndrome

A

New pulmonary infiltrate on chest X-ray with:

  • Fever
  • Cough
  • Chest Pain
  • Tachypnoea
21
Q

List laboratory features of sickle cell disease:

A

List laboratory features of sickle cell disease:

  • Hb Low (6-8g/dl)
  • Reticulocytes High (except in aplastic crisis)
  • Blood Film (sickled, boat, target cells, howell jolly bodies)
22
Q

Diagnosis: How does solubility test work?

A
  • reducing agent added
  • oxyHb —> deoxy Hb
  • Solubility decreases
  • Solution –> turbid (cloudy)
  • doesn’t differentiate AS from SS
    (AS: sickle cell trait // SS: Sickle cell anaemia)
23
Q

What is a definitive diagnosis of sickle cell disorder ?

A
  • Electrophoresis
    or
  • High Performance Liquid Chromatography (HPLC)

–> separates proteins according to charge

24
Q

Describe methods of management of painful crisis:

A

PAINFUL CRISIS MEASURES:

  • Pain relief (opioids)
  • hydration
  • keep warm
  • (if hypoxic) Oxygen
  • exclude infection (via tests)
25
Q

What 5 things is painful crises triggered by?

A
  • Infection
  • Exertion
  • Dehydration
  • Hypoxia
  • Psychological Stress
26
Q

When might exchange transfusion be used? (as management method)

A
  • stroke

- Acute chest syndrome

27
Q

under what conditions may haemopoietic stem cell transplantation be implied? (as management method)

A
  • under 16 with severe disease
28
Q

How might HbF be induced? (as management method)

A
  • Hydroxyurea

- Butyrate

29
Q

Explain the mechanism of the use of hydroxyurea for treatment of sickle cell disease?

A
  1. Increases production of HbF
  2. Decreases Sickle RBC stickiness
  3. reduces WBC production (in bone marrow)
  4. improves RBC hydration
  5. Generates NO –> improves blood flow
  • HbF inhibits HbS polymerisation
  • patients with higher HbF levels –> less complication + improved survival
  • so < 3 months SCD infants = no symptom
30
Q

What are some limitations of HSCT (hematopoietic stem cell transplantation)

A
  • donor availability = difficult
  • long length of treatment
  • transplant related mortality
  • long term (infertility, pubertal failure, organ toxicity, etc.)
31
Q

What are features of Sickle Cell “trait” ?

A
  • HbAS
  • Life expect = normal
  • blood count = normal
  • asymptomatic
  • caution: anaesthetic, high altitude, extreme exertion
32
Q

is sickle cell disease autosomal recessive or dominant?

A

recessive

33
Q

what are some lab features of SCD?

A
  • hb low
  • high reticulocytes (except in aplastic criss –> because bone marrow has shut down)

blood film shows:

  • sickled cells
  • boat cells
  • target cells
34
Q

how would you diagnose SCD ?

A
  • solubility test:

- HPLC

35
Q

how would you conduct a solubility test?

A
  • with reducing agaaent oxyhb is converted to deoxy hb
  • solubility decrease
  • solution becomes turbid
  • AA: translucent
    AS : opaque
    but doesn’t differnctate different AS forms
36
Q

describe main methods of managing SCD

A
  • ensure patient has adequate intake of folic acid
  • vaccinated against encapsulated bacteria
  • give penicillin to work against encapsulated bacteria if infected
  • monitor spleen size
  • give blood transfusion for acute anaemic events / chest syndrome / stroke
  • give antenatal / pregnancy care
37
Q

sickle cella anemia - HbSS only

A

not HbSC

38
Q

sickle cella anemia is both HbSC and HbSS

false / true

A

false

only HbSS

eMCD - Hae (11 decks)

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