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Haematology BL > Platelet disorders - BB > Flashcards

Platelet disorders - BB Flashcards

1
Q

3 inherited platelet disorders:

A
  1. Glanzmann thrombasthenia
    - Deficiency in IIB/IIIA
  2. Bernard-Soulier
    - Deficiency in IB
  3. Wiscott-Aldrich
    - Immunodeficiency
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2
Q

Glanzmann’s Thrombasthenia: - genetics

A

Autosomal recessive disorder

Functional deficiency of GPIIb/IIIa receptors on platelets - that allow for platelet aggregation

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3
Q

Glanzmann thrombasthenia - Findings:

A

Causes bleeding - often epistaxis or menorrhagia

Diagnostic findings:
- Prolonged bleeding time

  • Blood smear (e.g. epistaxis) - isolated platelets (no clumping)
    - – Absent platelet aggregation in response to stimuli
  • Abnormal Platelet aggregometry - platelets mixed with ristocetin, ADP, Arachadonic Acid (stimulants that should cause platelet aggregation)
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4
Q

Platelet aggregometry

A

Assessing platelet aggregation in response to stimuli

Platelets mixed with:

    • ristocetin
    • ADP
    • Arachidonic acid

(abnormal e.g. in glanzmann’s)

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5
Q

Bernard-Soulier Syndrome: Genetics:

A

Autosomal recessive disorder

Causing deficiency of GPIb platelet receptors

Results in large platelets

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6
Q

What do GPIb platelet receptors do

A

On platelets

Bind to vWF that has bound to damaged endothelium (subendothelial collagen)

Platelet adhesion

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7
Q

Key lab findings of bernard-soulier syndrome:

A

Presents with - Bleeding - often epistaxis or menorrhagia

Lab findings:

  • Prolonged bleeding time
  • Thrombocytopenia
  • Large platelets on peripheral blood smear
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8
Q

Giant platelets:

A

Seen in association with thrombocytopenia

Caused by rare inherited disorders such as Bernard-Soulier and otheres

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9
Q

Wiskott-Aldrich Syndrome

A

Immunodeficiency syndrome in infants

X-Linked disorder of the WAS Gene (WAS protein)
- Which is necessary for T-Cell cytoskeleton maintenance

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10
Q

Wiskott-Aldrich Syndrome - Triad:

A
  1. Immune dysfunction
  2. Decreased Platelets
  3. Eczema
    * Unuasual triad of symptoms
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11
Q

ITP:

A

Idiopathic Thrombocytopenic Purpura

  • Disorder of decreased platelet survival
  • Commonly caused by anti-GPIIb/IIIa antibodies
  • Platelet consumption by splenic macrophages
      • Resulting in splenomegaly
    • -> Thrombocytopenia (platelet deficiency)
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12
Q

ITP - Diagnosis and treatment:

A

Diagnosis of exclusion - rule out causes of bone marrow suppression to figure out why they are pooling in spleen

Treatment:
1- Steriods
2- IVIG - (pooled immunoglobulins from donors)
- Blocks Fc receptors in splenic macrophages
3- Splenectomy

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13
Q

TTP

A

Thrombotic Thrombocytopenia Purpura

The underlying cause is – decreased activity of ADAMTS13 (which is vWF cleaving protease)

Disorder of small vessel thrombus formation - that consumes platelets -> causing thrombocytopenia

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14
Q

vWF multimer formation:

A

Synthesised as monomer

Monomers link to endoplasmic reticulum –> forms dimers

vWF dimers more to Golgi –> where they form multimers

(stored in weibel-palade bodies/ alpha-granules as multimers)

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15
Q

ADAMTS13:

A

Enzyme (metalloprotease)

Breaks down/ cleaves vWF multimers

Prevents thrombotic occlusion of vessels

(deficient in TTP)

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16
Q

TTP Cause:

A
  • Severe ADAMTS13 deficiency (<10% normal)
  • Due commonly to: acquired autoantibody to ADAMTS13

Results in vWF multimers in areas of high shear stress (small vessels)
— Causing obstruction of small vessels

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17
Q

Type of anaemia that occurs when small vessels are obstructed (such as in TTP)

A

MAHA - Microangiopathic haemolytic anaemia

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18
Q

MAHA

A

Microangiopathic Haemolytic Anaemia

  • Haemolytic anaemia (raised LDH / lowered haptoglobin)
  • Caused by shearing of RBCs as they pass through thrombi in small vessels
  • Finding on blood smear - schistocytes

Seen in:

  • TTP
  • HUS
  • DIC
19
Q

MAHA is seen in which conditions

20
Q

What is the finding on blood smears in MAHA

A

Schistocytes - RBC fragments from shearing (haemolytic anaemia)

21
Q

Clinical Presentations of TTP:

A
  1. Fever - due to inflammation from small vessel occlusion and tissue damage
  2. Neurological symptoms - Headache, confusion, seizures
  3. Renal failure - occlusions of small vessels in kidney
  4. Petechiae + bleeding —– From low level of platelets
    * Symptoms not specific so rely on lab results
22
Q

TTP lab findings:

A

Blood results show:

  • – Haemolytic anaemia (MAHA)
  • – Thrombocytopenia (reduced platelets)
  • – Schistocytes on blood smear (MAHA)

PT/PTT - should be normal

Possible elevated D-dimer

23
Q

Why are PT/PTT findings normal in a patient with TTP?

A

Thrombi in TTP mostly contain platelets and therefore do not consume clotting factors

24
Q

Treatment of TTP:

A

Plasma exchange - removes antibodies

Platelet counts monitored to determine efficacy

25
Q

Difference between lab findings in TTP and DIC?

A

In TTP - PT/PTT should be normal

In DIC - PT/PTT are raised because clotting factors are consumed

26
Q

HUS clinical features

A

Haemolytic uraemic syndrome - commonly seen in children

Many similarities to TTP
- Usually no fever or CNS symptoms

Clinical features are:

  • MAHA
  • Thrombocytopenia
  • AKI
    - – Renal thrombi cause kidney injury - have uraemic syndrome
27
Q

What is associated with HUS:

A

Following GI infection with E.Coli 0157:H7

- Shiga-like toxin causes microthrombi

28
Q

DIC - how does it happen

A

Disseminated Intravascular Coagulation - occurs secondary to another process

  • Widespread activation of the clotting cascade
  • Many diffuse thrombi (with platelets + fibrin) - causing ishcaemia
  • Causes the consumption of clotting factors and platelets
  • Causes destruction of RBCs - MAHA (haemolytic anaemia)
29
Q

What processes cause DIC (secondary)

A

DIC is always secondary to another process

  1. Obstetric emergencies - amniotic fluid contains Tissue Factor
    - - DIC occurs in conjunction with amniotic fluid embolism
    - - Examples include:
    - abruption of the placenta
    - Major haemorrhage (post-partum)
  2. Sepsis - Many bacteria contain endotoxin, which activated the clotting cascade
    - - High levels of cytokines in infection can also trigger DIC
  3. Leukemia - Especially… Acute Promyelocytic Leukemia (APML)
  4. Rattlesnake bites - contains thrombin-like glycoproteins
    - - Causes diffuse activation of clotting cascade
30
Q

What do rattlesnake bites contain

A

Thrombin-like glycoproteins - within Venum cause diffuse activation of clotting

31
Q

Presentation of DIC:

A

Often presents as bleeding in addition to the setting of the primary illness

Diagnosis then made in the lab

Every haemostasis blood test will be abnormal in DIC

32
Q

Lab findings in DIC:

A
  1. Elevated PT/PTT/ Thrombin time (because of consumption of clotting factors)
  2. Low platelets (consumption of platelets)
  3. Low fibrinogen (consumption)
  4. All signs of MAHA (anaemia)
    • Low RBC (anaemia)
    • Schistocytes on blood smear
  5. Elevated D-Dimer - (breakdown of diffuse thrombi_
33
Q

Treatment for DIC:

A

1 - Treat underlying cause

  1. FFP (fresh frozen plasma) - to replace clotting factors
  2. RBCs, platelets replace
  3. Cryoprecipitate - for low fibrinogen
34
Q

Summary of 4 thrombocytopenias - all 4 letters (table)

35
Q

Uremia as a cause of platelet dysfunciton:

A

Significant renal dysfunction can lead to bleeding (platelet dysfunciton)
- Poor aggregation and adhesion of platelets

Caused by uremic toxins in the plasma:
- Uraemic Platelets still work fine in healthy serum

Lab findings:

  • Prolonged bleeding time (initial reason for measuring was to see if uraemic patients were fit for surgery)
  • Normal platelet count
  • Normal coagulation testing
36
Q

Causes of Thrombocytopenia:

A
  1. Decreased Production of platelets:
    • Chemotherapy, leukemia
    • Sepsis (bone marrow supression)
  2. Platelet Sequestration
    a- Splenomegaly
    b- portal hypertension
  3. Platelet destruction
    a. ITP
    b. TTP
37
Q

Measures of thrombocytopenia:

A

Normal platelet count: 150,000/ml to 400,000/ml

Bleeding occurs when platelet count is: <10,000/ml

38
Q

Treatment for thrombocytopenia:

A

Platelet transfusion

Most commonly occurs during chemotherapy

39
Q

Von Willebrand Disease: Overview and genetics

A

Most common inherited bleeding disorder - affects up to 1% of population

Many gene mutations - most commonly:
- autosomal dominant (males and females equally)

Mutations cause low level or dysfunction in vWF

40
Q

Clinical features of Von Willebrand Disease

A

Usually mild, non-life-threatening bleeding

    • Easy Bruising
    • Skin bleeding
    • Prolonged bleeding from mucosal surfaces
        • Severe nosebleeds
        • Menorrhagia
41
Q

Diagnosis of Von Willebrand Disease:

A

Normal platelet count

Normal PT

Increased PTT (if severe) - if very low factor VIII will also fall
     - Doesnt cause severe bleeding like in haemophelia (no joint/ deep tissue bleeding)

Increased Bleeding time

Ristocetin cofactor activity assay - to measure vWF activity levels

42
Q

Ristocetin cofactor activity assay

A

Used to diagnose Von Willebrand Disease - measures vWF activity

Ristocetin - antibiotic that is off market due to decrease in platelets

  - - Binds to vWF and platelet GPIb
  - - Causes platelet aggregation if vWF present
  - - No platelet aggregation means vWF is defective
43
Q

Treatment of Von Willebrand Disease

A
  1. vWF concentrate
  2. Desmopressin - increases vWF and factor VIII levels
    - - Also used in haemophelia A
  3. Aminocaproic acid - Antifibrinolytic drug
    - - Inhibits plasminogen activation to plasmin - this less breakdown of clots
44
Q

Heyde’s Syndrome

A

Rare condition

GI bleeding associated with aortic stenosis

Due to:

  1. increased angiodysplasia in AS
    - - Angiodysplasia is vascular malformations in GI tract makes them more prone to bleeding
  2. Deficiency of vWF
    - - High shearing forces caused by AF leads to uncoiling of vWF multimers
    - - Uncoiling exposes cleavage site for ADAMST13 - therefore overactive cleavage reducing the efficiency of vWF

*Improves after aortic valve surgery

Haematology BL (14 decks)

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