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Haematology BL > Platelet disorders - BB > Flashcards

Platelet disorders - BB Flashcards

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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

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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

Study These Flashcards
A

Schistocytes - RBC fragments from shearing (haemolytic anaemia)

21
Q

Clinical Presentations of TTP:

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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:

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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?

Study These Flashcards
A

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

24
Q

Treatment of TTP:

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A

Plasma exchange - removes antibodies

Platelet counts monitored to determine efficacy

25
Difference between lab findings in TTP and DIC?
In TTP - PT/PTT should be normal In DIC - PT/PTT are raised because clotting factors are consumed
26
HUS clinical features
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
What is associated with HUS:
Following GI infection with E.Coli 0157:H7 | - Shiga-like toxin causes microthrombi
28
DIC - how does it happen
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
What processes cause DIC (secondary)
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
What do rattlesnake bites contain
Thrombin-like glycoproteins - within Venum cause diffuse activation of clotting
31
Presentation of DIC:
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
Lab findings in DIC:
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
Treatment for DIC:
1 - Treat underlying cause 2. FFP (fresh frozen plasma) - to replace clotting factors 3. RBCs, platelets replace 4. Cryoprecipitate - for low fibrinogen
34
Summary of 4 thrombocytopenias - all 4 letters (table)
35
Uremia as a cause of platelet dysfunciton:
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
Causes of Thrombocytopenia:
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
Measures of thrombocytopenia:
Normal platelet count: 150,000/ml to 400,000/ml Bleeding occurs when platelet count is: <10,000/ml
38
Treatment for thrombocytopenia:
Platelet transfusion Most commonly occurs during chemotherapy
39
Von Willebrand Disease: Overview and genetics
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
Clinical features of Von Willebrand Disease
Usually mild, non-life-threatening bleeding - - Easy Bruising - - Skin bleeding - - Prolonged bleeding from mucosal surfaces - - Severe nosebleeds - - Menorrhagia
41
Diagnosis of Von Willebrand Disease:
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
Ristocetin cofactor activity assay
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
Treatment of Von Willebrand Disease
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
Heyde's Syndrome
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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