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Block 3 PATH Exam -- Platelet Disorders (#23)


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Breakdown of platelet distrubtion in body
2/3 circulate
1/3 are stored in the spleen
What is the lifespan of platelets?
7 - 10 days
What is epistaxis?
Nose bleed
Name 6 manifestations of PRIMARY hemostatic defects
Superficial purpura
Mucous membrane bleeding
Prolonged IMMEDIATE bleeding

"Oozy bruisy" patient
How does thromboxane effect platelet aggregation?

What is the role of NSAIDs?
Thromboxane mediates expression of Gp IIb/IIIa on platelets

NSAIDs inhibit Thromboxane formation from arachidonic acid
What is a normal platelet count (range)?
150 - 450 k
Ranges of different classifications of thrombocytopenia
(Mild, moderate, etc.)
(corresponding #s of platelets)
Mild - 80-120 k
Moderate - 50-80 k
Vigilant - 30-50 k
Worry - 20-30 k
Crisis - 10-20 k

PANIC - <10 k
Charactertistics of Wiskott-Aldrich Syndrome
X-linked inheritance

Small platelets

Assoc. w/ immunodeficiency, eczema
Characteristics of familial thrombocytopenia w/ AML
Dominant inheritance

Normal size/dysfunctional platelets

Propensity to develop AML
Amegakaryocytic thrombocytopenia w/ radio-ulnar synostosis

What are its main characteristics?
Dominant inheritance

Assoc. w/ hearing loss
Charecteristics of thrombocytopenia w/ absent radii (TAR)?
Recessive inheritance

Skeletal defect - absent radius
Characteristics of Bernard Soulier thrombocytopenia
Autosomal recessive

Large, dysfunctional platelets

Deficiency of GP 1b receptor on platelets
Characteristics of DiGeorge thrombyctopenia
Palate T-cell defect

Large platelets

Right heart problems
Characteristics of vWD 2B
Dominant inheritance

Platelet clumping on smear

Due to vWF structural defect
Benign Mediterranean Macrothrombocytopenia

What type of inheritance does it have?
Characteristics of MYH9-related thrombocytopenia
Dominant inheritance

Giant platelets
Neutrophil inclusions

+/- hearing loss, cataract, renal defect
Characteristics of Gray platelet syndrome
Dominant inheritance

Large, pale platelets

LACK of alpha granules
Characteristics of Amegakaryocytic thrombocytopenia (CAMT)
Recessive inheritance

Possible stem cell defect
Congenital thrombocytopenias w/ autosomal recessive inheritance (3)
Bernard Soulier
What is deficient/defective in Glanzmann's thrombastenia?
What two "factors" are required for Adhesion?
von Willebrand factor
Gp Ib
How do adhesion and aggregation differ in energy requirements?
Adhesion - NON-energy requiring

Aggregation - energy requiring
What drugs are assoc. w/ drug-induced thrombocytopenia (6)
Gold salts
Sulfa drugs
How are WBCs affected in ITP?
They're not
Normal number & morphology
What main change is visible in the BM of ITP?
Increased megakaryocytes
How do acute and chronic ITP compare in terms of age group of pts?
Acute - PRE-adolescent

Chronic - POST-adolescent
How do acute and chronic ITP compare in terms of sex predilection?
Acute - F:M equal

Chronic - F:M is 3:1
Which type of ITP is more often associated w/ infection?
How do acute and chronic ITP compare in terms of typical platelet counts?
Acute - < 20k

Chronic - 20-80k
How do acute and chronic ITP compare in terms of duration?
Acute - 2-6 weeks

Chronic - years
How do acute and chronic ITP compare in terms of resolution?
Acute - often resolves

Chronic - w/o treatment, resolution unusual
Above what platelet count does risk of bleeding drop below 5%?
> 10k
How do you treat ITP w/ a platelet ct < 20k?
Steroids, IVIg, anti-D

NOTE: anti-D is given to Rh- pts. who may receive Rh+ blood
How do you treat Asymptomatic ITP w/ platelet ct 20-30k?
How do you treat SYMPTOMATIC ITP w/ platelet ct 20-30k?
Treat as if platelets < 20k
How do you treat Asymptomatic ITP w/ platelet ct 30-100k?
Do nothing
How do you treat ITP w/ platelet ct 30-100k if minor bleeding?
How do you treat ITP w/ platelet ct 30-100k if major bleeding?
Treat as if platelets < 20k
When is relapse of ITP likely if treated w/ splenectomy?
In first 6 months
What are the 3 modalities of drug-induced thrombocytopenia?
Immune complex deposition (common)

Hapten "penicillin" type

Auto-sensitization of platelets
What drug is often associated w/ auto-sensitization of platelets?
Aldomet (methyldopa)
What are the major differences between HITT Type 1 and 2 (4)?
---Type 1---
Non-immune, CAN continue heparin, Occurs early, No sequelae

---Type 2---
Immune rxn, Must STOP heparin, Occurs later, DISASTER
What type of Ab is induced in HITT Type 2?

What is it targeted against?

Heparin-PF4 complex on platelets
What is the typical pentad of signs in TTP?
Low platelet count
Renal failure
Neuro deficits
Microangiopathic hemolytic anemia
(strands of fibrin acoross small vessels)
What causes congenital TTP?
Lack of ADAMSTS13 enzyme
(vWF multimers are not cut, causing clumping of platelets)
How is TTP treated?

If not treated, what is the mortality?
Plasma exchange
(remove Abs and replace ADAMSTS13)

90% fatality
What is HUS assoc. w/?
(causative factor)
E. Coli toxin
How does the renal failure in HUS compare w/ that in TTP?
It is much more pronounced in HUS
What symptoms does TTP commonly have that is not seen in HUS?
(differentiating factor?)
Neuro deficits
Mnemonic for pregnancy associated hemolysis/thrombocytopenia

Liver enzymes
Aggregation requires what two "factors" from platelets?
Presence of and ability to release granules
Ability to form Gp IIb/IIIa receptor
What is the function of the Gp IIb/IIIa receptor?
Binds fibrinogen
Thus, fibrinogen can link platelets

Required for AGGREGATION
What is the function of the Gp Ib receptor?
Binds sub-endothelial vWF
Thus, platelets can adhere to vessel wall

Required for ADHESION
Pooled platelet concentrate transfusion

How many units per donor?
Each unit is from an individual donor

SO, if 6 units, 6 donors
Pheresis unit

How many units per donor?
6-8 units come from a single donor
How long are platelets viable at room temp?
~5 days
What "normal" physiological processes can cause thrombocytosis (2)?
Peri-partum state

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