107 Platelet Disorders

Question 1

Thrombocytopathies most commonly are

Intrinsic thrombocytopathies are ___ common than extrinsic thrombocytopathies in small animals

von Willebrand’s disease is the most common ____thrombocytopathy and is seen in many breeds, whereas most of the other intrinsic platelet disorders are breed specific

Answer 1

inherited but also may be acquired.

more common

extrinsic

Question 2

Tx:
DDAVP
plt concentrate
cryo or plasma

Answer 2

only vWD type I
intrinsic disorders
any vWD

Question 3

Extrinsic platelet disorders are characterized by:

Answer 3

lack of a functional protein needed for platelet adhesion

Question 4

vWD in dogs is caused by:
vWF is a:
MoA:

Platelets contain only a small amount of:
majority

Answer 4

deficiency or dysfunction of von Willebrand factor (vWF)
plasma protein of variably sized multimers
1. mediates platelet hemostatic function
2. as well as circulates with and stabilizes Factor VIII

small
richest source is in the endothelial cells

Question 5

in plt vWD found in:

in EC vWF found in:

Answer 5

a-granules along with

weibel palade bodies

Question 6

inheritance:

Answer 6

Type 1 autosomal dominant or recessive
type II and III autosomal recessive

no sex pred

Question 7

3 types

Answer 7

Type I is a quantitative reduction in all multimers
-common
Type II vWD reductions large multimers (most important in hemostasis)
-rare
Type III vWD absolute lack of vWF
-rare

Question 8

C/S Petechiae and ecchymoses are:

Answer 8

uncommon
I - variable
II and III bad

Question 9

BMBT
time:
variables that alter results:
prolonged result is consistent with:

Answer 9

3 minutes

skin thickness, skin temperature, age, gender, hematocrit, intrinsic thrombocytopathia or von Willebrand’s disease

Question 10

definitive diagnosis:

Answer 10

measurement of the vWF : antigen concentration

Question 11

tx 3:

Answer 11

cryoprecipitate (1 unit/10 kg body weight IV within 8 hours of thaw)
1 unit equates to cryoprecipitate from 200 ml fresh frozen plasma

Desmopressin acetate (deamino 8-d-arginine vasopressin, DDAVP) 
-stimulate endothelial V2 receptors to release intracellular stores of vWF
ONLY Type 1 vWD patients have some response to DDAVP. Types II and III have little to no response to DDAVP

Question 12

Intrinsic platelet disorders are those:

Answer 12

inherent to platelet

Question 13

Chediak-Higashi syndrome (CHS):
inheritance:
species/breed:
MoA:
tx:

Answer 13

auto. recessive disease
prolonged bleeding times w normal platelet #
humans and cats
-intrinsic platelet storage pool deficiency
-altered lysosomal granule formation and abnormal degranulation in neutrophils and platelets
-platelet dense granules lacking in this disease

= aggregation response to collagen is absent

platelet concentrates has been shown to correct abnormal oral mucosal bleeding times

Question 14

Glanzmann's thrombasthenia:
inheritance:
species/breed:
MoA:
tx:

Answer 14

humans and dogs
Otterhounds and Great Pyrenees
deficiency in αIIbβ3 integrin
CS secondary to lack of fibrinogen binding to αIIbβ3

bone marrow transplantation and gene therapy
perioperative platelet-rich plasma

Question 15

clot retraction assay can be used as a screening tool in:

how do you do it?:

Answer 15

patients w normal RBC and plt #
retraction is impaired by:
thrombocytopathia
abnormalities in fibrinogen
some coagulation defects

5 ml of whole blood into a sterile glass tube (without any anticoagulant)

• wooden applicator is inserted into the tube and blood
• tube then is sealed with plastic paraffin film before incubation at 37° C
• assessment of clot formation and clot retraction is noted over 8 to 24 hours
• within 2 to 4 hours a normal clot retracts markedly
• results are recorded as complete clot retraction (retraction occurred and serum was found surrounding the clot) or failed clot retraction (no serum was found surrounding the clot)

Question 16

Greater Swiss Mountain Dog:

Answer 16

P2Y12 receptor
bled excessively after an ovariohysterectomy
lack of a functional P2Y12 receptor prevents activation via ADP-induced outside-in signaling for fibrinogen binding on the platelet surface at the αIIbβ3 integrin

important because of the growing use of clopidogrel as an antithrombotic agent. Clopidogrel blocks ADP from binding at the P2Y12 receptor, reducing platelet activation

Question 17

Canine Scott syndrome (CSS)
MoA:
Dx:
Tx:

Answer 17

German Shepherd Dogs
autosomal recessive
inability for phosphatidylserine to be externalized for the creation of a procoagulant surface
-also have a decreased microparticle release

Dx: flow cytometry because typical coagulation testing and point-of-care analysis with the Platelet Function Analyzer-100 or thromboelastography did not show a difference between platelet function of affected and nonaffected dogs

Spontaneous hemorrhage CANNOT be prevented by treatment

however, perioperative cryopreserved platelet-rich plasma transfusions plus a postoperative antifibrinolytic agent has been used with success

Question 18

Idiopathic asymptomatic macrothrombocytopenia in Cavalier King Charles Spaniels (CKCS)

Answer 18

inherited autosomal recessive platelet defect
mutation in β1-tubulin likely leads to altered proplatelet formation in megakaryocytes

Norfolk Terriers
CKCS have not been found to have any clinical bleeding or any abnormalities on platelet aggregation testing

Question 19

Aquire plt dysfunction:

acquired vWD

Answer 19

hypothyroidism

hydroxyethyl starch and dextran solutions also have been implicated in acquired vWD

Question 20

Drugs

Answer 20

aspirin, ticlopidine, clopidogrel, as well as some antibiotics and nonsteroidal antiinflammatory drugs

Question 21

Uremic:

Answer 21

defects in platelet adhesion, secretion, and aggregation

• defects in vWF function (probably receptor binding) are thought to play a major role
• normal to increased vWF levels, but platelet function can be improved in the uremic patient by transfusion of cryoprecipitate or administration of DDAVP
• > nitric oxide and prostacyclin that can alter vascular tone and platelet function
• some of the uremic toxins are believed to act as direct platelet inhibitors by competing for receptor binding