Chapter 67 - Thrombocytopenia

Question 1

What is the hormone responsible for platelet production? Where is it produced? How is it regulated?

Answer 1

• Thrombopoietin, synthesized by the liver at a basal rate
• Concentration in circulation regulated by its binding and uptake by platelets.
• Decrease in platelet numbers: less thrombopoietin can be bound, greater concentration of free hormone in the blood => stimulate megakaryocyte activity in the bone marrow.

Question 2

Can petechiae be seen with both thrombocytopenia and thrombocytopathia?
What is the mechanism?

Answer 2

• Mostly thrombocytopenia (whereas ecchymoses (bruising) occurs with both).
• Platelets release throphogens responsible for keeping the endothelial cell junctions tight. Low platelet numbers: less tightness => extravasation of red blood cells can occur. This does not seem to happen with platelet dysfunction (thrombocytopathia).
• In the brain, endothelial tight junctions do not depend on trophogens: brain bleed without trauma is rare even with severe thrombocytopenia

Question 3

What are the 4 breeds that are more frequently seen with idiopathic ITP? Sex predisposition ?

Answer 3

Breeds:

• Cocker Spaniel,
• Old English Sheepdogs (Bobtail),
• German Shepherds
• Poodles

Female dogs are more likely.

Question 4

What are the 4 breeds that are more frequently seen with idiopathic ITP? Sex predisposition ?

Answer 4

• female dogs,
• Cocker Spaniel,
• Old English Sheepdogs (Bobtail),
• German Shepherds
• Poodles

Question 5

Is immune-mediated thrombocytopenia common in cats?

Answer 5

No.

Question 6

Causes of secondary ITP?

Answer 6

Causes of secondary ITP:

• neoplasia,
• numerous drugs, toxins,
• infectious agents: Tick-borne diseases (Rocky Mountain spotted fever, ehrlichiosis, babesiosis, anaplasmosis), leishmaniasis, leptospirosis, Bartonella, heartworm disease, and viral diseases (e.g. feline leukemia virus feline infectious peritonitis, feline immunodeficiency virus)
• inflammatory conditions,
• possibly vaccines

Question 7

What are the different platelet transfusion products? What is their storage lifespan and in vivo efficacy ? (from Textbook + Silverstein)

Answer 7

• Platelet-rich plasma (PRP)
• Platelet concentrates (PC)
  For PRP and PC: half-life = less than 5 days with continuous gentle agitation at room temperature. One unit/10kg of dog = maximum platelet increase by 40x10^9/L.
• Cryopreserved platelets in dimethylsulfoxide (DMSO): 6 months at −20 °C, but much lower activity than fresh PC (2.5 units of cryopreserved PCs needed for same platelet increment as with 1 unit of fresh PC)
• Lyophilized platelet products: stored at 4° C for up to 12 months, in vivo: minutes (indication: arresting active hemorrhage rather than preventing future hemorrhage or raising platelet count)
• Whole blood: 10 ml/kg of FWB = maximum platelet increase of 10x10^9/L