ISSN 2398-2969      

Thrombocytopenia

icanis

Introduction

  • Thrombocytopenia is a clinical sign and NOT a diagnosis - investigation is directed at identifying underlying cause.
  • Causes: artifact, decreased production, increased destruction or increased consumption or sequestration of platelets. Thrombocytopenia can be inherited or acquired.
  • Signs: may be no clinical signs or signs of bleeding.
  • Diagnosis: hematology with film examination.
  • Treatment: depends on cause.
  • Prognosis: depends on cause.
    Print off the owner factsheet Thrombocytopenia (decreased platelet count) to give to your client.

Pathogenesis

Etiology

Inherited thrombocytopenia 

  • Macrothrombocytopenia: this has been documented in several dog breeds including the Cavalier King Charles Spaniel Cavalier King Charles Spaniel, Norfolk Norfolk Terrier and Cairn Terriers Cairn Terrier. Usually associated with a mutation of B1 tubulin and results in decreased numbers of large platelets. Affected dogs are usually asymptomatic despite platelet counts ranging from 30 x 109/L to 150 x 109/L. 
  • Breed-associated thrombocytopenia: Greyhounds Greyhound often have lower platelet counts than other breeds although the cause of this is unknown. 
  • Cyclic hematopoiesis Cyclic hematopoiesis of Grey Collies: autosomal recessive condition in grey collies leading to cyclical neutropenia and thrombocytopenia. A high mortality rate is associated with this condition. 

Acquired thrombocytopenia 

  • Artifact. 
  • Common due to platelet clumping. 
  • Patients are asymptomatic.

Decreased platelet production

Increased platelet destruction/clearance

  • Immune-mediated thrombocytopenia (IMTP) Immune-mediated thrombocytopenia can be primary, or secondary to infectious diseases or neoplasia: 
    • IMTP is usually associated with severe thrombocytopenia (<30 x109/L). 
    • Increased incidence in certain breeds including the Cocker Spaniel Cocker Spaniel may suggest a genetic link.
    • Secondary to infections with Ehrlichia, Anaplasma, Borrelia, Babesia, Leishmania and Distemper.

Increased platelet loss or consumption

  • Disseminated intravascular coagulopathy (DIC) Disseminated intravascular coagulation.
  • Acute severe hemorrhage (theoretical cause of thrombocytopenia unlikely in practice).
  • Snake envenomation.

Platelet sequestration 

Predisposing factors

General

Pathophysiology

  • Platelets produced by megakaryocytes in the marrow.
  • Megakaryopoiesis takes 4 weeks and circulating platelets have a lifespan of 6 days under normal circumstances.
  • Suppression of platelet precursors in marrow → drop in number of platelets released to circulation.
  • Short lifespan of platelets means that thrombocytopenia may be seen before other cytopenias in marrow disease.
  • In DIC generalized intravascular coagulation consumes platelets.
  • Immune mediated destruction of platelets can be primary or secondary:
    • Primary → production of antibodies against platelets.
    • Secondary → platelets destroyed due to cross reaction of antibodies against other things, eg drugs.
  • Low platelet counts may cause spontaneous bleeding.

Timecourse

  • May be chronic before clinical signs recognized.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Simpson K, Chapman P & Klag A (2018) Long-term outcome of primary immune-mediated thrombocytopenia in dogs. J Small Anim Pract 59, 674-680 PubMed
  • Schwartz D, Sharkey L, Armstrong P J, Knudson C, Kelley J (2014) Platelet volume and plateletcrit in dogs with presumed primary immune-mediated thrombocytopenia. J Vet Intern Med 28(5),1575-1579 PubMed
  • Botsch Vet al (2009) Retrospective study of 871 dogs with thrombocytopenia. Vet Rec 164 (12), 647-651 PubMed.
  • Jans H E, Armstrong P J & Price G S (1990) Therapy of Immune Mediated Thrombocytopenia. J Vet Intern Med 4, 4-7 PubMed

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