Equis ISSN 2398-2977

Thrombocytopenia: overview

Contributor(s): Ruth Morgan, Han van der Kolk

Introduction

  • Thrombocytes (or platelets) are produced from megakaryocytes of bone marrow and have a normal life span of 3-5 days. Thrombocytopenia is defined as a platelet count of <100 g/l.
  • Platelet counts in horses are slightly less than in other species.
  • Horses under the age of 3 have higher normal platelet counts.
  • Cause: decreased production, increased use. Usually occurs as a result of another underlying disease.
  • Signs: hemorrhage due to thrombocytopenia takes the form of petechiation or ecchymoses of mucous membranes, although severe bleeding episodes can occur.
  • Diagnosis: platelet count in peripheral blood, supported by a confirmatory blood smear.
  • Treatment: treat underlying disease. Corticosteroids, azathioprine and vincristine.
  • Prognosis: depends on successful treatment of the underlying disease process.

Pathogenesis

Etiology

  • Decreased production of thrombocytes.
  • Increased peripheral destruction of thrombocytes.
  • Increased consumption of thrombocytes due to the dysregulation of the coagulation process.

Decreased platelet production

Increased platelet production

Increased platelet use

Pathophysiology

  • The major physiologic activities of the thrombocyte are associated with hemostasis.
  • Hemorrhage only occurs when the platelet count falls <30,000/ul.
  • Hemorrhage due to thrombocytopenia takes the form of petechiation or ecchymoses of mucous membranes, although severe bleeding episodes can occur.
  • As thrombocytes adhere to a damaged vessel wall active substances like histamines, serotonin and some major components of the factor VIII complex are released.
  • The mechanism for blood coagulation consists of an intrinsic, as well as an extrinsic system. The intrinsic system consists of factors essential for clot formation like VIII, IX, XI, and XII.
  • The activated partial thromboplastin time (APTT) detects disorders in the intrinsic system. If the APTT is abnormal, it can be assumed that there is a disorder involving a deficiency of one of the factors mentioned before.
  • Disseminated intravascular coagulation   Disseminated intravascular coagulation  (DIC) is characterized by both hypercoagulation and increased fibrinolytic activity and is always secondary to a primary disease process. DIC is usually accompanied by thrombocytopenia.
  • Since only a few normal thrombocytes are required for clotting, clotting time is usually normal in thrombocytopenia.

Timecourse

  • Usually an acute onset.

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.
  • Boudreaux M D & Humphries D M (2013) Identification of potential platelet alloantigens in the Equidae family by comparison of gene sequences encoding major platelet membrane glycoproteins. Vet Clin Pathol 42, 437-442 PubMed.
  • Cian F et al (2013) Leukemic small cell lymphoma or chronic lymphocytic leukemia in a horse. Vet Clin Pathol 42 (3), 301-306 PubMed.
  • Dunkel B (2013) Platelet transfusion in thrombocytopenic horses. Equine Vet Educ 25, 359-362 VetMedResource.
  • Pusterla N & Madigan J E (2013) Equine granulocytic anaplasmosis. J Equine Vet Sci 33, 493-496 VetMedResource.
  • Langdon Fielding C et al (2011) Rattlesnake envenomation in horses: 58 cases (1992-2009). JAVMA 238, 631-635 PubMed.
  • Hardefeldt L Y, Schambow R & Peek S F (2010) Successful treatment of presumptive immune mediated thrombocytopenia and dermatitis with azathioprine in a pregnant mare. Equine Vet Educ 22 (10), 495-500 VetMedResource.
  • Perkins G A et al (2005) Ulcerative dermatitis, thrombocytopenia, and neutropenia in neonatal foals. J Vet Intern Med 19 (2), 211-216 PubMed.
  • Fey K & Sasse H H L (1998) Relapsing immune-mediated thrombocytopenia of unknown origin in a stallion. Equine Vet Educ 10, 127-132 VetMedResource.
  • Sellon D C (1998) Thrombocytopenia in horses. Equine Vet Educ 10, 133-139 VetMedResource.
  • Sellon D C, Levine J, Millikin E et al (1996) Thrombocytopenia in horses: 35 cases (1989-1994). J Vet Intern Med 10 (3), 127-132 PubMed.
  • Humber K A, Beech J, Cudd T A et al (1991) Azathioprine for treatment of immune-mediated thrombocytopenia in two horses. JAVMA 199, 591-594 PubMed.


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