Platelet Abnormalities

Description

Platelets (or thrombocytes) are responsible for primary haemostasis, the formation of a temporary platelet plug that initially seals any breach to a blood vessel wall. Bleeding disorders may occur if platelets are deficient (thrombocytopenia) or if the platelets are unable to function adequately (thrombocytopathia). Thrombocytopenia may be a primary disease due to disease of the bone marrow that reduces the production of platelets or it may occur secondary to another insult.

Primary Thrombocytopenic Disease

The aetiology of primary thrombocytopenic disease is often uncertain and it is therefore also known as idiopathic thrombocytopenia. Some cases of primary thrombocytopenia may occur due to autoimmune responses directed at platelets and, although the bone marrow may contain adequate normal megakaryocytes, this disease results in a reduced peripheral blood thrombocyte count. Immune-mediated thrombocytopaenia occurs most commonly in young animals.

Secondary Thrombocytopenic Disease

Secondary thrombocyopaenic disease is fairly common in adult domestic animals and it may be associated with diseases that depress the production of platelets or increase their consumption or sequestration:

• Diseases that cause bone marrow suppression
  • Aplastic anaemia caused by ingestion of bracken, administration of oestrogens or of chloramphenicol or sulphonamide antibiotics. Prolonged use of phenylbutazone or salicylate may cause the same disease.
  • Myelophthisis, the displacement of the normal tissues of the bone marrow by another cell or tissue type may also reduce the function of the megakaryocytes. Possible diseases include myelofibrosis and immunoprliferative or myeloproliferative neoplastic disease.
  • Radiotherapy or myelosuppressive chemotherapy may cause reversible bone marrow suppression.
• Diseases that cause increased destruction of platelets
• Diseases that cause sequestration of platelets usually involve some enlargement to the spleen as this is the major organ where platelets are stored outside of the circulation. Examples include:
  • Haemangiosarcoma of the spleen and liver
  • Splenic enlargement under general anaesthesia with certain agents such as barbiturates and phenothiazines

• Associated with diseases which cause [bone marrow]] depression.
• The bone marrow is depleted or devoid of megakaryocytes, and there is a nil or markedly reduced peripheral blood thrombocyte count.
• Secondary thrombocyopenic disease is seen in the following conditions:
  1. Severe viral infections.
     • For examople, ICH, feline panleucopenia, mucosal disease, swine fever.
  2. Severe protozoal infections.
     • For example, in the UK, Haemobartonella may be a cause.

• 1. Other miscellaneous causes.
     • Severe bacterial infections.
       • For example, Staphylococci, and those Gram -ve bacteria producing endotoxins (e.g. Pseudomonas or Salmonella spp.).
     • Liver disease.

Thrombocytopathia

Von Willebrands, Angiostrongylus, colloids, granule disease.

• A rare inherited condition.
• Recorded in the dog.
• Characterised by defective thrombocyte formation.
  • Poor adhesiveness.
  • Poor aggregations.
  • Poor platelet factor release.