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 thrombocytopenia 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.

• 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.
  3. Plant intoxications.
     • For example, bracken, kale, or ragwort poisoning.
  4. Drug-induced conditions.
     • High doses of oestrogens and salicylate.
     • Prolonged use of phenyl butazone.
  5. bone marrow neoplasia.
     • For example, lymphosarcoma or myeloid leukaemia.
  6. Radiation.
     • May cause damage to the bone marrow if it is severe and generalised.
  7. 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.