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===Primary Thrombocytopenic Disease===
===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 - Anatomy & Physiology|bone marrow]] may contain adequate normal megakaryocytes, this disease results in a reduced peripheral blood thrombocyte count. [[Immune Mediated Thrombocytopenia|Immune-mediated thrombocytopenia]] occurs most commonly in young animals.
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 - Anatomy & Physiology|bone marrow]] may contain adequate normal megakaryocytes, this disease results in a reduced peripheral blood thrombocyte count. [[Immune Mediated Thrombocytopaenia|Immune-mediated thrombocytopaenia]] occurs most commonly in young animals.
===Secondary Thrombocytopenic Disease===
===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.
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 - Anatomy & Physiology|bone marrow]] suppression'''
**'''Aplastic anaemia''' caused by ingestion of bracken, administration of oestrogens or of [[Chloramphenicol|chloramphenicol]] or [[Sulphonamides|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 - Anatomy & Physiology|bone marrow]] depression.
* Associated with diseases which cause [bone marrow]] depression.
* The [[Bone Marrow - Anatomy & Physiology|bone marrow]] is depleted or devoid of megakaryocytes, and there is a nil or markedly reduced peripheral blood thrombocyte count.
* The [[Bone Marrow - Anatomy & Physiology|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:
* Secondary thrombocyopenic disease is seen in the following conditions:
*# Severe protozoal infections.
*# Severe protozoal infections.
*#* For example, in the UK, Haemobartonella may be a cause.
*#* For example, in the UK, Haemobartonella may be a cause.
*# Other miscellaneous causes.
*# Other miscellaneous causes.
*#* Severe bacterial infections.
*#* Severe bacterial infections.