Previously known as Idiopathic thrombocytopaenic Purpura . Idiopathic simply means of unknown cause. Now the disease is known to be immune mediated it has kept the same acronym ITP but changed its name to Immune Mediated Thrombocytopaenic Purpura.
This is bleeding disorder caused by a low platelet count. ITP occurs when the immune system cells produce antibodies against the platelets. Once the antibody, which is a foreign protein, is attached to a platelet the spleen destroys the platelets. Platelets are produced from the fragmentation of bone marrow megakaryocytes and are then released into the circulation where their average life span is eight to 12 days. Aged platelets are removed from the circulation by tissue macrophages especially in the spleen, ITP is mainly a disorder of accelerated platelet destruction when antibodies bind to platelet membranes, enhancing platelet clearance by the mononuclear phagocyte system. This process is mostly in the spleen but the liver also plays its part. If many platelets are destroyed, the affected animal will have significant bleeding and bruising. It seems, like most auto immune conditions, to affect bitches more than dogs, especially in middle age and when speyed.
There are several acquired causes of thrombocytopaenia which also need to be considered before assuming it is auto immune. This group includes the toxic effect of some drugs, other toxins, viral, rickettsial and protozoan infections. Chronic hepatitis, Myeloid leukemia and some tumours such as haemangiosarcoma may all cause significant reduction in the platelet count. It can be quite difficult to confirm the specific cause
In milder cases an affected dog may present with some lethargy, weakness and nosebleeds. The skin and mucous membranes of the mouth may show pinpoint purplish coloured spots known as Petechiae. If more seriously affected there may be spontaneous bleeding so blood is seen in the urine and stools. On examination the Vet may be able to detect enlargement of the spleen.
Treatment involves corticosteroids either alone or in combination with immunosuppressive drugs. Most dogs do recover with either single or multiple courses of treatment as there can be a tendency to relapse.
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