What causes Thrombocytopenia in a healthy dog?

I may add she was a 7 year old female toy poodle who we lost to this illness the week before christmas,i just want to know why a perfectley healthy dog can be normall one day and dispite all the vet help she could possibly get still die.

Causes of Canine Idiopathic ThrombocytopeniaNumerous conditions may cause acquired thrombocytopenia including whole-body irradiation; drugs (levamisole, sulfonamide, antibiotics); toxins; viral, rickettsial or protozoan infections; chronic hepatitis; myelogenous leukemia; tumors (hemangiosarcoma); Addison's disease; vitamin B12 or folate deficiencies; severe iron deficiency or immune-mediated disorders. Overdose of intravenous heparin may induce severe thrombocytopenia in cats. Increased platelet destruction commonly results from overly-active macrophage system or immune-mediated mechanisms. Immune-mediated thrombocytopenia (ITP) is one of the most common causes of thrombocytopenia in dogs where the dog's immune system produces antibodies which attack and destroy the blood cells.Hereditary disorders causing thrombocytopenia are the Wiskott-Aldrich syndrome, a severe immunodeficiency disease characterized eczema.The most common infectious cause of thrombocytopenia in dogs is ehrlichiosis Infection with Ehrlichia canis and, less commonly, with E. platysand E. ewingii cause thrombocytopenia. Other infections causing thrombocytopenia include infectious canine hepatitis virus, distemper vaccination, peritonitis, dapsone therapy, myasthenia gravis, immune-mediated hemolytic anemia (IMHA) (the ITP and IMHA may occur simultaneously). Drug sensitivity leading to thrombocytopenia may develop within a few days of initiation of drug therapy. Discontinuance of the offending drug is rapidly accompanied with return to the normal platelet levels.Thrombocytopenia in animals is also often associated with DIC, a disorder when the dog's blood clotting mechanisms are activated throughout the body instead of being localized to an area of injury. As a result, the blood clotting factors (proteins) are used up to such a degree that they not available to form clots at sites of real tissue injury.Severe bleeding, whether acute or chronic, is unlikely to cause thrombocytopenia because of the extra platelets stored in the spleen and other sites.Females and small breeds of dogs, such as Cocker Spaniels, appear predisposed to immune-mediated thrombocytopenia, and the cause of this condition remains unknown. Most affected dogs are middle-aged females or spayed females.

The old English sheep dog, cocker spaniel, and poodle have an increased susceptibility to this disorder, although it occurs in all breeds. It is more common in females than males. he main problem for dogs affected by IMT is increased bleeding. Your dog may have nosebleeds, bruising on the gums or skin, and/or blood in the stool or urine (seen as a darker than normal colour). Your dog may also appear weak or lethargic.About half of dogs with IMT experience only one episode of thrombocytopenia, and respond well to treatment within a few days. Some dogs will have occasional relapses, which may be associated with stressors such as another illness, or travel. Unfortunately, some dogs may not make it. Dogs with Thrombocytopenia should not be bred. The rest depends if your dog has primary thrombocytopenia or secondary thrombocytopenia. This disease may appear on its own or may occur with diseases like lupus or hemolytic anemia. Since the disease is more common in certain breeds, it appears there may be an inheritable component of it.

www.gopetsamerica.com/dog-health/canine-idiopathic-thrombocytopenia.aspx I Googled this, in dogs, and came up with the above link. Hope it works.