IMMUNE-MEDIATED Thrombocytopenia (iTP)
What is Immune-Mediated Thrombocytopenia (ITP)?
Immune-mediated Thrombocytopenia (ITP) is an autoimmune disease where the immune system attacks and destroys blood platelets. Autoimmune diseases result when the body's immune system does not recognise itself and cells that normally attack invading viruses and bacteria begin attacking the body's own cells, causing damage. In dogs with immune-mediated thrombocytopenia (ITP), the body's platelets are attacked and destroyed, resulting in reduced numbers of platelets in the blood vessels. Platelets (also called thrombocytes) are cells that are needed to form blood clots and repair damaged blood vessels. Thrombocytopenia occurs when there are too few platelets in the blood. Adequate numbers of platelets are essential for survival. If platelet numbers are too low, uncontrolled bleeding can occur, and if treatment is unsuccessful, the patient can die from excessive blood loss.
What are the symptoms of ITP?
Unfortunately, symptoms of low platelet count often don’t become obvious until the count has dropped to dangerous levels. If your dog is exhibiting the following symptoms of low platelet count, do not delay in seeking veterinary help.
Lethargy & loss of appetite
Pinpoint sites of bleeding called petechiae (see illustrations below)
Larger areas of bleeding called ecchymoses (bruising)
Bleeding from the nose or gums; blood in the urine; blood in the stool (often noted as black, tarry stool); bleeding from the penis or vulva
Coughing or vomiting blood; difficulty breathing
Prolonged bleeding after a traumatic injury
Other evidence of bleeding, such as minor cuts and scratches that continue to bleed; a heat cycle that seems prolonged or excessive; skin bruising after playing or grooming
Bleeding in other places leading to other clinical signs: e.g. bleeding into the eyes can cause blindness or bleeding into the brain can cause seizures
Blood loss can also cause anaemia (low red blood cell count), resulting in pale gums, increased breathing rate, and weakness
These images illustrate petechiation on the gums and abdomen.
(Photos: Leah Cohn, DVM, PhD, DACVIM)
What causes ITP?
Primary ITP:
Occurs without an identifiable underlying cause and is likely due to a malfunction in the immune system.
Predisposing factors:
Age (often affects young adults to middle aged dogs)
Breed (smaller dogs more often affected but can be seen in any dog including English Springer Spaniels)
Secondary ITP:
The immune system destroys platelets because of an underlying disease or trigger.
Predisposing factors:
Drug administration (e.g. antibiotics, chemotherapy drugs, oestrogen)
Infectious diseases such as parvovirus, canine infectious hepatitis virus, canine distemper, leptospirosis, many tick-borne diseases (e.g. Lyme disease), salmonella, heartworm, other bacterial or fungal infections
Neoplasia (e.g. multiple myeloma, lymphoma, leukaemia, hemangiosarcoma)
Inherited (e.g. von Willebrand's disease in the Dobermann and other breeds)
Toxins & venoms (e.g. zinc, Xylitol, snake bites)
Miscellaneous (e.g. splenic enlargement, bone marrow disorders)
How is ITP diagnosed?
Diagnosing an animal with platelet disease begins with a thorough history and physical examination. A blood sample will be taken to perform a platelet count. Healthy dogs have a platelet count between 175,000-500,000 platelets per microlitre of blood, and anything below is diagnosed as low. Platelet counts of less than 20,000 to 30,000 per microlitre of blood make spontaneous bleeding likely. (A count from a machine is not enough to confirm a low count because platelets may clump together in a blood sample causing it to seem low artificially. Therefore, a blood smear should be prepared and examined under a microscope by a trained expert.)
The Vet will take your dog’s recent history into account, so be sure to report any trauma involving bleeding, which may indicate that the low count is caused by haemorrhaging. A coagulation profile (testing the clotting capability of your dog’s blood) may also be performed. Additional diagnostic tests are used to investigate any suspected underlying causes of the problem - these may include additional blood tests, X-rays, ultrasound, or bone marrow sample tests. A diagnosis of ITP is typically made after excluding other causes for a low platelet count.
What treatment is available for ITP?
ITP is caused by an overactive immune system so initial treatment is aimed at suppressing the immune system and stabilising the patient. Additional therapy may include intravenous fluids and supportive care. If the underlying cause of the ITP can be treated, that therapy is also generally initiated. During treatment, frequent blood testing is required to ensure an adequate response to therapy. If your dog responds to treatment, medication dosages will be gradually adjusted and blood testing repeated periodically to monitor for relapses.
Immunosuppressive drugs: Steroids such as prednisone are the most common medication prescribed to help block the destruction of platelets. If this doesn't work or if the side effects are not tolerable, additional immunosuppressive drugs can be given to manage the condition (e.g. azathioprine, cyclosporine).
Chemotherapy medication: Can cause a temporary increase in the number of platelets.
Intravenous immunoglobulin: A blood product containing antibodies can cause a short-lived reprieve from rapid platelet destruction in some animals.
Supportive care: This includes cage rest, exercise restriction and eliminating any activities that would cause bleeding. Dogs should be monitored closely for signs of spontaneous bleeding. In many cases, a blood transfusion may be required to replenish lost red blood cells. Occasionally, a special transfusion of platelets is also necessary.
What is the outlook for dogs with ITP?
ITP generally responds to treatment and the outlook for the majority of affected dogs is good. However, for some the disorder can be fatal. Even for those that respond well, relapses may occur in the future. Research studies have shown varying relapse rates from 9% to 31%. Unfortunately, if a dog relapses once, there is about a 50% chance that it will happen again. Typically, the first relapse will happen within a year of the initial diagnosis. Your Vet is therefore likely to recommend periodic recheck examinations and repeat blood tests for the rest of your dog's life to help identify and treat relapses early.
Steroids are the mainstay of treatment for managing ITP, however these drugs are associated with several side effects. Much like people, dogs receiving steroid treatment will have an increased appetite which may lead to weight gain. They will often exhibit increased thirst and urination. Administration of an excessive dose of steroids can lead to other disorders too, therefore requiring careful monitoring. Additionally, although suppressing the immune system will help manage the ITP, it will also make the dog more susceptible to infections.
Fortunately, patients don't typically require immunosuppressive medication for life. Steroids are typically prescribed in a “tapering” dose, meaning that they are slowly decreased over several months. Repeat platelet counts should be performed whenever the dose of immunosuppressive medications is altered. Owners should be well informed of the clinical signs associated with thrombocytopenia and understand the importance of monitoring for those signs in the future.
If you would like any help or further information relating to ITP, we would be happy to hear from you. We would also be extremely grateful if ESS owners would help us to monitor this disorder in ESS by reporting online any confirmed diagnosis or the death of your ESS from the condition by clicking on either of the links below. All information provided will be treated in the strictest confidence.
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