Immune Mediated Thrombocytopenia (IMTP) in dogs
What is IMTP?
Immune Mediated Thrombocytopenia (IMTP) is a condition where the body’s immune system, which normally fights infection, starts to damage and destroy platelets. Platelets are cells required to clot blood and prevent bleeding. If enough platelets are destroyed then spontaneous bleeding can occur. If a large quantity of blood is lost then anaemia (having a low red blood cell count) can also be present.
What causes IMTP?
In most dogs IMTP occurs without any underlying cause. In this situation it is referred to as primary (or idiopathic) IMTP. However, in other cases there is an underlying reason or trigger factor that results in the body damaging and destroying platelets, and this is termed secondary IMTP. Possible trigger factors include certain infectious or inflammatory diseases, particular classes of drugs or, sadly in some patients, underlying cancer.
What are the signs of IMTP?
A common clinical sign that occurs in patients with IMTP is unexplained (or spontaneous) bleeding. This can result in the following:
- Bruising on the skin
- Bleeding from the nose or mouth
- Blood in stool or black stool
- Blood in vomit
- Blood in urine
In some dogs signs specific to the location where bleeding has occurred can be present. For example if bleeding occurs in the brain then neurological signs can develop.
If a large quantity of blood is lost resulting in anaemia then signs of this can develop which would include:
- Pale gums
- A fast heart rate
- Increased breathing rate and effort
- Decreased appetite
- Being quiet and lethargic
How is IMTP investigated?
A thorough history and physical examination may give important information regarding any potential underlying cause for IMTP – for example whether the patient has been receiving any drugs, was vaccinated recently or has a history of travelling abroad.
If IMTP is suspected from the history and clinical findings, blood tests will be performed to determine the platelet count (number), clotting times and whether anaemia is present. Other blood tests will be carried out to check general body organ function, and urine tests will often be performed to check for any evidence of urinary tract infection.
Advanced imaging of the chest and abdomen is frequently recommended for patients with suspected IMTP. This may involve X-rays, CT scanning or an ultrasound scan. These investigations help to rule out any evidence of inflammatory disease or cancers that could be acting as triggering factors for the IMTP. The diagnosis of primary IMTP is usually made by ruling out other underlying problems.
How is IMTP treated?
Primary IMTP is usually treated with drugs to dampen down the immune system which has become overactive i.e. immunosuppressive therapy. Most often this means treatment with steroids over a period of several months, although sometimes additional immunosuppressive treatment may also be required. In pets which are very anaemic a blood transfusion may be needed, and a blood-typing test is often performed before the transfusion. A transfusion can help to stabilise the patient while further investigations are performed, and it gives time for treatment of the IMTP to start working.
In patients where an underlying trigger factor for IMTP is identified, this condition also needs to be treated if possible. In some situations this can be simple, for example by stopping a medication. However, in other situations, for example where there is underlying cancer, treatment can be more challenging. Even those patients that are diagnosed with secondary IMTP are likely to need immunosuppressive therapy.
Why should I bring my pet to NDSR for diagnosis and treatment of IMTP?
Our medicine service is led by a team of recognised, accredited Specialists and we aim to provide the best possible treatment for your pet in our state-of-the-art hospital. Our medicine team is supported by imaging and anaesthesia Specialists, and dedicated out-of-hours vets and nurses. We have extensive experience of managing critically ill patients, often with complex medical complaints.
What is the long term outlook for pets with IMTP?
The long term outlook for patients with IMTP can be variable. Unfortunately, in a proportion of patients it can prove difficult to stop the immune mediated platelet destruction and in some cases the bleeding can be life threatening.
Conversely patients with primary IMTP that respond to immunosuppressive therapy can do very well, although it is possible for relapses to occur, either during the course of therapy or when treatment has been discontinued.
The outlook for patients with secondary IMTP will often depend on the severity of the underlying disease process.
If you have any questions about your dog's condition, or his or her treatment, please do not hesitate to contact us.