Immune Mediated Thrombocytopenia (IMTP)
What is thrombocytopenia?
The term thrombocytopenia refers to a condition where a patient has lower than normal levels of circulating platelets. This may be due to increased loss (i.e. hemorrhage), increased destruction (i.e. immune disease), increased consumption (i.e. clotting abnormalities) or decreased production (i.e. disease within the bone marrow). Immune mediated destruction of platelets is one of the more common problems we see here.
Why are platelets important?
Platelets are cells within the blood that play a critical role in normal blood clotting functions. They are produced in the bone marrow (like the red and white blood cells) and are then released into the circulation.
What are the causes of IMTP?
Immune mediated plated destruction can be due to a variety of underlying problems that trigger an abnormal immune response. Things such as infections (bacterial, viral), drugs, certain cancers, etc have all been implicated as potential causes of IMTP. It is also possible that no underlying problem is found in which case it is called idiopathic IMTP. This is the most common cause of life threatening thrombocytopenia in dogs. In order to diagnose the idiopathic form of the disease however, the other potential causes need to be ruled out.
What are the signs of IMTP?
Because thrombocytopenia leads to problems with normal clotting, the most common signs you may notice at home are bruising, blood in the stool or the urine or nose bleeds. In some instances thrombocytopenia can lead to bleeding into the abdomen, chest, brain or spinal cord. In these cases clinical symptoms may include labored breathing, abdominal distension or neurologic signs.
How is IMTP diagnosed?
Routine blood tests will show low platelet levels however the key is in looking for a cause for the low platelets. Your veterinarian may perform blood tests to look for specific infectious diseases such as Ehrlichia or heartworms. Since cancer is also a potential trigger of this disease your veterinarian may perform chest x-rays or an abdominal ultrasound.If no underlying cause is found then a diagnosis of primary IMTP is made and immunosuppressive therapy is begun.
How is IMTP treated?
The mainstay of therapy, aside from treating the underlying cause, is immunosuppressive therapy. Prednisone is one of the main medications used but there are other drugs that may be required as well (i.e. Azathioprine, Cyclophosphamide). Regardless of the type of therapy that your veterinarian chooses, frequent rechecks will be an extremely important part of the plan. If the thrombocytopenia is severe, your veterinarian may recommend hospitalizing your pet for observation and more aggressive treatment. Unfortunately, a blood transfusion will not supply enough platelets to reverse thrombocytopenia. If the low platelets however have led to blood loss and subsequent anemia, then a transfusion may be indicated. The prognosis with IMTP can be quite variable and depends on the underlying cause, response to therapy or drug complications. Overall, if there is no severe underlying disease and your pet responds well to therapy, the prognosis is generally good although lifelong medication may be required.
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