Immune-mediated hemolytic anemia (IMHA) and immune-mediated thrombocytopenia (ITP) are diseases in which the body’s own immune system attacks and destroys its red blood cells (IMHA) or platelets (ITP).

The medication most commonly prescribed to shut off the immune system which is attacking the red blood cells and platelets is a corticosteroid hormone called prednisone.

The prognosis for both diseases is highly variable and depends on the underlying cause if one is present.

What is it?            

• Immune-mediated hemolytic anemia (IMHA) and immune-mediated thrombocytopenia (ITP) are diseases in which the body’s own immune system attacks and destroys its red blood cells (IMHA) or platelets (ITP). Signs that develop are caused by massive, often sudden, depletion in red blood cells or platelets. One of the major functions of red blood cells is to carry oxygen from the lungs to all other tissues in the body. When there are inadequate numbers of red blood cells (anemia), the body becomes starved for oxygen. You may notice depression, listlessness, panting, loss of appetite, weakness, or reluctance to exercise.
• The major function of platelets is to help form blood clots to stop bleeding. Destruction of large numbers of platelets can results in pinpoint bleeding in the skin or gums, or bleeding from the nose. Less commonly, blood can be seen in the stool (either dark brown or black if it is digested or bright red if it is not) or urine. Severe anemia can result from excessive bleeding. About 50% of the time IMHA and ITP will occur together.
• Both IMHA and ITP can be classified as either “primary” or “secondary”. In primary disease, no underlying cause of the immune destruction can be found. In comparison, secondary IMHA or ITP occurs when the immune system inadvertently destroys its own red blood cells or platelets secondary to an immune attack directed against an underlying condition such as cancers or infections, or exposure to certain drugs or toxins. If any underlying condition is the cause for IMHA or ITP, it is critical to attempt to correct that problem while simultaneously treating the anemia or low platelet count.           
  IMHA and ITP frequently occur in dogs. Primary IMHA or ITP is extremely rare in cats. It is believed that cocker spaniels, toy and miniature poodles and Old English sheepdogs are breeds predisposed to IMHA. The latter two breeds and standard poodles are also at increased risk to develop ITP. Most affected dogs are middle aged females. No breed or sex predilection is seen in cats. There is no scientific evidence to suggest that these diseases are caused by anything you ordinarily feed your pet or by where you live.

Diagnosis

• The diagnosis of IMHA or ITP requires evaluation of blood smears, complete blood count (CBC), chemistry panel, and urinalysis. Specialized blood test such as a Coombs’ test and titers for certain tick borne diseases are often necessary. Since the bone marrow is the site of red blood cell and platelet production, a bone marrow aspirate or biopsy may be required in patients where the working ability of the bone marrow is in question. Diagnostic imaging studies such as radiographs (x-rays) and ultrasound are often necessary to rule out an underlying disease (i.e., cancer) that may have precipitated the problem.

Treatment

• Treatment of IMHA and ITP relies on suppressing the immune system’s attack against the red blood cells and platelets, respectively. The medication most commonly prescribed to shut off the immune system is a corticosteroid hormone called prednisone. Side effects of this drug include an increased appetite, increased thirst, increased urination and increased anxiety, most often seen as pacing, panting and restlessness. Therapy must be continued until there is laboratory evidence that the anemia has resolved and there is no ongoing destruction of red blood cells or platelets. This will require frequent recheck examinations and blood tests to monitor the success of the therapy. If the immune system has been adequately suppressed, the dosage of prednisone can be slowly tapered, often over the course of several months. The goal is to find the lowest dose of medication that manages the disease; hopefully medications can be discontinued altogether. Frequent rechecks to monitor the response to therapy are extremely important.
• If adequate suppression of the immune system does not occur, additional medications such as cyclophosphamide, azathioprine, danazol, or cyclosporine may be tried. These drugs can have more serious side effects than prednisone. Your veterinarian will go through side effects if these medications are prescribed.
• In some dogs and cats, the destruction of red blood cells or platelets is so severe that a life-threatening anemia can occur. Blood transfusions may be necessary to stabilize these pets until the bone marrow can produce enough cells to keep up with the demand for red blood cells and platelets, and until the drugs being given to suppress the immune system have had time to work.

Prognosis

• The prognosis for both diseases is highly variable and depends on the underlying cause if one is present. Complications related to the disease or drug therapy may further alter prognosis. In some patients, life-long drug therapy is required to control the disease. Some patients with severe disease do not respond to therapy. Relapses are not unusual and may occur months to years after the initial episode. Vaccinations may lead to recurrence.