Immune
Mediated Thrombocytopenia (IMT) is a serious disease in which the
body’s immune system destroys the platelets in the blood. The name
of this disease is a bit complicated but if we take each word by
itself, it becomes more understandable. Immune Mediated means that
the body’s own immune system is at the root or cause of the disease.
Thrombocytopenia means inadequate numbers of platelets (thrombocytes)
in the blood.
The
causes for development of IMT are many and they all relate to
factors that cause the immune system to be tricked into thinking
that the platelets are no longer part of the body.
The immune system suddenly sees the platelet as a foreign
element and proceeds to destroy it, much in the same way it would
destroy a bacteria or virus. We know that
certain drugs (particularly antibiotics containing sulfur);
vaccines, viral infections, bacterial infections, cancer and others
have all been related to the development of IMT.
Why one patient gets IMT while another does not is still a mystery.
Causes
and Consequences of IMT:
Platelets are blood elements that are responsible for
blood clotting. When a blood vessel is torn or broken, the
platelets clog up the hole while it is repaired. Normally there are
over 200,000 platelets in each milliliter of blood. If the number
of platelets reduce below 80,000, there is the potential for
spontaneous bleeding. Bleeding can be visible to the owner at the
gums, from the nose, in the urine or feces. Or, it can occur
internally in the brain, heart, kidneys, lungs or joints etc. and
cause pain, rapid deterioration and even death.
While the platelets are being destroyed, there is an
inflammatory response which will often lead to fever, inappetence,
and malaise.
Diagnosis
of IMT:
Any bleeding pet has to be suspected of having IMT.
Often times, the diagnosis is made as a result of low platelets
found on a routine blood screen. Typically other reasons for
bleeding must be ruled out using a coagulation profile and an immune
panel is helpful in determining if there are abberations in the
immune system.
Goals of
Therapy and Treatment:
Treatment for IMT involves the following:
-
Trying to determine and eliminate the causal factor
(remove drugs, treat infections, remove cancer etc).
-
Suppress the
immune system’s activity to stop the destruction.
-
Replace
platelets if the count is dangerously low, or if there is
evidence of spontaneous bleeding.
The first drug we use is
Prednisone
(a form of cortisone). Given at high doses, this drug will inhibit
the immune system’s ability to kill the red cells. Often times, we
must add additional drugs such as Vincristine,
Cyclophosphamide, Azathiaprine or
Cyclosporine, all of which are very potent drugs. All of
these drugs have side effects that are fairly common. In general,
the positive, life saving effects of the drugs outweigh the negative
side effects, however, these patients must be monitored carefully
both at home and with laboratory tests.
For patients that are severely thrombocytopenia (lack of
platelets), transfusions may be necessary to provide platelets until
their body can produce more. Transfusions can be life saving, but
they do pose some risk of adverse reaction where the body rejects
the new cells.
Because prednisone can cause stomach ulcers, we
typically administer drugs to help protect the stomach during the
course of treatment.
