Blood cells known as platelets take care of small tears in your dog's blood vessels. When your dog's immune system prevents platelets from doing their job, a condition called immune mediated thrombocytopenia, or IMT, develops. IMT usually occurs in middle-aged dogs and breeds that might be predisposed to this condition, such as poodles, Old English sheepdogs and cocker spaniels.
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Causes
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When your dog's immune system mistakenly identifies platelets as invading organisms, antibodies cover these platelets. Spleen cells called phagocytes, which normally destroy old platelets, attack the antibody-coated platelets at a much higher rate. The underlying cause for the immune system's actions are unknown. Possible triggers include genetic factors, vaccines, toxins and viral or bacterial infections. If IMT occurs while your dog's body is releasing antibodies to fight off a toxin or infection, the antibodies could mistake platelets with the invading organisms if their surface structures are similar.
Symptoms
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The loss of platelets in IMT causes spontaneous bruising, which often appears as large bruises made up of smaller spots. The easiest places to spot these include the gums, belly and whites of the eyes. Small amounts of blood might be seen in stool or urine. Nose bleeds could also occur. In severe cases, internal bleeding in vital areas such as the spinal cord or brain poses a life-threatening risk.
Diagnosis
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Diagnosis of IMT involves blood work to determine platelet count and red blood cell count. Other methods include urine tests, bone marrow analysis, fecal analysis and x-rays or ultrasound to check the internal organs. Other conditions that cause low platelet count, such as artificial estrogens and tick-borne diseases, must be ruled out. If tests show a normal platelet count accompanied by abnormal platelet function, possible causes such as overuse of aspirin or pancreatitis should be checked for before a diagnosis is made.
Treatment
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Treatment of IMT centers on suppressing the immune system in order to reduce the destruction of platelets and the production of antibodies. Corticosteroids, such as prednisone, are the most commonly used medications, although side effects such as increased appetite often occur. Stronger immune-suppressing medications such as azathioprine can be used if steroids prove ineffective or cause severe side effects. Most medications begin to work within three to five days. A splenectomy, or surgical removal of the spleen, can be performed if medications don't work or if IMT occurs repeatedly after medications are no longer taken.
Relapses
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Frequent blood counts taken while medication dosage gradually lessens can help detect relapses before outward symptoms appear. These counts typically take place up to three weeks after dosage changes and just before a new change occurs. If a relapse is found, medication is increased and long-term drug therapy might be necessary. Side effects associated with long-term use of medications, such as weight gain, could develop.
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