Immune-mediated thrombocytopenia

What is ... ?: 

 Thrombocytopenia means a reduction in platelets (thrombocytes). Platelets (one of the cell types in the blood) play an important role in the clotting process; thus the main result of a decrease in platelets is increased bleeding - for example, nosebleeds.

In immune-mediated thrombocytopenia (IMT), the reduction happens because there is increased destruction of platelets by the body's own immune system, at a rate faster than they are produced in the bone marrow. IMT may be secondary to some other process (such as an infection, tumour, or drug reaction) or it may be primary, meaning that no other causative factor can be found. It is more common in certain breeds, suggesting an inherited genetic susceptibility. IMT may occur by itself or with other conditions like systemic lupus erythematosus and immune-mediated hemolytic anemia.
 

How is ... inherited?: 

unknown. It is more common in female dogs than in males.

What does ... mean to your dog & you?: 

 The main problem for dogs affected by IMT is increased bleeding. Your dog may have nosebleeds, bruising on the gums or skin, and/or blood in the stool or urine (seen as a darker than normal colour).  Your dog may also appear weak or lethargic.

Many dogs with IMT experience only one episode of thrombocytopenia, and respond well to treatment. Some dogs will have occasional relapses, which may be associated with stressors such as another illness, or travel. Unfortunately some dogs with this disorder die acutely because of severe internal bleeding.
 

How is ... diagnosed?: 

 With signs of increased bleeding, your veterinarian will do a CBC (complete blood count), which will show a dramatic drop in platelet numbers. Bleeding does not occur until the platelet count is below 25,000/µl of blood. (Normal levels are above 200,000).

Then it is a matter of ruling out other possible causes of thrombocytopenia, which are many. Any disorder that causes increased widespread excessive bleeding will cause a drop in platelets, simply because they are being used up (consumptive coagulopathy).
 

How is ... treated?: 

 Corticosteroids are given to slow platelet destruction, initially at high doses which are gradually tapered as platelet levels stabilize and begin to rise again. The response to treatment is usually good. If platelet levels continue to fall despite steroid therapy, other immunosuppressive drugs can be given.Blood or platelet-rich plasma transfusions may be required, to supply oxygen to the tissues and to control bleeding.
 
Aftyer recovery, ongoing monitoring is needed to identify any relapse early, and stressful circumstances should be avoided where possible.

For the veterinarian: 

CBC (with manual differential) will usually be normal unless bleeding causes anemia. A peripheral blood smear should be evaluated for platelet clumping, size and morphology. Coagulation profiles (also usually normal with ITP) should be done to rule out intrinsic and extrinsic coagulation defects that may be causing a general consumption of peripheral platelets. Other differentials for thrombocytopenia include reduced production secondary to lymphoma, myeloproliferative disease, and preleukemic states. Bone marrow cytology is usually not necessary unless there are other abormalities; increased numbers and immaturity of megakaryocytes indicate a regenerative response, in contrast to an unresponsive or preregenerative bone marrow. Regeneration should be evident within 3 to 5 days of an acute thrombocytopenic episode. 

The diagnosis of primary IMT is made if no causes of secondary IMT can be found, which is most often the case. Secondary IMT may be caused by certain drugs (cephalosporins, gold compounds and others), neoplasia, infectious diseases (eg. canine distemper), or other immune-mediated disorders such as SLE or IMHA.
 

Breeding advice: 

Dogs that have had an episode of immune-mediated thrombocytopenia should not be used for breeding.
 
FOR MORE INFORMATION, PLEASE SEE YOUR VETERINARIAN.
 

Resources: 

Neel JA, Birkenheuer AJ, Grindem CB. Thrombocytopenia. In: Bonagura JD, Twedt DC, eds. Kirk's Current Veterinary Therapy XIV. Missouri: Saunders Elsevier, 2009:281-287.
Stone M. Immune-mediated thrombocytopenia. In: Côté E, ed. Clinical Veterinary Advisor Dogs and Cats. Missouri: Mosby Elsevier, 2007:1079-1080.
Sargan DR. Thrombocytopenia. In IDID - Inherited diseases in dogs:web-based information for canine inherited disease genetics.


What breeds are affected by ... ?
Tags: