What is immune-mediated thrombocytopenia?
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 there is an inherited component. IMT may occur by itself or with other conditions like systemic lupus erythematosus and autoimmune hemolytic anemia.
How is immune-mediated thrombocytopenia inherited?
unknown. However it is more common in certain breeds, which suggests that there is an inherited component.
What breeds are affected by immune-mediated thrombocytopenia?
The old English sheep dog, cocker spaniel, and poodle have an increased susceptibility to this disorder, although it occurs in all breeds. It is more common in females than males.
For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive. We have listed breeds for which there is a consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.
What does immune-mediated thrombocytopenia 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.
About half of dogs with IMT experience only one episode of thrombocytopenia, and respond well to treatment within a few days. 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 immune-mediated thrombocytopenia 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 30,000 per cubic millimetre 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).
For the veterinarian: Coagulation profiles 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. A bone marrow aspirate will distinguish between increased destruction or decreased production. If megakaryocytes are readily observed on low power or extremely numerous, the most likely cause of the thrombocytopenia is immune-mediated.
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.
How is immune-mediated thrombocytopenia 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.
Dogs that have had an episode of primary immune-mediated thrombocytopenia should not be used for breeding.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Reagan, W.J., Rebar, A.H. 1995. Platelet disorders. In E.J. Ettinger and E.C. Feldman (eds.) Textbook of Veterinary Internal Medicine, p. 1964-1976. W.B. Saunders Co., Toronto.
Thompson, J.P. 1995. Immunologic disease. In E.J. Ettinger and E.C. Feldman (eds.) Textbook of Veterinary Internal Medicine, p. 2002-2029. W.B. Saunders Co., Toronto.
Copyright © 1998 Canine Inherited Disorders Database. All rights reserved.
Revised: July 23, 2001.This database is a joint initiative of the Sir James Dunn Animal Welfare Centre at the Atlantic Veterinary College, University of Prince Edward Island, and the Canadian Veterinary Medical Association.