Can you rule in immune-mediated thrombocytopenia?

Can you rule in immune-mediated thrombocytopenia?

Jul 01, 2002

Signalment: Canine, Yorkshire Terrier, 11-year-old, female spayed, 15 lbs.

Clinical history: The dog presents for acute onset of vomiting.

Table 1: results of laboratory tests
Physical examination: The findings include rectal temperature 101.0° F, heart rate 140/min, respiratory rate 25/min, pink mucous membranes, normal capillary refill time, and normal heart and lung sounds. While shaving the dog for the ultrasound study, ecchymoses of the abdominal skin were noted. Abnormal physical findings are ecchymoses of the abdominal skin and moderately painful abdomen.

Laboratory results: A complete blood count, serum chemistry profile and urinalysis were performed and are outlined in Table 1.

Radiographic review: Survey thoracic and abdominal radiographs were done. The thoracic radiographs are normal. The abdominal radiographs show an enlarged spleen.

Ultrasound examination: Photos 1-3(L-R)
Ultrasound examination: Thorough abdominal ultrasonography was performed. The dog was positioned in dorsal recumbency for the ultrasonography. The ultrasound images provided are from this dog's liver.

My comments: The liver shows a uniform echogenicity. No cancerous masses noted within the liver parenchyma. The gallbladder is moderately distended, and its walls are slightly thickened and hyperechoic. The gallbladder does contain some sludge material and possibly multiple small calculi. The spleen shows uniform echogenicity - no cancerous masses noted. The left and right kidneys are similar in size, shape and echotexture. No cancerous masses or calculi were noted in either kidney. The urinary bladder is distended with urine and contains some urine sediment material - no cancerous masses or calculi noted. The stomach and intestines are normal. The pancreas shows uniform echogenicity.

Case management: In this case, immune-mediated thrombocytopenia and chronic cholecystitis are the clinical diagnosis. The management of the immune-mediated thrombocytopenia should include prednisone at 2-4 mg/kg orally divided into twice-a-day administration and doxycycline.

In those areas known to have ehrlichiosis, it is not unusual to have both immune-mediated thrombocytopenia and canine ehrlichiosis occurring in the same dog at the same time. The abdominal pain detected on palpation is most compatible with a chronic cholecystitis.

When the gallbladder contracts from eating and/or movement, it causes abdominal pain, nausea and vomiting. I would manage the gallbladder disease with daily administration of antibiotics and Denosyl SD4. I would also consider feeding the dog exclusively a diet formulated for liver disease such as Prescription Diet L/D. I would recommend only medical care for the gallbladder disease right now and if the dog was not responding to medical care, then an exploratory laparotomy would be recommended for possible surgical removal of the gallbladder.

The total platelet count needs to be normal before any surgery is attempted.

Brief review Immune-mediated thrombocytopenia is the most common cause of severe thrombocytopenia in dogs, and bleeding is typically associated with a total platelet count <40,000/µl.

Typical treatment recommendations for immune-mediated thrombocytopenia involve administration of various drugs. Corticosteroids (prednisone 2-4 mg/kg orally divided into twice a day administration or dexamethasone 0.2 mg/kg intravenously administered twice daily, if vomiting) are the primary treatment and act primarily to impair clearance of antibody-coated platelets by macrophages.

Vincristine (0.02 mg/kg intravenously one time) is also frequently administered as an initial therapy in addition to corticosteroids. Vincristine may increase total platelet counts in dogs with immune-mediated thrombocytopenia through several proposed mechanisms, including stimulation of thrombopoiesis, increased fragmentation of megakaryocyte cytoplasm to release new platelets, and impairment of macrophage activity, leading to decreased phagocytosis of platelets.

Because many dogs with immune-mediated thrombocytopenia respond to corticosteroids ± vincristine and that the cost and/or potential adverse effects of other immunosuppressive agents are considerable and their efficacy has not been well documented, administration of other immunosuppressive drugs, such as cyclosporin, azathioprine, danazol and intravenous immunoglobulin is withheld unless the dog fails to respond to corticosteroids ± vincristine or develops serious adverse drug effects (thromboembolism, gastrointestinal ulceration).

Splenectomy is generally not done unless splenic masses are identified. Blood transfusions may be required in dogs with immune-mediated thrombocytopenia experiencing extensive mucosal surface bleeding, which appears to occur most frequently into the gastrointestinal tract and may be difficult to quantify.

Packed RBC transfusions are administered to provide severely anemic dogs with the necessary oxygen-carrying support. Platelet transfusions (fresh whole blood, platelet-rich plasma or platelet concentrate) are not recommended in most dogs with immune-mediated thrombocytopenia because the platelets are destroyed within minutes to hours of transfusion.

However, in thrombcytopenic dogs with severe, uncontrolled or life-threatening bleeding, platelet transfusions are indicated and may provide short-term hemostasis despite the lack of a measurable increase in total platelet count assessed one and 24 hours post-transfusion. While there is a risk of life-threatening bleeding is dogs with immune-mediated thrombocytopenia, most dogs with immune-mediated thrombocytopenia, despite severe thrombocytopenia, experience minimal bleeding in the form of petechiae and ecchymoses and do not bleed excessively even during surgery, potentially because the young, large platelets noted with increased thrombopoiesis are more hemostatically active.

Thus, in dogs with immune-mediated thrombocytopenia exhibiting only a mild bleeding tendency and undergoing surgery (splenectomy or removal of a tumor suspected to be the antigenic stimulus for development of immune-mediated thrombocytopenia), platelet transfusions may not be necessary in the operative period but should be available in the event of excessive bleeding.