Page 1425 - Small Animal Internal Medicine, 6th Edition

CHAPTER 87 Disorders of Hemostasis 1397

receiving dexamethasone than in those receiving prednisone. thrombocytopenic dogs and cats, it is imperative to deter-
Because an acute upper GI tract bleed is usually catastrophic mine whether the patient has platelet aggregates by evaluat-
VetBooks.ir in a dog with thrombocytopenia, prednisone is my drug ing a blood smear or the graphics from the analyzer (see Fig.
87.1). I have followed up several of these cats for months to
of choice. H 2 antihistamines such as famotidine (0.5-1 mg/
kg PO q12-24h) or proton pump inhibitors (omeprazole
with treatment, questioning the diagnosis of IMT. Interest-
0.5-1 mg/kg, PO, q24h) should be used in combination with years, and their platelet counts do not increase markedly
the corticosteroids. ingly, a high proportion of these cats also have regenerative
FWB, stored blood, or packed RBCs should be adminis- or nonregenerative anemia, neutropenia, lymphocytosis, or
tered as needed to maintain adequate oxygen-carrying combinations thereof, so an infectious process such as ana-
capacity (see Chapter 82, “Transfusion Therapy”). In my plasmosis or ehrlichiosis cannot be excluded. The cytopenias
experience, in addition to immunosuppressive doses of may resolve for no apparent reason, only to have a decrease
corticosteroids, cyclophosphamide given intravenously (IV) in another cell line months later. Because most of these cats
2
or PO in a single dose of 200 to 300 mg/m is effective for do not bleed, the clinician should be aware that increasing
inducing remission. However, it should not be used as a drug dosages or adding drugs may cause more problems
maintenance agent because it may result in sterile hemor- than monitoring the platelet count. My treatment of choice
rhagic cystitis when used on a long-term basis. Vincristine for cats with IMT or immune-mediated cytopenias is a com-
2
at a dose of 0.5 mg/m given IV traditionally has been rec- bination of dexamethasone (4 mg total dose, q1-2 wk) and
2
ommended for dogs with IMT. This drug stimulates mega- chlorambucil (20-30 mg/m PO q2wk). I have also success-
karyocyte endomitosis, resulting in early platelet release fully used human intravenous immunoglobulin G in a
from the bone marrow. However, because vinca alkaloids limited number of cats with immune-mediated cytopenias.
bind to tubulin, the platelets released prematurely are not See Chapter 73 for more discussion of IMT.
fully functional (tubulin is responsible for platelet aggrega-
tion), and the patients may have further bleeding before the PLATELET DYSFUNCTION
platelet count increases. As discussed in Chapters 72 and 82, The presence of primary hemostatic bleeding in a patient
human intravenous immunoglobulin (0.5-1 g/kg IV, single with a normal platelet count is highly suggestive of a plate-
dose) has been used successfully in dogs with refractory or let dysfunction syndrome, although vasculopathies and
life-threatening IMT. Transfusion of platelet concentrates enhanced fibrinolysis should also be considered. Platelet
may be indicated, but platelet numbers rarely increase sig- dysfunction syndromes can be congenital or acquired (Box
nificantly given that the thrombocytopenia is due to periph- 87.5); however, they rarely result in spontaneous bleeding.
eral consumption. In a retrospective study (Ng et al., 2016), More often a prolonged BMBT is noted preoperatively in
the transfusion of cryopreserved platelets to 43 thrombocy-
topenic dogs had no influence on survival.
Failure to induce remission, which normalizes the platelet BOX 87.5
count, is usually the result of insufficient drug (low doses or
the need for a second agent), insufficient duration of therapy Platelet Function Defects in Dogs and Cats
(the drugs have not yet had time to become effective), or an
incorrect diagnosis. In the event of one of these, the treat- Hereditary
ment protocol can easily be amended, with the thrombocy- vWD (many breeds)
topenia usually resolving as a result. Azathioprine (50 mg/ Macrothrombocytopenia (Cavalier King Charles Spaniel)
2
m PO q24-48h) is effective in maintaining remission but is Glanzmann’s thromboasthenic thrombopathia
not a good agent for inducing remission. In some dogs aza- (Otterhound, Great Pyrenees)
thioprine is better tolerated than long-term corticosteroid Canine thrombopathia (Basset Hounds, Foxhounds, Spitz,
German Shepherd Dogs)
therapy, although close hematologic monitoring is recom- Collagen deficiency diseases or Ehlers-Danlos syndrome
mended given its myelosuppressive properties and low (many breeds)
potential for hepatotoxicity. See Chapters 72 and 73 for addi- Scott syndrome (lack of platelet procoagulant activity;
tional information and drug dosages. German Shepherd Dogs)
The prognosis is good in most dogs with IMT, although
they may require lifelong treatment. Dogs with refractory Acquired
IMT can be successfully treated with pulse-dose cyclophos- Drugs (prostaglandin inhibitors, antibiotics,
phamide, human immunoglobulin, mycophenolate mofetil, phenothiazines, vaccines)
or splenectomy. Secondary to diseases (myeloproliferative disorders,
IMT has become more prevalent in cats over the past few systemic lupus erythematosus, renal disease, liver
years. The typical clinical presentation is different from dogs disease, dysproteinemias)
in that most cats have chronic thrombocytopenia that does vWD, von Willebrand disease.
not lead to spontaneous bleeding. A platelet count of 10,000 Modified from Boudreaux MK: Inherited intrinsic platelet disorders.
to 30,000/µL is relatively common in an otherwise healthy In Weiss DJ, Wardrop KJ, editors: Schalm’s veterinary hematology,
cat without spontaneous bleeding. As discussed earlier, in ed 6, Ames, Iowa, 2010, Wiley-Blackwell, p 619.