Page 514 - Problem-Based Feline Medicine

506 PART 7 SICK CAT WITH SPECIFIC SIGNS

may be responsible for some alterations in ACT and trait, page 504 and Vitamin K responsive coagu-
aPTT. lopathy in the Devon Rex, page 515).
Hemostatic abnormalities are subclinical. ITP may be concurrent with other autoimmune dis-
eases, e.g. hemolytic anemia, myasthenia gravis, and
systemic lupus erythematosus.
Diagnosis
Clinical signs and work-up of the primary disease.
Clinical signs
Primary ITP is rare. There is usually marked thrombo-
IMMUNE-MEDIATED
THROMBOCYTOPENIA (ITP) cytopenia and signs are typical of platelet disorder
bleeding, including petechiation, epistaxis, melena
and hematuria.
Classical signs
Signs of an underlying disease may be present, e.g.
● Platelet disorder bleeding (e.g. prolonged
lymphadenopathy with lymphoma.
bleeding after venepuncture, melena,
epistaxis, petechiation). Splenomegaly may be present due to hyperplasia,
extra-medullary hematopoiesis and neoplasia.
Thrombocytopenia may be an incidental finding in a
Pathogenesis work-up.

In ITP, platelets become antigenic leading to acceler- Anemia and associated signs vary.
ated platelet destruction by the macrophage–mono-
cyte system, particularly in the spleen.
Diagnosis
In primary, or idiopathic, ITP an underlying disease
is not found and the disease is considered to be auto- Rule out other causes of thrombocytopenia based on
immune. clinical signs and work-up.
In secondary ITP, a primary, or underlying, disease is Hemostatic testing reveals thrombocytopenia, normal
found, e.g. FeLV infection, where there is immune- PT and aPTT, and normal to increased fibrinogen
9
complex deposition on the surface of infected platelets. level. Platelet counts < 10 × 10 /L (10 000/μl) are stated
● Lymphoma is another primary disease associated to mildly prolong ACT, but this effect is poorly docu-
with ITP, and ITP may be the mechanism of throm- mented.
bocytopenia associated with various other neo-
Bone marrow biopsy reveals increased numbers of
plasms.
megakaryocytes.
● Thrombocytopenia caused by anti-thyroid drugs
(propylthiouracil, methimazole, carbimazole) is Demonstration of platelet or megakaryocyte-associated
presumed to be immune-mediated because affected antibody by immunofluorescence (test may not be
cats may have antinuclear antibodies. readily available). Platelet and megakaryocyte-associated
● Modified live virus vaccination has been associ- neutrophils have also been reported.
ated with thrombocytopenia and thrombocytopathia
Response to immunosuppressive therapy.
in dogs, typically occurring within 2–4 weeks of
vaccination. Thrombocytopenia varies from a sub-
clinical, self-limiting fall within normal range to
Differential diagnosis
severe thrombocytopenia requiring immunosup-
pressive therapy. Post-vaccinal thrombocytopenia Megakaryocytic hypoplasia is distinguished from ITP
or thrombocytopathia has been suspected in cats on the basis of identification of a disease that causes
based on post-vaccinal bleeding in cats with other- decreased platelet production, e.g. myeloid leukemia,
wise sub-clinical hemostatic defects (see Hageman on bone marrow biopsy.