Page 504 - Problem-Based Feline Medicine

496 PART 7 SICK CAT WITH SPECIFIC SIGNS

leukemia, myelodysplastic syndrome, multiple mye- Signs due to anemia (e.g. pale mucous membranes,
loma, malignant histiocytosis and mast cell tumor. tachycardia) and local effects of hemorrhage (e.g.
● Infections causing generalized bone marrow failure hematoma formation) vary with severity and acuteness
or dyshematopoiesis. Infectious agents include of blood loss.
feline leukemia virus, feline immunodeficiency
Signs of underlying hematopoietic neoplasia, FeLV
virus, Histoplasma capsulatum, and, possibly,
or FIV infection, or histoplasmosis include fever,
Ehrlichia spp.
inappetence, weight loss, lymphadenopathy, hepato-
– Feline panleukopenia virus infection causes
splenomegaly, dyspnea and diarrhea.
transient myelosuppression, but acute thrombo-
● FeLV or FIV infection may cause gingivitis.
cytopenia is due to disseminated intravascular
coagulation. Fever may be present due to spontaneous infection
● Cytotoxic anticancer drugs and large-field radia- secondary to concurrent neutropenia.
tion therapy produce predictable dose-dependent
effects.
– Cats are more sensitive to azathioprine toxicosis
Diagnosis
than dogs, probably because of decreased levels
of thiopurine methyltransferase, the enzyme History and physical examination findings are consis-
responsible for the drug’s metabolism. tent with a primary disease (e.g. drug therapy).
● Idiosyncratic, immune-mediated, and toxic drug
A complete blood count will reveal thrombocytopenia.
reactions have been reported with chlorampheni-
● Artifactual thrombocytopenia is common in cats.
col, griseofulvin (especially in FIV-infected cats),
A platelet count generated by a laboratory instru-
cephalosporins, ribavirin, albendazole, anti-thyroid
ment or manual count should be verified with a
drugs (propylthiouracil, methimazole, carbima-
blood smear, and the blood smear should be closely
zole), and phenobarbital.
examined for platelet clumps.
Occasionally no cause is found and/or megakaryocytic
Bone marrow biopsy will reveal megakaryocytic
hypoplasia is the only bone marrow abnormality. Some
hypoplasia. Concurrent erythroid hypoplasia, myeloid
of the idiopathic cases are due to immune-mediated
hypoplasia and neoplasia may also be identified.
mechanisms. A diagnosis of immune-mediated hypo-
● If feline leukemia virus infection is suspected but
plasia is usually based on ruling out other causes of
peripheral blood tests are negative, then obtain a
megakaryocytic hypoplasia, presence of other disorders
fluorescent antibody (FA) or PCR test on a bone
that are typically immune-mediated, and response to
marrow aspirate or ELISA test on a bone marrow
immunosuppressive therapy.
core biopsy. It should be noted that PCR testing
has not been standardized and is more likely to
Clinical signs give false-positive results than ELISA and FA if
the laboratory does not maintain the highest
In most cases thrombocytopenia is noted during work-
standards of quality control.
up of the primary disease or work-up of other signs, e.g.
fever.
Clinical bleeding is occasionally the chief complaint or
Differential diagnosis
noted during examination or work-up.
Other causes of thrombocytopenia are usually asso-
Spontaneous bleeding includes petechiation, ecchy-
ciated with normal to increased platelet counts on bone
moses, epistaxis, ocular hemorrhages, hematuria and
marrow biopsy. For many of these causes the primary
melena.
disease is sufficiently characterized on routine work-up
Excessive bleeding is usually first noted as bleeding to explain thrombocytopenia without the need for bone
from venepuncture sites. Biopsy sites, suture lines marrow biopsy. Other causes of thrombocytopenia
and other local lesions may also bleed excessively. include: