Page 572 - Problem-Based Feline Medicine

564 PART 8 CAT WITH ABNORMAL LABORATORY DATA

Because normal feedback inhibition of erythrocytosis Treatment
does not occur, circulating erythropoietin levels are
Primary polycythemia should be treated with phle-
usually very low.
botomy and intravenous fluids to reduce PCV to
Polycythemia vera is very rare in cats. below 60%.
There is often leukocytosis and thrombocythemia. Ten ml/kg/day of blood should be removed, and replaced
with an equivalent volume of fluid (0.9% NaCl or bal-
The erythrocytes produced in polycythemia vera are
anced electrolyte solution) or the cat’s own plasma.
morphologically normal.
● Regular phlebotomies may be adequate to maintain
PCV. If phlebotomies are required more than once
Clinical signs a month to maintain PCV < 60%, hydroxyurea ther-
apy should be tried.
Mucosae are dark pink.
Bone marrow can be suppressed using hydroxyurea
Bleeding may occur from numerous sites, e.g. nose,
indefinitely (15–30 mg/kg q 24 h with food, reduce
gums, skin, gastrointestinal tract, urinary tract or in the
dose to 15 mg/kg q 24–48 h after 7–14 days).
eye.
● Complete blood counts should be performed every
Central nervous system signs such as seizures, abnor- 7–14 days until PCV is normal, then every 3–4
mal behavior, ataxia and blindness often occur because months.
of reduced vascular perfusion of the central nervous ● When using hydroxyurea, serious bone marrow
system. depression resulting in anemia, thrombocytopenia
and leukopenia may occur, so cats receiving the
There may be a history of polydipsia and polyuria.
drug need to be monitored carefully. If leukopenia,
Dilated tortuous retinal vessels and retinal hemor- thrombocytopenia or anemia develops, stop the
rhage may be observed on ophthalmic examination. drug until blood counts are normal, and then
resume at a lower dose.
A systolic ejection murmur (hemic murmur) may be
present over the base of the heart secondary to abnor-
Prognosis
mal viscosity.
The prognosis for polycythemia vera is guarded,
Diagnosis depending on the response to treatment and the inci-
dence of side effects of the therapies used.
Polycythemia vera is diagnosed when there is a combi-
nation of marked erythrocytosis (PCV > 60), low or
EXCESSIVE BLOOD TRANSFUSION
undetectable serum erythropoietin levels, normal
OR OVERDOSE OF EXOGENOUS
plasma protein concentration and normal blood O
2 ERYTHROPOIETIN
saturation levels.
The bone marrow has increased cellularity with ery- Classical signs
throid hyperplasia or panhyperplasia. There is rela-
● Injected mucus membranes.
tively normal maturation of erythroid precursors and
● Weakness.
cells have normal morphology, with no evidence of
● CNS signs including seizures.
neoplasic features. Myeloid to erythroid ratio may be
normal, or reflect erythroid hyperplasia.
Clinical signs
Differential diagnosis This is a potential, although previously unreported,
cause of polycythemia.
Polycythemia vera needs to be differentiated from other
more common causes of erythrocytosis, such as dehy- Expected clinical signs are those of erythrocytosis, i.e.
dration, hyperthyroidism and chronic hypoxic car- weakness, injected mucus membranes and neurological
diac or pulmonary disease. signs.