Page 250 - Problem-Based Feline Medicine

242 PART 4 CAT WITH URINARY TRACT SIGNS

Prevention ● Weight loss (95–98% of cats).
● Polyphagia (65–75%), decreased appetite
Obesity, physical inactivity and repeated long-acting
(19–28%).
steroid or megestrol acetate administration are pre-
● Hyperactive, restless, aggressive (68–81%),
ventable risk factors for type 2 diabetes.
lethargy (15–25%).
Individuals predisposed to type 2 diabetes by low ● Tachycardia (57–65%), heart murmur (10–54%).
insulin sensitivity (as evidenced by increased fasting ● Polyuria/polydipsia (45–55%).
glucose concentrations) or reduced beta cell function ● Vomiting (33–50%), diarrhea (30–45%).
(evidenced as impaired glucose tolerance) should not ● Panting (13–28%).
become obese, and may benefit from a high-protein, ● Muscle weakness/tremors (15–20%).
low-carbohydrate diet.
An enlarged thyroid gland or glands are palpable in
more than 80% of cats.
HYPERTHYROIDISM*** ● These are located anywhere from the larynx to the
thoracic inlet.
Classical signs ● Most are 0.5–1 cm in size, although occasionally
they are up to 3 cm.
● Weight loss.
● Hyperactive, restless, aggressive.
● Polyphagia.
Diagnosis
● Tachycardia.
● Polyuria/polydipsia. Increased plasma total thyroxine (T ) concentration
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(> 64 nmol/L (5 μg/dl)) is considered diagnostic of
See main reference on page 304 for details (The Cat hyperthyroidism.
With Weight Loss and a Good Appetite).
2–10% of hyperthyroid cats have a total T concentration
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between 26–64 nmol/L (2–5 μg/dl), and require addi-
Clinical signs tional testing for diagnosis.
Polyuria/polydipsia is present in approximately 50% In mild (early) hyperthyroidism, total T may be within
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of hyperthyroid cats, and may be the major presenting the normal range.
complaint.
Severe concurrent illness will also suppress total T
● Renal blood flow and glomerular filtration rate are 4
concentration.
increased in hyperthyroidism, leading to an
increased water and solute load on the renal tubule. If clinical signs suggest hyperthyroidism or a mass is
This may exceed the tubular reabsorptive capacity palpable in the neck, but total T is normal, either:
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and cause medullary washout. In hyperthyroid ● Repeat total thyroxine measurement in 1–3 weeks,
humans, impaired concentrating ability is present. or
● Because of the advanced age in many hyperthyroid ● Measure free T (best option, but must use assay
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cats, concurrent renal failure is also common. validated for cats), or
● Perform a T (triiodothyronine) suppression test
Typically, a disease of old cats, as the average age is 3
(hyperthyroid cats have little or no suppression), or
12–13 years. It is very rare in cats < 8 years of age.
● Perform a TRH stimulation test (hyperthyroid cats
Weight loss is present in nearly all cats. have no increase in total T after TRH).
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Urine specific gravity ranges from 1.006–1.060 in
Two major presenting forms occur; either restless,
hyperthyroid cats.
hyperactive, and polyphagic (approximately 80% of
cats), or depressed and anorexic (10–30% of cats). Approximately one third of hyperthyroid cats have
mild to moderate azotemia. Many of these cats have
Signs suggest cardiac, GIT or renal disease.
underlying renal failure, but others have pre-renal
Typical signs of hyperthyroidism: azotemia associated with thyrotoxic cardiac failure.