Lect. 6 - Feline hyperthyroidism Flashcards
What hematologic abnormalities may be seen in feline hyperthyroidism?
non-specific signs such as mild- moderate erythrocytosis
What serum biochemical abnormalities may be seen in feline hyperthyroidism?
liver enzyme increases, over 90% of cases see an increase in ALT.
ALP, AST and GGT increases may also occur.
Why might you conduct urinalysis in th eprocess of diagnosis of feline hyperthyroidism?
helps to differentiate diseases with similar clinical signs.
urinary GLU should be checked to rule out diabetes.
UPC and SDMA should be checked to rule out renal disease.
What type of diganostic imaging techniques might you use in the diagnosis of feline hyperthyroidism?
Thoracic radiography (cardiomegaly, effusions)
Echocardiography
Scintigraphy
Total T4 function test in the diagnosis of feline hyperthyroidism is…?
A Very specific method (very few false positives)
Scintigraphy helps to
confirm the diagnosis of hyperthyroidism.
Downside is the Accumulation of radioactive isotopes.
Hyperthyroidism confirmed with what basic evaluations in cats?
Individual cat’s history and clinical signs. Plus Increased Serum TT4↑
Cinical severity Correlates with TT4 concentration meaning?
the more severe the clinical signs, the higher the TT4 concentrations.
TSH is species specific and there are No specially designed assay for cats. The homology with canine and human TSH, is
With canine TSH 95%
With human TSH 78%
What is the most sensitive serum indicator of hyperthyroidism in cats?
FreeT4
FreeT4 concentrations are high in over >97-98% of cases.
However, this isn’t sufficient for diagnosis alone.
As a diagnostic test freeT4 has greater sensitivity but poorer specificity than TT4 concentration.
TSH in hyperthyroid cats is typically…?
Almost all hyperthyroid cats have undetectable TSH concentration.
However TSH is not useful as a sole test because a high portion of healthy cats also have undetetcable levels of TSH.
A detectable TSH concentration more likely reflects?
euthyroidism
because Almost all hyperthyroid cats have undetectable TSH concentration.
T4 within normal limits, but cat with overt
clinical signs of hyperthyroidism
What do you do next?
> TT4 repeated, potentially with different technique
FNA neck region
Scintigraphy
TSH measurement
best first-line diagnostic test for felline hyperthyroidism
Measurement of circulating total T4 concentration.
In cats with appropriate clinical signs, a high total T4 concentration is consistent with hyperthyroidism.
Rarely, cats with few supportive clinical signs may exhibit a
high total T4 concentration and retesting may be required to confirm the diagnosis.
In cats with appropriate clinical signs, finding a normal total T4 concentration (within the reference interval) cannot be
used to exclude the disease and other tests may be required.
Hyperthyroidism is frequently associated with elevated
liver enzyme activities that increase in parallel with thyroid hormone elevations.
Neither free T4 nor TSH concentration should be used alone to diagnose hyperthyroidism, but they can be used as
a second line diagnostic tests to help support diagnosis.
What can interfere with the T4 measurement in hyperthyroid cats?
T4 concentrations can be affected by medications, disease states, and nutrition.
age of Most hyperthyroid cats
Most cats are >10 y (median 13 y)
(Only 5% <10a.)
Classical sign: weight loss despite of increased appetite.
Clinical signs of hyperthyroid cats
Weight loss
Most commonly recognized sign
Often associated with increased appetite
(polyphagia)
Hyperactivity
Nervousness, restlessness, aggressive behavior
Anxiety and restlessness
Can be obvious to owners (the cat yowls)
Aimless pacing and easily interrupted sleep pattern
Skin changes
Dull or matted hair coat
Most important differential diagnoses in association with hyperthyroid cats
- Diabetes mellitus
- Exocrine pancreatic insufficiency (EPI)
- Enteropathies
- Malignant lymphoma
- Cardiomyopathy (Feline hypertrophic
cardiomopathy)
typical Cardiac abnormalties in hyperthyroidism
Murmurs, gallop rhythm, tachycardia (>240 beats
per minute)
Thyroid hormones are both
Inotropic
Chronotropic
Mechanism behind why some cats with hyperthyroidism have cardiac hypertrophy.
Some cats with hyperthyroidism have a cardiac hypertrophy that is mediated by enhanced production of myocardial contractile proteins under the influence of increased concentration of circulating thyroid hormones.
The hypertrophy is reversible on return to euthyroidism.
Why does ALT increase with hyperthyroidism?
thyroid hormones are cytotoxic so they damage hepatocytes. ALT is a cytoplasmic enzyme within hepatocytes and is released with increased T3/4.
ALP also increases, but not as much. Its an enzyme found on hepatocyte cell membranes.