Lect. 6 - Feline hyperthyroidism

Question 1

What hematologic abnormalities may be seen in feline hyperthyroidism?

Answer 1

non-specific signs such as mild- moderate erythrocytosis

Question 2

What serum biochemical abnormalities may be seen in feline hyperthyroidism?

Answer 2

liver enzyme increases, over 90% of cases see an increase in ALT.

ALP, AST and GGT increases may also occur.

Question 3

Why might you conduct urinalysis in th eprocess of diagnosis of feline hyperthyroidism?

Answer 3

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.

Question 4

What type of diganostic imaging techniques might you use in the diagnosis of feline hyperthyroidism?

Answer 4

Thoracic radiography (cardiomegaly, effusions)
Echocardiography
Scintigraphy

Question 5

Total T4 function test in the diagnosis of feline hyperthyroidism is…?

Answer 5

A Very specific method (very few false positives)

Question 6

Scintigraphy helps to

Answer 6

confirm the diagnosis of hyperthyroidism.

Downside is the Accumulation of radioactive isotopes.

Question 7

Hyperthyroidism confirmed with what basic evaluations in cats?

Answer 7

Individual cat’s history and clinical signs. Plus Increased Serum TT4↑

Question 8

Cinical severity Correlates with TT4 concentration meaning?

Answer 8

the more severe the clinical signs, the higher the TT4 concentrations.

Question 9

TSH is species specific and there are No specially designed assay for cats. The homology with canine and human TSH, is

Answer 9

With canine TSH 95%
With human TSH 78%

Question 10

What is the most sensitive serum indicator of hyperthyroidism in cats?

Answer 10

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.

Question 11

TSH in hyperthyroid cats is typically…?

Answer 11

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.

Question 12

A detectable TSH concentration more likely reflects?

Answer 12

euthyroidism

because Almost all hyperthyroid cats have undetectable TSH concentration.

Question 13

T4 within normal limits, but cat with overt
clinical signs of hyperthyroidism

What do you do next?

Answer 13

> TT4 repeated, potentially with different technique
FNA neck region
Scintigraphy
TSH measurement

Question 14

best first-line diagnostic test for felline hyperthyroidism

Answer 14

Measurement of circulating total T4 concentration.

In cats with appropriate clinical signs, a high total T4 concentration is consistent with hyperthyroidism.

Question 15

Rarely, cats with few supportive clinical signs may exhibit a

Answer 15

high total T4 concentration and retesting may be required to confirm the diagnosis.

Question 16

In cats with appropriate clinical signs, finding a normal total T4 concentration (within the reference interval) cannot be

Answer 16

used to exclude the disease and other tests may be required.

Question 17

Hyperthyroidism is frequently associated with elevated

Answer 17

liver enzyme activities that increase in parallel with thyroid hormone elevations.

Question 18

Neither free T4 nor TSH concentration should be used alone to diagnose hyperthyroidism, but they can be used as

Answer 18

a second line diagnostic tests to help support diagnosis.

Question 19

What can interfere with the T4 measurement in hyperthyroid cats?

Answer 19

T4 concentrations can be affected by medications, disease states, and nutrition.

Question 20

age of Most hyperthyroid cats

Answer 20

Most cats are >10 y (median 13 y)

(Only 5% <10a.)

Classical sign: weight loss despite of increased appetite.

Question 21

Clinical signs of hyperthyroid cats

Answer 21

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

Question 22

Most important differential diagnoses in association with hyperthyroid cats

Answer 22

• Diabetes mellitus
• Exocrine pancreatic insufficiency (EPI)
• Enteropathies
• Malignant lymphoma
• Cardiomyopathy (Feline hypertrophic
  cardiomopathy)

Question 23

typical Cardiac abnormalties in hyperthyroidism

Answer 23

Murmurs, gallop rhythm, tachycardia (>240 beats
per minute)

Thyroid hormones are both
Inotropic
Chronotropic

Question 24

Mechanism behind why some cats with hyperthyroidism have cardiac hypertrophy.

Answer 24

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.

Question 25

Why does ALT increase with hyperthyroidism?

Answer 25

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.