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Small Animal Medicine > Endocrinology - Hyperthyroidism > Flashcards

Endocrinology - Hyperthyroidism Flashcards

1
Q

What is feline hyperthyroidism?

A

A multi-system disorder resulting from the overproduction and secretion of thyroid hormones

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2
Q

True or false: Feline hyperthyroidism is the most common endocrinopathy of cats.

A

TRUE

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3
Q

Whatis the pathophysiology of hyperthyroidism?

A

Autonomous production of T4 from funcitonal thyroid tumors

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4
Q

What can cause hyperthyroidism in cats?

A

Benign multinodular adenomatous hyperplasia and/or thyroid adenomas (>95%) or thyroid carcinoma

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5
Q

What can cause hyperthyroidism in dogs?

A

Thyroid adenocarcinomas

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6
Q

What are the risk factors for hyperthyroidism (unless I mention otherwise, all questions are regarding cats)?

A

Canned food, variable iodine content and other dietary factors, age, use of cat litter, indoor housing, regular exposure to lawn and flea control products

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7
Q

True or False: Hyperthyroidism is likely multifactorial.

A

TRUE

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8
Q

What is the signalment for hyperthyroidism?

A

Senior cats - 8 years or older (mean age is 13 years)

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9
Q

What historical clinical features are associated with hyperthyroidism?

A

Weight loss (>90%), polyphagia (80%), hyperactivity, vomiting, polydipsia/polyuria, hair coat changes, diarrhea/increased fecal volume, panting, and anorexia/hyporexia

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10
Q

What clinical features on PE are associated with hyperthyroidism?

A

From most to least common: palpable thyroid, thin, tachycardia, hyperactive/difficult to examine, heart murmur, skin changes, small kidneys, increased temperature, and gallop rhythm

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11
Q

How does hyperthyroidism affect the cardiovascular system?

A

Increase sympathetic tone and increased metabolic rate +/- systemic hypertension. It can cause hypertrophied cardiac muscle

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12
Q

On PE what physical exam findings will you find with hyperthyroidism?

A

Tachycardia, murmurs, and gallop rhythm

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13
Q

Since hypertension is an associated complication with hyperthyroidism, what must you do when you suspect hyperthyroidism?

A

evaluate the BP

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14
Q

How is hyperthyroidism diagnosed?

A

Consider signalment, history, and PE findings (palpate thyroid)
Consider clin path findings
Specific endocrine diagnostics

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15
Q

What specific endocrine diagnostics can be done for hyperthyroidism?

A

thyroid hormone concentrations, T3 suppression test, and thyroid scintigraphy

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16
Q

What will you find on CBC in hyperthyroid patients?

A

Mild erythrocytosis with a variably present stress leukogram

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17
Q

What will you find on serum biochemistry in patients with hyperthyroidism?

A

Elevated ALT and/or ALP and variably present azotemia

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18
Q

Why can hyperthyroidism mask underlying disease?

A

Because it increases renal blood flow

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19
Q

What will you find on UA in a patient with hyperthyroidism?

A

variable USG and proteinuria

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20
Q

True or False: A majority of cats with hyperthyroidism will have a high total T4.

A

TRUE

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21
Q

Is a high TT4 diagnostic?

A

Yes - typically it is safe to assume that if a cat has an elevated TT4 then it is hyperthyroid

22
Q

Does a normal TT4 rule out hyperthyroidism?

A

No, cats with early or mild hyperthyroidism will have a normal TT4 therefore one TT4 within the referencerange does not rule it out

23
Q

If hyperthyroidism is suspected but TT4 is normal, what can be done?

A

Recheck in 3-6 weeks or use additional diagnostics such as fT4ed, T3 suppression test, or thyroid scintigraphy

24
Q

What does a fT4ed measure?

A

free, unbound fraction of thyroid hormone

25
Q

What is a fT4ed sensitive diagnostic for?

A

hyperthyroidism

26
Q

Since fT4ed is sensitive for diagnosing hyperthyroidism, is it diagnostic as a stand alone test in cats?

A

no - it should not be used as a stand alone

27
Q

When is a T3 suppression test indicated?

A

To confirm diagnosis when clinical suspicion of hyperthyroidism and high-normal TT4

28
Q

In nnormal cats, what will the T4 level be during the T3 suppression test?

A

T4 will fall tp <50% of pre-levels

29
Q

In hyperthyroid cats, what will happen during a T3 suppression test?

A

There will be minimal suppression

30
Q

When is thyroid scintigraphy indicated?

A

To determine the extend of disease or to confirm hyperthyroidism in equivcal cases

31
Q

How is hyperthyroidism treated?

A

Anti-thyroid medication, dietary iodine restriction, radioactive iodine administration, and surgery

32
Q

What are the indications for anti-thyroid drugs?

A

Long-term management of hyperthyroidism, short-term stabilization of patients with hyperthyroidism prior to definitive treatment, and challenge therapy to determine effect of return to euthyroid state on clinical signs and renal function

33
Q

What anti-thyroid drug is commonly used?

A

methimazole

34
Q

What is the mechanism of action of methimazole?

A

Inhibitor of thyroid hormone synthesis via inhibition of thyroid peroxidase

35
Q

What are the adverse effects of methimazole?

A

GI effects, facial excoriatiions, blood dyscrasias, and hepatotoxicity

36
Q

Why would you want to restrict iodine in hyperthyroid patients?

A

because iodine is required for hormone synthesis

37
Q

What is the curative therapy (and gold standard) for hyperthyroidism?

A

radioactive iodine therapy

38
Q

How does radioactive iodine therapy work?

A

It isolates in the funcitoning cells of the thyroid, which are the ones that are overproducing thyroid hormone, and spares the atrophied cells

39
Q

What precautions need to be taken if radioactive iodine therapy is done?

A

The patient should be isolated for a variable period of time

Their feces needs to be collected and isolated until the radiation wears off

40
Q

How long does it take for the patients to become euthyroid after radioactive iodine therapy?

A

within 3 months

41
Q

What surgical option is there for hyperthyroid patients?

A

thyroidectomy - surgical resection of affected thyroid tissue

42
Q

What are the potential complications associated with thyroidectomies?

A

Laryngeal paralysis, hypoparathyroidism, and hypothyroidism

43
Q

What should be considered when chosing the appropriate treatment for a hyperthyroid patient?

A

effectiveness of therapy, durability of therapy, potential side effects or complications, ease for the client, quality of life for the cat, if a follow up is required, cost, and feasibility

44
Q

Canine hyperthyrodidsim is almost always associated with what?

A

thyroid adenocarcinomas

45
Q

What is treatment for canine hyperthyroidism focused on?

A

treating the tumor

46
Q

What are the treatments for canine hyperthyroidism?

A

surgical resection, radiation therapy, and methimazole for palliative care

47
Q

What can cause dietary hyperthyroidism?

A

raw meat diets and fresh/dried gullets

48
Q

What should the fT4 level be in patients with canine hyperthyroidism?

A

It can be normal - there amy be a false elevation from T4-autoantibodies

49
Q

How should you approach a canine with high TT4?

A

Get a thorough history, do a PE, or so an fT4 to rule out antibody interference

50
Q

If dietary contributors are ruled out and fT4 is high in a canine patient, what should be done?

A

Evaluate for thyroid neoplasia with thoracic radiographs, cervical and abdominal ultrasound, cross-sectional imaging, and thyroid scintigraphy

Small Animal Medicine (100 decks)

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