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ACVIM Specialty 2023 > Endocrine: Hyperthyroidism and some acromegaly > Flashcards

Endocrine: Hyperthyroidism and some acromegaly Flashcards

1
Q

What are some theoretical triggers for feline hyperthyroidism?

A
  • TSH receptor mutations, leading to decreases in expression on Gi proteins, resulting in sustain secretion of thyroid hormone?
  • Increased iodine or goitrogens in canned cat food?
  • PBDEs in the environment?
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2
Q

What percent of cats with hyperthyroidism have bilateral adenomas? What is the prevalence of carcinomas?

A

Adenomas - 50% bilateral
Carcinoma - 1-2%

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3
Q

How does hyperthyroidism increase GFR?

A
  • Decreased afferent arteriolar resistance
  • Increased hydrostatic pressure from increase cardiac output (chronotropic and inotropic effects)
  • Increases chloride ion channels in the proximal tubule/loop => decreased chloride load sensed by the macula dense => increased GFR
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4
Q

What changes might be noticed on the CBC of hyperthyroid cats?

A

Mild erythrocytosis (likely due to increased cellular oxygen demand)

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5
Q

What are the detrimental effects of hyperthyroidism on the kidneys?

A

Local activation of RAAS => hyperfiltration of the nephrons => glomerular capillary hypertension, proteinuria, and potential glomerulosclerosis

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6
Q

What is the mechanism of action of methimazole?

A

Inhibits thyroid peroxidase => blockade of thyroid hormone synthesis

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7
Q

After starting methimazole, when should the cat be rechecked?

A

Every 2-3 weeks, run T4, CBC, Chem until well controlled

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8
Q

What are potential side effects of methimazole?

A
  • V/D/anorexia
  • Facial excoriation
  • Anemia, thrombocytopenia, leukopenia
  • Coagulopathy (rare)
  • ELE (rare, idiosyncratic)
  • Myasthenia gravis (rare)

Usually occur in the first 3 months

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9
Q

What percent of cats fed Y/D develop a normal TT4?

A

42% in 21-60 days
83% in 61-180 days
Takes longer in cats with a higher TT4

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10
Q

Is the Y/D diet clinically effective?

A

Questions about clinical efficacy - lack of weight gain and tachycardia persist in some cats despite a normal TT4

Failure of ELE to normalize in most cats

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11
Q

If a cat is treated with I131, when should they be rechecked?

A

1, 2, and 6 months after: CBC/chem, UA, BP and TT4

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12
Q

What clinical signs are observed with acute thyrotoxicosis or a thyroid storm?

A

Fever, tachycardia, tachypnea, V/D, CNS signs, hypokalemia

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13
Q

How is acute thyrotoxicosis treated?

A

Methimazole, beta blockers, treat specific abnormalities

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14
Q

In dogs, what is the most common cause of hyperthyroidism?

A

Functional, malignant carcinoma
- 70% arise from the follicular cells
- 30% arise from the medullary cells or parafollicular cells
Adenoma in 10-30%

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15
Q

The long acting release form of pasireotide (once monthly injection) had what benefits in cats over 6 months?

A

Decreased IGF-1 and mean insulin resistance, median insulin dose dropped from 1.5 to 0.3.

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16
Q

Cats with acromegaly demonstrate what changes on abdominal US?

A

Enlargement of the kidneys, adrenals, pancreas +/- liver

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17
Q

IGF-1 increased 2-4 weeks after starting what drug? What did it predict?

A

Increased (300-670) after starting insulin in new diabetics and predicted remission

18
Q

How frequently do cats undergoing stereotactic radiation for HS achieve a decrease in the required insulin dose?

A

95% experienced a decrease in dose
62% achieved permanent remission

19
Q

How long did it take for insulin resistance to improve after stereotactic radiation?

A

Median to lowest insulin dose 9.5 months

20
Q

What is a potential side effect of stereotactic radiation for HS?

A

Hypothyroidism

21
Q

In cats undergoing hypophysectomy, what is the peri-operative morbidity rate?

A

10-15%

22
Q

In cats undergoing hypophysectomy, what percent achieve improved control of diabetes and when?

A

95% of surviving cats, remission in 71%
Improved quickly - 9 days median

23
Q

Is the MST better for hypophysectomy or stereotactic radiation?

A

Practically, neither (1070 days vs 853 days in one study, 1350 days in another)

24
Q

What is cabergoline?

A

Dopamine receptor agonist

25
Q

Does IGF-1 concentration vary with body weight/obesity?

A

Not in one study

26
Q

After 6 weeks of levothyroxine treatment, hypothyroid dogs displayed what?

A

Increased activity levels

27
Q

How long should levothyroxine be discontinued before performing thyroid function testing?

A

At least one week

28
Q

How can GH potentially be used to differentiate between hypothyroid dogs and euthyroid sick dogs?

A

Hypothyroid dogs had higher GH concentrations that euthyroid dogs (presumably from increased TRH activity). Also had increased GH after TRH administration, while euthyroid dogs did not

29
Q

What changes can be seen on ECG in hypothyroid dogs?

A

Bradycardia, decreased P wave and R wave amplitude - resolve with levothyroxine

30
Q

In cats with primary, adult onset hypothyroidism, thyroid atrophy is rare. What occurs instead?

A

Goitrous thyroid hyperplasia, resulting in a palpable mass

31
Q

In cats with euthyroid illness, what thyroid hormone were predictors of mortality?

A

Lower T4 and TSH predicted mortality

32
Q

What percent of cats with thyroid cysts are hyperthyroid?

A

93%

33
Q

What are thyroid cysts on necropsy?

A

Usually cystadenoma or carcinoma

34
Q

Do thyroid cysts resolve with I131?

A

Hyperthyroidism resolved in 92% of cats, but cysts only resolved in 50%. More likely to resolve if smaller (>8cm)

35
Q

Are abdominal ultrasound and thoracic radiographs needed in hyperthyroid cats or prior to I131 therapy?

A

Not necessarily - low incidence of findings in both papers (only 8% of cats had a change in treatment plan due to CXR) - base on individual cat

36
Q

What is the coagulation status of hyperthyroid cats?

A

Higher fibrinogen, AT activity, and VwF:Ag concentration BUT are not more likely to be hypercoagulable

37
Q

What dose of I131 can be used in cats with mild to moderate hyperthyroidism and results in a cure rate of >95% with a reduced frequency of hypothyroidism and azotemia?

A

2 millicures (lower than the historic 4)

38
Q

Cats with bilateral hyperthyroidism or multiple affected foci were more likely to develop what post I131?

A

Hypothyroidism

39
Q

Higher thyroid/salivary gland ratios on scintigraphy is related to what outcome post-I131?

A

Persistent hyperthyroidism

40
Q

What percent of cats developed recurrent hyperthyroidism in the years (600-2000 days) after thyroidectomy?

A

44%

ACVIM Specialty 2023 (38 decks)

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