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Small Animal Medicine > Endocrinology - Hypothyroidism > Flashcards

Endocrinology - Hypothyroidism Flashcards

1
Q

What does TBG stand for?

A

thyroid hormone binding globulin

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2
Q

What does TSH stand for?

A

thyroid stimulating hormone - thyrotropin

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3
Q

What does TRH stand for?

A

Thyrotropin releasing hormone

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4
Q

What does T4 stand for?

A

Thyroxine

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5
Q

What does TgAA stand for?

A

Thyroglobulin antibodies

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6
Q

What does T4AA stand for?

A

T4 autoantibodies

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7
Q

What does NTI stand for?

A

non-thyroidal illness

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8
Q

What does ED stand for? (in relation to the thyroid not male pee pee issues)

A

equilibirum dialysis

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9
Q

What does RIA stand for?

A

radioimmunoassay

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10
Q

The thyroid hormone has a lot of functions. It is important to keep in mind that ___ ______ ______ escapes the adverse effects of excess or insufficiency.

A

No organ system

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11
Q

What is the major secreted thyroid hormone?

A

T4

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12
Q

What is the major biologically active thyroid hormone?

A

T3

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13
Q

Is T3 or T4 more potent?

A

T3

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14
Q

What form of hormone, bound or unbound, is biologically active and able to mediate regulatory feedback?

A

The unbound (free) form

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15
Q

What are the 2 major categories of primary hypothyroidism?

A

Lymphocytic thyroiditis or idiopathic thyroid degeneration

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16
Q

What is lymphocytic thyroiditis?

A

Lymphocytic infiltration with progressive destruction of thyroid follicles

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17
Q

How can inflammation in cases of lymphocytic thyroiditis be measureD?

A

In the serum by measuring antibodies to thyroid components - usually thyroglobulin

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18
Q

True or False: You will see clinical signs well before extensive damage by lymphocytic thyroiditis occurs.

A

False - extensive destruction occurs before clinical signs of hypothyroidism develops

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19
Q

What is idiopathic thyroid degeneration?

A

Loss of thyroid parenchyma and then replaced by adipose and fibrous tissue

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20
Q

What breeds are over represented by hypothyroidism?

A

Doberman, golden retriever, labrador retriever, and cocker spaniel

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21
Q

When do clinical signs due to hypothyroidism typically develop?

A

in middle aged animals

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22
Q

What general clinical signs are associated with hypothyroidism?

A

Decreased metabolic rate, skin/haircoat changes (most common), neurologic, ocular, and myxedema coma

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23
Q

What clinical signs are associated with decreased metabolic rate?

A

lethargy, dullness, weight gain without polyphagia

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24
Q

What skin/haircoat changes are associated with hypothyroidism?

A

Alopecia, hyperpigmentation, and pyoderma

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25
Q

What neurologic clinical signs are associated with hypothyroidism?

A

Peripheral neuropathy, central vestibular disease, subclinical myopathy, and less commonly (seizures, laryngeal paralysis, megaesophagus, MG, and others)

26
Q

What ocular clinical signs are associated with hypothyroidism?

A

corneal lipid

27
Q

What is a myxedema coma?

A

life-threatening hypothermia, bradyarrhythmias, and rapid deterioration in the mental state

28
Q

What clinical pathology is associated with hypothyroidism?

A

Normocytic, normochromic, non-regenerative anemia (30% of dogs), hypercholesterolemia (75% of dogs), hypertriglyceridemia, and a normal UA

29
Q

What thyroid screening test is used to rule out hypothyroidism?

A

Total thyroxine (TT4)

30
Q

What forms of T4 does TT4 screen for?

A

bound and unbound

31
Q

True or False: A TT4 can diagnose hypothyroidism.

A

False - you should never use a low T4 in isolation to diagnose hypothyroidism

32
Q

Why is as TT4 screen helpful in ruling out hypothyroidism?

A

Because very few true hypothyroid dogs will have a normal T4

33
Q

What can cause a low TT4 in euthyroid dogs?

A

Breed variation, age, random fluctuations/diurnal rhythm, drugs, and non-thyroidal illness

34
Q

What drugs can cause a decrease in TT4 and fT4, an increase in TSH, and clinical signs of hypothyroidism?

A

Sulfonamides

35
Q

What drugs can cause a decrease in TT4, a decrease to normal fT4, a normal TSH, and no clinical signs?

A

glucocorticoids

36
Q

What drug can cause a decreae in TT4 and fT4, an increase in TSH (but within the reference range), and no clinical signs?

A

Phenobarbital

37
Q

What is non-thyroidal illness/sick euthyroid syndrome?

A

A syndrome where there are low thyroid levels in a patient with a fully functioning thyroid

38
Q

What can cause sick euthyroid syndrome?

A

systemic illness, surgery, trauma, and malnutrition

39
Q

How does sick euthyroid syndrome effect thyroid diagnostics?

A

It commonly decreases TT4, decreases fT4, and rarely increases TSH

40
Q

What is the ‘amazing-perfect’ diagnosis for euthyroid sick syndrome?

A

low TT4 and fT4 with a high TSH

41
Q

What should you do if a patient has a concurrent illness but you suspect a thyroid problem?

A

Wait until the concurrent illness has resolved

42
Q

What is the use for fT4 screening test?

A

It is used in place of TT4 as a screening test or as a follow-up to a low TT4 if there is a non-thyroidal illness

43
Q

What causes an elevated TSH level?

A

Lack of negative feedback in primary hypothyroidism

44
Q

What is the use for a TSH test?

A

It is used in combination with TT4 and/or fT4 to support a diagnosis of primary hypothyroidism

45
Q

True or False: Elevated TSH is highly specific for hypothyroidism

A

TRUE

46
Q

What thyroid screening test is not helpful to test for hypothyroidism in dogs and why?

A

Total T3 because a large proportion of TT3 is not made in the thyroid gland, and it is not the predominate circulating hormone - 90% of hypothyroid dogs have a normal TT3

47
Q

How can thyroiditis be diagnosed?

A

Via antibodies (serum thyroglobulin autoantibodies) in circulation during the inflammatory phase of disease

48
Q

What is the thyroiditis antibody that circulates in dogs?

A

anti-thyroglobulin

49
Q

How is the serum thyroglobulin autoantibodies test used?

A

To add support to suspicion of hypothyroidism when TT4/FT4+TSH is equivocal

50
Q

What is the serum T3 and T4 autoantibody test used to do?

A

Clarify unexpected T4 or T3 results - it also supports diagnostic lymphocytic thyroiditis

51
Q

When should you consider treatment trials?

A

When you have low TT4 and a normal TSH, normal TT4 and positive T4AA, and/or normal TT4 and high TSH with clinical suspician

52
Q

How is hypothyroidism treated?

A

Levothyroxine sodium - 0.02 mg/kg BID

53
Q

When is it critical to monitor treatment for hypothyroidism?

A

After 6-8 weeks of supplementation

54
Q

With appropriate treatment, all clinical signs of hypothyroidism are ______.

A

reversible

55
Q

What is important to inform your clients about the dermatologic abnormalities associated with hypothyroidism and treatment?

A

they can get worse before they get better

56
Q

When monitoring response to treatment, what do you want to measure and when?

A

Serum T4 - 4-8 weeks after initiating therapy, when signs of thyrotoxicosis develop or when there has been minimal response to therapy
T4 and TSH - 4-6 hours after administration of supplementation if autoantibodies are present, you cannot monitor with T4 and need to use fT4ED

57
Q

Where should the post-dose T4 level be in response to treatment?

A

in the upper half or above the reference range

58
Q

Where should the TSH levels be in response to treatment?

A

in the reference range

59
Q

The dose of thyroid hormone supplementation should be reduced if the post-pill T4 is greater than what value?

A

6 micrograms/dl

60
Q

What is the life expectancy of a dog with hypothyroidism?

A

it should be normal with normal treatment

Small Animal Medicine (100 decks)

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