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Endocrine > Thyroid > Flashcards

Thyroid Flashcards

1
Q

The alpha subunit of TSH is identical to that of ___, ____, ____

A

LH, FSH, hCG

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2
Q

What action does TSH have at the thyroid

A

stimulates iodine uptake
thyroid hormone production and release
upregulate TPO

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3
Q

What substances can inhibit thyroid hormone production?

A

glucocorticoids, somatostatin, dopamine

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4
Q

Describe embryonic development and migration of the thyroid gland

A

HPT axis develops by 11 weeks
thyroid starts to function by 18 weeks
migrates via thyroglossal duct from base of tongue to neck

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5
Q

The thyroid gland takes up iodide via ______ under TSH stimulation

A

Na/I symporter

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6
Q

Iodine is ______ and then incorporated into thyroglobulin tyrosyl residues by TPO

A

oxidized/organified

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7
Q

What is the Jod-Basedow phenomenon

A

in setting of longstanding iodine deficiency, patients exposed to high doses of iodine become hyperthyroid

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8
Q

What is the Wolff- Chaikoff effect

A

in setting of longstanding high levels of iodine, organification is transiently blocked to protect from hyperthyroidism
decrease in iodine transport allows for escape and normal thyroid hormone synthesis

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9
Q

Under what conditions is TBG increased

A

hyperestrogenic states- pregnancy, estrogen therapy

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10
Q

Under what conditions is TBG decreased

A

steroids, glucocorticoids, protein malnutrition, cirrhosis, nephrotic syndrome

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11
Q

What is the action of 5’MDIs

A

conversion of T4 to T3 in peripheral tissue
an upregulation of thyroid activity
stimulated by TSH

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12
Q

What is the action of 5- MDIs

A

removes inner iodine, converting T4 to rT3 (inactive)

a downregulation of thyroid activity

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13
Q

Thyroid hormone is critical for neurogenesis and _______ in the brain

A

myelination

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14
Q

What is the effect of thyroid hormone on carbohydrate metabolism?

A

Stimulates glucose absorption, increases gluconeogenesis and glycogenolysis.

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15
Q

What is the effect of thyroid hormone on lipid metabolism?

A

Increases hepatic LDL cholesterol receptors, increases lipolysis
stimulates metabolism of cholesterol to bile acids- hypercholesterolemia in hypothyroid state

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16
Q

What is the effect of thyroid hormone on cardiac function?

A

stimulates cardiac contractility, increases O2 consumption, enhanced sensitivity of tissue to catecholamines

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17
Q

What is the effect of thyroid hormone on bone turnover?

A

stimulates both bone formation and resorption, but resorption prevails in hyperthyroid state

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18
Q

What is the effect of thyroid hormone on the gut?

A

stimulates gut motility

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19
Q

What lab findings are expected in central hypothyroidism

A
  • low T4

- TSH is low or inappropriately normal

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20
Q

What lab findings are expected in primary hypothyroidism

A
  • elevated TSH
  • normal or low T4
  • normal or low T3; remains normal until late in course of hypothyroidism
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21
Q

What lab findings are expected in hyperthyroidism/ thyrotoxicosis

A

low TSH

normal or high T3/ T4

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22
Q

What lab findings are expected in central hyperthyroidism

A

high T3/T4

TSH is high or inappropriately normal

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23
Q

TSI is the causative agent in _______

A

Graves disease

bind TSH receptor, mimic action of TSH

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24
Q

Anti-TPO is the causative agent in __________

A

Hashimoto’s thyroiditis

antibody against enzyme that oxidizes and organifies iodide

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25
Q

List symptoms of hyperthyroidism

A

 Nervousness, agitation, irritability
 Palpitations, tachycardia, atrial fibrillation, exertional dyspnea
 Heat intolerance, increased perspiration, dehydration
 Tremor
 Weight loss or gain
 Hyperdefecation
 Muscle weakness, fatigue
 Menstrual disturbance and infertility
 Insomnia
 Orbitopathy and dermopathy (seen exclusively in Graves’ disease)
 Lid lag, stare

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26
Q

List causes of high uptake thyrotoxicosis

A

Graves disease
toxic multinodular and solitary hyperfunctioning nodules
TSH secreting pituitary adenoma
selective pituitary thyroid hormone resistance

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27
Q

What antibodies are characteristic of Graves disease

A

TSI

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28
Q

What are the most common extra-thyroid manifestations of Graves disease

A

orbitopathy- diplopia, eye irritation, proptosis
associated with smoking

dermopathy- less common

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29
Q

Toxic multinodular and solitary hyperfunctioning nodules are more common in _____ patients

A

older

vs Graves, more common in younger

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30
Q

Why does hyperemesis gravidum present as high uptake thyrotoxicosis

A

cross reactivity of hCG at TSH receptor

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31
Q

What are causes of low uptake thyrotoxicosis

A 
subacute thyroiditis
silent thyroiditis
post partum thyroiditis
struma ovarii
factitious hyperthyroidism
32
Q

Subacute thyroiditis is usually preceded by ______

A

upper respiratory infection

33
Q

What symptom can distinguish subacute vs silent thyroiditis

A

thyroid gland tenderness in subacute but not silent

34
Q

What is the mechanism of increased thyroid hormone in subacute thyroiditis

A

increased release (but NOT production) of thyroid hormone

35
Q

What is the prognosis of subacute thyroiditis

A

self-limited condition
may pass through hypothyroid phase prior to recovery
treat symptomatically

36
Q

______ thyroiditis may have an autoimmune component, usually resolves completely, and the thyroid gland is not tender

A

post-partum

37
Q

What is struma ovarii

A

ovarian tumor with thyroidal elements that autonomously produce thyroid hormone

38
Q

What drugs are used to treat hyperthyroidism

A

PTU

Methimazole

39
Q

What is the mechanism of action of PTU/ methimazole

A

Inhibit iodination of tyrosyl groups in thyroglobulin and coupling to form T3 and T4.

40
Q

Why is there delay in onset of action of PTU/ methimazole?

A

no effect on stored thyroglobulin- must deplete thyroglobulin stores before peripheral thyroid hormone levels begin to decline

41
Q

Why does PTU act faster than methimaxole

A

additional activity of inhibiting conversion of T4 to T3 peripherally

42
Q

What therapy is appropriate for treatment of hyperthyroidism in pregnancy?

A

PTU is the treatment of choice in the first trimester

During the remainder of pregnancy (and at all other times), methimazole is felt to be safer due to the lower risk of hepatoxicity

43
Q

What are adverse effects of PTU and methimazole

A

agranulocytosis
hepatic toxicity
urticaria, rash
vasculitis, arthralgias

44
Q

What is used to ablate thyroid in Graves, thyroid cancer?

A

radioactive I-131

45
Q

What are signs of thyroid storm?

A

thyrotoxicosis, fever, mental status changes

46
Q

How is thyroid storm treated?

A

PTU, beta blocker, glucocorticoids (block T4–> T3)

47
Q

What antibodies are characteristic of Hashimoto’s thyroiditis?

A

anti-TPO

48
Q

What is the drug of choice for hormone replacement in hypothyroidism?

A

levothyroxine- consistent potency, long duration

49
Q

In what settings is liothyronine used?

A

myxedema coma- faster onset

impaired T4–> T3 conversion due to 5’ deiodinase defect

50
Q

How is TSH used to evaluate the effectiveness of a thyroid hormone replacement dose?

A

High TSH = dose is too low. Low TSH = dose is too high.

51
Q

What is myxedema coma?

A

Defined as severe hypothyroidism associated with mental status changes and hypothermia.
Can have associated respiratory failure, hypotension, bradycardia, and hyponatremia

52
Q

How is myxedema coma treated?

A

levothyroxine, possibly liothyronine, glucocorticoids, supportive care

53
Q

TSH may be _____ during the recovery phase from illness, but usually returns to normal within a few months

A

elevated- not indicative of hypothyroidism

54
Q

What are some medical reasons for decreased conversion of T4 to T3

A

caloric restriction
major systemic illness
drugs- PTU, glucocorticoids, propranolol, amiodarone

55
Q

In illness, rT3 is increased due to _____ 5’MDI activity

A

decreased

56
Q

Give a differential diagnosis for thyroid nodules

A 
Adenoma (functioning or nonfunctioning)
Cysts (simple, complex)
Colloid nodules
Developmental abnormalities 
Granulomatous disease
Abscess
Carcinoma
57
Q

What features make malignancy more likely in a patient presenting with a thyroid nodule

A

Age 60
Positive family history, especially for medullary CA or MEN2
Rapid enlargement of the nodule
Hoarseness, dysphagia
History of head/neck irradiation, especially for papillary CA
A cold nodule in the setting of Graves’ disease
Firm or hard or fixed nodule
Cervical lymphadenopathy
Vocal cord paralysis

58
Q

Describe workup of a thyroid nodule

A
  • if TSH is normal or high- do FNA

- if TSH is low, do radionuclide imaging

59
Q

FNA cannot distinguish between ______ and ______

A

follicular adenoma and follicular carcinoma- need to see tissue architecture to distinguish between these two

60
Q

What type of thyroid cancer is suspected if:

  • complex branching papillae with fibrovascular cores associated wiht folicles
  • cells are cuboidal, nuclei are overlapping
  • nuclear clearing (orphan annie eye cells)
  • longitudinal nuclear grooves
  • psammoma bodies
A

papillary thyroid cancer

61
Q

Metastases in papillary thyroid cancer occur via:

A

lymphatics

62
Q

How is papillary thyroid cancer treated?

A

thyroidectomy +/- radio ablation

63
Q

What gene mutations are associated with papillary thyroid cancer?

A

RET, BRAF, NTRK

64
Q

What is the prognosis for papillary thyroid cancer

A

excellent

65
Q

What type of thyroid cancer is suspected if:

  • follicular differentiation
  • invasion of adjacent thyroid parenchyma
  • capsule forms
A

follicular

66
Q

Follicular thyroid cancer secretes _____

A

thyroglobulin- used as a tumor marker

67
Q

Follicular thyroid cancer metastasizes:

A

hematogenously

68
Q

How is follicular thyroid cancer diagnosed?

A

cannot dx by FNA, need a full tissue specimen to assess architecture, invasion of capsule

69
Q

What type of thyroid cancer is suspected if:

  • firm rapidly growing mass
  • de-differentiated cells that do not secrete thyroglobulin
  • spindle or squamoid cells
  • cells are pleiomorphic
A

anaplastic

70
Q

What mutation is associated with anaplastic cancer

A

BRAF

71
Q

_______ is a malignancy of the C cells of they thyroid gland

A

medulary

72
Q

What type of thyroid cancer is suspected if:

  • polygonal, plasmacystoid, or spindle cells
  • cells have granular cytoplasm and uniform round nuclei
  • amyloid deposits
A

medullary

73
Q

Medullary cancers secrete _____

A

calcitonin

74
Q

List the features of MEN1

A

Parathyroid hyperplasia
Pancreatic islet cell tumors (gastrin, insulin, glucagon, somatostatin, VIP, pancreatic
polypeptide)
Pituitary adenoma

chromosome 11; MENIN gene, loss of tumor suppression

75
Q

List the features of MEN2a

A

Parathyroid hyperplasia
Thyroid - medullary carcinoma of the thyroid (defining feature of MEN2)
Adrenal - pheochromocytoma

chromosome 10, RET oncogene activation in MEN 2a and 2b

76
Q

List the features of MEN2b

A 
Medullary CA of the thyroid 
Pheochromocytoma
NOT parathyroid
Marfanoid habitus
Mucosal neuromas - usually present before other manifestations arise.

Endocrine (19 decks)

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