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CM 1A: Heme/Onc/Endo > Lecture 16: Thyroid Disorders Part 1 > Flashcards

Lecture 16: Thyroid Disorders Part 1 Flashcards

1
Q

What is the cell that makes thyroid hormone? Where does it get stored?

A

Follicular cells make thyroid hormone.

Colloid is where thyroid hormone is stored.

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2
Q

What does high T3 and T4 inhibit?

A

Both TRH and TSH.

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3
Q

What is thyroglobulin? (Tg)

A

Large glycoprotein synthesized by follicular cells of the thyroid; released into the colloid.

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4
Q

What mineral is required for normal thyroid function? What enzyme processes it?

A

Iodine is required.

Thyroid peroxidase (TPO) processes it.

30x more iodine in your thyroid than serum.

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5
Q

Where is iodine deficiency most common in and what conditions is it associated with?

A

Common in developing countries.
Goiters, hypothyroidism, mental retardation.

Russia has iodine deficiency

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6
Q

Clinical

Kearra, a 13-year-old female, has an intrinsic genetic deficiency that stops her from producing thyroglobulin. What would we expect to happen…
○ To her T3 and T4 levels?
○ To her TSH and TRH levels?

A

T3/T4 = Low
TSH/TRH = High

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7
Q

Clinical

Pari, a 31-year-old female from India, has suffered from lifelong iodine deficiency. What would we expect to happen…
○ To her T3 and T4 levels?
○ To her TSH and TRH levels?

A

T3/T4 = Low
TSH/TRH = High

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8
Q

Clinical

Michael, a 64-year-old male, just had a total thyroidectomy for thyroid cancer. What would we expect to happen to his thyroglobulin level?

A

Low

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9
Q

What is a Tg molecule?

A

Precursor to multiple T3/T4

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10
Q

What is the most common thyroid hormone?

A

T4

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11
Q

What happens to T3 and T4 in the plasma?

A

Binds to plasma protein.
T4 is 99.8% bound.
T3 is 70-99% bound.

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12
Q

Which thyroid hormone is released to tissues daily? Why?

A

T3 is released daily because it has a lower binding affinity.
T4 is only released every 6 days.

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13
Q

What happens to T4 once it is absorbed by tissues?

A

It is converted to T3 by deiodinases

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14
Q

What proteins bind T3 and T4?

A
  • Thyroxine-binding globulin (TBG) 80% of T3/T4.
  • Transthyretin (TTR)
  • Albumin
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15
Q

What is rT3? Why is it alarming if we have a lot?

A

rT3 is metabolically INactive.

It is elevated in states of trauma, shock, burn patients, etc…

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16
Q

Clinical

What would happen to the absorption of oral thyroid hormone
replacement therapy if a pt took this medication with a meal?

A

Less absorption than normal

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17
Q

Clinical

What would happen if someone was deficient in TBG, but otherwise metabolically normal…
○ To their total T3 and T4 levels?
○ To their free (unbound) T3 and T4 levels?
○ To their TSH and TRH levels?

A
  • Total T3/T4 = decreased.
  • Free T3/T4 = same.
  • TSH/TRH = no change.
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18
Q

Clinical

Estrogen increases the levels of TBG. If someone had high estrogen levels (e.g. pregnancy, contraception), what would happen…
○ To their total T3 and T4 levels?
○ To their free (unbound) T3 and T4 levels?
○ To their TSH and TRH levels?

A
  • Total T3/T4 = increased
  • Free T3/T4 = same
  • TSH/TRH = same
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19
Q

Clinical

Jamal is a healthy, euthyroid 22-year-old male who presents for a routine physical. As part of his physical, he has thyroid function studies drawn. Should we expect to see higher levels of serum T3 or serum T4 on labs?

A

Serum T4 would be higher.

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20
Q

Clinical

What would an elevated level of reverse T3 (rT3) suggest?

A

Increased stress on the body.

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21
Q

Clinical

Would we expect to see symptoms of hyperthyroidism (overactive thyroid), hypothyroidism (underactive thyroid), or euthyroidism (normally functioning thyroid) in a patient with elevated rT3?

A

Underactive thyroid symptoms.
Hypothyroidism because rT3 is metabolically inactive.

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22
Q

What is the general effect of thyroid hormones on tissues?

A

Increased functional activity.

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23
Q

Which thyroid hormone binds with greater affinity to cell receptors?

A

T3 has 10-15x more affinity.

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24
Q

What complex is formed by T3 binding to receptors?

A

Thyroid receptor-Retinoid x receptors (TR-RXR complex)

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25
Q

What does the TR-RXR complex do?

A

Altering gene expression, usually causing a target gene to be expressed.

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26
Q

What are the growth effects of thyroid hormone?

A
  • Promotes growth of skeletal tissue and skeletal maturation.
  • Promotes growth/maturation of brain in fetal phase, first few years of life.

Fetal thyroid levels are checked on birth.

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27
Q

What are the effects of thyroid hormone on carbohydrate metabolism?

A

Promotes all aspects:
* Glucose absorption/uptake
* Gluconeogenesis
* Glycolysis
* Insulin secretion

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28
Q

What are the effects of thyroid hormone on fat metabolism?

A

Promotes all aspects:
* Increased FFA and decreased body fat
* Decreased concentrations of cholesterol, phospholipids, and TGs.
* Reduce fatty deposits in liver.

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29
Q

What are the effects of thyroid hormone on BMR?

A
  • Increased thyroid hormone = 60-100% increase in BMR.
  • Decreased thyroid hormone = 50% reduction in BMR.
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30
Q

Clinical

Iris is a 6-year-old female with congenital hypothyroidism (underactive thyroid) that has not been treated well up to this point. What effect would we expect to see on her stature (height), and why?

A

Short due to decreased bone growth.

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31
Q

Clinical

What body habitus would you expect a patient with chronic, untreated hyperthyroidism to have, and why?

A

Very skinny, thin body habitus due to increased BMR.

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32
Q

Clinical

Diego is a 44-year-old male who suffers from obesity, hyperlipidemia, and fatty liver disease. He has been told he has a thyroid abnormality on his labs. Would you expect him to be hyper-, hypo-, or euthyroid?

A

Hypothyroidism

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33
Q

What are the effects of thyroid hormone on the heart?

A
  • Minor increase will increase heart strength.
  • Major increases will weaken heart due to protein catabolism.
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34
Q

What are the effects of excess or reduced thyroid hormone on muscles?

A
  • Excess = muscle weakness due to protein catabolism.
  • Reduced = sluggish, slow post-contraction relaxation.
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35
Q

What are the effects of thyroid hormone on the endocrine system?

A

Increased secretion of most hormones.

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36
Q

Clinical

Latisha is an obese 32-year-old female with heavy menses and a history of thyroid disease. Assuming her thyroid is causing her irregular menses, what thyroid disorder is she more likely to have (overactive or underactive)?

A

Underactive thyroid. (Hypothyroidism)

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37
Q

Clinical

Robert is an 87-year-old male with hypothyroidism and dementia. He presents with acute onset of increased anxiety, agitation and insomnia.
His daughter says “I think he has not been taking his thyroid medication the way he is supposed to.” Is he more likely to have taken extra doses of his thyroid hormone therapy, or have missed doses?

A

Extra doses, since he has signs of increased agitation and insomnia

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38
Q

What tests make up a typical thyroid panel?

A
  • TSH
  • T3
  • T4
  • Free T4/FT4
39
Q

What can interfere with TSH tests? What should we do?

A

Check thyroid levels at the same time because TSH is highest at 10pm and lowest at 10am.

40
Q

What two interpretations can we infer from a high TSH?

A
  • Low T3/T4 (usual)
  • Overfunctioning pituitary gland
41
Q

What interpretations can we infer from a low TSH?

A
  • High T3/T4
  • Underfunctioning pituitary
  • Underfunctioning hypothalamus
42
Q

What drug can affect TSH, T3/T4?

A

Lithium can cause simultaneous increased TSH with decreased T3/T4.

43
Q

When do we use Free T4? When can we not?

A

We can use it to reduce confounding factors if serum protein levels are off.
Neonates have high levels of FT4 so we prefer total T4 for neonates.

44
Q

What two interpretations can we infer from an elevated T3/T4 or elevated FT3/FT4?

A
  • Excess amounts of thyroid hormone.
  • Increased serum proteins, such as TBG.
45
Q

What two interpretations can we infer from low levels of T3/T4 or FT3/FT4?

A
  • Insufficient amounts of thyroid hormone
  • Protein-depleted state
46
Q

What usually causes just low T3/FT3?

A

Decreased conversion of T4 to T3, aka liver disease or severe illness.

47
Q

What usually causes low T4/FT4 only?

A

T3-only medications such as cytomel.

48
Q

Where is TBG released from?

49
Q

When do we order a TBG level?

A

Determining if a patient is hypo/hyperthyroid or if they just have abnormal levels of bound/unbound T3/T4.

50
Q

What 2 interpretations can we infer from high TBG?

A
  • Elevated estrogen
  • Infectious hepatitis
51
Q

What 4 interpretations can we infer from low TBG?

A
  • Hypoproteinemia
  • Ovarian failure
  • Elevated testosterone levels
  • Major Stress
52
Q

When is a TRH stimulation test used?

A
  • Differentiate etiology of hypothyroidism
  • Evaluate degree of pituitary suppression in hyperthyroidism pts.
53
Q

What can interfere with a TRH stimulation test?

A
  • Exaggerated in women/pregnancy
  • Diminished in the elderly and those with MDD.
54
Q

What is a normal TRH stimulation test?

A

2x increase in baseline TSH within 30 minutes.

55
Q

If we have no increase in TSH in a TRH stimulation test, what kind of hypothyroidism is it?

A

Secondary hypothyroidism

56
Q

If we have a delayed increase in baseline TSH after a TRH stimulation test, what kind of hypothyroidism is it?

A

Tertiary hypothyroidism

57
Q

If we have a blunted TSH response due to maximal pituitary suppression by T3/T4 in a TRH stimulation test, what does that suggest?

A

Hyperthyroidism

58
Q

What is the most common demographic for hypothyroidism?

A

Female pts > 60

59
Q

What can occur to a fetus due to maternal hypothyroidism?

A

Decreased IQ, since thyroid hormone is needed for brain development in a fetus.

60
Q

What are the 3 types of hypothyroidism?

A
  • Primary: failure of thyroid to release T3/T4
  • Secondary: failure of pituitary to release TSH
  • Tertiary: failure of hypothalamus to release TRH
61
Q

What is the MC etiology of hypothyroidism worldwide? Developed countries?

A

Worldwide: Iodine deficiency
Developed: Hashimoto’s thyroiditis

62
Q

What two medications can induce hypothyroidism?

A
  • Amiodarone
  • Lithium
63
Q

What kind of symptoms does hypothyroidism typically present?

A
  • Fatigue, general weakness, weight gain
  • Dry skin, hair loss
  • Dysphagia, constipation, poor appetite
  • Cognitive impairment, paresthesias
  • Depression
  • Hoarseness
  • Arthralgias, myalgias
  • Dyspnea
  • Lower libido, ED, irregular menses
64
Q

What kind of signs does hypothyroidism typically present?

A
  • Weight gain
  • Dry skin, spare/coarse hair, thin/brittle nails
  • Bradycardia, edema
  • Delayed DTR relaxation, carpal tunnel syndrome
  • Thinning of the outer eyebrows
  • Serous effusions
  • Cold extremities
65
Q

What labs should we order for an initial workup of hypothyroidism?

A
  • Serum TSH/FT4
  • CMP
  • CBC
66
Q

What labs screen for hashimoto’s thyroiditis?

A

Anti-thyroid peroxidase antibody (anti-TPO)
Anti-thyroglobulin antibody (anti-Tg)

67
Q

What would prompt us to order a thyroid US?

A

Presence of thyromegaly or thyroid nodule on PE.

68
Q

What kind of patients may have limited thyroid US results?

69
Q

What might an enlarged thymus suggest?

A

Autoimmune thyroiditis

70
Q

What might an enlarged pituitary suggest?

A

Hyperplasia of TSH-secreting cells

71
Q

What pulmonary condition are people with hypothryoidism at higher risk for?

A

Bacterial pneumonia risk

72
Q

What is the life-threatening crisis of hypothyroidism?

A

Myxedema Crisis

73
Q

What is the classic patient that has a myxedema crisis?

A

Elderly women who have a stroke or stop taking their thyroid medications.

74
Q

What is the typical presentation for a myxedema crisis?

A
  • Hypothermia
  • Hypotension
  • Hypoventilation
  • Hyponatremia
  • Hypoglycemia
  • Cognitive impairment
75
Q

What is the treatment for a myxedema crisis?

A

IV levothyroxine therapy
If in myxedema coma, add IV T3 also.
Supportive:
* Warming blankets
* Intubation
* Tx underlying cause

76
Q

What is subclinical hypothyroidism? MC demographic?

A
  • Normal serum FT4 with elevated TSH.
  • MC in seniors.
77
Q

How does subclinical hypothyroidism present?

A

Asymptomatic or mild.

78
Q

How is subclinical hypothyroidism treated?

A

Observation if no s/s.
Trial of LT4 if symptomatic.
Usually resolves spontaneously.

79
Q

What is the first-line therapy for hypothyroidism?

A

Levothyroxine (synthetic T4)

80
Q

What are the second-line options for hypothyroidism?

A
  • Combined T3/T4: Armour thyroid
  • Synthetic T3: Liothyronine
81
Q

What should you evaluate for prior to starting levothyroxine?

A
  • Adrenal insufficiency
  • Angina
82
Q

What are the dosing considerations for levothyroxine?

A
  • Take on empty stomach with water at regular time.
  • ~4 weeks peak response
  • Different preps = different bioavailability
83
Q

What is the main goal of hypothyroidism therapy?

A

Normalizing TSH levels

84
Q

What is the BBW of all thyroid medications?

A

Do not use as treatment for obesity.

85
Q

Clincal

A patient has an increased TSH level. What, if any, adjustment should be made to her thyroid hormone replacement medication?

A

Increased her thyroid hormone dose, which will lower her TSH.

86
Q

Clinical

A patient has a normal TSH level. What, if any, adjustment should be made to her thyroid hormone replacement medication?

A

Keep thyroid hormone medication dosage the same.

87
Q

Clinical

A patient has an decreased TSH level. What, if any, adjustment should be made to her thyroid hormone replacement medication?

A

Decrease her thyroid hormone dosage, which will increase her TSH.

88
Q

History of what conditions may require slightly higher TSH?

A

History of CAD or AFIB.

89
Q

What are we worried about in very low levels of serum TSH?

A
  • Risk of Afib
  • Osteoporosis
90
Q

What is levothyroxine indicated for?

A
  • Hypothyroidism
  • TSH suppression (Cancer/goiter)
91
Q

What kind of patients need slightly less levothyroxine?

A

Elderly or CAD.

92
Q

What are the SE of levothyroxine?

A

Hyperthyroidism effects.

93
Q

What are the CIs of levothyroxine?

A
  • Allergy
  • Acute MI
  • Thyrotoxicosis
  • Uncorrected adrenal insufficiency
94
Q

What is in armour thyroid?

A

Ground-up animal thyroid

CM 1A: Heme/Onc/Endo (28 decks)

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