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Flashcards in Thyroid Deck (73):
1

What is the physiology of the thyroid hormones?

  • TSH stimulates the thyroid to make thyroid hormones T4 and T3
  • T3 has primary activity
  • Tissues convert T4 to T3

2

What is the normal thyroid gland size? (TN)

  • 15-20 g

3

What patients are at increased risk of thyroid disease? (TOP)

  • Women >45, Men >60
  • Type 1 Diabetes
  • Celiac disease
  • Postpartum Women
  • Family history of thyroid disease
  • Head/Neck cancers treated with external beam radiation
  • Previous radioactive iodine treatment
  • Previous thyroid surgery

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4

What % of patients receiving treatment for hypothyroidism have TSH values outside the target range? (CMAJ)

  • 1/3

5

What is the most sensitive and specific test for the investigation and management of primary thyroid dysfunction? (TOP)

  • TSH

6

What symptoms are associated with Hypothyroidism and Hyperthyroidism? (TOP)

Hypothyroid

Hyperthyroid

  • Weight Gain
  • Fatigue
  • Cold Intolerance
  • Menstrual Irregularities (Menorrhagia)
  • Depression
  • Constipation
  • Dry Skin
  • Bradycardia
  • Hair loss
  • Weight Loss
  • Fatigue / Restlessness
  • Heat Intolerance
  • Menstrual Irregularities (Amenorrhea/Oligomenorrhea)
  • Anxiety
  • Diarrhea
  • Sweating
  • Palpitations/tachycardia/afib
  • Hair loss

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7

What acronym can be used for the signs and symptoms of hyperthyroidism? (TN)

  • THYROIDISM
    • Tremor
    • Heart rate up
    • Yawning (fatigued)
    • Restlessness
    • Oligomenorrhea/Amenorrhea
    • Intolerance to heat
    • Diarrhea
    • Irritability
    • Sweating
    • Muscle wasting/weight loss

8

What eye changes can be seen with Graves’ disease? (TN)

  • NO SPECS (in order of changes usually)
    • No signs
    • Only signs: lid lag, lid retraction
    • Soft tissue: periorbital puffiness, conjunctival injection, chemosis
    • Proptosis/Exophthalmos
    • Extraocular (Diplopia)
    • Corneal abrasions (since unable to close eyes)
    • Sight loss

9

What findings on physical exam can be seen in Hypothyroidism and Hyperthyroidism? (TOP)

Hypothyroid

Hyperthyroid

  • Bradycardia/Bradypnea
  • Hair thinning
  • Delayed relaxation phase of reflexes
  • Pseudo-myotonia

 

  • Tachycardia, HTN
  • Thyroid – Nodules and Goiter, Bruits
  • Graves – Eye irritation, periorbital edema, proptosis, ophthalmoplegia, lid lag, lid retraction

10

What test should be ordered for suspected pituitary disease? (TOP)

  • FT4 (NOT TSH)

11

What TSH value is typically seen in patients with thyrotoxicosis? (TOP)

  • < 0.1 mU/L

12

What is considered euthyroid, or a normal TSH? (TOP/CMAJ)

  • 0.2 – 4.0 mU/L
  • 0.45 – 4.50 mIU/L (CMAJ)

13

What tests should be ordered to diagnose hypothyroidism and hyperthyroidism after an abnormal TSH level? (TOP)

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14

When should thyroid antibodies (anti-TPO) be ordered and how many times? (TOP)

  • Hypothyroidism (TSH > 4 mU/L) due to suspected autoimmune thyroid disease
  • Serum antibody (anti-TPO) should only be performed ONCE for the diagnosis

15

What risks have been associated with subclinical hypothyroidism and subclinical hyperthyroidism? (TOP/CMA POEM)

  • Subclinical HYPOthyroidism – ischemic heart disease
    • ONLY in those with TSH 10 – 19 mIU/L (CMA POEM)
  • Subclinical HYPERthyroidism – atrial fibrillation and flutter

16

What medication should be used for thyroid replacement? (TOP)

  • L-Thyroxine
    • Do NOT use T3, T3/T4 combinations, or desiccated thyroid

17

What can interfere with the absorption of levothyroxine? (CMAJ)

  • Food
    • 1-hour before breakfast or at bedtime >3-hours after final meal of the day
  • Medications (e.g. bile acid sequestrants, phosphate binders, aluminum-containing antacids) and Supplements (e.g. calcium, iron)
    • 4-hour separation advised

18

What is the target TSH for patients on thyroid replacement? (TOP)

  • Euthyroid range (0.2 – 4.0 mU/L)

19

In which patients can a higher upper limit of TSH be acceptable in the treatment of hypothyroidism? (CMAJ)

  • Elderly (>65 yr) – up to 6 mIU/L

20

How long does it take for TSH equilibration after any thyroxine dosage change? (TOP/CMAJ)

  • 8-12 weeks
  • 4-8 weeks (CMAJ)

21

Once a stable thyroxine dose is achieved, how often should TSH be repeated? (TOP)

  • Yearly

22

What is the target TSH for patients on thyroxine therapy after surgery for thyroid cancer? (TOP)

  • < 0.1 mU/L in moderate to high risk patients (prevent regrowth of cancer)
    • Reduces recurrence rates of thyroid cancer by ~40%
  • 0.1 – 0.5 mU/L in low risk patients

23

What is the risk of subclinical hypothyroidism in pregnant patients? (TOP)

  • Risk of cognitive impairment in the infant

24

What is the evidence for screening for thyroid disease early in pregnancy? (CMA POEM/NEJM)

  • No evidence that screening lowers the risk of cognitive impairment in infants
  • RCT of pregnant women in first 16 weeks of pregnancy with TSH and T4 measured
  • TSH in top 2.5% or T4 in bottom 2.5% classified as thyroid deficient
  • Randomized to 150 mcg levothyroxine or usual care
  • No significant difference in the 3-year-olds’ mean IQ scores between the groups

25

By how much will women on thyroxine replacement therapy require an increase in dosage during pregnancy? (TOP)

  • 50%

26

In pregnant patients receiving thyroxine replacement, when and how often should TSH be performed? (TOP)

  • TSH when pregnancy confirmed
  • Repeat every 4 to 6 weeks based on TSH levels
    • INCREASED demand for thyroxine during pregnancy

27

What is the target TSH level for pregnant patients on thyroxine? (TOP)

  • 1st trimester = 0.2-2.5 mU/L
  • 20+ weeks = 0.2 – 3.5 mU/L

28

What should be ordered for pregnant patients with a history of Grave’s disease and when should endocrinology be consulted? (TOP)

  • TSH receptor antibody (TRAB)
    • Refer if TRAB ≥5x normal

29

How should TSH be monitored in patients on lithium therapy? (TOP)

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30

How does amiodarone affect thyroid hormones? (TOP)

  • Amiodarone may cause elevated FT4 in the presence of normal TSH
    • Drug effect to inhibit T4 to T3 conversion

31

How should TSH be monitored in patients on amiodarone? (TOP)

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32

What is the differential diagnosis for Hypothyroidism?

  • Primary (90%)
    • Thyroiditis
      • Hashimoto’s – Autoimmune, most common
      • Silent – Painless and can predispose to permanent
      • Subacute – Painful and often viral illness previously
      • Postpartum
      • Irradiation
    • Iatrogenic
      • Radioactive I131
      • Thyroidectomy
      • Drugs: Lithium, Amiodarone
    • Congenital
    • Other – Sick Euthyroid (severe medical illness), Iodine deficiency, Idiopathic
  • Secondary/Tertiary
    • Diseases of Pituitary or Hypothalamus
      • Tumour, Surgery, Infarction (Sheehan’s), Irradiation

33

What is the recommendation regarding screening for hypothyroid disease? (USPSTF 2015)

  • No evidence of benefit

34

If a patient is symptomatically hypothyroid but their TSH is low, what should be done?

  • Repeat TSH with T4

35

When would anti-thyroid peroxidase (TPO) and anti-thyroglobulin (TG) be performed?

  • Suspect autoimmune (Hashimoto’s)
  • Nodular goiter
  • Recurrent miscarriage

36

What TSH, T4 and T3 levels would be expected in subclinical, primary, secondary and sick euthyroid hypothyroidism?

 

TSH

T4

T3

Subclinical

High

Normal

Normal

Primary

High

Low

Low

Secondary

Low

Low

Low

Sick Euthyroid

Anything

Normal/Low

Low

37

What acute emergency can occur with hypothyroidism?

  • Myxedema Coma – confusion, bradycardia, bradpnea, hypothermia

38

How should a myxedema coma be managed?

  • Go to ER
  • Levothyroxine IV, Hydrocortisone IV, warming blankets
  • Rule out Adrenal Crisis

39

How should levothyroxine be dosed in patients diagnosed with hypothyroidism?

  • Levothyroxine (T4) 1.7 mcg/kg/day (typical 100-125 mcg/day for 70 kg adult)
    • Elderly may only require 0.5 mcg/kg
    • In adults >50 titrate from 25-50 mcg/day increasing 25 mcg/month
      • Caution in heart disease as well
    • Adjust medication every 6 weeks due to T4 half-life of 7 days

40

Why is levothyroxine not recommended for children?

  • Not until pubertal growth complete

41

What is painful subacute thyroiditis also called? (TN)

  • De Quervain’s

42

How should pain be managed in patients with thyroiditis?

  • Trial NSAIDs initially for 3 days
  • If not improving, then discontinue and start prednisone 40 mg, then taper to lowest effective dose by 5-10 mg q1week
    • Should respond in 48h, reconsider diagnosis if does not
    • First line for severe pain

43

How can hyperthyroid and hypothyroid symptoms be managed in patients with thyroiditis?

  • Hyperthyroid
    • Often mild and unnecessary to treat
    • Consider Propranolol 40-120 mg
    • Do NOT use Thionamides as primary problem is not thyroid hormone synthesis
  • Hypothyroid
    • Often mild and unnecessary to treat
    • If TSH >10, can treat with 50-100 mcg T4 for 6-8 weeks and discontinue
    • Reevaluate TSH at 6 weeks to determine if hypothyroid is permanent

44

What % of patients with painless thyroiditis will have permanent hypothyroidism? (TN)

  • 10%

45

What % of women will have post-partum thyroiditis?

  • 5-10% of women
  • Often mild and transient
  • Presents as initially hyperthyroid, then hypothyroid, then recovery
  • Increased risk of permanent hypothyroid and should screen yearly

46

What type of hyperthyroidism is more common in women and what type is more common in the elderly?

  • Grave’s disease – Younger Women
  • Toxic Nodular Goiter – Elderly

47

What is the differential diagnosis of hyperthyroidism?

  • Primary
    • Grave’s disease – toxic diffuse goiter (most common)
    • Toxic Adenoma or Multinodular Goiter (most common in elderly)
    • Thyroiditis
      • Painless/Silent
      • Post-partum
      • Subacute – painful
      • Irradiation
      • Drug-induced – lithium, amiodarone, interferon
    • Iodine exposure
    • Exogenous thyroid hormone
    • Ectopic thyroid hormone – Ovarian tumor, Hydatiform mole
  • Secondary
    • Pituitary adenoma

48

What antibody would be elevated in Grave’s disease?

  • TSH Receptor Antibody or Thyroid Stimulating Immunoglobulin (TSI)

49

When should a Radioisotope Uptake Scan be performed?

  • Nodule or Goiter

50

What are the different results that can come from a Radioisotope Uptake Scan?

  • Low in thyroiditis (or exogenous T4) – the gland isn’t working harder
  • Diffusely high – Grave’s
  • Focally high
    • Multiple areas – Multinodular Goiter
    • One area – Toxic adenoma

51

What TSH, T4 and T3 levels would be expected to be seen in hyperthyroidism: subclinical, primary, secondary and T3 thyrotoxicosis?

 

TSH

T4

T3

Subclinical

Low

Normal

Normal

Primary

Low

High

High

Secondary

High/N

High

High

T3 thyrotoxicosis

Low

Normal

High

52

What acute emergency can occur with hyperthyroidism?

  • Thyroid Storm

53

How should Thyroid Storm be managed?

  • ABCs, O2, IVs
  • Propylthiouracil (PTU) 100 mg PO/NG stat and 300 mg PO q6h
  • Iodine 2-3 drops PO q6h, 1h after PTU
  • Dexamethasone 2mg IV q6h – decrease immune response and peripheral T4 to T3 conversion
  • Propranolol 20 mg PO q6h
  • Cooling blankets

54

What are 2 treatments that can be used for hyperthyroidism?

  • Propylthiouracil (PTU)
  • Methimazole

55

How should propylthiouracil (PTU) be prescribed for hyperthyroidism?

  • Inhibits thyroid hormone synthesis and peripheral conversion of T4 to T3
  • Preferred in pregnancy
  • Start at 100 mg TID, can often decrease to 50-150 mg daily

56

How should Methimazole be prescribed for hyperthyroidism?

  • Only inhibits thyroid hormone synthesis
  • 15-60 mg/day divided TID, maintain at 5-15 mg/day
  • Reduce dose by 1/3 once TSH normalizes

57

Which of MMI (Methimazole) or PTU (Propylthiouracil) is preferred for the treatment of hyperthyroidism? (TN)

  • MMI – longer duration of action (daily dose), more rapid efficacy, lower incidence of side effects
    • Contraindicated in pregnancy (Teratogenic)

58

What is the pathophysiology behind Grave’s Disease?

  • Caused by autoantibodies to the thyrotropin (TSH) receptor (TSHR-Ab)
    • Activate the receptor, thereby stimulating thyroid hormone synthesis and secretion as well as thyroid growth (causing a diffuse goiter)

59

How should Grave’s Disease be treated?

  • Initially on beta-blocker and thionamide (short-term treatment of symptoms until PTU or Methimazole take effect)
  • Once Euthyroid, consider radioactive-iodine ablation
    • One-time pill which is usually curative
    • Must follow radioactive protocol for 1 week after
    • Lower complications than surgery
  • Surgery if large obstructive goiter
  • Require full thyroid replacement at 1.7 mcg/kg after definitive treatment

60

What is the pathophysiology behind Grave’s Disease?

  • Caused by focal or diffuse hyperplasia independent of TSH due to TSH receptor mutations most commonly

61


How should Toxic Adenoma and Multinodular Goiter be treated?

  • Initially on beta-blocker (Atenolol 25-50 mg daily or Propranolol 20-40 mg BID-QID) and Thionamide
  • Radio-iodine ablation or surgery is preferred to long-term Thionamide
  • Require full thyroid replacement at 1.7 mcg/kg after definitive treatment

62

What is the risk of cancer for any given thyroid nodule?

  • 5%

63

What is the risk of progressing to malignancy in 5 years in a benign (U/S or negative FNA) thyroid nodule? (CMA POEM/JAMA)

  • 0.3% in 5 years

64

What are risk factors for malignancy in patients with a thyroid nodule?

  • Demographics – Filipino and Vietnamese race
  • Personal history
    • Ultrasound features
      • Hypoechogenic
      • Increased vascularity
      • Irregular Margins
      • Microcalcifications
      • Absence of Halo
    • Lymphadenopathy
    • Head and Neck irradiation
    • Bone Marrow transplant
  • Family history – Thyroid cancer in 1st degree relative

65

What is the differential diagnosis for a thyroid nodule?

  • Benign
    • Colloid nodule
    • Cyst
    • Thyroiditis
    • Benign follicular neoplasm
      • Increased risk of malignancy and are often removed
  • Malignant
    • Papillary (70-75%)
    • Follicular (10%)
    • Medullary (3-5%)
    • Anaplastic (<5%)
    • Lymphoma (<1%)

66

What is the first test to perform in a patient with a thyroid nodule?

  • TSH + Thyroid U/S

67

When would a radioiodine uptake scan be performed in patient with a thyroid nodule (CMAJ)?

  • Radioisotope Thyroid Scan (Technetium-99) – only if TSH is LOW < 0.3 mU/L (HYPERthyroid)
    • Hyperfunctioning (Hot) Nodule
      • No FNA is needed – cancer does not have high function
    • Hypofunctioning (Cold) Nodule
      • FNA is needed – must evaluate for cancer

68

When would an FNA be performed given a patient with a thyroid nodule?

  • Only if nodule >1 cm or 5 mm with risk factors for malignancy
  • Otherwise follow with U/S q6-12 months, eventually increasing interval

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69

What is the false negative rate for FNA in a thyroid nodule?

  • 5% false negative rate

70

What should be done if the FNA of a thyroid nodule is Bethesda III (atypia or follicular lesion of undetermined significance)? (CMAJ)

  • Repeat FNA at least 3 months later (to avoid false-positive)

71

What is considered a stable change in size for a thyroid nodule on ultrasound?

  • <15% increase in size
    • If unstable, repeat FNA regardless of previous result

72

At what size is surgery performed for a thyroid nodule regardless of FNA result?

  • >4 cm

73

Outline the approach for investigating a patient with a thyroid nodule.

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