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Primary Care > Thyroid > Flashcards

Thyroid Flashcards

1
Q

What is the physiology of the thyroid hormones?

A
  • TSH stimulates the thyroid to make thyroid hormones T4 and T3
  • T3 has primary activity
  • Tissues convert T4 to T3
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2
Q

What is the normal thyroid gland size? (TN)

A
  • 15-20 g
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3
Q

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

A
  • 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
Q

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

A
  • 1/3
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5
Q

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

A
  • TSH
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6
Q

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

A

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
Q

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

A
  • THYROIDISM
    • Tremor
    • Heart rate up
    • Yawning (fatigued)
    • Restlessness
    • Oligomenorrhea/Amenorrhea
    • Intolerance to heat
    • Diarrhea
    • Irritability
    • Sweating
    • Muscle wasting/weight loss
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8
Q

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

A
  • 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
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9
Q

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

A

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
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10
Q

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

A
  • FT4 (NOT TSH)
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11
Q

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

A
  • < 0.1 mU/L
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12
Q

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

A
  • 0.2 – 4.0 mU/L
  • 0.45 – 4.50 mIU/L (CMAJ)
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13
Q

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

A
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14
Q

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

A
  • Hypothyroidism (TSH > 4 mU/L) due to suspected autoimmune thyroid disease
  • Serum antibody (anti-TPO) should only be performed ONCE for the diagnosis
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15
Q

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

A
  • Subclinical HYPOthyroidism – ischemic heart disease
    • ONLY in those with TSH 10 – 19 mIU/L (CMA POEM)
  • Subclinical HYPERthyroidism – atrial fibrillation and flutter
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16
Q

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

A
  • L-Thyroxine
    • Do NOT use T3, T3/T4 combinations, or desiccated thyroid
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17
Q

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

A
  • 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
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18
Q

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

A
  • Euthyroid range (0.2 – 4.0 mU/L)
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19
Q

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

A
  • Elderly (>65 yr) – up to 6 mIU/L
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20
Q

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

A
  • 8-12 weeks
  • 4-8 weeks (CMAJ)
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21
Q

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

A
  • Yearly
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22
Q

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

A
  • < 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
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23
Q

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

A
  • Risk of cognitive impairment in the infant
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24
Q

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

A
  • 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
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25
Q

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

A
  • 50%
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26
Q

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

A
  • TSH when pregnancy confirmed
  • Repeat every 4 to 6 weeks based on TSH levels
    • INCREASED demand for thyroxine during pregnancy
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27
Q

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

A
  • 1st trimester = 0.2-2.5 mU/L
  • 20+ weeks = 0.2 – 3.5 mU/L
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28
Q

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

A
  • TSH receptor antibody (TRAB)
    • Refer if TRAB ≥5x normal
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29
Q

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

A
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30
Q

How does amiodarone affect thyroid hormones? (TOP)

A
  • Amiodarone may cause elevated FT4 in the presence of normal TSH
    • Drug effect to inhibit T4 to T3 conversion
31
Q

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

A
32
Q

What is the differential diagnosis for Hypothyroidism?

A
  • 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
Q

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

A
  • No evidence of benefit
34
Q

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

A
  • Repeat TSH with T4
35
Q

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

A
  • Suspect autoimmune (Hashimoto’s)
  • Nodular goiter
  • Recurrent miscarriage
36
Q

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

A

TSH

T4

T3

Subclinical

High

Normal

Normal

Primary

High

Low

Low

Secondary

Low

Low

Low

Sick Euthyroid

Anything

Normal/Low

Low

37
Q

What acute emergency can occur with hypothyroidism?

A
  • Myxedema Coma – confusion, bradycardia, bradpnea, hypothermia
38
Q

How should a myxedema coma be managed?

A
  • Go to ER
  • Levothyroxine IV, Hydrocortisone IV, warming blankets
  • Rule out Adrenal Crisis
39
Q

How should levothyroxine be dosed in patients diagnosed with hypothyroidism?

A
  • 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
Q

Why is levothyroxine not recommended for children?

A
  • Not until pubertal growth complete
41
Q

What is painful subacute thyroiditis also called? (TN)

A
  • De Quervain’s
42
Q

How should pain be managed in patients with thyroiditis?

A
  • 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
Q

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

A
  • 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
Q

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

A
  • 10%
45
Q

What % of women will have post-partum thyroiditis?

A
  • 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
Q

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

A
  • Grave’s disease – Younger Women
  • Toxic Nodular Goiter – Elderly
47
Q

What is the differential diagnosis of hyperthyroidism?

A
  • 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
Q

What antibody would be elevated in Grave’s disease?

A
  • TSH Receptor Antibody or Thyroid Stimulating Immunoglobulin (TSI)
49
Q

When should a Radioisotope Uptake Scan be performed?

A
  • Nodule or Goiter
50
Q

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

A
  • 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
Q

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

A

TSH

T4

T3

Subclinical

Low

Normal

Normal

Primary

Low

High

High

Secondary

High/N

High

High

T3 thyrotoxicosis

Low

Normal

High

52
Q

What acute emergency can occur with hyperthyroidism?

A
  • Thyroid Storm
53
Q

How should Thyroid Storm be managed?

A
  • 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
Q

What are 2 treatments that can be used for hyperthyroidism?

A
  • Propylthiouracil (PTU)
  • Methimazole
55
Q

How should propylthiouracil (PTU) be prescribed for hyperthyroidism?

A
  • 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
Q

How should Methimazole be prescribed for hyperthyroidism?

A
  • 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
Q

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

A
  • MMI – longer duration of action (daily dose), more rapid efficacy, lower incidence of side effects
    • Contraindicated in pregnancy (Teratogenic)
58
Q

What is the pathophysiology behind Grave’s Disease?

A
  • 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
Q

How should Grave’s Disease be treated?

A
  • 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
Q

What is the pathophysiology behind Grave’s Disease?

A
  • Caused by focal or diffuse hyperplasia independent of TSH due to TSH receptor mutations most commonly
61
Q

How should Toxic Adenoma and Multinodular Goiter be treated?

A
  • 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
Q

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

A
  • 5%
63
Q

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

A
  • 0.3% in 5 years
64
Q

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

A
  • 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
Q

What is the differential diagnosis for a thyroid nodule?

A
  • 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
Q

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

A
  • TSH + Thyroid U/S
67
Q

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

A
  • 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
Q

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

A
  • Only if nodule >1 cm or 5 mm with risk factors for malignancy
  • Otherwise follow with U/S q6-12 months, eventually increasing interval
69
Q

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

A
  • 5% false negative rate
70
Q

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

A
  • Repeat FNA at least 3 months later (to avoid false-positive)
71
Q

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

A
  • <15% increase in size
    • If unstable, repeat FNA regardless of previous result
72
Q

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

A
  • >4 cm
73
Q

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

A

Primary Care (12 decks)

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