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Thyroid Flashcards

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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
**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)**
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)**
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
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.**
Primary Care
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