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ENDOCRINOLOGY > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Where are thyroid hormone (T3) receptors located?

A

Nucleus

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2
Q

What is the function of calcitonin? Where is it produced

A
  • Inhibits bone resorption
  • Important clinical tumor marker for medullary thyroid cancer
  • Parafollicular C cells of thyroid gland
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3
Q

Where can ectopic thyroid tissue be found?

A

Anywhere along thyroglossal duct, tongue base (lingual), mediastinum

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4
Q

What is the recommended daily intake for iodine? What happens if you don’t have enough?

A
  • Adults: 150 micrograms
  • Pregnant women: 200 micrograms
  • Children: 90 micrograms
  • <100: iodine deficiency
  • <50: will result in goiter and hypothyroidism
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5
Q

List the steps to thyroid hormone synthesis

A
  1. Active transport of iodide across basement membrane of thyroid cell via NaI sypmporter
  2. Oxidation of iodide and iodination of tyrosyl residues in TG (organification)
  3. Linking pairs of iodotyrosine molecules within TG to form iodothyronines T3 and T4 (coupling)
  4. Pinocytosis and then proteolysis of TG with release of free T3/T4 into circulation
  5. Deiodination of iodotyrosines within thyroid cell, with conservation of the iodide
  6. Intrathyroidal 5’ deiodination of T4 to T3
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6
Q

Draw thyroid hormone production

A
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7
Q

How does the Na-I symporter derive its energy?

A

From the Na-K ATPase creating the ion gradient

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8
Q

What other tissues express NIS?

A

Salivary, gastric, breast (may light up on radioiodine scans or cause sialadenitis and gastritis with radioactive iodine treatment)

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9
Q

Mutations in pendrin (PDS or SLC26A4 gene) cause ___

A

Congetnial hypothyroidism (dyshormonogenesis) and hearing loss.

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10
Q

How do PTU and methimazole work?

A
  • How do PTU and methimazole work?
  • PTU also decreases peripheral conversion of T4 to T3
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11
Q

What conditions cause increased thyroglobulin?

A
  • Thyroiditis
  • Nodular goiter
  • Graves
  • Papillary and follicular thyroid cancer (useful tumor marker)
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12
Q

How does excess iodide inhibit thyroid hormone production?

A
  • Inhibits iodide trapping
  • Inhibits TG iodination (Wolff-Chaikoff effect)
  • Inhibits thyroid hormone release from glands
  • Note: these actions are transient and the normal thyroid gland escapes after 10-14 days. Excess iodine can be used to prevent thyroid gland exposure to radiation injury (ex. after nuclear power accidents)
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13
Q

What is the Jod-Basedow effect?

A

Iodine load inducing hyperthyroidism in some patients with multinodular goiter, latent Graves disease and rarely in those with normal thyroid glands

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14
Q

What proteins carry thyroid hormone around in circulation?

A
  • Thyroid binding globulin (TBG)
  • Transthyretic (previously thyroxine-binding prealbumin)
  • Albumin
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15
Q

Name 3 conditions that can increase thyroxine binding globulin

A
  1. Estrogen (pregnancy, estrogen therapy)
  2. Hepatitis
  3. Drugs: tamoxifen, 5-fluorouracil, methadone, heroin
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16
Q

Name 2 conditions that can decrease thyroxine binding globulin

A
  1. Inherited
  2. Androgens
  3. Drugs: danazol, L-asparginase
  4. Increased clearance: nephrotic syndrome, severe liver disease, protein-losing enteropathy
17
Q

List the deiodinase enzymes and their functions

A
  • D1: most abundant, converts T4 to T3, expressed in liver, kidney, periphery
  • D2: very sensitive to low T4, converts T4 to T3 in brain/pituitary gland
  • D3: inactivates T4 to rT3
18
Q

The alpha subunit of TSH is common to what other hormones?

A
  • LH
  • FSH
  • placental hormone hCG
19
Q

How does chronic illness impact thyroid hormones

A
  1. Decreased conversion of T4 to T3
  2. Rise in serum rT3
  3. Decrease in total and free T4
  4. Suppression of TSH
20
Q

List 2 indications for measuring thyroglobulin

A
  1. Detection of residual or recurrent epithelial thyroid cancers (papillary, follicular, Hurthle cell)
  2. Differentiating hyperthyroidism due to exogenous thyroid hormone (TG suppressed) vs. endogenous forms such as Graves (TG elevated or normal)
21
Q

List 4 indications for testing TSI

A
  1. Pregnant women to define risk of neonatal hyperthyroidism
  2. To differentiate Graves vs. postpartum thyroiditis in women who are breastfeeding (and cannot have radionucleotide scan)
  3. To diagnosed Graves in euthyroid patietns with thyroid-related ophthalmopathy
  4. To predict if Graves patients will relapse after antithyroid drugs are discontinued
22
Q

Describe physical exam findings of the thyroid gland in of Hashimoto thyroiditis

A
  • Enlarged
  • Firm
  • Finely nodular surface
23
Q

Describe physical exam findings of the thyroid gland in of Graves disease

A
  • Enlarged
  • Smooth
  • Rubbery
  • May have a bruit
24
Q

List the differential diagnosis for hypothyroidism

A
  • Hashimoto thyroiditis
  • Radioactive iodine therapy
  • Subtotal thyroidectomy for Graves/nodules/cancer
  • Excessive iodide intake (kelp, radiocontrast dyes)
  • Subacute thyroiditis (usually transient)
  • Iodide deficiency (rare in North America)
  • Inborn errors of thyroid hormone synthesis
  • Drugs: lithium, amiodarone, interferon-alpha
  • Secondary: hypopituitarism (adenoma, pituitary ablative therapy, pituitary destruction)
  • Tertiary: hypothalamic dysfunction
25
Q

List the signs of hypothyroidism in newborns

A
  • Respiratory difficulty
  • Cyanosis
  • Jaundice
  • Poor feeding
  • Hoarse cry
  • Umbilical hernia
  • Retardation of bone maturation (ex. absence of proximal tibial and distal femoral epiphysis in a full term infant with BW >2500 g)
26
Q

List 4 ways which hypothyroidism may contribute to anemia

A
  • Impaired hemoglobin synthesis as a result of T4 deficiency
  • Iron deficiency from menorrhagia
  • Folate deficiency from impaired intestinal absorption of folate
  • Pernicious anemia (associated autoimmune disease)
27
Q

List a differential diagnosis for hyperthyroidism

A
  • Graves disease (diffuse toxic goiter)
  • Toxic adenoma (Plummer disease)
  • Toxic multinodular goiter
  • Subacute thyroiditis
  • Silent thyroiditis
  • Factitious thyrotoxicosis
  • Rare forms: ovarian struma, metastatic thyroid carcinoma (follicular), hydatiform mole, hamburger thyrotoxicosis, TSH-secreting pituitary tumor, pituitary resistance to T3 and T4
28
Q

List the classification of eye changes in Graves disease

A
  • NO SPECS
  • 0: No signs or symptoms
  • 1: Only signs, no symptoms (upper lid, retraction, stare, lid lag)
  • 2: Soft tissue involvement
  • 3: Proptosis
  • 4: Extraocular muscle involvement
  • 5: Corneal involvement
  • 6: Sight loss (optic nerve involvement)
29
Q

List the side effects of methimazole. When do they usually occur?

A
  • Pruritic rash (5%)
  • Agranulocytosis
  • Cholestatic jaundice
  • Acute arthritis
  • Usually in the first 3 months (?liver disease and agran are idiosyncratic)
30
Q

List 2 complications of thyroid surgery

A
  • Hypoparathyroidism
  • Recurrent laryngeal nerve injury
31
Q

Why is PTU preferable to methimazole in thyroid storm?

A
  • Also blocks conversion of T4 to T3
  • However still contraindicated in children
32
Q

List 3 teratogenic effects of methimazole

A
  1. Aplasia cutis
  2. Choanal atresia
  3. TEF
33
Q

List 4 ultrasound characteristics of malignant thyroid nodules

A
  • Microcalcifications
  • Irregular borders
  • Hypoechoic
  • Increased intranodular vascularity
  • Taller than wide
34
Q

List 5 risks associated with hyperthyroidism during pregnancy (mom or fetus)

A
  • IUGR/SGA
  • Preterm delivery
  • Early spontaneous abortion
  • Preeclampsia
  • Neonatal graves
  • Weight loss
  • Weak muscles
  • Atrial fibrillation
35
Q

List 4 poor outcomes associated with neonatal Graves

A
  • Thrombocytopenia
  • HSM
  • Jaundice
  • Hypoprothrombinemia
  • Heart failure
  • Death
  • Irritability, flushing
  • Tachycardia, hypertension
  • Poor weight gain
  • Thyroid enlargement and exophthalmos
36
Q

List a differential diagnosis for congenital hypothyroidism with ABSENT uptake on scan (salivary glands only)

A
  • Thyroid agenesis (genes: TTF1, TTF2, PAX8)
  • TSH receptor defect
  • Iodide trapping deects
  • TSH receptor blockade by maternal blocking antibodies or anti-thyroid meds
  • Iodine excess (iodine contrast, iodide containing meds)

ENDOCRINOLOGY (21 decks)

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