thyroid

Question 1

effects of thyroid hormone

Answer 1

CNS: memory, concentration, mood, thermoregulation
MSK: bone/mm growth
CV: HR, BP, contractility
liver: lipid metabolism
GI: motility, appetite
kidney: fluid retention, edema, GFR
repro: fertility, menstrual cycles
skin, hair, nails, and ocular

Question 2

iodine metabolism

Answer 2

inorganic iodine organified by thyroid peroxidase
organic I + tyrosine = iodotyrosine
MIT and DIT coupling to T3 and T4 (thyroid peroxidase)
peripheral conversion of T4 to T3 for organ use (4-5x more potent)

Question 3

circulating thyroid hormone

Answer 3

bound by TBG, TBPA, and albumin

T4 -> T3 in cells, T3 activates nuclear receptors -> increased RNA and protein synthesis

Question 4

signs/sx of hyperthyroidism

Answer 4

nervous, irritable, difficulty sleeping, bulging eyes or unblinking stare, goiter, light period/menstrual irregularities, frequent BMs, warm moist palms, excessive vomiting in pregnancy, hoarse/deep voice, dry/sore throat, difficulty swallowing, rapid/irregular heartbeat, infertility, wt loss, sweating, 1st trimester miscarriage, fam hx thyroid dz or DM

Question 5

hyperthyroidism in the elderly

Answer 5

may have atypical presentation: absent goiter, anorexia w wasting, palpitations, AFib, CHF

Question 6

increased RAIU etiologies of hyperthyroidism

Answer 6

Graves dz, TSH-secreting tumor, pituitary resistance to T4, trophoblastic dz, toxic adenoma, multinodular goiter

Question 7

decreased RAIU etiologies of hyperthyroidism

Answer 7

thyroiditis, ectopic thyroid tissue, medication-induced (exogenous thyroid hormone, amiodarone, iodinated radiocontrast dye)

Question 8

tx for hyperthyroidism

Answer 8

antithyroid meds: thionamides (methimazole, PTU), iodides
radioactive iodine
surgery (subtotal thyroidectomy)
adjunct tx: b-blockers

Question 9

MOA of methimazole

Answer 9

thyroid peroxidase inhibitor (prevents organification of I and coupling), decreasing thyroid hormone production
*DOC for most patients

Question 10

specific ADRs of methimazole

Answer 10

teratogenic- causes lack of fetal skin, choanal atresia (blocks posterior nasal passage)

Question 11

MOA of PTU

Answer 11

thyroid peroxidase inhibitor (prevents organification of I and coupling), decreasing thyroid hormone production
also prevents peripheral conversion of T4 to T3
*DOC in pregnancy/lactation and during thyroid storm

Question 12

ADRs of thionamides

Answer 12

minor: pruritic rash, arthralgia, fever, transient leukopenia - try other agent but 50% cross-sensitivity
major: agranulocytosis (w fever, malaise, sore throat), aplastic anemia, arthralgia, lupus-like syndrome, hepatotoxicity (*PTU)
* do not try other agent if major ADR experienced

Question 13

MOA, uses, and types of iodine for hyperthyroid

Answer 13

MOA: blocks thyroid hormone release, inhibits thyroid hormone synthesis, decreases gland vascularity
use: pre-surgery or after RAI tx
Lugol’s solution or saturated K-iodide solution

Question 14

ADR of iodine

Answer 14

hypersensitivity rxn, iodism (metallic taste, burning mouth, GI upset), gynecomastia

Question 15

potassium iodide for nuclear exposure

Answer 15

K-iodide competitively inhibits uptake of radioactive iodine, decreasing risk thyroid cancer after exposure to RAI

Question 16

RAI-131 MOA, use, and ADR

Answer 16

m/c tx for hyperthyroidism
MOA: concentrates in thyroid causing follicular necrosis
C/I in children, pregnancy/lactation
ADR: hypothyroid, B-rays have 1 mm penetration = possible effect on surrounding tissue

Question 17

surgical resection of thyroid in hyperthyroid

Answer 17

last resort

Question 18

b-blockers for hyperthyroid

Answer 18

adjunctive therapy
propranolol, atenolol, metoprolol
block B-receptors, partially block conversion of T4 to T3
may require 2x normal dose to control sx and HR, may be helpful in thyroid-induced arrhythmia
*caution with asthma, COPD

Question 19

thyroid storm

Answer 19

life-threatening, medical emergency
thyrotoxicosis, fever, tachycardia, tachypnea, dehydration, delirium, n/v/d
precipitated by infection, trauma, surgery, withdrawal of antithyroid meds
20% mortality w aggressive tx, duration 72 hr w tx (PTU, iodides, propranolol, steroids, support)

Question 20

signs/sx of hypothyroidism

Answer 20

tiredness, forgetful/slow thinking, moody/irritable, depressed, inability to concentrate, thinning/loss of hair, dry skin, puffy eyes, goiter, hoarse/deep voice, dry/sore throat, difficulty swallowing, slower HR, heavy period/menstrual irregularities, infertility, constipation, mm weakness/cramps, wt gain, cold intolerance, elevated cholesterol, fam hx of thyroid dz or DM

Question 21

hypothyroidism in the elderly

Answer 21

may have atypical presentation: failure to thrive, hoarseness/deafness, confusion/ataxia, depression

Question 22

hypothyroidism in neonates and children

Answer 22

neonate: mental retardation
child: growth retardation

Question 23

hypothyroidism etiologies

Answer 23

primary: Hashimoto’s dz, s/p thyroid ablation, drug-induced (anti-thyroid, lithium, amiodarone)
secondary: pituitary insufficiency (dec TSH), hypothalamic dysfxn (dec TRH)

Question 24

levothyroxine

Answer 24

synthetic T4, DOC for hypothyroidism

no antigenicity, uniform potency, low cost

Question 25

levothyroxine drug and food interactions

Answer 25

inc thyroid hormone clearance w enzyme inducers (take in morning on empty stomach w water): rifampin, carbamazepine, phenytoin
impaired thyroid hormone absorption: Fe, antacid, Ca, sucralfate, soy, fiber, coffee
inhibits T4 -> T3: amiodarone

Question 26

liothyronine

Answer 26

synthetic T3 for hypothyroid dx - helps differentiate between 1’ and 2’ hypothyroid

Question 27

liotrix

Answer 27

synthetic T4:T3 in 4:1 ratio (to mimic normal 5:1)

*predictable potency, expensive, no benefit over levothyroxine

Question 28

thyroid USP

Answer 28

derived from hog, beef, sheep thyroid glands, variable ratio of T4:T3
inexpensive but unpredictable hormonal stability, antigenic
*rarely used except in older stable pts who won’t switch to newer products

Question 29

myxedema coma

Answer 29

end stage of uncontrolled, long-standing hypothyroidism
hypothermia, delirium, coma; 60-70% mortality
tx: aggressive IV thyroxine, glucocorticoids, and supportive measures
sx improvement in 24h, then switch to oral levo once stable