Endo Exam 1: Bethishou Thyroid

Thyroid hormone secretion follows the pathway: hypothalamus () → pituitary gland () → thyroid gland (T4/T3) → peripheral tissues (T4 → T3), with negative feedback of T4 and T3 back to the pituitary and hypothalamus

TRH, TSH

Hyperthyroidism symptoms include increased metabolism, heat intolerance, decreased LDL, weight loss despite increased appetite, ______, ______, osteoporosis, muscle weakness, warm moist skin, increased sweating, diarrhea, irregular/infrequent/skipped periods, and nervousness/anxiety/palpitations/emotional changes

Tachycardia, AFib

(KNOW) Normal TSH range is ______ mIU/L; in hyperthyroidism, TSH is ______ (specifically < ______).

0.4-4, LOW, <0.4

(KNOW) Normal free T4 range is ______ ng/dL; in hyperthyroidism, free T4 is ______ (specifically > ______).

0.8-1.8, HIGH, >1.8

(KNOW) Normal total T3 range is ______ ng/dL; in hyperthyroidism, total T3 is ______ (specifically > ______).

80-180, HIGH, >180

(KNOW) Normal thyroid antibodies level is < ______; in hyperthyroidism (Graves' disease), antibodies are HIGH, specifically ≥ ______.

1.75, 1.75

Causes of thyrotoxicosis (hyperthyroidism) include Graves' disease (most common in the US), thyroiditis (viral or autoimmune), toxic adenoma (benign tumors producing thyroid hormone), multinodular goiters, and drug-induced causes such as ______ and ______.

Amiodarone, biotin

In Graves' disease, thyrotropin receptor antibodies (TRAbs) bind to TSH receptors, increasing synthesis and release of T3 and T4; excessive TSH receptor stimulation leads to enlargement of the thyroid gland, called a ______; TRAbs also bind to fibroblasts in skin causing ______ and fibroblasts around the eye causing ______.

Goiter, dermopathy, exophthalmos

Consequences of untreated hyperthyroidism include weight loss and osteoporosis (bone loss), ______, ______, and cardiovascular death (heart effects), tremor, and depression

Subclinical hyperthyroidism is defined as ______ TSH with ______ T4 and T3

AFib, HF, Decreased, normal

Potential consequences of untreated subclinical hyperthyroidism include increased all-cause mortality, increased risk of AFib, increased risk of HF, and increased risk of ______ (specifically in post-menopausal women)

Hip fractures

(KNOW) Treat subclinical hyperthyroidism if TSH < ______ and the patient is: age > ______ y/o, ______ (menopausal status), has CVD or high CVD risk, or is < ______ y/o with ______

0.1, 65, post-menopausal, 65, symptoms

(KNOW) Thyroid storm is a life-threatening medical emergency with symptoms of fever, tachycardia, HTN, delirium, dehydration, coma, vomiting, and diarrhea; precipitating factors include infection, trauma, surgery, withdrawal from ______, and ______ treatment.

(KNOW) The treatment for thyroid storm is ______ and ______.

ATD (anti-thyroid drugs), RAI (radioactive iodine), Propylthiouracil, methimazole

Hypothyroidism symptoms include slowed metabolism, fatigue, low energy, cold intolerance, increased LDL and TG, weight gain/obesity, ______ (heart rate change), growth developmental delays in childhood, muscle cramps, dry skin/hair/nails, constipation, heavier than normal periods, infertility, developmental delays, and depression

Bradycardia

The most common cause of hypothyroidism is ______ disease, an autoimmune thyroiditis that occurs most often in women of ______ age, involves ______ and ______ cell-mediated destruction of the thyroid gland, causes permanent and progressive damage, and is diagnostic when antibodies to ______ and ______ are present

Hashimoto's, child-bearing, B, T, thyroid peroxidase, thyroglobulin

Other causes of hypothyroidism include iatrogenic hypothyroidism (status post radioactive iodine or surgery), ______ deficiency, and thyroid ______

Risks of untreated subclinical hypothyroidism include progression to overt hypothyroidism (if autoimmune), CV effects, ______, and ______ effects

Iodine, hypoplasia, Hyperlipidemia, neuropsychiatric

Probably treat subclinical hypothyroidism if TSH > ______, or TSH is ______ with symptoms, antibodies, or CVD risk; if not treated, check again after ______ months (watch and wait).

10, 5-10, 3

Thionamides inhibit the ______ of thyroid hormones by inhibiting thyroid peroxidase enzymes, blocking the oxidation of ______

Synthesis, iodine

Iodides inhibit the ______ of thyroid hormones, acutely blocking hormone release, inhibiting hormone synthesis, and decreasing the ______ and ______ of the thyroid gland

Release, size, vascularity

Propylthiouracil (PTU) uniquely inhibits ______ conversion of T4 to T3, and this effect is dose-related

Peripheral

Among hypothyroidism medications, ______ (brand names Levoxyl, Synthroid, Triosint, Unithroid) is the BEST option, containing synthetic T4, with an approximate equivalent dose of ______ mcg and a long half-life with an IV formulation available

Levothyroxine, 100

______ (brand names Cytomel, Triostat) contains synthetic T3, has an approximate equivalent dose of ______ mcg, and has a short half-life.

Liothyronine, 25

Liotrix (synthetic T4:T3 in a ______ ratio) and desiccated thyroid (from cow or pig, T4:T3 ratio ______, with variation in hormone content and antigenicity) are both ______ (recommended/not recommended)

4:1, 2-5:1, not recommended

Advantages of levothyroxine as the drug of choice include being chemically stable, inexpensive, available as an IV formulation, free of antigenicity, active when given orally, and preferred in ______

Levothyroxine brand and generic are ______ (interchangeable/not interchangeable), so patients should stick with one brand

Pregnancy, Not interchangeable

Hyperthyroid surgery is rapid and effective, used for symptomatic/large goiters or malignancy, but is invasive and causes ______ hypothyroidism

Radioactive iodine is used for poor surgical candidates and is contraindicated in ______ and ______

Permanent, Pregnancy, breast-feeding

Anti-thyroid drugs (ATD) are used in patients with a high likelihood of ______, and are 1st-line treatment in children, adolescents, and ______

Remission, pregnancy

Before surgery, thionamides are used to normalize thyroid function over ______ weeks; BBs are used perioperatively to control heart rate; and iodides (SSKI/Lugol's) are given before surgery to decrease gland vascularity and inhibit hormone synthesis over ______ days

6-8, 7-10

Surgical complications for hyperthyroidism treatment include permanent hypothyroidism, potential ______ (risk), and potential ______ damage (risk).

Hypoparathyroidism, vocal cord

SSKI dosing is ______ drops in water/juice TID; Lugol's solution dosing is ______ drops TID; prior to surgery, ______ mg is used for 7–10 days preoperatively

1-2, 5-7, 50-100

Radioactive iodine is a colorless, tasteless liquid that concentrates in the thyroid and destroys overactive thyroid cells by emitting ______ rays; it takes ______ to ______ to achieve a euthyroid state, and pregnancy is an ______ contraindication

Beta, 6 months, 1 year, absolute

Beta-1 selective agents are preferred for hyperthyroid patients with respiratory disease, including ______, ______, ______, and ______

Metoprolol, atenolol, nebivolol, bisoprolol

For BB-intolerant patients, a non-DHP CCB such as ______ dosed at ______ mg every 8 hours can be used

Diltiazem, 120

Thionamides do not inactivate circulating T3/T4; symptoms improve within ______ weeks as circulating hormone levels decrease, and ______ (T4/TSH) normalizes before ______ (T4/TSH).

4-8, T4, TSH

Remission with thionamides may be achieved within ______ months of treatment; treatment may then be discontinued but monitoring should continue every ______ months

12-24, 6-12

Methimazole (MMI) has a ______ (longer/shorter) half-life and duration of action than PTU, and is dosed ______ (frequency), while PTU is dosed ______

Longer, once per day, TID

Thionamide dosing is tapered to the lowest dose needed to maintain euthyroid status, starting with a ______ (high/low) initial dose

High

Initial MMI dosing is based on free T4 level: Free T4 1–1.5x ULN → ______ mg; 1.5–2x ULN → ______ mg; 2–3x ULN → ______ mg. Initial PTU dosing is ______ mg/day given TID

5-10, 10-20, 20-40, 50-150

Dose adjustments (every 4–8 weeks) are MMI ______ mg/day or PTU ______ mg/day; MMI is approximately ______ times more potent than PTU

5-10, 50-100, 20

Thionamide adverse effects include hepatotoxicity (avoid use if LFTs > ______x ULN at baseline; PTU carries a Black Box Warning), agranulocytosis (avoid if ANC < ______ at baseline), pruritic rash, arthralgias, lupus-like syndrome, and N/V (administer with food).

5, 1000

MMI is recommended over PTU EXCEPT in two situations: ______ and ______

1st trimester of pregnancy, thyroid storm

Thionamide monitoring: baseline pregnancy test, CBC/ANC, LFTs, and thyroid function tests; repeat TFTs every ______ weeks until euthyroid; once euthyroid, decrease dose by ______% and repeat TFTs every ______ months

4-8, 30-50, 2-3

Levothyroxine replacement dosing is ______ mcg/kg/day based on ideal body weight; a lower starting dose of ______ mcg once daily may be considered in adults with CVD or age > 50; if > 50 y/o with CVD, consider a halved dose of ______ mcg daily

1.6, 25-50, 12.5-25

Levothyroxine monitoring: check TSH ______ weeks after initiation, dose change, or formulation change; adjust dose by ______ mcg based on labs and symptoms; once euthyroid, monitor every ______ months

6-8, 12.5-25, 6-12

Liothyronine (T3) may help patients who remain symptomatic despite euthyroid status on levothyroxine; dosing is ______ mcg daily (lower dose of ______ mcg in elderly or CVD patients), available as ______, ______, and ______ mg tablets, adjusted by ______ mcg every 1–2 weeks

Evidence to support routine combination therapy of levothyroxine plus liothyronine is ______ (sufficient/insufficient).

25, 5, 5, 25, 50, 12.5, Insufficient

Levothyroxine should be taken on an ______ stomach to increase bioavailability, ______ minutes before food, or at bedtime or ______ hours post-meal, and taken ______ (consistently/as needed).

Patients should avoid taking levothyroxine with other medications that affect absorption, and should stick with ______ (one brand or generic, not therapeutically equivalent) with follow-up TFTs after ______ weeks

Desiccated thyroid is not first-line, is derived from pork, cow, or sheep, may be ______, has common shortages, and has an initial dose of ______ mg daily

Empty, 30-60, 4, consistently, One brand or generic, 6-8, Antigenic, 15-30

Medications that interfere with levothyroxine absorption (do NOT take together) include bile acid sequestrants such as ______, PPIs/sucralfate/H2RAs, ______ sulfate, ______, phosphate binders, multi-vitamins, ______, and orlistat

Medications that increase levothyroxine clearance include ______, ______, ______, and ______.

Colesevelam, ferrous, calcium, fluoroquinolones, Phenobarbital, phenytoin, rifampin, carbamazepine

Hypothyroidism in pregnancy increases the risk of miscarriage, ______ delivery, ______, impaired intellectual development, and postpartum hemorrhage

______ is the drug of choice for hypothyroidism in pregnancy (pregnancy Category A).

2025 guidelines target TSH < ______ mIU/L if untreated, and < ______ mIU/L if treated, during pregnancy

Preterm, pre-eclampsia, Levothyroxine, 4, 2.5

Thyroid hormone demand increases in pregnancy due to increased ______ proteins, decreased ______ hormone concentration, and increased thyroid metabolism, requiring a ______% increase in the pre-pregnancy levothyroxine dose

During pregnancy, monitor TSH and T4 every ______ weeks during the first half of pregnancy, with a re-check at week ______

Binding, free, 20-30, 4, 26-32

In Graves' disease and pregnancy, radioactive iodine is ______, and surgery is not recommended (especially in the ______ trimester); anti-thyroid drugs are the treatment of choice

Contraindicated, 1st

______ is the drug of choice in the first trimester of pregnancy, given at the lowest possible dose; thionamide doses should be adjusted to maintain free T4 within ______% of the upper normal limit of the nonpregnant reference range.

PTU (propylthiouracil), 10

Use PTU specifically for two situations: ______ and ______.

1st trimester of pregnancy, thyroid storm

MMI adverse effects specific to the first trimester of pregnancy include ______ and ______

A: Aplasia cutis, embryopathy

KNOW

What signs, symptoms, and labs suggest hyperthyroidism in LM? ______

Graves' disease sxs (heat intolerance, tremor, palpitations), suppressed TSH, elevated free T4, and elevated total T3

Before initiating therapy, what other labs or monitoring should be obtained? ______

Pregnancy test, LFTs, CBC/ANC, medication list, thyroid abs, and PMH

Assuming labs are within normal limits, what is the pharmacotherapy plan? ______

Counseling on side effects, follow-up/monitoring, and pregnancy risks

Methimazole (MMI) 20 mg/day plus BBs for palpitations, tremor, and heat intolerance (choosing a higher dose, then titrate down), with follow-up in 4-8 weeks with thyroid function tests

Three months later, LM reports missing her period and a urine pregnancy test confirms pregnancy; her thyroid function tests are euthyroid on methimazole 20 mg daily. What change should be made to her therapy? ______

Switch to PTU 100 mg TID, using a 20:1 conversion ratio, since PTU is preferred only for the 1st trimester