Thyroid Flashcards
What is your thyroid test of choice
TSH! thyroid stimulating hormone, released form anterior pituitary
What is graves disease
AI d/o (Abs stimulate thyroid to make hormones) resulting in hyperthyroidism in early phase
can progress to hypothyroid later if there is gland destruction
What is a thyroid storm
severe thyrotoxicosis (excess thyroid hormone)
What is goiter
enlargement of thyroid gland
can occur in hyper or hypothyroidism
What is the role of the thyroid
Normal growth and development in kids
metabolic stability in adults
The first way the thyroid is regulated is
TSH secreted by anterior pituitary
Negative feedback on anterior pituitary is from circulating free thyroid hormone, and release of TRH from hypothalamus
Extrathyroidal deiodination of T4 to T3 is regulated by
nutrition nonthyroid hormones ambient temps drugs illness
How id thyroid hormone synthesized
Iodide transported from plasma to apical membrane of the cell, and coupled to TG
Hormone stored as colloid moves back towards basal membrane where T4 is secreted
Where are the thyroid hormones formed and secreted
T4: secreted from thyroid ONLY
T3: 80% made from breakdown of T4 (5-monodeiodinase in extrathyroidal peripheral tissues converts T4 to T3)
How are T4 and T3 transported in the bloodstream
They are bound to 3 proteins; thyroxine binding globulin, transthyretin, and albumin
99.6% are bound
What are UNbound thyroid hormones able to do
diffuse into cell elicit biologic effect regulate TSH (thyrotropin)
Where are thyroid hormone receptors found
in hormone responsive tissues;
pituitary, liver, kidney, heart, skeletal muscle, lung, intestine
(T3 has more affinity for these receptors than T4)
How does the body preserve homeostasis
by altering number of thyroid receptors
ex: starvation lowers T3 hormone and receptors
What thyroid hormone gives the negative feedback
T3!
When there is too much T3, it gives negative feedback to the thyroid to stop releasing TSH, and hypothalamus to stop releasing TRH
What are S/Sx of thyrotoxicosis
warm moist skin sweating tachycardia dyspnea tremor, weak weight loss menstrual irregularity graves: exophthalmos
What are S/Sx of hypothyroid
pale, cool, puffy skin always cold bradycardia HTN PE reduced appetite, weight gain
Many hypothyroid patients on treatment dont see weight loss, so what do they do
double the thyroid med dose causing heart and bone problems
advise patient that taking thyroid medication will NOT correct their weight gain
What is Hashimotos
AI destruction of thyroid gland
early dz has goiter
What can cause hypothyroidism
Hashimotos drug induced dyshormonegensis radiation congenital (cretinism) Seconadary (TSH deficiency)
What will primary hypothyroid labs show
High TSH (>4.5) Decreased free T4
What will secondary hypothyroid labs show
TSH within or below normal limits
Free/total T4 and T3 are low
antithyroid peroxidase Abs and anti-TG abs elevated if AI
What will subclinical hypothyroid labs show
High TSH (>4.5) Normal free T4
What lab do you not need to diagnose hypothyroidism
T3, free or total
When should subclinical hypothyroid be treated
Only if TSH >10, or if pt has iron deficiency anemia
-Controversial because some say there is no improvement with treatment, others say Tx can help improve lipid profiles and LV function
How should you treat and monitor hypothyroidism in pregnant women
Adjust replacement therapy (increase dose from 25-50%)
First trimester: monitor TSH monthly- goal is 2-2.5
second trimester: goal TSH <3
third trimester: goal TSH <3.5
postpartum: check TSH at 6 weeks
What labs shouldyou order for different thyroid disorders
Screening: TSH and fre T4
Hypo: TSH, anti-TG abs, anti-TPO abs
Hyper: TSH, free T4, I uptake scan, anti-TPO and anti-TG abs
Thyroid nodule: FNA, I uptake scan, Tc scan, US
Increased thyroid binding globulin will show what lab values
elevated total T4 and T3
*free T4 and TSH will not be affected
What drugs can cause low serum T4 or T3
Naproxen
Octreotide (somatostatin analog)
Phenobarbitol
Phenytoin
What drugs increase TSH (hypothyroid)
Phenytoin Amiodarone Dopamine antagonist salicylates naproxen estrogen or androgen excess
What disorders can alter lab results
severe illness pregnancy chronic protein malntr hepatic failure nephrotic syndrome
What is first line for treating hypothyroidism
Levothyroxine; synthetic T4 that is relatively inexpensive, chemically stable, with uniform potency dose daily (half life 7 days) WHITE TABLET is 50 mcg; relative dose is 100mcg so usually Rx 2 white pills
If you change a dose of levothyroxine, how long do you wait to recheck lab values
4-5 weeks; half life is 7 days, wait 4-5 half lives
apps. 6 weeks
How are T4 and TSH related
non-linearly
small changes in T4 can have enormous changes in TSH
How do you take levothyroxine
with water, on an empty stomach, 1 hr before breakfast
food impairs it’s absorption (as well as mucosal diseases- sprue, diabetic diarrhea, ileal bypass surgery)
-give meds that interact with levothyroxine 4 hours after T4 dose
What can impair absorption of levothyroxine in the GI tract
*cholestyramine (bile acid resin)
*calcium carbonate
sucralfate
aluminum hydroxide
*ferrous sulfate
dietary fiber
espresso
*histamine blockers, PPI
What drugs increase T4 clearance
Rifampin
carbamazepine
phenytoin
*selenium deficiency and amiodarone block conversion of T4 to T3
What do some people say happens when they take T3 (Cytomel)
they get a burst of energy
but; some formulations deliver too much T3
What is Armour thyroid
Dessicated pork thyroid gland
Most patients require this dose once they reach steady state
1.7 mcg/kg/day levothyroxine
dose is based on ideal body weight, not actual body weight
How do you dose young patients w/ long standing dz or pt <45 w/o cardiac disease
Start on Levothyroxine 50mcg daily, increase to 100mcg daily after 1 month
Recommended dosing for older patients with CAD on levothyroxine
Start 25 mcg per day
titrate up 25mcg at monthly intervals
Why do pregnant women need a higher thyroxine dose
increased degredation by placental deiodinase
increased T4 pool size
transfer of T4 to fetus
also may need to increase dose in post-menopausal women
What are some disease drug interactions in hypothyroidism
High serum digoxin values 2/2 decreased drug distribution
Decreased sensitivity to warfarin (low K clotting factors)-
Excess thyroid hormone can lead to
HF
angina pectoris
MI
-hyperremodeling of cortical and trabecular bone= reduced bone density and increased risk of Fx
What is the least allergenic levothyroxine tables
50mcg tab (WHITE) no dye, few excipients- try this in pts suspected of thyroid hormone allergy
What are symptoms of hyperparathyroid
nervous anxiety emotionally labile palpitations menstrual disturbance heat intolerance **Weight loss with increased appetite**
Hyperthyroid PE findings include
warm, smooth moist skin
fine hair
graves: exopthalmos and pretibial myxedema
How do you treat hyperthyroidism
anti-thyroid drugs (first line in kids, teen, and pregnant)
RAI
surgery
Advantages and disadvantages of anti-thyroid drugs are
Ad: non-invasive, low cost, low risk permanent hypothyroid
Dis: low cure rate, drug interactions, hard to comply
What are the Thiourea (antithyroid) drugs
Propothyrouracil and Methimazole
Preferential substrates to iodinating peroxidase= inhibited coupling of mono/diiodityrosine so T3 and T4 do not form
Take 4-8 weeks to see normalization of thyroid hormone
What are the pharmacokinetics behind thiourea drugs
mostly absorbed in GI tract (peak concentration 1hr s/p eating)
concentrated in thyroid gland
excreted in urine
How are Thiourea drugs doses
PTU: 300-600 mg daily, TID/QID
MMI: 30-60mg daily, BID/TID
-can also give them as one dose
change dose on a monthly basis (allow T4 to reach steady state)
ADE of thiourea drugs are
Pruritic maculopapular rash benign transient leukopenia agranulocytosis arthralgias Lupus like syndrome *hepatotoxicity
When is the only time PTU is considered a first line drug
First trimester pregnancy, at lowest possible dose to maintain maternal T4 in normal-high range
WHY? because in first trimester, embryopathy associated w/ MMI is worse than hepatotoxicity associates with PTU
When on thiourea drugs while pregnant, your goal is to
prevent fetal goiter and suppress fetal thyroid function
*PTU <200= not likely to get fetal goiter
What is the MOA of Iodides
block thyroid hormone release
inhibit thyroid hormone synthesis (interfere w/ intrathyroidal iodide utilization)
decrease size and vascularity of thyroid gland
*BUT- thyroid hormone synthesis still continues, so you get a thyroid full of stored hormones that cant release them
When should you give potassium iodide
7-14 days preoperatively
*If giving w/ RAI, give SSKI 3-7 days after Tx so radioactive iodide can concentrate in the thyroid
ADE of Iodides are
salivary gland swelling
iodism (metallic taste, burning mouth/throat, sore teeth and gums, gynecomastia)
Radioactive iodine is the best Tx for
toxic nodules
toxic multinodular goiter
*good cure rate of hyperthyroid
Disadvantages of RAI are
permanent hypothyroidism
Cant get pregnant for 6-12 months; can NOT breast feed
When s surgery used in hyperthyroidism
If pregnant and have major ADE from anti-thyroid drugs
if you have a coexisting susp nodule
