Thyroid Disorders - Exam 3 Flashcards
TRH stands for ____ and comes from the _____. TSH stands for _____ and comes from the ______
Thyrotropin Releasing Hormone-> hypothalamus
Thyroid Stimulating Hormone -> Ant Pit
Describe the HPT axis in simplied terms
When there is no thyroid present, T3/T4 levels will _____ and TSH/TRH levels will _____
T3/T4 will decrease
TSH/TRH will increase
What will a pt with hyperthyroidism, ther T3/T4 levels will be ______ and TSH/TRH will be ______
T3/T4 will be increased
TSH/TRH will be decreased
A pt with hypothyroidism, their T3/T4 levels will be _____ and TSH/TRH levels will be ______.
T3/T4 will be decreased
TSH/TRH will be increased
_____ large glycoprotein synthesized by follicular cells of the thyroid; released into the colloid. _____ element actively absorbed by the thyroid for hormone synthesis
thyroglobulin
iodine aka no iodine no T3/T4 because it cannot be sythesized
____ enzyme; helps process iodine for use by thyroid ~1 mg/week requirement. Commonly added to table salt
Thyroid Peroxidase (TPO)
What is the difference between T3 and T4?
the number of iodine groups attached
When thyroid hormones are needed organified Tg (with attached T3/T4 molecules) is absorbed via
____ into the thyroid cells
pinocytic vesicles
Once in the blood, 99% of T3 and T4 bind immediately with _____ synthesized by the _____. ______ primary binding protein (80% of T3/T4)
plasma proteins
liver
Thyroxine-binding globulin (TBG) -
Most T4, once absorbed by _____, is converted to T3 by _____
tissues
deiodinases
_____ is metabolically active and is less stable, aka more easily unbound. ____ is more balanced and harder to unbind. What form is the storage form? ____ binds to the receptors with 10-15x more affinity
T3
T4
T4
T3
What would happen to T3/T4 if someone was deficient in TBG, but otherwise metabolically normal? What about to their free T3/T4? TSH/TRH?
total T3/T4 would decrease
Free T3/4 would be normal
TSH/TSH levels would be normal
Estrogen increases the levels of TBG. If someone had high estrogen levels (e.g. pregnancy, contraception), what would happen to their total T3/4? Free T3/T4? and TSH/TRH?
TOTAL T3/4 would increase
Free T3/4: normal
TSH/TRH: normal
What symptoms would you expect to see on a pt with elevated rT3?
hypothyroid s/s
_____ enzyme helps turn T4 into T3?
iodinase
What are some physiologic effects of thyroid on metabolism?
-Growth: especially of skeleton and brain
-Carb metabolism
-Fat metabolism: burns fat, decreases cholesterol, decreases fat stores
-Vitamin metabolism: increases baseline needs for vitamins
-Basal metabolic rate: hyper 60-100% increase. Hypo: up to 50% decrease
-body weight: help to decrease/maintain healthy body weight
What physiologic effects does the thyroid have on the organ systems?
-increased blood flow to tissues
-increased cardiac output
-increased heart rate
-increase heart strength with SLIGHT increase in thyroid hormone
- excitatory/depressive on nerve stimulation
- muscle weakness/sluggishness
-increased breathing rate/depth
- increase hormones secretion from other endocrine glands
What is the effect on the heart of a major increase in thyroid hormone?
weakened heart due to long-term and excessive protein catabolism
**Light periods can indicate _____. Heavy periods can indicate _____
light: can be hyper or hypo
**heavy: HYPO only!
What lab tests make up a thyroid panel?
Thyroid Stimulating Hormone - TSH
Triiodothyronine (total) - T3
Thyroxine (total) - T4
Free Thyroxine Index (unbound) - Free T4 or FT4
What are some interfering factors for TSH lab? What about the time of the day?
severe illness, NSAIDs (very protein bound)
time of the day (TSH is low in the AM and highest in the PM)
a high TSH indicates _____ or _____. _____ T3/4
a low TSH indicates ______. _____ T3/4
hypothyroidism or not enough thyroid meds. Not enough T3/4
primary hyperthyroidism. too much T3/4
primary hyperthyroidism has to due with the _____. Secondary is _____. Tertiary is _____-
thyroid itself
pituitary gland
hypothalamus
What are interfering factors of T3/T4? Does this indicate total or free?
estrogen meds
protein bound drugs )NSAIDs, phenytoin, androgens, lithium)
total unless it specifically says FREE
What is the interfering factor of FREE T3/4 lab?
Neonates have higher levels of FT4; typically screened using total T4
Why would you want to order a free T3/T4?
What thyroid labs does Professor Jensen recommend you order together?
Helps reduce confounding factor of serum protein levels
TSH and Free T4
What does an elevated T3, T4, Free T3, and Free T4 indicate? What does low indicate?
Excess amounts of thyroid hormone
Hyperthyroid states
Acute thyroiditis
Excess dosing of thyroid meds
Not enough thyroid hormone
Low T3/Free T3: decreased conversion of T3 aka liver disease or severe illness
Low T4/Free T4: pt is on T3 medication only
When is TBG used? Where is it released from?
Evaluation of abnormal total T3 or total T4 levels
Can help determine if patient is truly hypo/hyperthyroid versus just having abnormal levels of bound/unbound T3/T4
liver
What does elevated TBG indicate? low TBG?
elevated: elevated estrogen or infectious hepatitis
low: low proteins, ovarian failure, elevated testosterone levels, major stress
When is the TRH stimulation test used? What are some interfering exaggerated factors? diminished factors?
Assessment of pituitary response to TRH
Can help differentiate etiology of hypothyroidism
Can help evaluate degree of pituitary suppression in hyperthyroid pts
exaggerated in women and pregnancy
diminished in the elderly and in pts with MDD
What is a normal TRH stimulation test look like? Secondary hypo? tertiary? Hyper?
2x increase in baseline TSH within 30 minutes of TRH IV bolus
May also be seen in hypothyroidism due to severe illness
secondary: no increase in TSH
tertiary: delayed increase in baseline TSH 60-120 minutes
Hyper: Blunted TSH response due to maximal pituitary suppression by T3/T4
What are the pt stats for hypothyroidism? _____ is the leading cause worldwide. _____ is resource-rich countries
Roughly 1% of US patients - 5% of pts >60 y/o
5-8x more common in women
iodine deficiency
Hashimoto thyroiditis
What are the causes of primary, secondary and tertiary hypothyroidism?
Primary - Due to failure of thyroid to release T3 and T4
Secondary - Due to failure of pituitary to release TSH
Tertiary - Due to failure of hypothalamus to release TRH
What two medications are associated with hypothyroidism?
Amiodarone and Lithium
Fatigue
weight gain
dry skin
hair loss
constipation
poor appetite
cognitive impairment
cold intolerance
What am I?
______ is puffiness of face, hands and feet
hypothyroidism
myxedema
Hypothyroidism, TSH will be _____ and Free T4 to be _____. What other lab abnormalities would you expect?
TSH will be increased and Free T4 will be decreased
anemia, lipid abnormalities, hyponatremia (due to retaining fluid), hypoglycemia, elevated prolactin
If Hashimoto’s Thyroiditis what two antibody tests are possible to be positive. Which one is more likely to be positive?
90-95% chance of (+) anti-thyroid peroxidase antibody (anti-TPO)
70% chance of (+) anti-thyroglobulin antibody (anti-Tg)
When is imaging considered on a pt with hypothyroidism? What is the tool of choice? What other findings are possible? What do they indicate?
Consider if thyromegaly or thyroid nodule noted on exam
Thyroid Ultrasonography - noninvasive, relatively inexpensive
Enlarged thymus - possible if autoimmune thyroiditis is present
Enlarged pituitary - possible if hyperplasia of TSH-secreting cells occurs
What are some common complications of hypothryoidism?
CVD
adrenal disease
infertility
increased risk of bacterial pneumonia
increased risk of megacolon
_____ severe, life-threatening hypothyroidism. Often triggered by infection, illness, cold exposure, or drug use. What is the classic pt?
Myxedema Crisis
elderly women who have a stroke or stop taking thyroid meds
hypothermia
hypotension
hypoventilation
hyponatremia
hypoglycemia
cognitive impairment
mild confusion to coma
may see rhabdomyolysis and AKI
What am I?
What is the tx?
Myxedema Crisis
IV levothyroxine (LT4) therapy (if coma, add on IV T3)
Supportive care: warming blankets, intubation, tx of underlying cause
How do you define subclinical hypothryroidism? What is the MC pt type? How does it present? What is the tx?
Normal serum FT4 with TSH above reference range
MC in elderly (>65 y/o) pts - up to 13%
asymptomatic or mild hypothyroid s/s
observation if no s/s. May do trial of LT4 if symptomatic
1/3 of cases resolve spontaneously within 2 years
What is the first line tx for hypothyroidism? What do you need to screen for before starting? **What are threed important education points?
levothyroxine
valuate clinically for adrenal insufficiency/angina before start
- need to take at the same time every day on an empty stomach with a sip of water
- diff manufacturers make blood levels differ slightly so I need to know if you tablet changes
- peak response is usually seen in 4 weeks
Name some instances that you would need to increase the thyroid medication. What are the two major ones?
Medications - many anticonvulsants, sertraline, bile acid-binding resins, PPIs
**Increased estrogen - pregnancy, estrogen-containing medications
GI Disorders - celiac disease, IBD, lactose intolerance, gastritis
**Weight gain - over 10% body weight aka the heavier the person, the more medication they need to take
Name some instances that you would need to decrease the thyroid medication. What are the two major ones?
**Decreased estrogen - cessation of estrogenic meds, postpartum, post-oophorectomy
Increased androgen - starting testosterone therapy
**Weight loss - over 10% body weight
What is the BBW for all thyroid hormones?
All thyroid hormone replacement therapies carry a black box warning against the use of thyroid hormone replacement as a treatment for obesity.
**When a pt who has already been dx with hypothryroidism has an elevated TSH, what is the first question you should ask?
Verify how patient is taking medication!
If a hypothyroid pt has a hx of CAD or atrial fibrillation, where does their TSH level need to fall?
May need high-normal TSH if pt has history of CAD or atrial fibrillation
What would you do if a hypo pt has a normal TSH but is still symptomatic?
May consider free T3/T4 levels to evaluate adequacy of therapy
May consider T3 supplement or changing to combination T3/T4 (controversial)
If a hypo pt has a low TSH, what are you thinking?
too much thyroid meds
other medications: NSAIDs, opioids, CCBs, steroids
What does a suppressed TSH put you at risk for?
risk of atrial fibrillation, osteoporosis
What is the recommended starting dose for levothyroxine? What is the titration recommendations?
25-75 mcg daily OR 1.6 mcg/kg; titrate every 4-6 weeks to euthyroid status
first line is Levothyroxine!!
What are the SE of levothyroxine? What are the monitoring recommendations?
s/s of hyperthyroidism
TSH Q 4-6 wks after start/dose changes, then Q 6-12 mo
What is second line for hypothyroidism?
Liothyronine (LT3)
all SE, dose and monitoring are the same at levothyroxine
______ is a 1/4 ratio of T4/T3, made from beef or pork. What is the grain to mcg equivalent? What is the titration recommendation?
Desiccated Thyroid: 2nd line
65 mg (1 grain) = ~88-100 mcg of levothyroxine
titrate every 6 weeks to euthyroid status
______ state of excessive levels of T3 and T4.
_____ increased state of thyroid function
Thyrotoxicosis
Hyperthyroidism
What are the pts stats for Thyrotoxicosis?
Roughly 1% of US patients - 5% of women >60 y/o
5x more common in women
Higher incidence in smokers
_____ is the MC cause of thyrotoxicosis. What antibodies are commonly found? Which on is unique to this dz?
Graves Disease
**Thyroid-stimulating Ig (TSI) - (+) in 65% of cases
May also see (+) anti-TPO (75%) and (+) anti-Tg (55%)