Exam 5 Thyroid Flashcards
what is a goiter
enlargement of thyroid gland
hypothyroidism vs hyperthyroidism
hypo= inadequate thyroid hormone produciton
hyper= (thyrotoxicosis) over production of thyroid gland (hyperfunction of the gland)
what is thyroditis
inflammation and destruction of the thyroid gland
ex: hashimoto
name the cascade of thyroid hormone release
- hypothalamus sends thyrotropin releasing hormone (TRH) to pituitary
- pituitary sends thyroid stimulating hormone (TSH) to the thyroid via circulation
- thyroid synthesizes and releases T3, T4 and Calictonin
what acts as the negative feedback control for the thyroid hormones
T3 and T4 negative feedback to hypothalamus and pituitary
what molecule is needed to produce thyroid hormones and must come from the diet
iodine
Ex: iodized salt
is there more T4 or T3 secreted by thyroid
90% is T4
majority (80%) of T3 is created by the breakdown of T4
1/3 of T4 converted to T3
what is the active form of T3/4
free T3/4- metabollically active
most is bound in proteins= not biologically available for use
thyroxine binding globuline (TBG (99% bound of T4 and 70% of T3)
what comes on a thyroid panel
TSH
total T4
Free T3/4
Free T4 index - FT4I
(calculation that shows how much T4 there is relative to binding globulin)
why order a thyroid panel
screen for thyroid disease / function of thyroid
monitor treatment of thyroid disorders
assess treatment of hypothyroidism (levothyroxine therapy)
what is the most important test in evaluating thyroid function
TSH: more stable in the blood than T3/4
all newborns get this test to screen for congenital hypothyroidism
if TSH is high what does this mean for T3 and T4
T3/4 will be low= hypothyroidism
pituitary recognizes low levels of - very sensitive
small changes in T4 cause large changes in TSH
if TSH is low what does this mean for T3 and T4
T3/4 will be high= hyperthyroidism
what is the goal of treating hypothyroidism (levothyroxine treatment)
provide adequate amount of exogenous T4 to minimize TSH secretion
name some disorders that would increase TSH
HYPOthyroidism (congenital=cretinism and primary)
secondary HYPERthyroidism
pituitary adenoma
hashimoto’s thyroditis (autoimmune)
amiodarone/ dopamine antagonist= drugs
ectopic TSH producing tumors
TSH producing pituitary adenoma
name some disorders that would decrease TSH
primary HYPERthyroidism
secondary HYPOthyroidism
- TSH near zero!!
Tertiary HYPO thyroidism
graves disease (autoimmune)- has no effect on TSH levels
glucocorticoids= drugs
excessive exogenous thyroid hormone
high levels of chronic gonadotropin
what is primary hypothyroidism?
Secondary?
Tertiary?
primary: problem with thyroid
secondary: problem with pituitary
tertiary: problem with hypothalamus
what is primary hyperthyroidism?
secondary?
primary: problem with thyroid
secondary: problem with pituitary
in which disorder would TSH levels be near zero!!!
secondary hypothyroidism
what test is a direct measure of ALL circulating T4 (thyroxine)
total T4
this is protein bound and free
what are the critical values for Total T4
low: myxedema coma (under 2mcg/dl) due to hypothyroid, protein deficiency
- causes everything to slow down (hypotension, bradycardia, lethargy, etc)
high: thyroid storm (over 20 mvg/dl)
due to: hyperthyroid, too much iodine, high levothyroxine med, hepatitis
- causes hyper everything speeds it up
-hyperthermia, dehydration, shock
what test is not affected by fluctuations in TBG (thyroid binding globulin)
free T3/4
- aka good for evaluating ppl with protein abnormalities
what test is most accurate indicator of T4 activity
free T4
used if not enough info from TSH
when should you check free T3 and T4
when suspect HYPER thyrodiism
need to rule out T3 toxicosis
what are thyroid immunoglobulins
what are the types
IgG antibodies directed against thyroid receptor antigens
3 types
1. thyroid peroxidase (TPOAb or Anti-TBO= anti thyroid peroxidase antibody)
- thyroglobulin (TgAb or Anti-Tg= anti thyroglobulin antibody)
- TSH receptor Antibody (TRAb= anti TSH receptor antibody)
- TSI
- TBII
what would cause elevated TPOAb, TgAB
In order of most prevalence:
hashimoto disease
also graves, but most likely hashimoto
other autoimmune diseases (type 1 diabetes)
pregnancy
goiter, isolated thyroid nodule, cancer
when should you order a TPOAb
to confirm Hasimotos (though you dont have to treat)
or when pt with subclinical hypothyroidism to determine Tx plan (aka present with hypo but labs in normal range)
what thyroid test helps confirm graves
anti TSH receptor antibody (TRAb)
checks for anti TSH receptor antibodies that would cause the continous firing of the receptor
Two types TSI and TBII
what do nuclear thyroid scans do
measure thyroid funciton
evaluate thyroid nodules
find causes of hyperthyroidism / plan treatment for hyper/nodule
see spread of thyroid cancer
when should you order a thyroid ultrasound
initial evaluation of a thyroid nodule!!!!!!!!!!!
what is radioactive iodine uptake and scan used for
determine if cancerous or not and if spread
give the radioactive iodine and generally hypo = too little taken up and hyper= too much
IN NODULES:
HOT: high uptake- BENIGN
COLD- low uptake CANCER-> nonfunctioning tissue
what can congenital hypothyroidism cause
irreversible damage to CNS
developmental defects
symptoms of HYPO thyroid
fatigue
cold intolerance
dry skin
constipation
weight gain
depression
bradycardia
menorrhagia
symptoms of HYPER thyrodisim
anxiety
weakness
tremor
palpitation
heat intolerance
weight loss
exophthalmia
goiter
what do you do if you get a high TSH
first repeat TSH and check free T3/4 and index
if normal= original = error
if TSH still high= and free T4 low then hypothyroid
if TSH high but free T4 normal= subclinical hypothyrodism
same for low TSH but opp TSH low, high T4/T3= hyper
is HYPER or HYPO thyroidism more common
hypo = 95% of cases
what test would you order for pt with goiter
ultrasound + thyroid panel
if a pts TSH is low and Free T3/4 high what does this indicate
hyperthyroidism
what else could you order for a pt with hyperthyroidism and a goiter after the ultrasound
radioactive iodine uptake to determine if cancerous and then a biopsy
cold means cancer = low uptake
refer
what would you order for a pt complaining of flu like symptoms and an enlarged thyroid
thyroid panel
how long does it take for TSH levels to respond to levothyroxine treatment
4-6 weeks!!!!
what does high levels of thyroid peroxidase antibodies indicate (TPOAb)
hashimoto thyroiditis = elevated TPOAb
what is the first and primary test done to check thyroid
TSH
most sensitive and specific screening lab
what condition would you exepct in person with HIGH TSH
low TSH
high TSH= hypo
low TSH= hyper
pt with thyroid nodule should have what initial study
ultrasound and thyroid panel
