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CPD Endocrine Review: Thyroid

Where is the thyroid?
anterior neck C5-T1
though it can slip down the neck and into the thorax in some older folks

How much does a normal thyroid weigh?
10-20grams

What nutrient is concentrated in the thyroid?
iodine

What nutrient is it important to take if you are exposed to a nuclear radiation accident?
iodine, in the form of potassium iodide tablets, seaweed, bladderwrack
Japanese after Hiroshima/Nagasaki survived better with big seaweed diet
immediately, to prevent the thyroid from uptaking too much radioactive iodine

What sign do you see in some populations that they are chronically deficient in iodine?
goiter on neck

What happens to an infant who doesn't produce enough thyroid and isn't diagnosed or treated?
cretinism
hypo for 3 months-->irreversible abnormalities in brain development

What food is often iodinated around the world, besides salt?
flour

How did physicians assess thyroid function up until the 1960's?
basal metabolic rate based on temperature

If a pt has primary hypothyroidism, what will the TSH level be?
high

What is T4 synthesized on and covalently linked to in the follicle?
thryoglobulin in colloid

What do parafollicular C-cells make?
calcitonin

How much thyroid hormone is usually stored in the gland?
enough for 2-4 weeks

What can cause the stored hormone to "spill" out?
infection = itises

How does the follicle trap inorganic iodide?
by trapping it against a concentration gradient via sodium/iodide transporter protein

Which is the most active form of thyroid hormone?
T3

What amino acid is combined to make thyroid hormone?
tyrosine

Why would some doctors prefer synthetic thyroid to treat autoimmune disease?
they want to avoid introducing another organic antigen that could provoke further AI
no science supporting this yet

What do you get when you add a MIT to a DIT?
T3
mono and di iodo tyrosine

What happens when the thyroid is signalled to release hormone?
the hormone is unbound from thyroglobulin
unbound MIT and DIT are deiodinated within the epithelial cell and the iodide is recovered (???)
released hormones are also deiodinated in peripheral tissue to release free iodide for kidney excretion

What glands control the thyroid?
hypothalamus and anterior pituitary

What is made by the thyrotroph cells in the anterior pituitary?
TSH, thyroid stimulating hormone

What do you call it if a person is hypothyroid because the hypothalamus isn't working right?
tertiary hypothyroid
secondary is ant pit, primary is gland itself dysfx

What does TSH activate when it binds to the thyroid epithelium?
adenylate cyclase-->incr cAMP-->initiation and exocytosis of hormone

What mint herb is used in Ayurveda that also activates adenylate cyclase?
Coleus forskohlii
has very long history of use in tx

Which hormone influences the level of TSH the most?
T3 at the pituitary

What class do thyroid hormones belong to?
steroid-like
they aren't based on cholesterol like real steroids
they are poorly soluble in water and require carrier proteins in the blood

What are the three main thyroid carrier proteins?
thyroxine binding globulin (TBG)(remember that thyroglobulin is the protein that stays in the follicle)
transthyretin
albumin

What percentage of T3 and T4 in the blood is usually free, or unbound?
.05%
hardly any

What functions are stimulated by T3 and T4?
O2 consumption, heat production, metabolic rate
lipid synthesis, lipid oxidation
cholesterol synthesis, cholesterol degradation
protein synthesis and degradation
drug metabolism
catecholamine receptor sensitivity
glucose absorption and neogenesis

What are the effects of excess thyroid hormone?
fast heartbeat, vasodilation, warm skin, incr GI motility, incr bone turnover, incr muscle contraction

What thyroid condition presents with constipation, fatigue, dry skin?
hypothyroid

Why might a hypothyroid person present with HTN even though their heart rate is slow?
vasoconstriction (per notes, not sure about this yet)

What are some of the environmental causes of reduced thyroid function?
chlorine, bromine, fluoride (hallogens replace iodine)
estrogens (disrupt tyrosine's binding to iodine)
perchlorate, pertechnetate, thiocyanate (inhibit iodine pump)

How did doctors assess thyroid function up until the 1960's?
basal metabolic rate based on temperature

What's the most sensitive thyroid lab?
TSH

If you have an elevated thyroglobulin in the serum, what do you suspect?
viral infection
thyroglobulin should stay in follicle

Main binding hormone for thyroid in blood?
thyroxine binding globulin
TBG

What other hormones might you test for, besides TSH?
total and free serum T3, T4
TRH
thyroid stimulating immunoglobulin
anti-thyroid peroxidase antibody = anti-TPO (thyroiditis)
anti-thyroglobluin antibody (thyroiditis)
long acting thyroid stimulating antibody (LATS, Graves)

Are cysts on your thyroid a big worry?
probably not

What autoimmune thyroid disease can cause fibrosis of the gland?
Hashimoto's

Who gets acute thyroiditis?
kids, it's unusual, most bacterial, tender neck

How long will thyroid function be reduced after a sub-acute thyroiditis?
2-3 months

How many new mothers suffer from postpartum thyroiditis?
5-10%

What nutrients can be given to support thyroid hormone production?
tyrosine, selenium, iodine, iron, zinc, vitamins A, B2, B3, B6, E

What does selenium do?
help with T4-->T3 conversion

What does iron do?
cofactor in conversion of phenylalanine to tyrosine

What is Fucus vesiculosus?
brown seaweed containing iodine

A patient with high T3 and extremely low TRH and TSH most likely has what?
factitious hyperthyroidism: they're overmedicating, probably to loose weight
do radioactive iodine scan---the uptake is low

What's another reason for increased thyroid hormone without the very low TRH and TSH?
acute infection causing spill of stored hormone
transient hyperthyroidism secondary to thyroiditis

An elder with fatigue, aches, a slow mind, weight loss and heart palpitations might have what?
apathetic hyperthyroidism
labs usu show very low TSH and high free T4, free T3 may also be increased
don't assume it's hypo, elders can slow down when it's hyper too

What happens to a woman's cycle when she's hyperthyroid?
abnormal frequency of menses (and infertility)

What's the most common malignant thyroid cancer?
papillary

What inactive version of thyroid hormone is manufactured when a person is starving or cachexic?
rT3
increased in Wilson's syndrome, sx: hypo

What infiltrative diseases can affect the thyroid?
sarcoidosis, amyloidosis, hemochromatosis

How do goitrogens work?
they inhibit the iodine pump or disrupt enzymes
incl: drugs for Graves
cassava, sweet potatoes, lima beans, peanuts, pine nuts, soy
brassica family (raw, incl cabbage, radish, brussel sprouts, turnips, cauliflower, kohlrabi, cassava, rutabab)

How do you inactivate a food goitrogen?
cook it

A dwarf with puffy features, an enlarged tongue and dry skin might have what?
cretinism
also has marked mental retardation
myxedematous endemic cretinism in Congo

How early do you have to treat cretinism to prevent lasting effects?
within first 3-4 weeks

Why don't we have more cretinism here?
infants are tested for thyroid with very first heel stick blood test

What commonly used medications completely block absorption of thyroid supplements?
antacids

What other meds may lower thyroid hormone levels?
beta blockers
SSRI's
tricyclic antidepressants
ORAL HYPOGLYCEMICS
anti-seizure meds
LITHIUM for depression/mania, may be permanent, sulfonurea is goitrogen
antacids don't forget

A person with carpal tunnel and diminshed DTR's may also have which thyroid condition?
hypo

How does low thyroid cause follicular hyperkeratosis (bumps on back of arm)?
lower vitamin A levels
thyroid helps convert beta carotenes to vitamin A
hair follicles can't mature if no vit A

Which part of the eyebrow may thin with hypothyroid?
lateral third, will grow back with thyroid replacement

What is the most common organic cause of depression?
hypothyroidism

What gynecologic conditions are associated with hypothyroid?
PMS, irreg, infert, PCOS, fibrocystic breast dz

What systemic conditions are assoc?
depression, HTN, high chol, hyperhomocysteinemia, atherosclerosis, MI

Which thyroid condition might you suspect if a person has high cholesterol & TG's, mild normo-normo anemia and high CPK (or other skeletal muscle enzyme)?
hypothyroid

What happens to the high cholesterol when the thyroid condition is treated?
it resolves

What can cause SECONDARY hypothyroid?
tumors of pit or other, head trauma, radiation, postpartum infarct (Sheehans), infx (meningitis)

When a person has secondary hypothyroid, how might they present?
with multiple hormone deficiencies and mass effects if tumor
check extraocular motion

If a patient has Addison's dz too and you treat only the hypothyroid what might happen
you could kill them by increasing metabolic rate-->circulatory collapse

What are the other contraindications to thyroid replacement?
recent MI or other cardio compromise
untreated thyrotoxicosis
sensitivity or allergy to meds (some bovine, porcine)
autoimmune dz might indicate synthetic instead of natural
uncorrected adrenal cortical insufficiency

What are some of the signs and symptoms of hyperthyroidism?
warm moist skin
periorbital and facial edema
proptosis
conjunctival injection
exopthalamos (80% of cases dt Graves, mostly bilateral but also 15-28% of unilateral)
increase in mass of retrobulbar CT
bilateral gross enlargement of medial and lateral rectus muscles
upper eyelid retraction
dry eyes
pretibial myxedema (skin thickening, no pitting)
lid lag
thyromegaly = goiter
bruit over thyroid???
tachycardia
A fib
prominent S4 sound
flow murmurs
find hand tremor
fast return phase for DTR's
anemia

What is the most common cause of hyperthyroidism?
Grave's dz
antibody vs thyroid TSH receptor-->continuous stimulation of gland
non-suppressible overproduction of hormone

If a pregnant woman has Graves, what happens to the fetus?
antibodies cross placenta and overstimulate fetal thyroid
results in fetal demise, preterm birth, or in less severe cases fetus survives to birth and gets better
born hyperthyroid
???questions about hyperplasia
are Graves Abs in breast milk???
notes say rate of clearance varies and neonatal Graves may have immediate or delayed onset
may last weeks to months

Does Graves disease ever go away?
yes, it sometimes spontaneously remits

Do toxic solitary and multinodular goiters remit?
no
hyperfunction in some nodules
toxic multinodular more in elderly

Hyperfunctioning or "hot" nodules are more likely to be benign or malignant?
benign

What can you find out using a radioactive iodine scan?
high uptake and Ab's present-->primary hyperthyroid ie Hashimotos
high uptake but no Ab's-->Plummer's syndrome (toxic solitary or multiple thyroid nodules)
low uptake-->thyroiditis or thyrotoxicosis factitia

What's the difference between thyrotoxicosis and thyroid storm?
depends
some say the thyrotoxicosis is an umbrella term for all hyperthyroid
others say it only means very high levels ie storm

What distinguishes thyroid storm?
abrupt onset hyper
fever, weakness, muscle wasting
restlessness, emotion swings, confusion, psychosis, coma
hepatomegaly, jaundice
cardiovascular collapse (shock)

What are the four main types of thyroid cancer?
papillary (#1), follicular, medullary (makes calcitonin), anaplastic/undifferentiated (deadly)

What populations are more likely to have thyroid cancer?
young women but women have way more thyroid dz anyway
a man with a thyroid nodule-->greater index for suspicion

Is a hard solitary nodule likely to be B9 or Malignant?
malig esp if cold (nonfunctional)

What about a multinodal presentation?
benign

What is the most common type of thyroid cancer?
papillary

What are some risk factors for thyroid cancer?
radiation exposure to head, neck, chest, esp in infacy or childhood (tx for thymus, tonsils, acne, lymphoma)

What population gets more follicular carcinoma?
elderly
15% of thyroid cancers
more malignant than papillary, lots of mets
usu unilateral but familial is bilateral
autosomal dominant

What is the pathology of medullary carcinoma?
proliferation of parafollicular cells (C cells)
producing calcitonin
calcitonin normally lowers serum Ca++ and phosphate
usually those levels are normal with this cancer
Dx: bx

What happens to people with anaplastic carcinoma of the thyroid?
rapid and painful enlargment of the thyroid
80% die within a year of dx
10-15% of all thyroid cancer

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