thyroid Flashcards
only _____ thyroid hormone has biological effects
unbound
t4 source vs t3 source
T4 only source is thyroid gland
T3 <20% comes from thyroid gland. most is produced by breakdown of T4 by deiodinase enzyme
binding affinity T3 vs T4
T3 has a 10-15x higher binding affinity than T4
t/f: all thyrotoxicosis is hyperthyroidism
false
the symptoms of thyrotoxicosis can be described as
speeding up and heating up
ex hyperactive, sweating, palpitations, weight loss w/ inc appetite, diarrhea, etc
diagnostics of thyrotoxicosis
decreased TSH (due to negative feedback)
increased T3, T4
RAIU
TSAbs if grave’s disease
what are the most common causes of thyrotoxicosis with increased RAIU
Grave’s disease
toxic adenoma
multinodular goiter
which is the most common cause of hyperthyroidism
Grave’s
describe actions of grave’s?
autoimmune: actions of thyroid-stimulating antibodies (TSAbs) against thyrotropin receptor
thyroid enlarged 2-3x normal
disproportionate increase in T3 relative to T4
description of toxic adenoma?
“hot nodule”
autonomous thyroid nodule, benign tumor producing thyroid hormone
description of multinodular goiter?
autonomous follicles
most common causes of thyrotoxicosis with suppressed RAIU
subacute thyroiditis
painless thyroiditis
exogenous thyroid hormone
meds containing iodine
describe subacute thyroiditis/treatment?
systemic symptoms like flu: fever, malaise, myalgia
self limiting: ANTITHYROID DRUGS ARE NOT INDICATED
treatment is symptom management: beta blockers, NSAIDS, prednisone
describe painless thyroiditis/treatment?
painless/silent– can happen postpartum. self-limiting: antithyroid drugs are not indicated. give propranolol or metoprolol
what can cause ingestion of exogenous thyroid hormone
overtreatment, pharmacy errors, accidental– ground beef contaminated
what medications contain iodine that can induce thyrotoxicosis
amiodarone
withhold ____ for 24-48 hours prior to laboratory testing
biotin
antithyroid medications
methimazole first line
propylthiouracil
when to consider surgery for thyrotoxicosis
large thyroid gland >80g
severe ophthalmopathy
lack of remission
when is radioactive iodine the choice therapy for thyrotoxicosis
toxic nodules & multinodular goiter
disadvantages for radioactive iodine
permanent hypothyroidism
worsening ophthalmopathy: avoid in eye disease
contraindicated in pregnancy and breastfeeding, defer pregnancy x 6 months
what is the limitation to methimazole
possible teratogen, avoid 1st trimester pregnancy
surgery downside for thyrotoxicosis
leads to permanent hypothyroidism
what are the limitations for propylthiouracil
hepatotoxicity
limited to: 1st trimester pregnancy, thyroid storm, patients with adverse effects to methimazole
thyroid storm
life threatening medical emergency
primary hypothyroidism: causes
hashimoto’s, iatrogenic
what is central hypothyroidism
dysfunction of pituitary or hypothalamus
what is hashimoto’s
autoimmune; antithyroid peroxidase antibodies, presents as goiter/ hypothyroidism
what causes iatrogenic hypothyroidism
destructive amounts of radiation, surgery
pituitary disease of central hypothyroidism culprit is __
TSH
hypothalamic disease of central hypothyroidism culprit is ___
TRH deficiency
hypothyroidism presentation can be described as
slowing and cooling
children: delays growth, development
dry skin, cold intolerance, weight gain, constipation, weakness
diagnosis of hypothyroidism
increased TSH for primary
inappropriately normal TSH for secondary
autoantibodies in hashimoto’s
treatment of hypothyroidism
levothyroxine
liothyroxine
higher incidence of cardiac adverse events
desiccated thyroid
antigenic in allergic/sensitive patients
levothyroxine at excessive doses can cause
heart failure, angina, MI, decreased bone density
starting dose for levothyroxine
25 mcg for elderly with known cardiac disease
50 mcg for most
titrating levothyroxine
25 mcg increments monthly
average maintenance dose is 125 mcg
levothyroxine with food
food impairs absorption
TSH normal range
0.5 to 4.5
levothyroxine drug interactions
H2RAs, PPIs, rifampin, carbamazepine, phenytoin
myxedema coma
decompensated hypothyroidism: need IV levothyroxine and IV hydrocortisone
pregnancy with hypothyroidism
increase levothyroxine dose 20-30%: 2 additional tablets a week
