thyroid Flashcards
effects of thyroid hormone
CNS: memory, concentration, mood, thermoregulation MSK: bone/mm growth CV: HR, BP, contractility liver: lipid metabolism GI: motility, appetite kidney: fluid retention, edema, GFR repro: fertility, menstrual cycles skin, hair, nails, and ocular
iodine metabolism
inorganic iodine organified by thyroid peroxidase
organic I + tyrosine = iodotyrosine
MIT and DIT coupling to T3 and T4 (thyroid peroxidase)
peripheral conversion of T4 to T3 for organ use (4-5x more potent)
circulating thyroid hormone
bound by TBG, TBPA, and albumin
T4 -> T3 in cells, T3 activates nuclear receptors -> increased RNA and protein synthesis
signs/sx of hyperthyroidism
nervous, irritable, difficulty sleeping, bulging eyes or unblinking stare, goiter, light period/menstrual irregularities, frequent BMs, warm moist palms, excessive vomiting in pregnancy, hoarse/deep voice, dry/sore throat, difficulty swallowing, rapid/irregular heartbeat, infertility, wt loss, sweating, 1st trimester miscarriage, fam hx thyroid dz or DM
hyperthyroidism in the elderly
may have atypical presentation: absent goiter, anorexia w wasting, palpitations, AFib, CHF
increased RAIU etiologies of hyperthyroidism
Graves dz, TSH-secreting tumor, pituitary resistance to T4, trophoblastic dz, toxic adenoma, multinodular goiter
decreased RAIU etiologies of hyperthyroidism
thyroiditis, ectopic thyroid tissue, medication-induced (exogenous thyroid hormone, amiodarone, iodinated radiocontrast dye)
tx for hyperthyroidism
antithyroid meds: thionamides (methimazole, PTU), iodides
radioactive iodine
surgery (subtotal thyroidectomy)
adjunct tx: b-blockers
MOA of methimazole
thyroid peroxidase inhibitor (prevents organification of I and coupling), decreasing thyroid hormone production
*DOC for most patients
specific ADRs of methimazole
teratogenic- causes lack of fetal skin, choanal atresia (blocks posterior nasal passage)
MOA of PTU
thyroid peroxidase inhibitor (prevents organification of I and coupling), decreasing thyroid hormone production
also prevents peripheral conversion of T4 to T3
*DOC in pregnancy/lactation and during thyroid storm
ADRs of thionamides
minor: pruritic rash, arthralgia, fever, transient leukopenia - try other agent but 50% cross-sensitivity
major: agranulocytosis (w fever, malaise, sore throat), aplastic anemia, arthralgia, lupus-like syndrome, hepatotoxicity (*PTU)
* do not try other agent if major ADR experienced
MOA, uses, and types of iodine for hyperthyroid
MOA: blocks thyroid hormone release, inhibits thyroid hormone synthesis, decreases gland vascularity
use: pre-surgery or after RAI tx
Lugol’s solution or saturated K-iodide solution
ADR of iodine
hypersensitivity rxn, iodism (metallic taste, burning mouth, GI upset), gynecomastia
potassium iodide for nuclear exposure
K-iodide competitively inhibits uptake of radioactive iodine, decreasing risk thyroid cancer after exposure to RAI
RAI-131 MOA, use, and ADR
m/c tx for hyperthyroidism
MOA: concentrates in thyroid causing follicular necrosis
C/I in children, pregnancy/lactation
ADR: hypothyroid, B-rays have 1 mm penetration = possible effect on surrounding tissue
surgical resection of thyroid in hyperthyroid
last resort
b-blockers for hyperthyroid
adjunctive therapy
propranolol, atenolol, metoprolol
block B-receptors, partially block conversion of T4 to T3
may require 2x normal dose to control sx and HR, may be helpful in thyroid-induced arrhythmia
*caution with asthma, COPD
thyroid storm
life-threatening, medical emergency
thyrotoxicosis, fever, tachycardia, tachypnea, dehydration, delirium, n/v/d
precipitated by infection, trauma, surgery, withdrawal of antithyroid meds
20% mortality w aggressive tx, duration 72 hr w tx (PTU, iodides, propranolol, steroids, support)
signs/sx of hypothyroidism
tiredness, forgetful/slow thinking, moody/irritable, depressed, inability to concentrate, thinning/loss of hair, dry skin, puffy eyes, goiter, hoarse/deep voice, dry/sore throat, difficulty swallowing, slower HR, heavy period/menstrual irregularities, infertility, constipation, mm weakness/cramps, wt gain, cold intolerance, elevated cholesterol, fam hx of thyroid dz or DM
hypothyroidism in the elderly
may have atypical presentation: failure to thrive, hoarseness/deafness, confusion/ataxia, depression
hypothyroidism in neonates and children
neonate: mental retardation
child: growth retardation
hypothyroidism etiologies
primary: Hashimoto’s dz, s/p thyroid ablation, drug-induced (anti-thyroid, lithium, amiodarone)
secondary: pituitary insufficiency (dec TSH), hypothalamic dysfxn (dec TRH)
levothyroxine
synthetic T4, DOC for hypothyroidism
no antigenicity, uniform potency, low cost
