Thyroid Dysfunction Flashcards
Treatments for Graves
Meds, radioactive iodine (I131– kills off cells), surgery
medications for Graves
- antithyroid drugs–inhibit synthesis of thyroid hormone (methimazole, propylthiouracil)
- beta blockers - reduce systemic hyperadrenergic symptoms and effects (tremor, palpitations)
preferred antithyroid drug
methimazole preferred due to PTU effects on liver
when might you use propylthiouracil instead of methimazole in Graves?
pregnant women
what symptom common between hypothyroid and hyperthyroid
fatigue
when to treat hypothyroidism with TSH
almost all will treat with TSH >10. WHether to treat between 5-10 mIU/L controversial
preferred medication for hypothyroid treatment
levothyroxine- synthetic T4
treatment goal for hypothyroidism
between 1-2.5
- somewhere in nl range
Myxedema coma
extreme hypothyroidism so severe it can progress to death unless diagnosed promptly and treated vigorously
- usually inciting event
- high mortality– endocrine emergency
Sxs of myxedema coma
decreased cardiac output, bradycardia, respiratory depression, edema, altered mental status, hypothermia, metabolic derangements
Does the thyroid produce more T3 or T4
T4 (80-100 micrograms/day compared to 3-6 micrograms per day)
Which thyroid hormone is more active
T3
Deiodinase
converts T4 to T3
types 1 and 2 convert T4 to T3, but type 3 converts T4 to rT3 (inactive)
how is thyroid hormone transported
in blood, most is bound to proteins (TBG, TBPA, albumin)
is there a higher concentration of T3 or T4 in the blood
T3 (0.2% total TH vs 0.02%)
proteins binding T4 in blood
thyroxine binding globulin(TBG), thyroid binding prealbumin (TBPA), albumin
proteins binding T3 in blood
Thyroxine binding globulin, albumin
halflives of T3 vs T4
T3 = 1 day vs 7 days for T4
Causes of increased total T4 and total T3
- hyperthyroidism/thyrotoxicosis
- increased binding proteins (i.e. Estrogen increased like in pregnancy)
- thyroid hormone resistance (rare)
causes of increased free T4 and free T3
hyperthyroid/thyrotoxicosis and thyroid hormone resistance
** binding protein issues not important
causes of decreased total or free T4 and T3
- hypothyroidism
- decreased serum protein binding
- Euthyroid sick syndrome (nonthyroidal illness)
- drugs
- liver or kidney disease (total T4, total T3)—mostly has to do with binding proteins
Euthyroid sick syndrome/nonthyroidal illness
pt is sick for some other reason and not underlying thyroid disease; have elevated circulating cortisol, free fatty acids, cytokines that cause upregulation or type 3 deiodinase, so you get inactivation of thyroid hormone
- also have mild central hypothyroidism– have nl to decreased TSH at pituitary
- abnormal thyroid labs with inappropriately low TH (esp T3)and low or nl TSH
nl TSH level
0.4-4.0
what test do we use to look at thyroid function
TSH level - single best screening test for thyroid dysfunction
- indicates person’s thyroid hormone ‘set point’
what is the relative level of TSH in primary hypothyroidism
elevated (lack of negative feedback)
what is the relative level of TSH in primary hyperthyroidism
suppressed (excess negative feedback)
when is TSH not reliable
abnormal pituitary (panhypopituitarism, TSHoma, idiopathic central hypothyroidism)
sxs of hyperthyroidism
nervousness, weight loss, change in appetite – normally increased, fatigue, tremor, heat intolerance, palpitations, hyperdefecation, trouble sleeping, diaphoresis
Labs in Overt hyperthyroidism/thyrotoxicosis
increased free T4 and free T3 but low TSH
subclinical hyperthyroidism
low TSH but nl free T3 and T4
thyrotoxicosis
high levels of circulating thyroid hormone
- can be due to overproduction of T3, T4 or high release of preformed/stored T3 adn T4 (not true hyperthyroidism)
How to determine cause of thyrotoxicosis
- thyroid uptake and perhaps radioactive iodine scan
- If TSH suppressed, should be no iodine uptake since TSH stimulates iodine uptake/synthesis of T3/T4
- “normal” or elevated iodine uptake in setting of low TSH is abnormal– autonomous production – True hyperthyroid
- low uptake - hormone excess due to high release of preformed thyroid hormone
radioactive iodine uptake
gives info on category of hyperthyroidism/thyrotoxicosis
What does high iodine uptake in setting of low TSH mean
true hyperthyroid– pattern gives info on etiology (Graves’ vs hot nodule vs multinodular goiter)
Etiologies of Low uptake Hyperthyroidism
- Subacute thyroiditis (granulomatous thyroiditis (viral); de Quervain’s)
- Chronic lymphocytic thyroiditis (Hashimoto’s), postpartum thyroiditis,
- radiation-induced thyroiditis,
- infectious thyroiditis, -Drug-induced thyroiditis,
- ectopic thyrotoxicosis (factitious or struma ovarii)
etiology of high uptake hyperthyroidism with low TSH
- Thyrotropin receptor Ab (Graves’; Hashitoxicosis)
- Thyroid autonomu (toxic adenoma, toxic multinodular goiter—MNG)
- HCG (hydatidiform mole, choriocarcinoma)
- TSH (TSH-oma –pit tumor, thyroid hormone resistance
which hyperthyroidism conditions are painful
Granulomatous thyroiditis, radiation-induced thyroiditis, infectious thyroiditis
Graves disease
type of hyperthyroidism where you have Ab to TSH receptor, constantly activating it to make more thyroid hormone
Destructive thyroiditis
examples = subacute/granulomatous and postpartum
clinical course of destructive thyroiditis
have initial hyperthyroid phase with high free T4 and low TSH then transition to low free T4 with high TSH
- about 20-25% remain hypothyroid
labs in overt hypothyroidism
elevated TSH, low free T4
subclinical hypothyroidism
high TSH but nl free T4; small decrease in T4 can have a large increase in TSH
sxs of hypothyroidism
mental slowness, weight gain, appetite change- usually decreased, fatigue, muscle cramps, cold intolerance, bradycardia, constipation, hypersomnia, dry skin
main categories of hypothyroidism
primary and central (secondary/tertiary)
etiologies of primary hypothyroidism
- Chronic autoimmune (Hashimoto’s) thyroiditis
- Transient hypothyroidism (silent or postpartum thyroiditis, subaute or granulomatous thyroiditis)
- iatrogenic (thyroid surgery/thyroidectomy, radioactive iodine, external neck irradiation)
- iodine deficiency or excess
- drugs
- infiltrative diseases
- infections
- congenital
drugs that can cause hypothyroidism
antithyroid, lithium, amiodarone, tyrosine kinase inhibitors, Fe, cholestyramine, phenytoin, carbamazepine
infiltrative diseases causing hypothyroidism
hemochromatosis, sarcoidosis, amyloidosis, fibrous (Reidel’s) thyroiditis, scleroderma
infections that can cause hypothyroidism
M. tuberculosis, P. carinii
Hashimoto’s thyroiditis
autoimmune condition where you have antibodies that destroy the thyroid’s ability to make thyroid hormone
Thyroid autoantibodies in Hashimotos
TPO (thyroid peroxidase)
Tg (thyroglobulin)
- some have anti- TSHR Ab
(thyroid stimulating hormone receptor Ab)
is hypothyroidism more common in males or females
females
what thyroid antibodies are present in Graves’ disease
- most have Anti-TSHR Ab
- some also have Anti-TG (50-80%)and Anti-TPO (50-80%)
what other conditions besides Graves and Hashimoto’s might you see thyroid antibodies
- normal population (TG, TPO)
- relatives of those with autoimmune thyroiditis (TG, TPO)
- Type I DM (TG, TPO)
- Pregnant women (TG, TPO)
positive thyroid Ab with elevated TSH, what proportion develop hypothyroidism
rate of 5% per year. If just Abs alone ~2% per year
hypothyroid treatment goal
~ 0.5-3
