Thyroid Disorders Flashcards
What is colloid composed of?
Thyroglobulin, which is made of tyrosine residues that serve as sites for TH synthesis
3 things that inhibit TRH
Glucocorticoids, DA, somatostatin
4 steps of TH synthesis
- 1) Iodide transport (trapping) through Na-iodide symporter (NIS)
- 2) Oxidation / incorporation into TG (organification). Regulated by thyroid peroxidase (TPO). TPO is upregulated by TSH.
- 3) Coupling of MIT (monoiodotyrosine) and DIT to form T3 and T4
- 4) TSH stimulates TPO and transcription of TG
What 2 things inhibit proteolysis / release of TH?
Excessive iodine and lithium
3 TH binding proteins
Thyroid binding globulin, transthyretin, and albumin
What increases thyroid binding globulin concentration?
Hyperestrogenic states: pregnancy, exogenous estrogens
What decreases thyroid binding globulin? (5)
Androgens, glucocorticoids, protein malnutrition, nephrotic syndrome, cirrhosis.
What inhibits 5’MDI? (6)
Illness, caloric deprivation, malnutrition, glucocorticoids, beta-blockers, amiodarone, and PTU
Half life for T4/3
T4 is 7 days
T3 is 1 day
Wolff-Chaikoff Effect
Protects against iodine excess. Thyroid peroxidase (TPO) is shut down so TH isn’t made in excess. Normally, a subsequent decrease in I → escape from this effect and resumption of normal TH synthesis. However, if there is no escape from this effect, I-induced hypothyroidism may occur.
Jod-Basedow Phenomenon
When pxs who have accommodated to chronic iodine deficiency are exposed to high doses of iodine → hyperthyroidism.
TH effects Neurogenesis Metabolism Weight Cholesterol Heart Bone Childhood growth GI GU Renal
- Neurogenesis: absence during early life → irreversible MR (cretinism). TH regulates transcription of myeline basic protein.
- Metabolism: increases metabolic rate, O2 consumption, heat production, glucose absorption, GNG, glycogenolysis, hepatic LDL receptors, lipolysis, and metabolism of cholesterol to bile acids.
- Hyperthyroidism doesn’t cause universal weight loss b/c it stimulates appetite. Also causes muscle wasting.
- Hypothyroidism may involve weight gain of 10-20 lbs (not obese)
- Hypercholesterolemia occurs w/ hypothyroidism
- Heart – stimulates contractility, increases O2 consumption, enhances sensitivity to catecholamines. Hyperthyroid causes tachycardia and increased contraction force.
- Bone – stimulation of bone formation and resorption (increased urine / serum Ca), but overall resorption prevails. Hyperthyroid → osteoporosis.
- Hypothyroidism may blunt growth in childhood.
- GI – stimulates gut motility. Hyperthyroid → hyperdefecation. Hypothyroid → constipation.
- GU – TH affects ovulation, so excess / deficiency → menstrual irregularities / infertility. High TRH stimulates hyperprolactinemia → anovulation
- Renal – necessary for normal renal free water excretion
T3/4 levels in primary hypothyroidism
T4 is low. T3 often remains normal.
Indications for TSH screening (10)
Women > 60 y/o (older women have highest rates of thyroid disease), family hx, sxs of hyper / hypothyroidism, goiter, hyperprolactinemia, hypercholesterolemia, infertility / menstrual irregularity, cardiomyopathy / arrhythmia, osteoporosis, before getting pregnant.
Apathetic thyrotoxicosis
Population
2 main sxs
More common in older pxs. Usually involves cardiac problems (A fib, CHF), and / or osteoprosis
Thyroid storm
3 main characteristics
Causes (5)
Treatment (5)
- Severe thyrotoxicosis + mental status changes + fever.
- Caused by underling hyperthyroidism plus acute precipitant: not taking meds, surgery, MI, CVA, infection.
- Treatment
- PTU – decreases production and blocks T4 → T3
- Propranolol – treats hyperadrenergic sxs and blocks T4 → T3
- Potassium iodide AFTER PTU – blocks TH release
- Glucocorticoids – blocks T4 → T3 conversion
- Supportive care
Does hyper stimulation of TSH receptor cause high or low iodine uptake?
High
Does leak of TH cause high or low iodine uptake?
Low
What percentage of iodine is normally taken up by the gut?
25%
Graves' Disease I uptake Population Which cells make TSI? What increases risk of orbitopathy? Signs / sxs of orbitopathy (8) Risk if untreated Treating dermopathy
- High I uptake
- More common in younger people. 9x more common in women.
- TSI is made in B lymphocytes.
- Smoking increases risk of orbitopathy.
- Sxs / signs include proptosis / exophthalmos, eye irritation / pain, dryness, photosensitivity, periorbital edema, exposure keratopathy, diplopia / gaze paralysis, loss of color vision
- If untreated, risk of A fib, bone loss, and thyroid storm.
- Treat dermopathy w/ corticosteroids
Toxic multinodular goiter (TMNG) / Solitary hyperfuctioning nodules I uptake level Population Presentation Cause
- High I uptake
- More often seen in older pxs.
- May present as “apathetic hyperthyroid”. Hot and cold areas seen on nuclear imaging.
- May be due to activating mutations of TSH receptor.
TSH secreting tumors I uptake level Elevated levels of what? Sx Treatment (2)
- High iodine uptake.
- Normal / high TSH, high T4, high alpha subunit.
- May have visual field defects.
- Tx w/ tumor resection and somatostatin analogs.