Thyroid Flashcards
3 hormones the thyroid gland secrete
Triiodothyronine (T3),t1/2 1-2 dys (9%)
Thyroxine (T4), t1/2 6-7 dys (90%)
Calcitonin
synthesis of thyroid hormones requires what?
iodine
what thyroid hormone is more potent?
T3 is 4x more potent
most of it is from peripheral conversion of T4 to T3
what inhibits the conversion of T3 to T4?
beta-blockers, corticosteroids, amiodarone
what produced thyrotropin-releasing hormone (TRH)
hypothalamus
what inhibit iodine uptake by the thyroid (can’t produce thyroid hormone as well)
cardiac glycosides
bromine
fluorine
lithium
when does TSH peak?
early morning
what impairs the coupling of 1 DIT and 1 MIT or 2 DIT’s to form T 3 and T4 ?
Sulfonylureas, thionamides
what proteins bind thyroid hormone?
Thyroid Binding Globulin (TBG)
Albumin
Thyroid Binding PreAlbumin (TBPA)
what blocks the release of Hormones following proteolytic cleavage from the thyroglobulin
high levels of iodide or lithium
how much of thyroid hormone is bound?
99% (only free hormone has biological effect)
what does thyroid hormone do?
basal metabolic rate influence growth through stimulation of growth hormones synthesis and action body temp fetal development cardiac rate and contractility peripheral vasodilations red cell mass and circulatory volume respiratory drive peripheral nerves (reflexes) hepatic metabolic enzymes bone turnover skin and soft tissue effects
normal range of total T4? (free and bound)
4.5-12.5 mcg/dL
what is the normal TSH range?
0.4-5.5
what is a more reliable lab than total T4 and T3?
Free T4 (FT4)
when is sensitive TSH increased?
primary hypothyroidism
when is sensitive TSH decreased?
primary hyperthyroidism
what is elevated w/ an increased thyroid binding globulin?
total T4 is elevated
Total T3 is elevated
Serum TSH concentration above statistically defined upper limit of reference range
Serum free thyroxine within reference range
sub-clinical hypothyroidism
what is the biggest time sub-clinical hypothyroidism is significant?
pregnant women
increased risk of placental abrusption, pre term delivery
women w/ thyroid autoantibodies have an increased risk for what?
spontaneous abortion
do you tx for sub-clinical hypothyroidism?
definitely is pregnant
still unclear for other populations
S/S of hypothyroidism
Tiredness Lethargy, Muscle pains Weight gain Intolerance to cold Dry skin, Coarse skin Bradycardia Mental impairment Dry thinning hair
effects of hypothyroidism on CV system
systolic dysfunction reduced oxygen uptake during exercise diastolic HTN increased arterial stifness increased total cholesterol and LDL insulin resistance decreased fibrinolytic capacity decrease activity of VW factor and factor VIII
what effect does hypothyroidism have on digitalis?
decreased volume of distribution
what effect does hypothyroidism have on insulin?
impaired degradation
what effect does hypothyroidism have on warfarin?
delayed catabolism of clotting factors
what causes primary hypothyroidism?
hashimoto's Dz iodine deficency iatrogenic hypothyroidism (radioactive iodine ingestion, post thyroidectomy)
Causes of secondary hypothyroidism
pituitary decrease (TSH is low/normal and thyroid levels low hypothalamic dz- TRH deficiency, very rare but due to cranial irradiation, trauma, neoplastic dz
risk factors for hypothyroidism?
pospartum women
family hx of autoimmune thyroid disorders
previous head and neck of thyroid irradiation or surgery
other autoimmune endocrine (DM1, adrenal insuff.)
non-endocrine issues (celiac dz, vitiligo, MS, pernicious anemia, trisomy 21)
S/S of hypothyroidism in elderly patients
Hoarseness Deafness Confusion Dementia Ataxia Depression Dry skin Hair loss
An autoimmune disease resulting in fibrosis of the thyroid gland, antibodies to TSH receptor
Selective destruction of thyroid gland ↓ thyroid hormone and ↑ TSH levels
Hashimoto’s thyroiditis
what is the most common cause of hypothyroidism?
hashimoto’s thyroiditis
Congenital (infantile) hypothyroidism results in…….
dwarfism and mental retardation (cretinism)
problem that occurs w/ hypothyroidism patients appear to have edema beneath skin. these patients will often present in a coma
myxedema
clinical symptoms of myxedema
Hypothermia
Advanced hypothyroid symptoms
Altered sensorium (from delirium to coma)
thyroid drug from beef or pork thyroid gland. Dose is in a grain (60 mcg of T4) but has unpredictable stability. not used very often
Thyroid USP Armour
purified pork thyroblobulin also does in a grain but is standardized biologically with a ratio of T4:T3
thyroglobulin
synthetic T4 medication that is a good choice as long as not on a drug that inhibits conversion of T4 to T3.
levothyroxine
synthetic T3, good if one a medicaiton that inhibits peripheral conversion of T4 to T3.
liothyronine
synthetic T4:T3 that is expensive.
liotrix
ADRs of thyroid USP and thyroglobulin
allergic rxn
DOC for hypothyroidism
levothyroxine
a switch from synthroid to generic levothyroxine can be significant enough to what?
mess a patient up, the amounts in the tablets themselves can be slightly off
Contraindications for levothyroxine
thyrotoxicosis
adrs w/ levothyroxine
arrhythmias tachycardia anginal pain cramps HA restlessness sweating weight loss osteoporosis
monitoring w/ levothyroxine
TSH every 6-8 weeks until normalized then every 6-12 months
if dose change check in 2-4 months
what drugs cause alter absorption w/ levothyroxine. take levothyroxine 2 hours before or 4 hours
Cholestyramine
Ferrous sulfate
Sucralfate
Aluminum hydroxide
what drugs cause increased metabolism of levothyroxine
Rifampin
Phenytoin
Carbamazepine
what interaction is there w/ oral contraceptives/ estrogen w/ levothyroine
Increase thyroid binding globulin, resulting in lower free thyroid hormone
what drugs inhibits synthesis and release of thyroid hormone
lithium
if a patient is on amoidoarone what drug should they recieve?
liothyronine
Sodium salt of the naturally occurring levorotatory isomer of T3. used for Initial therapy of myxedema (skin disorder) and myxedema coma
Short-term suppression of TSH in patients undergoing surgery for thyroid cancer.
Patients w/5’-deiodinase deficiency who cannot convert T4 to T3 (or on amiodarone)
liothyronine sodium
combo of T4 and T3 but isn’t more beneficial than levothyroxine.
liotrix (euthroid, thyrolar)
tx for myxedema coma
IV bolus w/ levothyroxine
maintenance of IV levothyroxine then switch to PO
IV hydocortisone until adrenal supression is R/O
supportive therapy- ventilation, euglycemia, BP, body temp
tx for congenital hypothyroidism
Initial therapy within 45 days of birth at 10-15mcg/kg/d, associated with improved IQ’s in treated infants
Dose progressively decreased to typical adult dose beginning 11-20 years
tx for hypothyroidism in pregnancy?
levothyroxine- need an increase of dose (20%)
hypothyroidism in pregnancy is associated w/ an increased risk of what?
still births
when is levothyroxine especially important in pregnancy.
first 12 weeks as that is when thyroid hormone is only supplied by mom
what is the cause of hyperthyroidism
Overproduction of endogenous hormone
Exposure to excess endogenous hormone
Elevated free and total T3, T4 or both serum concentrations
S/S of hyperthyroidism
Nervousness Anxiety Palpitations Increased basal metabolic rate (BMR) Weight loss Increased appetite Increased body temp (heat intolerance) Sweating Fine Tremor Tachycardia Classical ophthalmic signs
what is the most common cause of hyperthyroidism?
Graves’ disease
Autoimmune syndrome that includes hyperthyroidism, diffuse thyroid enlargement, myxedema, thyroid acropachy
Graves’ disease
what form in graves’ disease?
antibodies against thyroid cell
IgG types antibodies against TSH that bind to and activate the receptor
There is a disproportionate increase in T_ as compared to T_ in graves’
Disproportionate increase in T3 compared to T4
complications of graves’ disease and pregnancy
sponataneous abortion
premature delivery
low birth weight
eclampsia
what can cause subclinical or overt hyperthyroidism in pregancy
Inappropriate production of human chorionic gonadotropin (hCG)
what is the treatment for Graves’ dz in pregnancy
PTU at lowest effective dose)
a life threatening medical emergency characterized by:
Severe thyrotoxicosis, high fever (often > 103 F), tachycardia, tachypnea, dehydration, delirium-coma, N/V, and diarrhea
thyroid storm
precipitating factors for a thyroid storm
Infection, trauma, surgery radioactive iodine treatment, withdrawl from antithyroid drugs
tx for thyroid storm
suppression of thyroid hormone formation and secretions
anti-adrenergic therapy
administration of corticosteroids
what are thioamides that are used to treat hyperthyroidism
Propylthiouracil (PTU)
Methimazole (Tapazole)
what tioamide also inhibits D1 which deiodinates peripheral T4 to T3
PTU
in patients w/ Graves dz what effects do thioamides also do?
immunosupressive effect
indications for thioamides
Management of hyperthyroidism
Thyrotoxic crisis
In the preparation of patients for surgical subtotal thyroidectomy
what thioamide is typically used due to fewer side effects and more potent, but potential for teratogen effects
Methimazole (MMI)
ADRs w/ thioamides?
agranulocytosis (baseline WBC count) hepatotoxicity vasculitis rash, arthralgia, myalgia cholestatic jaundice LAD drug fever psychosis alopecia
how does potassium iodine (KI) help to tx hyperthyroidism
causes inhibition of thyroid hormone secretion and blocks conversion of T4 to T3
reduces size and vascularity of the gland
indications for iodines
Preoperatively for thyroidectomy (7-14 days)
Used after RAI (3-7 days), to allow RAI to concentrate in thyroid
contraindications for iodines
not to breastfeeding or pregnant women
ADRs of iodines
hypersensitivy rxn
lacrimation
conjuncitivits
agent of choice for graves, toxic autonomous nodules, toxic multinodular goiters. will lead to hypothyroidism
radioiodine
drug that may maybe used for temporary control of thyrotoxicosis in patients allergic to thioamides and iodine.
lithium carbonate
what drugs are used to ameliorate thyrotoxic symptoms :palpitations, anxiety, tremor, heat intolerance. adjunct therapy
beta-adrenergic antagonists
what are corticosteroids used for w/ thyroid problems
thyroiditis and thyroid storm
decrease thyroid action and immune response in graves’ disease
indications for thyroidectomy
large glands, severe ophthalmopathy, lack of remission on treatment
what must e done before a thyroidectomy
PTU or MMI until patient is euthyroid (6-8 weeks) followed by iodide x 10-14 days
Adrs of thyroidectomy
Hyperthyroidism
Hypothyroidism
Hypoparathyroidism
Vocal cord abnormalities
what drugs can interact w/ thyroid agents
warfarin lithium Diabetes meds- dose adjustments potassium iodine (in some expectorants) digoxin- may need dose adjustments amiodarone CNS depressants
what drugs cause decreased TSH
Dopamine Levodopa Bromocriptine Octreotide Amphetamin Glucorticoids: >0.5 mg/day dexamethasone 100 mg/day Hydrocortisone
what drugs cause increased TSH
Metoclopramide >1 mg/kg amiodarone Iodinated Contrast Media
what drugs cause increased Free T4
IVFurosemide >80mg/day IV heparin Amiodarone Iodinated contrastMedi NSAIDS: Salicylates >2g/day Salsalate >1.5-3g/day Diclofenac, Naproxen
what drugs decrease free T4
phenytoin
carbamazepine
what rx products have iodides
Amiodarone
Radiocontrast dye
Povidone iodine
Iodinated glycerol
what non-Rx things have iodides
Cough and cold
Kelp
Herbals
Dietary supplements/ weight loss products
Develops within 3-8 weeks after exposure in up to 5% pts with exposure to iodine
Treatment with thioamides and beta blockers
iodine induced hyperthyroidism
Up to 10% of amiodarone treated patients will develop
Treat with levothyroxine replacement
iodine induced hypothyroidism
up to 50% of patients on lithium will develop what?
hypothyroidsm (monitor TSH)
tx w/ levothyroxine
does stopping lithium allow a person to return to a normal thyroid state
no, not always
what is a med for Hep C or in chemo that can cause induced thyroid disease (usually hypothyroidism). can occur within 6-8 weeks or 6-23 months
interferon alpha (IFNalpha)
if you stop interferon alpha therapy will hypothyroidism resolve
yes (might take a few months)
