Thyroid Flashcards
Thyroid is a
2-lobed gland
Thryoid follicular cells oxidize iodide in process of
producing triiodothyronine (T3) and thyroxine (T4)
Pituitary gland secretes
thyroid-stimulating hormone (TSH) which
controls rate and release of T3 and T4
Hypothalamus secretes
thyrotropin- releasing hormone which
regulates the release of TSH
Low levels of serum thyroid hormones cause
increased secretion of
TSH, and subsequently T3, T4
Most of T3 and T4 is
bound, free T3 and T4 regulate metabolism
Hypothyroidism is a deficiency of
T4 usually. or a deficiency of iodine
Autoimmune or Hashimoto’s thyroiditis
- Infiltration of thyroid by lymphocytes
- Leads to fibrosis and decreased function of the gland
- May present with goiter, be euthyroid or hypothyroid
- Anti-thyroid antibodies serum titers are high
Primary hypothyroidism labs
High TSH (usually
≥ 10mlU/L
Low T4
Secondary
(central) hypothyroidism labs
Low T4
Do not see inverse
appropriate
elevation in TSH
Subclinical (early
hypothyroidism,
pre-clinical
hypothyroidism) labs
Normal T4
Elevation TSH
Transient hypothyroidism labs
phas of subacute thyroidits
Hypothyroidism S/S
• Symptoms
• Fatigue, constipation, weight gain, changes in menses
• Elderly: more subtle signs; ataxia, parasthesia, carpal tunnel,
psychiatric changes
• P.E.
• Thyromegaly, bradycardia, peripheral edema
Hypothyroidism LAB tests to do
- TSH (most widely used screening test), free T4
* Total cholesterol and LDL elevated
Hypothyroidism goal of treatment
• Restore patient to euthyroid state
Hypothyroidism products
- Natural thyroid extract
- T3 replacement (liothyronine)
- Liotrix (T3 and T4 combination product)
- Levothyroxine (T4), most common
Hypothyroidism when to initiate therapy
• TSH ≥ 10mlU/L
• TSH levels 5 -10 μIU/mL with goiter or positive antithyroid peroxidase
antibodies (or both).
Synthetic Levothyroxine
(Synthroid) Fast Facts
- Preparation of choice for thyroid replacement and suppression
- Stable compound
- Uniform content
- Low cost
- Lack of allergenic foreign protein
- Easy lab measurement of serum levels
• Generic form has comparable efficacy to brand and is more
cost-effective, but don’t alternate (DO NOT ALTERNATE)
Levothyroxine is easily
Easily absorbed from GI tract but erratic absorption
Levothyroxine is what exactly
Synthetic T4
Levothyroxine how does it work
T4 is converted to T3 so replaces both
• Peak T4 serum level in 2-4 hours
• Peak T3 slower because of time needed for conversion
Levothyroxine has a
Long half-life allows once-daily dosing
Levothyroxine elimination
Elimination: bile/feces
Levothyroxine requires
Requires 1 month to reach steady state
Consideration for Dosage of Levothyroxine
Patient’s age, duration of hypothyroidism, comorbidities
Thyroid hormones (levothyroxine) are safe in
Pregnancy: safe; increased metabolic rate during pregnancy may
necessitate higher dosing from baseline
You should recheck TSH in
6 to 8 weeks. Then in 6 months if stable. Can push this longer the more stable they are.
Goal TSH
0.4-4.0*
Levothyroixine should be taken
on an empty stomach
Levothyroxine in younger adults
adult patients or those with mild disease,
can start with full replacement (75-100mcg/d)
Levothyroxine related to hormone level, monitor
Related to hormone level: monitor TSH every 3-6 months
after dose established and after changes, then annually
Levothyroxine children ADR
restlessness, insomnia, accelerated bone
maturation and growth
Levothyroxine Adults ADR
increased nervousness, heat intolerance,
episodes of palpitations, tachycardia, chest pain, flushing
or unexplained weight loss
Levothyroxine Elderly ADR
chronic overtreatment increases the risk of atrial
fibrillation and accelerated osteoporosis
Levothyroixine drug interactions
Bile-acid sequestrants, iron salts, and antacids decrease
absorption; estrogens may decrease response.
• Drugs may decrease action of warfarin, digoxin, and beta
blockers.
Hyperthyroidism is a
Excess amount of thyroid hormone
Grave’s Disease
- Stimulation of thyroid gland by TSH receptor autoantibodies
- Usual negative-feedback mechansim bypassed
- Increased levels of thyroid hormones
Plummer’s Disease
• Toxic nodular goiter: hyperactive thyroid nodule
Thyrotosicosis Factitia
• Patient intentionally takes high doses of T4
Hyperthyroidism symptoms
Symptoms
• Palpitations, sweating, heat intolerance, weight loss
• P.E.
• Elevated BP, tachycardia, bruit over thyroid, exophthalmus
(Grave’s disease)
hyperthyroid diagnsotic testing
- Low or suppressed TSH, high free T4
* Nuclear thyroid scan is diagnostic
Treatment of Hyperthyroidism Antithyroid drugs
• Used in younger patients because of cancer concerns from
radioactive iodine
• Radioactive iodine ablation
- Adults over 40, increasingly used in younger patients also
* Contraindicated in pregnancy
treatment options for hyperthyroidism
Antithyroid drugs
• Used in younger patients because of cancer concerns from
radioactive iodine
• Radioactive iodine ablation
• Adults over 40, increasingly used in younger patients also
• Contraindicated in pregnancy
• Surgery
Antithyroid Drugs MOA
Reduce thyroid activity and hormone effects
• Mechanism of action
• Interfere with production of thyroid hormones
• Modify the tissue response to thyroid hormones
• Glandular destruction with radiation or surgery
Goitrogens
Agents that suppress secretion of of T3 and T4 to
subnormal levels
• Inversely increase TSH which in turn produces
glandular enlargement
• Antithyroid compounds used clinically include:
• Thioamides
• Iodides
• Radioactive Iodine
Thiourelynes - 2 main drugs
2 main drugs: methimazole and propylthiouracil
Thiourelynes - MOA
Major action: prevent hormone synthesis by
inhibiting the thyroid peridoxase-catalyzed reaction
to block iodine organification
Thiourelynes have
Short half-lives
Thiourelynes metabolized
• Metabolized in the liver
Thiourelynes high
relapse rates exist but are less likely if treated
for 18 to 24 months
