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Thyroid Hormones
Thyroid Hormone Action
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Thyroid gland is the largest endocrine gland in the
body
Thyroid hormones facilitate normal growth and
maturation of tissue by promoting an optimal level
of metabolism
Thyroid hormones affect virtually every organ
system in the body
Thyroid hormones are essential for fetal growth
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Cretinism(child w/lack of thyroid, a form of mental
retardation)
Happens when mother lacks thyroid hormone during
preggers/birthgiving
Thyroid Hormones
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Thyroid gland produces two hormones
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Tetraiodothyronine or thyroxine (T4)
Triiodothyronine (T3)
Proper levels of iodine are needed for
synthesis of thyroid hormones
Thyroid gland secretes mostly T4
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Peripheral tissues convert T4 to T3
T3 is more active than T4
Terminology
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Hypothyroid
Hyperthyroid
Euthyroid
Regulation of Synthesis
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Thyroid function is controlled by
thyroid stimulating hormone (TSH)
Secretion of TSH is stimulated by TRH
Feedback inhibition of TRH is occurs
with high levels of circulating thyroid
hormone
Regulation
Spectrum of Thyroid Disease
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Two general modes of presentation
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Changes in size or shape of gland
Changes in hormone secretion
Changes in Shape
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In hypothyroidism
Enlarged thyroid glands are often
referred to as goiters(mass in the
neck)
Goiters are common in developing
countries and are caused by an iodine
deficiency
Iodine Deficiency
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Relatively common in developing
countries
Iodized salt is usually used as primary
treatment
Iodine deficiency in children can cause
mental retardation and dwarfism or
cretinism
Laboratory Assessment
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TSH
T4
T3
Measurement of TSH is adequate for
diagnosis of most cases of hypo and
hyperthyroidism
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hyperthyroidism(TSH levels go down)
hypo(TSH elevated)
Hypothyroidism
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Most common clinical thyroid disorder
Majority have primary gland failure
Common causes
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Autoimmune thyroiditis
Silent thyroiditis
Drugs
Severe hypothyroidism is know as
myxedema
Symptoms
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Fatigue
Sleepiness
Mental impairment
Depression
Cold intolerance
Dry skin and other skin changes
Weight gain
Slow movement
Slow speech
Slow to respond
Hyporeflexia
Laboratory Diagnosis
Goals of Treatment
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Replace missing hormones
Relieve symptoms
Achieve euthyroid state
Drug Treatment
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Number of products available
None are more effective than synthetic
T4
Bioequivalence of synthetic T4
products are of concern
Don’t change manufacturers once
optimal dose has been determined
Consultation (levothyroxine)
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Follow administration instruction DO NOT take more than
recommended
Do not switch brands once stabilized on a particular product
Take on an empty stomach with a full glass of water at least
30 minutes before breakfast
Take at the same time each day
Administer apart from medications known to decrease
absorption
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Antacids
Calcium
Iron
Vitamin and mineral supplements
Consultation
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It may be several weeks before you
notice an improvement in your
condition
It may be necessary for you to take
this medicine for the rest of your life,
not a cure
Do not stop using this medicine
unless your doctor advises you to.
Hyperthyrodism
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Caused by excessive amounts of
circulating thyroid hormone
Most common type is “Graves” disease
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Hyperthyroidism
Diffuse thyroid enlargement
Exopthalmos
Abnormal skin finding
Hyperthyroidism
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Graves’ disease is most common
cause
Graves’ disease is an autoimmune
syndrome that includes
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Hyperthyroidism
Diffuse thyroid enlargement
Exopthalmos
Dermatological abnormalities
Other Causes
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Thyroid cancer
Iodine excess
TSH secreting pituitary tumors
Exopthalmos
Skin Changes
Clubbing
Signs and Symptoms
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Nervousness
Weakness
Fatigue
Heat intolerance
Tremor
Irritability
Tachycardia and/or palpitations
Weight loss
Hyperactivity
Hyperreflexia
Warm, moist skin
Laboratory Diagnosis
Goals of Treatment
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Relieve symptoms
Reduce thyroid hormone production
Achieve euthyroid state
Prevent long-term sequelae
Drug Treatment
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Beta blockers help relieve symptoms
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Used until more specific anti-thyroid therapy
begins to work
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Palpitations
Tremors
Anxiety
Heat intolerance
Given in addition to propranolol
Propranolol is treatment of choice
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The one drug out of top 200 used for tx of
hyperthyroidism
Other Therapy
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Drugs that reduce production of thyroid
hormone
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Iodine
Antithyroid drugs
Radioactive thyroid
Surgery
Iodine
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Large doses inhibit synthesis and release of
T4 and T3
T4 levels are reduced within 24 hours
Used prior to surgery for Graves’ disease
Drugs
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SSKI
(30mg I/drop)
Lugol’s solution
(6.3mg I/drop)
Dose is 200-400mg/day for 7-14 days before
surgery
Antithyroid Drugs
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Inhibit thyroid hormone synthesis by
interfering with iodination of tyrosine
Used before surgery or as primary
treatment
Drugs
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Propylthiouracil
Methimazole
Consultation
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Take this medicine with or without food.
Always take it the same way to make sure the
effects are the same
Do not stop taking this medicine except on the
advice of your doctor
If you are going to have surgery or dental surgery,
tell your doctor, dentist, or health care professional
that you are taking this medicine.
Side Effects
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Low rate of adverse reactions
Hepatotoxicity 0.1-0.2%
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Cholestatic jaundice 0.1-0.2%
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PTU
Methimazole
Agranulocytosis 0.3%
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Depression of bone marrow  so you don’t
synthesize/release granulocytes (help you
developing bacterial infections)
Indosyncratic hypersensitivity reaction
Can get infections and DIE, **must go back to
physician once in a while to get blood cell counts
Duration of Treatment
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Antithyroid drugs are given for 1-2 years
and then stopped
Relapse occurs in 40% of patients within 3-6
months after stopping
If replase occurs most patients will opt for
treatment with radioactive iodine rather that
go back to taking antithyroid medications
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If pts relapse, usually pts won’t want to go back
on antithyroid, they’d rather get radiodine tx