Chapter 66 Flashcards
The thyroid gland secretes ____ and _____, both of which modulate energy utilization and heat production and facilitate growth.
thyroxine (T4)
triiodothyronine (T3)
The follicular cells of the thyroid synthesize ______ which is then stored as colloid.
thyroglobulin
Biosynthesis of T3 and T4 occurs by iodination of?
tyrosine molecules in thyroglobulin
______ is essential for the synthesis of thyroid hormones.
Dietary iodine
Iodide is enzymatically oxidized by ________ _______ which also mediates the ionization of the tyrosine residues in thryoglobin to form monoiodotyrosine and diiodotyrosine.
thyroid peroxidase
________ molecules couple to form T3 and T4.
Iodotyrosine molecules
Secretion of free T3 and T4 into the circulation occurs after proteolytic digestion of ______ which is stimulated by _______.
thyroglobulin
TSH
T4 and T3 are tightly bound to these serum carrier proteins (3)
thyroxine-binding globulin (TBG)
thryroxine-binding prealbumin
albumin
The unbound or free fractions of T4 and T3 are the biologically (active or inactive?) fractions and represent only 0.04% of the total T4 and 0.4% of the total T3.
active
The normal thyroid gland secretes T4, T3 and _____, a biologically inactive form of T3.
reverse T3
T3 is derived from?
5’-deiodination of circulating T4 in peripheral tissues
Deionization of T4 can occur at the _____ ring, producing T3, or at the ______ ring, producing reverse T3.
outer ring- T3
inner ring- reverse T3
Hypothalamic thyrotropin releasing hormone (TRH) is transported through the ____________ to the thyrotrophs of the anterior pituitary gland where they stimulate synthesis and release of _______.
hypothalamic-hypophysial portal system
TSH
____ increases thyroidal iodide uptake and iodination of thyroglobin.
TSH
____ releases T3 and T4 from the thyroid gland by increasing ______ of thyroglobulin and stimulates cell growth.
TSH
Hydrolysis
Hypersecretion of TSH results in _______ _________.
Thyroid enlargement (goiter)
Circulating ___ exerts negative feedback inhibition of TRH and TSH release.
T3
Thyroid hormones increase basal metabolic rate by increasing ________ and _______ in several body tissues.
Oxygen consumption
Heat production
Thyroid gland function and structure can be evaluated by what 4 things?
determining serum hormone levels
imaging thyroid gland size and architecture
measuring thyroid antibodies
FNA
Total serum T4 and T3 measure the total amount of hormone bound to thyroid binding proteins by _________
radioimmunoassay
Total T4 and T3 levels are elevated in ___________.
hyperthyroidism
Total T4 and T3 levels are low in ___________.
hypothyroidism
Increase in _____ as with pregnancy or estrogen therapy, increases the total T4 and T3 without actual hyperthyroidism.
TBG
Free T4 levels are usually measured by…
measured directly
dialysis
ultrafiltration
Serum TSH is measure by ________ which uses at least two different monoclonal antibodies against different regions of the TSH molecule- allows for accurate discrimination btwn normal levels of TSH and levels below normal.
third-generation immunometric assay
TSH assay can diagnose _________ and __________.
hyperthyroidism and subclinical hyperthyroidism
Thyroidism in which there is elevated free T4 and suppressed TSH.
Hyperthyroidism
Thyroidism in which there are normal free T4 levels and supporessed TSH.
subclinical hyperthyoidism
In primary (thyroidal) hypothyroidism, serum TSH is _______ because of diminished feedback inhibition.
supranormal
In secondary (pituitary) and tertiary (hypothalamic) hypothyroidism, TSH is usually _____ but may be normal.
low
______ ______ measurements are useful in the followup of patients with papillary or follicular carcinoma.
serum thyroglobulin
After thyroidectomy and iodine-131 ablation therapy, thyroglobin levels should be less than _____ while the pt is on suppressive levothyroxine treatment- levels higher than this suggest persistent or metastatic disease.
0.5 mcg/L
Calcitonin is produced by _____ of the thyroid and has a minor role in calcium homeostasis
C-cells
Calcitonin meausrements are invaluable in the diagnosis of ________ ________ of the thyroid and for monitoring the effects of therapy.
medullary carcinomas
In thyroid imaging, ________ is concentrated in the thyroid gland and can be scanned with a gamma camera, yielding info about the size and shape and the location of the functional activity in the gland.
technetium-99m pertechnetate
Which type of thyroid nodule (hot/cold) is nonfunctioning and is usually associated with malignancy?
cold nodule
________ ________ evaluation is useful in the differentiation of solid nodules from cystic nodules and can be used to guide a clinician during an FNA.
thyroid ultrasound
____ of a nodule to obtain thyroid cells for evaluation is the best way to differentiate benign from malignant disease
FNA- fine needle aspiration
________ is the clinical syndrome that results from elevated circulating thyroid hormones.
Thyrotoxicosis
Clinical manifestations of thyrotoxicosis is due to the direct physical effects of the thyroid hormones as well as the increased sensitivity to _________.
catecholamine
Tachycardia, tremor, stare, sweating, and lid lag can be seen in hyperthryodism due to?
catecholamine hypersensitivity
Thyrotoxic crisis, or thyroid storm is a life threatening complication of hyperthyroidism that can be precipitated by
surgery
radioactive iodine therapy
severe stress (eg uncontrolled Diabetes mellitus, myocardial infarction, acute infection)
What are some of the symptoms of a patient experiences a thyroid storm?
fever flushing sweating significant tachycardia atrial fibrillation cardiac failure significant agitation restlessness delerium N/V, diarrhea
What is the hallmark of a thyroid storm?
hyperpyrexia (abnormally high fever) of proportion to other clinical findings
DDx: Thyrotoxicosis usually reflects excess secretion of thyroid hormones resulting from? (4)
Graves disease toxic adenoma mulitnodal goiter thyroiditis excessive ingestion of Thyroid hormone Rarely-thyroid hormone production from ectopic site
What disease is the most common cause of thyrotoxicosis? T/F: It is an autoimmune disease.
Graves disease
True
What are some of the possible features present in a patient with Graves disease?
Goiter, thyrotoxicosis, eye disease- ranging from tearing to proptosis, extraocular muscle paralysis, loss of site, thyroid dermopathy- significant skin thickening without pitting in a pretibial distribution (pretibial myxedema)
Thyrotoxicosis in Graves disease is due to?
overproduction of an antibody that binds to the TSH receptor
How does the overproduction of the antibody that binds to the TSH receptor effect the thyroid?
The thyroid stimulating immunoglobulins increase thyroid cell growth and thyroid hormone secretion.
The inflammatory reaction that contributes to the eye signs in Graves disease may be caused by _______ sensitized to antigens common to the oribital muscles and thyroid.
lymphocytes
The common manifestations of thyrotoxicosis are characteristic features of (younger or older?) with ________ disease, a diffuse _______ or the ____ signs, characteristic of Graves.
younger
Graves
goiter
eye signs
Older patients often do not have the florid clinical features of thyrotoxicosis, and the condition is termed ________ __________.
apathetic hyperthyroidism
What are a few clinical features of an older patient experiencing apathetic hyperthyroidism?
flat effect, emotional lability, weight loss, muscle weakness, congestive heart failure and atrial fib resistant to standard therapy
What are some of the possible effects of Graves disease on the eyes?
peroribial edema, conjunctival congestion, swelling, proptosis, extraocular muscle weakness, or optic nerve damage with visual impairment
What is a clinical manifestation of Graves that is characterized by skin thickening of the skin over the lower tibia without pitting?
pretibial myxedema
Which nail diseases are often found in patients with Graves?
onycholysis–seperation of of the fingernails from their nail beds
thryoid acropachy- clubbing
How do the levels of T4, T3 and TSH present in patients with thyrotoxicosis?
T4 and/or T3 are elevated and TSH is suppressed.
Thyroid stimulating immunoglobulin is usually elevated in thyrotoxicosis and may be useful in which patients?
Patients with eye signs who do not have other characteristic clincial features
What is a differential factor of Graves disease from EARLY SUBACUTE Hashimoto thyroiditis in lab findings?
There is an increased uptake of 123I in Graves disease- uptake is low in presence of
What are the two commonly used imaging techniques used to view the orbital muscles for possible enlargement, or signs of ophthalmopathy?
MRI
ultrasonography
What are the three treatment modalities used to control the hyperthyroidism of Graves?
antithyroid drugs
radioactive iodine
surgery
The thiocarbamide drugs (antithyroid drugs) _______, _______ and ______ block thyroid hormone synthesis by inhibiting thyroid peroxidase.
proplythiouracil
methimazole
carbimazole
Which antithyroid drug partially inhibits peripheral conversion of T4 to T3?
propylthiouracil
When treating hyperthyroidism with medical therapy, it must be administered for how long?
a prolonged period (1-2 years) or until the disease undergoes spontaneous remission
Patients who experience relapse of hyperthyroidism after medical therapy must undergo…
definitive surgery
radioactive iodine treatment
What are side effects of using thiocarbamide drugs to treat hyperthyroidism?
pruritis and rash
cholestatic jaundice
acute arthralgias (joint pain)
rarely- agranulocytosis (low levels of WBCs)
Patients may be instructed to discontinue medical therapy if sore throat or fever develops because these symptoms indicate _________.
agranulocytosis
At the onset of treatment, during the acute phase of thyrotoxicosis, _________ drugs help alleviate tachycardia, hypertension, and atrial fibrillation.
beta adrenergic blocking drugs
In terms of cost, efficacy, ease and short term side effects, radioactive iodine has greater benefits than surgery or antithyroid drugs. Down side: what usually develops after use?
Most patients become hypothyroid following its use.
What is often the treatment of choice in adults with Graves disease but is contraindicated in pregnant women?
131^I (to clarify, superscript 131 I )
What should be done differently in pts with severe thyrotoxicosis, very large glands or underlying heart disease when being treated with radioactive iodine (131I)?
They should be rendered euthyroid (normal thyroid function) with antithyroid medication before receiving radioactive iodine.
Why is it important for normal thyroid function to be obtained before treatment with radioactive iodine (131I) in patients withsevere thyrotoxicosis, very large glands or underlying heart disease?
It can cause a release of preformed thyroid hormone from thyroid hormone into circulation which can cause cardiac arrythmias and worsen the symptoms of thyrotoxicosis.
After administering radioactive iodine, the thyroid shrinks and patients become euthyroid over a periods of?
6 weeks to 3 months
What levels should be monitored when treatment with radioactive iodine is used? What can be given if hypthyroidism occurs?
Serum free T4 and TSH levels
levothyroxine
When does hypothyroidism occur in patients after being treated for hyperthyroidism?
ALWAYS- total thyroidectomy
frequently- subtotal thyroidectomy
smaller %- txt with antithyroid medications
For patients with very large glands and obstructive symptoms, multi nodular glands or for patients desiring pregnancy in the next year, what is the treatment of choice?
total or subtotal thyroidectomy
Before a thyroidectomy, patients must do what?
Receive antithyroid drugs for SIX WEEKS- to ensure euthyroid, and take oral saturation solution of potassium iodide daily for TWO WEEKS prior- to decrease vascularity of the gland
Solitary, toxic nodules (usually benign) occur more frequently in (older or younger?) patients.
older
Clinical manifestations of toxic adenomas are those of _______.
thyrotoxicosis
Physical exam of toxic adenoma shows what type of nodule?
distinct solitary nodule
What would the lab results for T4, T3 and TSH be for a patient with toxic adenomas?
suppressed TSH
significantly elevated T3
moderately elevated T4
Would a toxic adenoma appear hot or cold in a thyroid scan?
it would show a hot nodule of the affected lobe with complete suppression of the unaffected lobe
How are solitary toxic nodules (toxic adenoma) treated?
radioactive iodine
unilateral lobectomy may be required for large nodules (after rendered euthyroid by antithyroid drugs)
_______ _________ ______ occurs in older patients especially from iodine-deficient regions who are exposed to increased dietary iodine or receive iodine-containing radiocontrast dyes.
toxic multinodular goiter
Clinical presenting features in pts with a toxic multinodular goiter are?
tachycardia
heart failure
arrhythmias
Diagnosis of a toxic multinodular goiter can be confirmed by these lab results for levels of TSH, T4 and T3 and a thyroid scan exhibiting what?
suppressed TSH
elevated T3 and T4
thyroid scan- multiple functioning nodules
What is the treatment of choice for a toxic multinodular goiter?
131I ablation
In subclinical hyperthyroidism, what are the levels of T4, T3 and TSH like?
T4 and T3 levels are normal
TSH levels are suppressed
What are some of the causes of subclinical hyperthyroidism?
early presentation of hyperthyroidism- Graves disease, toxic adenoma, and toxic multinodular goiter
Pts with subclinical hyperthyroidism are at a higher risk for developing ________ _______ (esp. the older pts) and many have persistently suppressed TSH and should be treated with ________ _____ or ______ ______.
thiocarbamide drugs
radioactive iodine
A decrease in ______ _______ ______ is another indication for treatment for subclinical hyperthyroidism.
bone mineral density
What is the initial presentation of thyroiditis?
often that of hyperthyroidism- result of acute release of T4 and T3
How does thyroiditis present?
It initially presents as hyperthyroidism but may eventually result in clinical hypothyroidism.
Hyperthyroidism caused by thyroiditis can be readily differentiated from other causes by?
suppressed uptake of radioactive iodine, reflecting decreased hormone production by damaged cells
What is a rare type of thyroiditis in which the pt exhibits, high fever, redness of overlying skin and thyroid gland tenderness? It is often confused with subacute thyroiditis.
acute suppurative thyroiditis
An acute inflammatory disorder of the thyroid gland, probably secondary to a viral inf. in which the pt complains of fever and anterior neck pain and symptoms of hyperthyoidism are present- classic feature: exquisitely tender thyroid gland
subacute thyroiditis
What is the treatment for subacute thyroiditis?
nonsteroidal anti-inflammatory drugs and possibly prednisone if pain and fever are severe
_________ from destruction of normal thyroidal structure by lymphocytic infiltration results in hypothyroidism and goiter.
chronic thyroiditis
________ thyroiditis is more common in women and is the most common cause of goiter and hypothyroidism in the United States.
Hashimoto’s
How can chronic thyroiditis be differentiated from subacute thyroiditis?
in chronic, the gland is nontender to palpation and antithyroid antibodies are present in high titer
Patients with Hashimoto’s may have transient hyperthyroidism with low radioactive iodine uptake, owing to….
the release of T4 and T3 into the circulation
When an FNA is taken in a patient with chronic thyroiditis, what would you expect to see?
lymphocytes and Hurthle cells (enlarged basophilic follicular cells)
Hypothyroidism and significant glandular enlargement (goiter) are indications for _________ therapy.
levothyroxine
______ ______ exhibits typical features of thyrotoxicosis from ingestion of excessive amounts of thyroxine, often in an attempt to lose weight.
thyrotoxicosis factita
In a patient with thyrotoxicosis factita, how do the serum T4 & T3 and TSH levels present? Is radioactive iodine uptake present?
serum T4 & T3 levels are elevated and TSH is suppressed.. Radioactive iodine uptake is absent.
_____ ____ occurs when an ovarian teratoma contains thyroid tissue which secretes thyroid hormone.
Struma ovarii
What is the best imaging techinque to diagnose the presence of a struma ovarii?
a body scan demonstrating uptake of radioactive iodine in the pelvis
_________ ____ is due to proliferation and swelling of the trophoblast during pregnancy, with excess production of chorionic gonadatropin, which has intrinsic TSH-like activity
hydatidiform mole
Postpartum thyroiditis resembles ______ ________ in its clinical course and it usually occurs within the first ____ months after delivery.
subacute thyroiditis
6 months
Postpartum thyroiditis goes through a triphasic course of presentation; first presenting as _______ then _________ then _______. Or it may develop with only _________. pg 674
1) hyperthyroidism, hypothyroidism, euthyroidism
2) hypothyroidism
