Thyroid

Question 1

thyroid gland

Answer 1

-located below the larynx
-Synthesizes and secretes thyroid hormones - triiodothyronine (T3) and
tetraiodothyronine (T4)
-Thyroid hormones necessary for growth and development and metabolic processes,
also augment SNS function

Question 2

synthesis and release of thyroid hormones: uptake of iodine

Answer 2

Iodide actively transported into thyroid follicle cells. Uptake is stim
by TSH (thyrotropin) and inhibited by thiocyanate and perchlorate ion autoregulation

Question 3

synthesis and release of thyroid hormones: oxidation/organification

Answer 3

-Oxidation: iodide is oxidized by the enzyme peroxidase
-Organification: Oxidized iodine binds with tyrosine by iodinase enzyme to form monoiodotyrosine (MIT) and diiodotyrosine (DIT) residues

Question 4

synthesis and release of thyroid hormones: formation of T3 and T4

Answer 4

-Thyroid peroxidase catalyzes the coupling of MIT and DIT to
form triiodothyronine (T3) and tetraiodothyronine (T4 or thyroxine)
-This process also known as coupling. T4:T3 ratio = 4:1

Question 5

synthesis and release of thyroid hormones: secretion

Answer 5

TSH stimulates proteolysis and release of T3 and T4

Question 6

synthesis and release of thyroid hormones: conversion

Answer 6

of T4 to T3
-T4 is converted to T3 in peripheral tissues (T3 is 5X more
active than T4)

Question 7

synthesis and release of thyroid hormones: transport

Answer 7

-to target organs by thyroid-binding globulin, thyroid-binding prealbumin and albumin

Question 8

synthesis and release of thyroid hormones: control of release

Answer 8

-secretion of thyroid hormones regulated by TRH (hypothalamus) and TSH (anterior pituitary)
-thyroglobulin release stimulated by TSH
-T3 inhibits TRH and TSH secretion (negative feedback)
-production of thyroid hormone also regulated by rate of conversion of T4 to T3

Question 9

normal and abnormal thyroid function

Answer 9

-Normal thyroid – euthyrodism
-Primary thyroid disease – defect at thyroid
-Secondary – pituitary defect
-Tertiary – hypothalamic defect
-Hypothyroid – low T4, high TSH, impair growth and dvp, decrease in metabolic activity. Subclinical – abnormal lab values w/o symptoms
-Hyperthyroid – high T4, low TSH, hyperactivity of organ systems and speeds up metabolism

Question 10

hypothyroidism symptoms

Answer 10

-weakness
-fatigue
-lethargy
-cold intolerance
-decreased memory
-hearing impairment
-constipation
-muscle cramps
-arthralgias
-paresthesias
-anorexia
-moderate weight gain
-decreased perspiration
-menorrhagia
-depression
-hoarseness
-carpal tunnel syndrome
-dry, cool, coarse skin
-dull facial expression
-periorbital puffiness
-swelling of hands and feet
-bradycardia
-hypothermia
-decreased systolic pressure
-increased diastolic pressure
-decreased body and scalp hair
-anemia
-cardiomegaly (pericardial effusion)
-dilutional hyponatremia
-TSH > 20mIU/L*****

Question 11

hyperthyroidism

Answer 11

-fatigue and weakness
-heat intolerance
-increased appetite
-weight loss
-increased perspiration
-emotional lability, nervousness
-warm, moist skin
-exophthalmos
-palpitations and tachycardia
-increased systolic pressure
-dyspnea

Question 12

hypothyroidism

Answer 12

-Decline in release of T3 and T4, which causes TRH and TSH to increase
-In infants and children, causes irreversible mental retardation and impairs growth and dvp
-In adults, assoc with impairment of physical and mental activity, slowing of CVS, GI and neuromuscular fn
-When severe, causes myxedema. Very severe cases – Myxedema coma
-MC cause is autoimmune thyroiditis (Hashimoto’s disease). Iodine deficiency another cause of primary hypothyroidism.
-Can also be caused by drugs like lithium or amiodarone

Question 13

hypothyroid: levothyroxine (T4)

Answer 13

-synthroid, Levoxyl, Levothroid
-pregnancy category A
-available PO and IV; for IV - give 25-50 % of PO dose (myxedema coma)
-Dosing - Usual adult dose is 100-125 mcg qd. Increase by 25 mcg
increments q6-8 weeks.
-Elderly: Start lower. Usual dose range 50-100 mcg/day
-CV disease: Start even lower (12.5-25 mcg/day) and increase doses by 12.5-25 mcg q4 weeks
-Monitor T4, TSH and free T4 if necessary
-Bioavailability 80%, t ½ - 7 days, qd dosing, converted to T3 so
considered prodrug
-hormone content and bioavailability of brands may vary
-DOC for thyroid replacement
-also DOC for suppressive therapy for thyroid nodules, diffuse goiters and
thyroid cancer
-ADRs – rare if dosed and monitored appropriately. If occur, similar to SX
of hyperthyroid
-DDI – Several. Food and many drugs can decrease Levothyroxine absorption
-Take on empty stomach
-Refer to chart
-Levothyroxine may increase the effects of warfarin and TCAs

Question 14

hypothyroidism: liothyronine

Answer 14

-Cytomel (T3) PO 25-50 mcg
-Not really used b/c rare to have a
deficiency of T3 only
-Also, short half life, so may need frequent dosing and does
not increase T4 levels, so cant measure response to treatment

Question 15

other hypothyroid tx

Answer 15

-liotrix (Thyrolar) T4:T3 4:1 fixed ratio mixture
-thyroid extracts (Armour Thyroid)
-TRH (Protirelin) synthetic IV
-TSH (Thyrogen) synthetic I

Question 16

hyperthyroidism

Answer 16

-Grave’s disease - (toxic diffuse goiter) increased iodine uptake, autoimmune disease, stimulates TSH.
-Exophthalmos - inflammatory rxn of peri-orbital tissue and extraorbital muscles
-Toxic nodular goiter - more common in elderly (exophthalmus)
-Postpartum thyrotoxicosis (painless)
-Thyroid storm - acute attack of hyperthyroidism, requires aggressive treatment; symptomatic treatment includes beta blockers and CCBs
-TX OF HYPERTHYROIDISM- includes antithyroid drugs, surgery and radioactive iodide (RAI) treatment. Choice of treatment depends on the type and severity of hyperthyroidism and individual characteristics of the patient

Question 17

hyperthyroidism: thiourea drugs

Answer 17

-Propylthiouracil (PTU) and methimazole (Tapazole)
-Indications: used to treat Graves disease (used to induce remission or to control Sx prior to surgery or RAI).
-Also used for long term remission - Tx
is at least 1-2 years
-MOA - blocks the peroxidase catalyzed iodination and coupling during synthesis of T3 and T4. PTU also blocks the conversion of T4 to T3
-Pregnancy Implications: both are category D – but PTU is treatment of
choice for Grave’s Disease in pregnant patient.
-Precautions: Avoid in SULFA allergy
-ADRs: Rash, Hepatotoxicity, Agranulocytosis, sore throat, fever,
aplastic anemia, thrombocytopenia, weight loss, itch, joint pain, stiffness,
headache, alopecia (ADRs similar to those seen with sulfonamide
antibiotics)
-DDI – methimazole is a CYP450 inhibitor, both drugs can increase the
anticoagulant effects of Coumadin

Question 18

hyperthyroidism: ionic inhibitors

Answer 18

-thiocyante and perchlorate ions block the uptake of iodine
-examples include cabbage, cigarette smoke and nitroprusside

Question 19

hyperthyroidism: iodide salts

Answer 19

-used on short term basis to Tx acute thyrotoxicosis, to prepare pts for
surgery and to inhibit the release of thyroid hormones following RAI
treatment
-includes potassium iodide solutions (SSKI and Lugol’s solution)
-Pregnancy category D

Question 20

hyperthyroidism: radioactive iodine (RAI)

Answer 20

-Category X – destroys fetal thyroid tissue
-I-131 – t ½ is 5 days, Taken PO and rapidly absorbed from gut and
concentrated in thyroid gland where it emits beta particles that destroy
thyroid tissue, as tissue is destroyed, thyroid hormone levels return to
normal over several weeks. Can also be used to treat some forms of
thyroid cancer
-ADRs- Hypothyroidism, Metallic taste, Nausea, Swollen salivary glands
-Administration instructions: Dose varies by pt and extent of disease
so duration/specifics of following instructions may vary
-Drink plenty of fluids following administration
-Sleep alone for 3 to 5 nights after treatment, depending on the strength of the dose.
-Personal contact with children (hugging or kissing, for example), should be avoided for 3 to 7 days, depending on the strength of the dose.
-For the first 3 days after treatment, stay a safe distance away from others
(6 feet is enough). Avoid public places and drink plenty of water (to encourage the removal of radioactive iodine through the urine).
-For the first 3 days, do not share items (utensils, bedding, towels, and
personal items) with anyone else. Do your laundry and dishwashing
separately. Wipe the toilet seat after each use. Wash your hands often, and
shower daily

Question 21

hyperthyroid: surgery

Answer 21

remove all of thyroid gland and tx pt for hyperthyroid

Question 22

hyperthyroid: symptomatic tx

Answer 22

-BBs and CCBs
-tx sx of mild hyperthyroidism (tachycardia and HTN)