Lec 3 Thyroid Physiology/Therapy

Question 1

Tamoxifen

Perphenazine

Oral Contraceptives (Estrogen)

Answer 1

Increase TBG

(thyroxine binding globulin)

–> Decrease Free T4

Question 2

Phenytoin

Carbamazepine

Answer 2

Decrease TBG

Increase Free T4

free T4 = active thyroid hormones

Question 3

Thyroid Lab Test

Answer 3

• THYROID STIMULATING HORMONE (TSH)
  
  • most accurate and specific
• Free T4
  
  • Used with TSH for initial diagnosis
• Free T3
  
  • To see conversion abnormalities
• Total T4
  
  • not useful

Question 4

Hypothalamus

Answer 4

Produces TRH

TRH –> Pituitary

negative feedback from Thyroid Hormone

Question 5

Pituitary

Answer 5

Secretes TSH

TSH–> Thyroid

negative feedback from T3/T4

Question 6

Primary HypoThyroidism

Answer 6

Low fT4 / High TSH

Problem with the Thyroid Itself

Question 7

Secondary / Tertiary (Central)

Hypothyroidism

Answer 7

low T4 / low TSH *rarely normal

Issue is higher up the chain

Pituitary or Hypothalamus issue

Question 8

Thyroid Mediated HYPERthyroidism

Answer 8

HIGH T4 **or normal

Low TSH

HIGH T3

issue @ thyroid Level

Question 9

TSH-Mediated HYPERthryoidism

Answer 9

ALL LEVELS HIGH

fT4 / TSH / T3

issue with pituitary

Question 10

Radioactive Iodine Uptake Scan

RAIU

Answer 10

Adjunct Thyroid Function Test

Measures Iodine Utilization with radiolabled Iodide

Differentiates HYPERthyroidism etiology

graves disease

Question 11

Tests for Autoimmunity

Answer 11

Presense of Thyroid AB’s INDICATES AUTOIMMUNE PROCESS

but is not always SPECIFIC for a particular diagnosis/etiology

• Anti-TPO (thyroid peroxidase) Antibodies
• Thyroglobulin AB’s
• Antimicrosomal AB’s
• Thyroid Stimulating AB’s (TSab)

Question 12

Graves Disease

Answer 12

• Autoimmune production of TSab
  
  • stimulate thyroid hormone production from thyroid
• HYPERthyroidism
  
  • may REMIT, spontaneously
  • High T4 / Low TSH
    
    • • Goiter / TSaB
• 1st Line = Thioamides
  
  • 2nd = thyroidectamy / ablation

Question 13

Toxic Multinodular Goiter

TMNG

Answer 13

• HYPERthyroidism
  
  • >2 autonomous functioning thyroid nodules
    
    • –> secrete excess thyroid hormones
  • High T4 / Low TSH
• 1st line = Thyroidectamy
  
  • since the nodule will always be there
• 2nd line = thioamides

Question 14

Toxic Thyroid Adenoma

Answer 14

• HYPERthyroidism
  
  • ​Benign, HYPER-functioning thyroid tumor
    
    • can secrete Either T3 or T4 or BOTH
  • ​T4 can be low normal or high
    
    • TSH low
• 1st line = thyroidectamy / radioactive Iodine
• 2nd = Thioamides

Question 15

Adjunct Treatment for HYPERthyroidism

Answer 15

These only treat SYMPTOMS

• Adrenergic blockers
• Beta blockers
• CCBs

Question 16

Thioamides

PTU / MMI

Answer 16

• Block thyroid Synthesis
  
  • –> INHIBIT TPO
• ​Dose adjustments
  
  • due to long half life of T4
  • Dose needed FLUCTUATES

Question 17

Methimazole

Answer 17

First Line Therapy

Except in 1st trimester of pregnancy (PTU is preffered)

CROSSES PLACENTA & Appears in breast milk

• 10x more potent than PTU
• Longer half life, and higher concentration in thyroid gland

Question 18

Propylthiouracil

PTU

Answer 18

INHIBITS PERIPHERAL T4–>T3 CONVERSION

along with Inhibiting TPO

Preferred in 1st trimester of pregnancy over MMI

Question 19

Thioamide Adverse Reactions

Answer 19

• Leukopenia
  
  • ​–> Agranulocytosis
• Transaminitis
  
  • –> hepatoxicity
• Rash

Question 20

Potassium Iodide

Answer 20

Adjuct treatment for HYPERthyroidism

SSKI (super saturated potassium Iodide)

Lugols solution

CAN SHUT DOWN THYROID PRODUCTION

so we have to beware, only short term use

Question 21

RAI

Radioactive Iodine

Answer 21

HYPERthyroidism

High chance of Secondary Hypothyroidism

Question 22

Subtotaland Total THYROIDECTAMY

Answer 22

HYPERthyroidism treatment

surgical removal

leads to hypothyroidism

Question 23

Pregnancy & HYPERthyroidism

Answer 23

INCREASED TBG –> decreased fT4

Radioactive therapy is contraindicated

Must maintain T4 levels for the baby

PTU for 1st Trimester

greater risk of preterm delivery and heart failure

Question 24

Thyroid Storm

Answer 24

Acute Process

• Treatment = throw everything at it
  
  • ​Thioamide
  • Beta Blockers
  • SSKI
  • Steroid

Question 25

Hashimotos Disease

Answer 25

Hypothyroidism

Autoimmune disease with AB production against the thyroid

–> Fibrosis & decreased function of thyroid

Question 26

Lab of Hypothyroidism

Answer 26

Decreased TT4 / fT4

Increased TSH

Possibly + Antibodies for Hashimtos

Increased Cholesterol

Question 27

Hypothyroidism Pharmacotherapy

Answer 27

Levothyroxine Sodium (T4)

Liothyronine Sodium (T3)

Liotrix (4:1 Mixture)

Armour Thyroid (Natural Thyroid)

Question 28

Initiation & Dosage of

Levothyroxine

Answer 28

• Aggressive Start
  
  • ◦50-125 mcg/day: younger, larger, severely symptomatic patients
• Conservative
  
  • ◦12.5-25 mcg/day: older, smaller, risk for hyperthyroid complication
• Symptomatic improvement is typically evident within 2 weeks
• Aging may lead to reduction in dose due to T4 clearance

Question 29

Conservative Dosing Approach

Levothyroxine

Answer 29

• Elderly
  
  • –> can lead to HYPERthyroidism
    
    • ​–> OSTEOPOROSIS
    • ​​–> angina
• ​​Patients with Pre-existing CAD
  
  • –> angina issues

Question 30

Pregnancy

Levothyroixine

Answer 30

MORE TBG in pregnant women

due to INCREASE in estradiol concentration

INCREASE DOSE BY 50%

monitor TSH levels every 4 weeks and adjust dose

Question 31

Myxedema Coma

Answer 31

Life- Threatening

Long-standing, uncorrected hypothyroidism

• slow developing symptoms
• Thyroid Replacement ASAP
  
  • ​MUST BE IV
    
    • due to reduced GI absorption