Thyroid Pathophysiology

Question 1

What 2 hormones does the thyroid gland secrete?

Answer 1

Thyroxine (T4) and active T3

Question 2

Is the unbound or bound thyroxine that is important for biological effects/feedback?

Answer 2

Unbound (‘free’ hormone)

Question 3

What does the number on T4 & T3 tell us about the hormone?

Answer 3

It is the number of iodine atoms on tyrosine (hence T4, or T3)

Question 4

What happens to TSH release in hyper & hypothyroidism?

Answer 4

Hyperthyroidism = low TSH 
Hypothyroidism = high TSH 

• Remember them as opposites, so HYPER = LOW, HYPO = HIGH
• This is a negative feedback loop

Question 5

What 2 substances are always tested in a thyroid function test (TFT)?

Answer 5

TSH & T4

Question 6

How long does it take for TSH levels to adjust in hypo/hyperthyroidism?

Answer 6

3-4 weeks

Question 7

In hyperthyroidism, is T4 or T3 higher?

Answer 7

T3.

Question 8

Why aren’t TSH levels always high in hypothyroidism?

Answer 8

Because TSH levels takes time to adjust.

Question 9

What is thyroiditis?

Answer 9

It is an inflammation of the thyroid gland which can either be:

1. Viral
2. Postpartum
3. Autoimmune
4. Drug-induced

Question 10

What are the symptoms of viral thyroiditis?

Answer 10

Flu like symptoms + hyperthyroidism, then hypothyroidism

Question 11

What treatment is used for viral thyroiditis?

Answer 11

NSAIDs + short course of steroids + b blockers

Question 12

What drugs can cause thyroiditis?

Answer 12

Lithium - hypo
Amiodarone - hyper or hypo
Iodide - hyper
Glucocorticoids/dopamine - hyper

Question 13

Why are the symptoms of hypothyroidism?

Answer 13

1. Lethargy/tiredness
2. Weight gain
3. Bradycardia
4. Dryness of skin/hair
5. Goitre = thyroid gland swelling
6. Constipation

Question 14

What can cause hypothyroidism?

Answer 14

1. Autoimmune destruction of thyroid gland - Hashimoto’s disease
2. Radioiodide/surgical treatment of hyperthyroidism
3. Drug-induced

Question 15

What is the treatment of hypothyroidism?

Answer 15

Thyroxine 100-200mcg/day
- 1.6mcg/kg
Take 30-60mins before food/drink

Question 16

When are TFT’s assessed in hypothyroidism?

Answer 16

After 6 weeks of treatment, to allow TSH levels to adjust, then every 6-12months

Question 17

What drug is used in severe hypothyroidism (include dose)?

Answer 17

IV liothyronine sodium 10-20mcg, increased to 60mcg daily.

Question 18

What are the symptoms of hyperthyroidism?

Answer 18

• OPPOSITE OF HYPOTHYROIDISM
  1. Weight loss
  2. Increased appetite
  3. Tremor
  4. Diarrhoea
  5. Sweating/heat intolerance
  6. Palpitations - tachycardia or AF
  7. Goitre

Question 19

Why are b-blockers given in hyperthyroidism?

Answer 19

To control the symptoms of tachycardia/palpitations/tremor

Question 20

Why should you be careful when giving b-blockers to a diabetic patient?

Answer 20

Because b-blockers can mask hypoglycaemic symptoms.

Question 21

What causes hyperthyroidism?

Answer 21

Graves disease - antibodies looking like TSH bind to thyroid glands & secrete excess thyroid hormones (T3/T4)

Question 22

What is the mode of action of carbimazole, & what is its dosing?

Answer 22

It prevents tyrosine/iodine interactions = reducing thyroid production
15-40mg daily, gradually reduced to 5-15mg

Question 23

How long is carbimazole used for in hyperthyroidism?

Answer 23

12-18 months

Question 24

What side effect should patients taking carbimazole report immediately?

Answer 24

Agranulocytis - lowering of WBCs & immunity = high risk of infections

They must report signs of sore throat, fever, etc

Question 25

Prophylthiouracil is a substitute for carbimazole. What is its dosing?

Answer 25

200-400mg daily, gradually reduced to 50-150mg daily

Question 26

Why is levothyroxine & carbimazole sometimes given together?

Answer 26

To balance hypo & hyperthyroidism states (avoiding under/overtreatment)

Question 27

What risk can increase if radioactive iodine is used as treatment?

Answer 27

Risk of hypothyroidism increases

Question 28

What are examples of some b-blockers used in hyperthyroidism?

Answer 28

1. Propanolol 2. Metoprolol 3. Nadolol

Question 29

What MUST be present before surgery in hyperthyroidism? | Why is this the case?

Answer 29

Normal thyroid function should be present before surgery to reduce palpitations/tachycardia -B-blockers are given to help with this

Question 30

Why is unactive T4 sometimes given before surgery?

Answer 30

To avoid bleeding risks associated with b-blockers

Question 31

What should replace anti-thyroid drugs 10-14 days before a thyroidectomy?

Answer 31

Potassium iodide - inhibits thyroid hormone release

Question 32

What complications can arise from a thyroidectomy?

Answer 32

1. Hypocalcaemia 2. Hypoparathyroidism 3. Hypothyroidism - These can be due to mistakenly removing the parathyroid gland, rather than thyroid.

Question 33

How often should TFT's be measured after a thyroidectomy?

Answer 33

At 2 and 6 months, then annually.

Question 34

How often should TFTs of anti-thyroid drugs be measured?

Answer 34

After 8 weeks of treatment, then every 3 months for a year, then annually

Question 35

What scoring system is used to measure the relapse risk of patients on anti-thyroid drugs? What does it take into account?

Answer 35

GREAT score - Age - Thyroid hormone levels - TSH receptor antibody levels - Size of thyroid gland

Question 36

What can cause a thyroid crisis?

Answer 36

1. Infection/stress 2. Surgery 3. Unprepared patient before surgery

Question 37

What is the management of a thyroid crisis?

Answer 37

B blockers (propanolol) + carbimazole + iodine (T4) + steroids (dexamethasone)