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)