Thyroid Pathophysiology Flashcards
What 2 hormones does the thyroid gland secrete?
Thyroxine (T4) and active T3
Is the unbound or bound thyroxine that is important for biological effects/feedback?
Unbound (‘free’ hormone)
What does the number on T4 & T3 tell us about the hormone?
It is the number of iodine atoms on tyrosine (hence T4, or T3)
What happens to TSH release in hyper & hypothyroidism?
Hyperthyroidism = low TSH Hypothyroidism = high TSH
- Remember them as opposites, so HYPER = LOW, HYPO = HIGH
- This is a negative feedback loop
What 2 substances are always tested in a thyroid function test (TFT)?
TSH & T4
How long does it take for TSH levels to adjust in hypo/hyperthyroidism?
3-4 weeks
In hyperthyroidism, is T4 or T3 higher?
T3.
Why aren’t TSH levels always high in hypothyroidism?
Because TSH levels takes time to adjust.
What is thyroiditis?
It is an inflammation of the thyroid gland which can either be:
- Viral
- Postpartum
- Autoimmune
- Drug-induced
What are the symptoms of viral thyroiditis?
Flu like symptoms + hyperthyroidism, then hypothyroidism
What treatment is used for viral thyroiditis?
NSAIDs + short course of steroids + b blockers
What drugs can cause thyroiditis?
Lithium - hypo
Amiodarone - hyper or hypo
Iodide - hyper
Glucocorticoids/dopamine - hyper
Why are the symptoms of hypothyroidism?
- Lethargy/tiredness
- Weight gain
- Bradycardia
- Dryness of skin/hair
- Goitre = thyroid gland swelling
- Constipation
What can cause hypothyroidism?
- Autoimmune destruction of thyroid gland - Hashimoto’s disease
- Radioiodide/surgical treatment of hyperthyroidism
- Drug-induced
What is the treatment of hypothyroidism?
Thyroxine 100-200mcg/day
- 1.6mcg/kg
Take 30-60mins before food/drink
When are TFT’s assessed in hypothyroidism?
After 6 weeks of treatment, to allow TSH levels to adjust, then every 6-12months
What drug is used in severe hypothyroidism (include dose)?
IV liothyronine sodium 10-20mcg, increased to 60mcg daily.
What are the symptoms of hyperthyroidism?
- OPPOSITE OF HYPOTHYROIDISM
1. Weight loss
2. Increased appetite
3. Tremor
4. Diarrhoea
5. Sweating/heat intolerance
6. Palpitations - tachycardia or AF
7. Goitre
Why are b-blockers given in hyperthyroidism?
To control the symptoms of tachycardia/palpitations/tremor
Why should you be careful when giving b-blockers to a diabetic patient?
Because b-blockers can mask hypoglycaemic symptoms.
What causes hyperthyroidism?
Graves disease - antibodies looking like TSH bind to thyroid glands & secrete excess thyroid hormones (T3/T4)
What is the mode of action of carbimazole, & what is its dosing?
It prevents tyrosine/iodine interactions = reducing thyroid production
15-40mg daily, gradually reduced to 5-15mg
How long is carbimazole used for in hyperthyroidism?
12-18 months
What side effect should patients taking carbimazole report immediately?
Agranulocytis - lowering of WBCs & immunity = high risk of infections
They must report signs of sore throat, fever, etc
Prophylthiouracil is a substitute for carbimazole. What is its dosing?
200-400mg daily, gradually reduced to 50-150mg daily
Why is levothyroxine & carbimazole sometimes given together?
To balance hypo & hyperthyroidism states (avoiding under/overtreatment)
What risk can increase if radioactive iodine is used as treatment?
Risk of hypothyroidism increases
What are examples of some b-blockers used in hyperthyroidism?
- Propanolol
- Metoprolol
- Nadolol
What MUST be present before surgery in hyperthyroidism?
Why is this the case?
Normal thyroid function should be present before surgery to reduce palpitations/tachycardia
-B-blockers are given to help with this
Why is unactive T4 sometimes given before surgery?
To avoid bleeding risks associated with b-blockers
What should replace anti-thyroid drugs 10-14 days before a thyroidectomy?
Potassium iodide - inhibits thyroid hormone release
What complications can arise from a thyroidectomy?
- Hypocalcaemia
- Hypoparathyroidism
- Hypothyroidism
- These can be due to mistakenly removing the parathyroid gland, rather than thyroid.
How often should TFT’s be measured after a thyroidectomy?
At 2 and 6 months, then annually.
How often should TFTs of anti-thyroid drugs be measured?
After 8 weeks of treatment, then every 3 months for a year, then annually
What scoring system is used to measure the relapse risk of patients on anti-thyroid drugs?
What does it take into account?
GREAT score
- Age
- Thyroid hormone levels
- TSH receptor antibody levels
- Size of thyroid gland
What can cause a thyroid crisis?
- Infection/stress
- Surgery
- Unprepared patient before surgery
What is the management of a thyroid crisis?
B blockers (propanolol) + carbimazole + iodine (T4) + steroids (dexamethasone)
