Hypothyroidism Flashcards
What are the causes of primary hypothyroidism?
Hashimoto’s thyroiditis
- Most common cause
- AI
- More common in women
Dietary iodine deficiency
Post thyroidectomy/ radioiodine Rx
Drug therapy (lithium, amioarone, anti-thyroid drugs e.g. carbimazole)
What is the cause of secondary hypothyroidism?
Pituitary failure
Give 4 actions of thyroid hormone?
- increases BMR
- bone demineralisation
- B-adrenergic action on heart and gut motility
- CNS activation
What is the HPT axis?
Hypothalamus-pituitary-thyroid axis
Explain the HPT axis?
Hypothalamus
v
TRH
v
Anterior pituitary
v
TSH
v
Thyroid gland
v
T3/T4
T3/T4 have negative feedback mechanism on on TRH and TSH
What is the pathophysiology?
T3/T4 are abnormally low due to underactivity of thyroid, so more TSH made to raise T3/T4 levels
What sx may be seen?
Wt gain Cold intolerance Bradycardia Constipation Tired Oligomenorrhoea Brain fog
What signs might you see?
Goitre + hoarse voice Dry/brittle nail/hair Alopecia Bradycardia Hyporeflexia Macroglossia?
What Ix do you do and what do you expect to see?
What other Ix can you do?
TFTs
High TSH, low/normal T3/T4
Antibody testing:
- anti-thyroid peroxidase (TPO)
- anti-thyroglobulin (Tg)
What is subclinical hypothyroidism?
High TSH, normal T4
What levels of TSH indicate clinical hypothyroidism?
> 10u/L
What is the biochemical thyroid picture for secondary hypothyroidism?
Low TSH, low T3/T4
What is the drug used to mx this and provide doses?
When should TFTs be done following meds?
Levothyroxine (T4)
50-100 mcg OD
Titrate up/down depending
TFTs should be done after 8-12w from starting/changing dose
What is the main marker used for monitoring?
TSH levels
What is the Mx of subclinical hypothyroidism?
Monitor for 6-12m
Treat if TSH > 10u/L
