Hypothyroidism Flashcards
What is included in the thyroid gland?
Pyramidal lobe
Right lobe
Isthmus
Left lobe
What are the 2 functions of the thyroid?
Synthesis of thyroid hormones
Secretion of calcitonin
What are the thyroid hormones?
T3 + T4
H ow does the thyroid maintain calcium + phosphate levels?
Through secretion of parathyroid hormone (PTH)
What is included in hypothyroidism?
Too little
Primary = overt/subclinical
Secondary = pituitary-hypothalamic dysfunction
Peripheral
What is primary overt hypothyroidism?
Clinically insufficient amount
What is primary subclinical hypothyroidism?
Can’t produce it
What is peripheral hypothyroidism?
Body not using what is there
What is included in hyperthyroidism?
Too much
Thyroidal origin
Pituitary disease - most common
Extrathyroidal origin
What are the hypothyroidism signs + symptoms?
Thinning hair
Goiter = abnormally enlarged thyroid gland
Slow metabolism (weight gain)
Dry skin
Jaundice = infants born with
Bradycardia
What are the causes of hypothyroidism?
Autoimmune thyroiditis
Iodine deficiency
Post thyroidectomy/radioactive iodine treatment
Drug induced
Peripheral resistance to thyroid hormone
Congenital disease - eg. thyroid agenesis
What is the diagnosis for hypothyroidism?
Symptoms
Thyroid function test (TFTs)
- TSH
- Free T4
What does TFT show if primary overt hypothyroidism?
Levels raised + FT4 low
What does TFT show if primary subclinical hypothyroidism?
TSH slightly raised
FT4 within normal range
What does TFT show if secondary hypothyroidism?
TSH low
FT4 low
What does TFT show if peripheral hypothyroidism?
rT3 low
How are thyroid hormones released?
Thyroid releasing hormone comes from hypothalamus
Stimulates TSH release
Goes to thyroid
Thyroid releases T3 + T4
What are the treatment aims for hypothyroidism?
Replace thyroid hormone
Correct TSH levels + resolved clinical symptoms
What is 1st line for hypothyroidism?
Levothyroxine
What is the usual starting dose for levothyroxine?
1.6mcg/kg rounded to nearest 25mcg dose
What is the dose of levothyroxine if patient >65 or pre-existing CVD?
Reduced starting dose of 25-50mcg OD
= due to risk of overtreatment
How do you monitor hypothyroidism/medication?
Initially TFTs every 3 months
Can take up to 6 months for TSH to stabilise
How is levothyroxine titrated?
In steps of 25mcg
What happens if TSH is within normal limits BUT symptoms are still present?
Test FT4 to investigate secondary hypothyroidism
When monitoring secondary hypothyroidism what should you do?
Only adjust dose dependent on FT4
Which medication influence the thyroid?
Dopamine
Glucocorticoid
Iodine
Metal ions
Phenobarbital
Beta-blockers
How do you take levothyroxine?
Take 30-60 mins before food or other medications
What are the interactions with levothyroxine?
Food - eg. milk
Medicines - eg. calcium, Fe, PPIs
Disease - eg. IBD/Coeliac
What are side effects of levothyroxine?
Flushing
Palpitations
Insomnia
Angina
Thyroid crisis
How is hypothyroidism + pregnancy linked?
Uncontrolled hypothyroidism can impair fertility
Insufficient thyroid hormone can have teratogenic effects
What happens if you’re pregnant + have hypothyroidism?
Need frequent TSH level monitoring
Increase levothyroxine dose dose by 25-50mcg
