Hypothyroidism & Hashimoto's Thyroiditis Flashcards
What is meant by hypothyroidism?
an inadequate production of thyroid hormones by the thyroid gland
it is 5-10x more common in females
What is the most common cause of hypothyroidism in the developed world?
Hashimoto’s thyroiditis
What causes Hashimoto’s thyroiditis?
- caused by autoimmune inflammation of the thyroid gland
- associated with antithyroid peroxidase (anti-TPO) or antithyroglobulin antibodies
What are the features of Hashimoto’s thyroiditis?
- initially it causes a goitre, which is followed by atrophy of the thyroid gland
- the goitre is firm and non-tender
- there may be a transient thyrotoxicosis in the acute stage
- this is followed by the features of hypothyroidism
it is 10x more common in women
What is the most common cause of hyperthyroidism in the developing world?
iodine deficiency
- iodine is added to foods, such as table salt, to prevent this
What are the other causes of primary hypothyroidism?
- secondary to treatment for hyperthyroidism
- medications
What medications for hyperthyroidism can result in hypothyroidism?
- all treatments for hyperthyroidism have the potential to cause hypothyroidism
- carbimazole
- propylthiouracil
- radioactive iodine
- thyroid surgery
What medications are associated with hypothyroidism?
LITHIUM:
* inhibits the production of thyroid hormones in the thyroid gland
- causes a goitre and hypothyroidism
AMIODARONE:
* interferes with thyroid hormone production + metabolism
- usually causes hypothyroidism but can also cause thyrotoxicosis
What is meant by secondary hypothyroidism?
- caused by hypopituitarism
- the pituitary gland is failing to produce enough TSH
- this is associated with a lack of other pituitary hormones (e.g. ACTH)
What are causes of hypopituitarism?
- tumours
- infection
- vascular causes (e.g. Sheehan syndrome)
- radiation
What is Sheehan syndrome?
- a rare condition in which there is injury to the pituitary gland as a result of extreme blood loss during childbirth
- some of the tissue in the pituitary gland dies as a result of oxygen deprivation
What are the symptoms of Sheehan’s syndrome?
agalactorrhoea:
* lack of breast milk production
- due to a lack of prolactin
amenorrhoea:
* absence of normal menstrual cycle
- due to lack of FSH & LH
hypothyroidism:
* due to lack of TSH
adrenal insufficiency:
* due to lack of ACTH
- results in low blood sodium + glucose
fatigue + loss of muscle mass:
* due to lack of growth hormone
in some women, this condition is mild and they are able to lactate
they may notice the other symptoms months-years after childbirth
What are the presenting features of hypothyroidism?
- weight gain
- fatigue
- dry skin
- coarse hair / hair loss
- constipation
- fluid retention (oedema, pleural effusion, ascities)
- heavy / irregular periods
- low BP
- cold intolerance
- decreased deep tendon reflexes / carpal tunnel syndrome
What are the investigations for diagnosing primary and secondary hypothyroidism?
primary hypothyroidism:
- T3 and T4 are low due to thyroid insufficiency
- TSH is high as lack of negative feedback means pituitary produces more TSH to try and stimulate the thyroid
secondary hypothyroidism:
- pituitary pathology results in low TSH
- as a result, T3 and T4 are also low
What is involved in the treatment for hypothyroidism?
oral levothyroxine
- the dose is titrated until TSH levels are normal
- levothyroxine is synthetic T4 which is metabolised to T3 in the body
How frequently should TSH levels be measured when taking levothyroxine?
- initially, TSH levels are measured monthly until stable
- once stable, TSH levels are checked less frequently unless they are symptomatic
How should the dose of levothyroxine be adjusted depending on TSH levels?
high TSH:
* the dose is too low and needs to be increased
low TSH:
* the dose is too high and needs to be reduced
What is the initial starting dose of levothyroxine?
50-100mcg OD
- for patients with cardiac disease, over 50 or severe hypothyroidism, the starting dose should be 25mcg OD
How often should thyroid function tests be checked after changing a dose of levothyroxine?
after 8-12 weeks
What are the side-effects of levothyroxine treatment?
- over-treatment results in hyperthyroidism
- reduced bone mineral density
- AF / worsening angina
What drugs interact with levothyroxine?
iron + calcium carbonate
- they reduce the absorption of levothyroxine
- need to be given at least 4 hours apart
What is congenital hypothyroidism?
What risk is associated with this?
- 1 in 4,000 babies are born with hypothyroidism
- if it is not diagnosed + treated in the first 4 weeks, it can result in irreversible cognitive decline
What are the features of congenital hypothyroidism?
How is it tested for?
- puffy face + macroglossia
- short stature
- delayed mental + physical milestones
- hypotonia
- prolonged neonatal jaundice
children are screened at 5-7 days using the heel prick test
What is meant by subclinical hypothyroidism?
- there is raised TSH but normal T3 / T4
- usually no obvious symptoms
- there is a risk of progressing to overt hypothyroidism
Who should be treated for hypothyroidism?
anyone with overt or subclinical hypothyroidism in which TSH > 10 mIU/L
What is the guideline for treatment of hypothyroidism when TSH > 10 mU/L?
consider offering levothyroxine IF:
- TSH > 10 mU/L on 2 separate occasions 3 months apart
What is the treatment for hypothyroidism when TSH is between 5.5 - 10 mU/L?
consider offering 6-month trial with levothyroxine if patient < 65 and:
- TSH level is 5.5 - 10 mU/L on 2 separate occasions 3 months apart
AND
- there are symptoms of hypothyroidism
- a “watch and wait” strategy is used in elderly patients (> 80)
- if asymptomatic, repeat TFTs in 6 months
