1B hyperthyroidism Flashcards
How do we control thyroid replacement?
Monitor TSH level and increase thyroid replacement dose till TSH falls to normal
What happens in Graves’ disease?
- Autoimmune disease where antibodies bind to and stimulate the TSH receptor in the thyroid
- Causes smooth goitre and hyperthyroidism
- Other antibodies bind to muscles behind the eye and cause exophthalmos
What is pretibial myxoedema?
Other antibodies cause pretibial myxoedema (hypertrophy) which is growth of soft tissue
Pretibial- in front of tibia
Myxoedema- swelling of lower limb
The swelling is non-pitting as it is solid
Not to be confused with myxoedema → hypothyroidism
What are the symptoms of Graves’?
What does the thyroid and its scan look like in Graves’?
- Diffuse goitre of moderate size and uniform radioiodine uptake
- Diffuse enlargement and engorgement of thyroid gland (broken line shows normal size)
What is toxic nodular goitre (Plummer’s disease)
- Not autoimmune, so:
- No pretibial myxoedema
- No exophthalmos
- Benign adenoma that is overactive at making thyroxine
What does the thyroid look like in Plummer’s disease and why?
- One cell has grown a lot on one side of the thyroid so that side is large
- This makes a lot of thyroxine which suppresses TSH and lack of TSH means the normal side of the gland atrophies and gets smaller
What is the first line investigation for Graves’ disease?
TSH receptor antibody (TRAb) (against the TSH receptor) measured in the bloodstream, positive in Graves’ disease.
How does the thyroid in Plummer’s disease look like on a radiograph?
taken up all the iodine
What are the effects of thyroxine on the sympathetic nervous system?
- Sensitises beta adrenoceptors to ambient levels of adrenaline and noradrenaline
- Thus there is apparent sympathetic activation
- Causes tachycardia, palpitations, tremor in hands, lid lag
What are the symptoms for hyperthyroidism?
- Weight loss despite increased appetite
- Breathlessness
- Palpitations, tachycardia
- Sweating
- Heat intolerance- feel hot in winter
- Diarrhoea
- Lid lag and other sympathetic features
What is a thyroid storm?
- Medical emergency- 50% mortality untreated
- Blood results confirm hyperthyroidism
- Need aggressive treatment
What is the criteria for thyroid storm?
When someone with hyperthyroidism has 2 or more of these features:
- Hyperpyrexia >41°C
- Accelerated tachycardia/arrhythmia
- Cardiac failure
- Delirium/frank psychosis
- Hepatocellular dysfunction; jaundice
What treatment options are there for Plummer’s disease?
- drugs
- radioiodine
- surgery (thyroidectomy)
What drugs are given for hyperthyroidism?
- Beta blockers
- Thionamides (thiourylenes; anti-thyroid drugs)
- Potassium iodide
What do beta blockers do?
- Helps with sympathetic symptoms- usually works immediately so given first
- It takes several weeks for anti thyroid drugs to have clinical effects e.g. reduced tremor, slower heart rate, less anxiety
- Can use non-selective (i.e. beta1 and beta2) beta blockers eg. propranolol to achieve these effects in the interim
NOT thyroid blockers
What are 2 examples of thionamides and how do they work?
- Propylthiouracil (PTU)
- Carbimazole (CBZ)
Stops thyroid production in thyroid gland itself:
- Good for daily treatment of hyperthyroid conditions like Graves’ and toxic thyroid nodule/toxic multinodular goitre
- Block thyroid peroxidase enzyme to stop making T3 and T4
- Doesn’t work straight away (4-6 weeks to start effect) since stored thyroxine needs to be used up
What can we give while waiting for thionamides to work?
Treatment may include propranolol beta blocker to rapidly reduce tremor and tachycardia while waiting for effect to take place
What are side effects of thionamides?
- Rashes (relatively common)
- More commonly for CBZ: Agranulocytosis (usually reduction in neutrophils)- rare and reversible on withdrawal of drug
- For PTU: liver failure - also v rare
How does potassium iodide work?
ONLY used if patient is headed for surgery- not for Graves’- increases vascularity; or for severe thyrotoxic crisis
- Good preparation of hyperthyroid patients for surgery- start taking it every day from 10 days before surgery
- It inhibits iodination of thyroglobulin and inhibits H2O2 generation and thyroperoxidase
- Overall, there’s inhibition of thyroid hormone synthesis and secretion → Wolff-Chaikoff effect
What effects does potassium iodide have on hyperthyroidism?
- Hyperthyroid symptoms reduce within 1-2 days
- Vascularity and size of gland reduce within 10-14 days
When do we follow up patients taking drugs for hyperthyroidism?
- Usually aim to stop anti-thyroid drug treatment after 18 months
- Review patient periodically including thyroid function tests for remission/relapse
How does radioiodine work?
- Swallow a capsule of 270 MBq (10mCi) of the isotope I(131)
- Don’t use if pregnant or child
What substance can we use for scans only and not treatment?
Tc-99m pertechnetate
