5 - Hyperthyroidism Flashcards
State two common causes of hyperthyroidism.
Graves’ Disease
Plummer’s Disease (toxic nodular goitre)
What type of disease is Graves’? Describe its mechanism.
autoimmune
An autoimmune antibody is produced that behaves like TSH and binds to the TSH receptor thus stimulating thyroid hormone production
What does a thyroid gland look like in Graves’ Disease?
The thyroid gland is smoothly enlarged (goitre) and the whole gland is active
What is the difference between a smooth and a nodular/cystic goitre?
smooth - enlargement of the entire gland
nodular/cystic - enlargements of only part of the gland
What is the direct effect of the antibodies on the eyes of a patient with graves?
lid lag
State some features of Graves’ Disease.
Rapid pulse Warm - heat intolerance Localised pretibial myxoedema Exophthalmos Excitability/nervousness Loss of weight despite increases appetite Muscle wasting Oligomenorrhoea/amenorrhoea Breathlessness, palpitations, tachycardia Sweating Diarrhoea Lid lag
What are the two defining features of Graves’ that are caused by different antibodies than the one that causes the hyperthyroidism?
exophthalmus
pretibial myxoedema
How is graves disease confirmed? What are the tests?
- on palpitation, the gland will feel very diffused and smoothly diffused
- give some radioactive iodine. On a scintigram, the whole gland will be active - ‘cold nodule’
What causes Plummer’s Disease?
a benign adenoma in the thyroid gland
How does Plummer’s disease differ from Graves’?
NOT autoimmune
NO pretibial myxoedema
NO exophthalmos
When examining the neck of someone with Plummer’s what may be seen?
a lump on one side of the neck
What will a technetium or iodine scan of the thyroid show in a patient with Plummer’s Disease?
Will see a hot nodule appear - all the iodine is taken up by one part of the gland
(some patients may have a multinodular goitre)
The rest of the thyroid gland will not be seen because the high thyroxine production will decrease TSH release from the anterior pituitary, the rest of the gland stops producing thyroxine and will shrink
Describe the effects of thyroxine on the sympathetic nervous system.
Thyroxine sensitises beta adrenoceptors to ambient levels of adrenaline and noradrenaline
So you get symptoms of having high adrenaline (tachycardia)
this means that small increasing anxiety can lead to panic attacks
What causes lid lag?
High adrenaline
What is thyroid storm (thyrotoxic crisis)?
give the features
This is a medical emergency (rare) When hyperthyroidism has been left so long that patients have at least two of the following: - Hyperpyrexia - Accelerated tachycardia/arrhythmia - Cardiac failure - Delirium/frank psychosis - Hepatocellular dysfunction, jaundice
What is the treatment for someone with thyroid storm?
any treatment of hyperthyroidism
need prompt and aggressive treatment
How can hyperthyroidism be treated?
- surgery (thyroidectomy)
- radioiodine
- drugs
Give the classes of drugs used in the treatment of hyperthyroidism
Thionamides
Potassium Iodide
Radioiodine
Beta Blockers
State two thionamides.
Propylthiouracil
Carbimazole
What are thionamides used to treat?
Graves’ Disease
Plummer’s Disease
When would you thionamides in the treatment of hyperthyroidism?
- before thyroidectomy to stabilise the patient (don’t want to give general anaesthetic to someone who is tachycardic with a labile heart rate)
- can be used after radioiodine treatment while you’re waiting for the clinical effects of the treatment
What is the mechanism of action of thionamides?
- inhibit thyroperoxidase
- —-> prevents the iodination of thyroglobulin
- —-> prevents coupling of MIT and DIT
Other than its main function in inhibiting thyroperoxidase, what else do thionamides do?
Suppress antibody production (in Graves’)
Reduces deiodination of T4 to T3
Why do thionamides have a delayed effect clinical effect on thyroid hormone levels?
(why is there a big delay between the biochemical effects and the clinical effects?)
does nothing to the thyroid hormone that has already been synthesised and is stored in the colloid ready for release
What would you give the patient temporarily whilst waiting for the thionamides to have their clinical effect?
Non-selective beta-blockers
This will reduce the effects of beta sensitisation by thyroxine
What are the unwanted effects of thionamides?
Agranulocytosis/granulocytopenia (rare and reversible with withdrawal of the drug)
Rashes
Carbimazole is a pro-drug. What is it converted to become active?
Methimazole
What are the implications of thionamides in pregnancy?
Thionamides can cross the placenta and is present in breast milk so it can cause foetal hypothyroidism
For a patient trying to conceive, give as low a dose as possible
(PTU is the preferred drug for pregnant women)
How long is someone kept on thionamides for?
18 months and then it is stopped
there is a 50:50 chance of relapse
When is potassium iodide used in the treatment of hyperthyroidism? Why?
(used in combination with other drugs)
- preparation of hyperthyroid patients for surgery
- thyroid storm
use this when you want an immediate effect
What is the mechanism of action of potassium iodide treatment?
If you give a massive dose of iodine it can turn off the thyroid gland
It inhibits the iodination of thyroglobulin and inhibits the production of hydrogen peroxide
What is the Wolff-Chaikoff effect?
The temporary reduction in thyroid hormones following ingestion of a large amount of iodine
Why is potassium iodide useful before surgery?
It reduces the size and vascularity of the thyroid gland
State some unwanted actions of potassium iodide.
(allergic reactions:)
Rashes
Fever
Angioedema
In what form is potassium iodide given?
Lugol’s Solution or Aqueous iodine
What conditions is radioiodine use to treat?
Graves’ Disease, Plummer’s Disease and Thyroid Cancer
What do radioiodine do?
shuts down the thyroid without surgery
Describe the mechanism of action of radioiodine.
Radioiodine is taken up by the thyroid gland and it accumulates in the colloid
From the colloid it emits beta particles that destroy the follicular cells
Describe the pharmacokinetics of radioiodine.
It is given orally as a single dose
Discontinue anti-thyroid drugs 7-10 days before radioiodine treatment to allow time for the thyroid to become really active again so that it takes up a lot of thyroid hormone
Radioactivity is negligible after 2 months
What cautions should patients taking radioiodine take?
Avoid close contact with small children for several weeks after receiving radioiodine
Contra-indicated in pregnancy and breast feeding
Name another molecule that is cheaper and can be used instead of radioiodine.
Technetium (99 Pertechnetate)
What happens in viral thyroiditis?
a virus attacking the thyroid gland and causing a fever
it also damages the thyroid follicles and all the stored thyroxine gets released
State some symptoms of viral thyroiditis (de Quervain’s thyroiditis).
Painful dysphagia
Pyrexia
Hyperthyroidism
Raised erythrocyte sedimentation rate
Describe how viral thyroiditis causes hyperthyroid effects.
The virus takes over the function of the thyroid and makes the thyroid produce more virus particles rather than producing thyroid hormone
It damages the thyroid follicles so that all the thyroxine gets released
The patient actually presents with hyperthyroid symptoms because of the release of stored thyroid hormone
What is the appearance of a thyroid scan in a patient with viral thyroiditis?
It is not visible in the scan because the thyroid gland isn’t taking up any iodine because no thyroid hormone is being synthesised
Describe the progression of viral thyroiditis from the time of presentation with hyperthyroid symptoms.
(THERE IS NO TREATMENT)
As it is viral, you just wait for the virus to eventually leave
Eventually, all the stored thyroxine in the colloid will run out (after around a month)
Then the patient will have hypothyroid symptoms
After another month the cells would have recovered and will start to produce thyroxine again so it will return to normal (euthyroid)
