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 and the whole gland is active
State some features of Graves’ Disease.
Rapid pulse Warm Localised pretibial myxoedema Exophthalmos Excitability/nervousness Loss of weight Muscle wasting Oligomenorrhoea/amenorrhoea
What are two defining features of Graves’ and what is it caused by?
Localised pretibial myxoedema
Exophthalmos
Antibodies cause both of these
Describe the appearance of a thyroid gland of a Graves’ patient in a thyroid scan using radioactive iodine.
The whole gland is smoothly enlarged and the whole gland is overactive
What causes Plummer’s Disease?
It is caused by a benign adenoma in the thyroid gland
How does Plummer’s disease differ from Graves’?
NO pretibial myxoedema
NO exophthalmos
NOT autoimmune
What will a technetium or iodine scan of the thyroid show in a patient with Plummer’s Disease?
All the iodine will be taken up by the overactive, tumorous part of the thyroid so you will see a hot nodule appear
The rest of the thyroid gland will not be seen because the high thyroxine production will decrease TSH release from the anterior pituitary and so the rest of the thyroid gland that is responding to TSH will not produce any thyroxine and will not take up iodine
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
What causes lid lag?
High adrenaline
What is thyroid storm (thyrotoxic crisis) and what are the features of thyroid storm?
This is a medical emergency that is a rare but important complication of hyperthyroidism Features: Hyperpyrexia Accelerated tachycardia/arrhythmia Cardiac failure Delirium/frank psychosis Hepatocellular dysfunction, jaundice
State four treatments for hyperthyroidism.
Thionamides
Potassium Iodide
Radioiodine
Beta Blockers
State two thionamides.
Propylthiouracil
Carbimazole
What are thionamides used to treat and when would you use it?
Graves’ Disease
Plummer’s Disease
You can use it before thyroidectomy to stabilise the patient (you wouldn’t want to give general anaesthetic to someone who is tachycardic with a labile heart rate)
It can be used after radioiodine treatment while you’re waiting for the clinical effects of the treatment
Describe the synthesis of thyroxine by follicular cells.
Thyroglobulin is a protein produced by the follicular cells
Iodine is taken up by the follicular cells
Thyroperoxidase, in the presence of hydrogen peroxide, iodinates the tyrosyl residues on the thyroglobulin to produce monoiodotyrosine or diiodotyrosine
Peroxidase transaminase then couples MIT and DIT to form T3 and T4, which is stored in the colloid
What is the mechanism of action of thionamides?
Thionamides inhibit thyroperoxidase
This prevents the iodination of thyroglobulin and coupling of MIT and DIT
It also inhibits peroxidase transaminase
Why do thionamides have a delayed effect on thyroid hormone levels?
Thionamides are quick in inhibiting synthesis of thyroid hormone but it does nothing to the thyroid hormone that has already been synthesised and is stored in the colloid ready for release
So there is a big delay between the biochemical effects and the clinical effects
What would you give the patient temporarily whilst waiting for thethionamides to have their clinical effect?
Non-selective beta-blockers
This will reduce the effects of beta sensitisation by thyroxine
Other than its main function in inhibiting thyroperoxidase, what else do thionamides do?
Suppress antibody production (in Graves’)
Reduces deiodination of T4 to T3
State some unwanted effects of thionamides.
Agranulocytosis/granulocytopenia (rare and reversible with withdrawal of the drug) Nausea Headaches Rashes Jaundice Joint pain
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
This means that you would want to give as low a dose as possible to a patient who is trying to conceive and is taking thionamides
Both drugs cross into breast milk but PTU does this less than CBZ
It is metabolised in the liver and excreted in the urine
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
