Hyperthyroidism Flashcards
What are two common causes of hyperthyroidism?
Graves' disease Nodular goitre (Plummer's disease)
What is Graves’ disease?
Autoimmune disease- antibodies bind to and stimulate TSH receptor in thyroid. This makes the thyroid overreactive and this leads to the thyroid becoming smoothly (goitre) enlarged and you get hyperthyroidism
In terms of the eyelids, how can you tell if a person has hyperthyroidism?
It causes lid lag (delay in eyelid moving down as you look down)
- nerve of eye under sympathetic ocntrol
- T4 makes B receptor more sensitive to adrenaline- Increase heartrate also as aresult
What is localised pretibial myxoedema?
hypertrophy of soft tissue in shins due to antibody binding to receptor– non pitting oedema
What is exopthalmos?
Another antibody binds to growth factors on muscles behind the eye –grow and push the eye forward
Pretibial myxoedema and exopthlamos is specific to
Grave’s
How can you image the thyroid?
By giving a patient radioactive iodine which will show up on a scintigram
What is Plummers disease?
Toxic nodular goitre- part of the thyroid has benign adenoma and is misbehaving
What is Plummer’s disease caused by?
A benign adenoma that is overactive at making thyroxine
What is the thyroid gland of someone with Plummer’s like?
There will be a visible lump on one side
What will you see if you do an iodine scan on someone with Plummer’s?
Antibody test
It will show the iodine going into the hot tumour. Because there is so much thyroxine coming from the tumour, the pituitary will stop making TSH and the rest of the thyroid will shrink away and stop making thyroxine so only the nodule is visible
Antibody test is negative as it is not due to autoimmune
What is the effect of thyroxine on the sympathetic nervous system?
It sensitises beta adrenoceptors to adrenaline and noradrenaline so normal amounts will have much stronger effects
Tachycardia, palpitations, tremor, lid lag
Give a brief summary of the symptoms of hyperthyroidism
Weight loss despite increased appetite Breathlessness Tachycardia Sweating Heat intolerance Diarrhoea Lid lag
What is a thyrotoxic crisis known as?
Thyroid storm– medical emergency
What is the mortality of a thyroid storm if untreated?
50%
What are the features of a thyroid storm?
Hyperpyrexia Accelerated tachycardia/arrhythmia Cardiac failure Delirium Hepatocellular dysfunction/jaundice
What is hyperpyrexia?
Temperature > 41 degrees
What is the treatment for a thyroid storm?
Surgery
Radioiodine
Drugs
What sort of drugs are used to treat hyperthyroidism?
Thionamides- Propylthiouracil and Carbimazole Potassium iodide Radioiodine -These reduce thyroid hormone synth Beta blockers-- propanalol non selective -Relieve symptoms
When are thionamides specifically given?
- Before thyroidectomy because you don’t want to give a general anaesthetic to someone who is tachycardic
- Following radioactive iodine treatment
How are thyroid hormones synthesised?
Iodine is taken up into follicular cells
Under the action of thyroperoxidase with hydrogen peroxide you get iodination of tyrosine residues in the thyroglobulin
You then get coupling of monoiodotyrosine and diiodotyrosine to form T3 and T4
This is taken up and released by cells into the circulation
What do thionamides do?
They inhibit thyroperoxidase hence inhibit iodination of tyrosine residues and coupling of tyrosine residues
So leads to reduction in production and secretion of T3 and T4
How long does it take for both the biochemical and clinical effects of thionamides take to become evident?
Biochemical- Hours
Clinical- A few weeks
Why is there this relationship between biochemical and clinical presentation?
There is a lot of stored thyroid hormone in follicular cells and the anti thyroid treatment only affects synthesis not storage
Due to the delayed clinical effect of thionamides, how would you deal with the symptoms in the short term?
Propanalol: Non-selective beta blocker
What are some other effects of anti thyroid hormones?
Suppress antibody production in Graves disease
Reduces the deiodination of T4 to T3 in peripheral tissues (done by propylthiouracil)
What are the unwanted effects of thionamides?
Administered
Metabolised by and excreted
Follow up consists of
Agranulocytosis/granulocytopenia
Rashes
Administered orally
Metabolised by liver and excreted in urine
- Usually aiming to stop anti-thyroid drug treatment after 18 months– wean off
- Review patients periodically inc thyroid function tests in case of relapse
Why are there concerns relating to pregnancy with thyroid disorder?
It is common in women around reproductive age and thionamides are able to cross the placenta and are secreted in the milk which can lead to foetal hypothyroidism
Why would a breastfeeding woman be put on PTU over carbimazole?
PTU crosses into the breast milk less than carbimazole
Why is the beta blocker that you use to treat the symptoms non-selective?
Reduces all the effects of excess stimulation of beta adrenoceptors
When is iodine used as treatment for hyperthyroidism?
Preparation of patients for surgery
Severe thyroid storm
How does iodine treatment work?
Hyperthyroid symptoms reduce within how many days
Vascularity and size of gland reduces wihtin how many days
You give such a large dose that the thyroid switches off because inhibits iodination of thyroglobulin and generation of hydrogen peroxide
2 days
10-14 days
What is the Wolff-Chaikoff effect?
There is temporary reduction in thyroid hormones following ingestion of large amounts of iodine
Why does the Wolf-Chaikoff effect occur?
It is autoregulatory, it occurs to prevent the thyroid form making too much thyroid hormone
How does iodine compare to thionamides in terms of time required for effects to be seen?
Iodine is quicker
What are the unwanted actions of iodine treatment?
Allergic reaction
Rashes
Fever
Angioedema
How is iodine administered?
Orally-Lugol’s solution or aqueous iodine
Max effects after 10 days continuous administration
What is radioiodine used to treat?
Graves’, Plummer’s and thyroid cancer
What does radioiodine treatment do?
Permanently switches off the thyroid without needing surgery
How does radioiodine work?
Thyroid follicular cells take up the iodine and it accumulates in the colloid, from there, it emits beta particles of radiation that destroy the follicular cells
7-10 days before radioiodine treatment, anti thyroid drugs are stopped, why is this?
This is so that the thyroid gland can become incredibly active so that it will take up a lot of the iodine when it is administered and maximum damage can be achieved
How is it administered
Single oral dose
Radioactive half life of
8 days
Radioactivity negligible after
2 months
Radioiodine cautions
Avoid close contact with small children for several weeks after
Contraindicated in pregnancy and breast feeding
Which drug reduces the size and vascularity of the thyroid gland?
Iodide
How does the thyroid uptake scan for thyroiditis look like? we didnt cover thyroiditis
What are the symptoms of viral thyroiditis?
Whole thyroid is unhappy, enlarged and inactive
Dysphagia Pyrexia Malaise Pain radiating to the ear Thyroid gland visibly enlarged and tender (on one side)
How does viral thyroiditis occur?
A virus attacks the thyroid and causes fever, it also damages the thyroid follicles and stored thyroxine is released. So gland is being damaged and prevented from making any new thyroxine but prevents as an overactive thyroid
What do you see in a technetium scan for viral thyroiditis?
There is no iodine uptake so you don’t see anything
How do you treat viral thyroiditis?
The patient just has to wait for about month until all the stored thyroxine has ran out and will be hypothyroid until their cells recover
