Hyperthyroidism Flashcards
What does TSH do?
Activates uptake of iodine into the thyroid follicular cell which eventually leads to formation of thyroxine
Activates proteolytic enzyme
How much thyroxine do we store?
Enough for one month
What enzyme allows release of thyroxine from the thyroid follicular cell? How does it do this?
Proteolytic enzyme- makes a hole in the cell
How does the negative feedback loop for thyroxine work?
T3 and T4 have negative feedback on the pituitary AND on the hypothalamus
What will TSH levels be in someone with primary hypothyroidism where the thyroid gland is destroyed?
High TSH
What does thyroxine do?
Increases a lot of metabolic processes
What is Graves disease?
An autoimmune condition where antibodies bind to and stimulate the TSH receptor in the thyroid causing a smooth goitre and hyperthyroidism
What happens to the thyroid in Graves disease?
Smooth goitre
How does Graves disease present?
CNS: Nervousness, excitability, restlessness, emotional instability, insomnia Exophthalmos Sweatiness Mostly female and young Weight loss with increased appetite High pulse Oligo/amenorrhea Swollen ankles and shins (pretibial myxoedema) Tremor Diarrhoea
What is Plummer’s disease? What type of condition is it? How does it differ from Grave’s symptomatically?
Benign toxic nodular goitre of thyroid (NOT autoimmune) that causes hyperthyroidism
NO pre-tibial myxoedema or exophthalmos
What are TSH, T3, T4 levels in someone with Plummer’s?
High T3 and T4
No TSH
How do we differentiate Plummer’s vs Grave’s?
In Plummer’s theres one large benign growth and the rest of the thyroid shrinks
In Graves the whole gland is enlarged
What is any non Grave’s hyperthyroidism classified as?
Plummer’s
aka toxic multi-nodular goitre or hot nodule
How does thyroxine effect the sympathetic nervous system? How does this present?
T3 makes beta receptors more sensitive to adrenaline /noradrenaline (doesn’t bind but makes downstream cascade faster).
This leads to sympathetic activation
Tachycardia, palpitations, tremor in hands (beta receptors in skeletal muscles), lid lag
What is lid lag and how do you test it?
Ask them to follow your finger take it really high up, to mid level and low down and if they have hyperthyroidism their eyelids will lag and stay up slightly too long due to excess adrenaline
What symptoms do you need to ask about when you suspect hyperthyroidism
Weight loss despite increased appetite Breathlessness Palpitations,tachycardia Sweating Heat intolerance Diarrhoea Lid lag and other sympathetic features
What is thyroid storm?
Medical emergency- 50% mortality untreated
Untreated hyperthyroidism= lots of excess thyroxine
What is treatment for a thyroid storm?
Urgent in hospital treatment
What are options for treating hyperthyroidism?
Surgery (thyroidectomy)
Radioiodine
Drugs
What drugs can be used for hyperthyroidism?
Thionamides- propylthiouracil and carbimazole
Potassium iodide
Radioiodine
Beta blockers (only helps with symptoms -fast acting)
How do thionamides work?
Inhibit thyroid peroxidase so reduce T3/T4 synthesis- takes weeks to show on blood test, so give beta blockers for first few weeks
What are side effects of thionamides?
Agranulocytosis- reduction of neutrophils (get sore throats)- reversible on withdrawal of drug
Rashes
When is iodine used to treat hyperthyroidism?
Preparing them for surgery (quick action)
If in a thyroid storm
Why is iodine not an ideal drug?
Its not for long term- only used for 10 days
Why is iodine used in hyperthyroidism before surgery?
Reduces vascularity and size of gland within 10-14 days (less bleeding)
Reduces hyperthyroid symptoms within 1-2 days
What is the main risk with thyroid surgery?
Cutting of recurrent laryngeal nerve which alters voice
Risk of losing parathyroid glands
Scar
Anaesthetic
How is radioiodine taken and what precautions must you take?
Swallow a capsule of 370 MBq
Stay away from pregnant people for a few days as you emit radiation
How does viral (de Quervain’s) thyroiditis present?
Painful dysphagia
Hyperthyroidism
Pyrexia
Thyroid inflammation
How is viral thyroiditis diagnosed?
They have no iodine uptake at all on thyroid scintigraphy (cells are too inflamed), this wouldn’t happen in Graves or Plummers
What happens long term in viral thyroiditis?
After a month of hyperthyroidism (all stored thyroxine is released) there is hypothyroidism as no new thyroxine has been synthesised, eventually even after that they will go back to normal (after 3 months- euthyroid)
In grave’s disease, where can antibodies also have an effect (apart from thyroid)?
Other Abs bind to muscles behind the eye and cause exophthalmos
Other Abs cause pretibial myxoedema
What is pretibial myxoedema?
Non-pitting (pitting is to do with cardiac failure and fluid build up) swelling that occurs on shins of patients with Grave’s disease- growth of soft tissue
How does graves disease appear on a radioiodine thyroid scan?
Uniform uptake of radioiodine due to presence of TSH receptors on entire gland
What imaging can we use to see the thyroid gland?
Thyroid scintigraphy
How does plummer’s appear on a Thyroid scintigraphy ?
A large mass (hot nodule)- doesn’t take up all the tracer as it’s not very active
What are symptoms of a thyroid storm?
Hyperpyrexia > 41oC accelerated tachycardia / arrhythmia cardiac failure delirium / frank psychosis hepatocellular dysfunction; jaundice
What do thioamides treat?
Grave’s
Toxic thyroid nodule/ toxic multinodular goitre
Give an example of a beta blocker and it’s impact
Propranolol
Rapidly reduces tremor and tachycardia
For a patient taking thionamides, what are aims of follow up?
Aim to stop antithyroid drug treatment after 18 months
Review patient periodically including thyroid function tests for remission/relapse
What is the role of beta blockers in thyrotoxicosis?
Several weeks for anti-thyroid drugs to work
Non-selective (ie B1 and B2) beta blockers are given e.g. propranolol to reduce symptoms (reduce tremor, slow HR, less anxiety)
What is the mechanism of potassium iodide?
Inhibits iodination of thyroglobulin
Inhibits hydrogen peroxidase generation and thyroperoxidase
Wolff-chaikoff effect - inhibition of thyroid hormone synthesis and secretion- presumed autoregulatory affect
What is the impact on the thyroid gland before and after treatment with thiouracil and thiouracil plus iodine?
Hyperplastic thyroid: Gland enlarged, tears and bleeds easily. Acinar hyperplasia and loss of colloid
After thiouracil: Gland mass increases, tear and bleeds more easily. Increased acinar cell hyperplasia, complete loss of colloid
After thiouracil and iodine: Gland shrinks, pale and firm, does not tear or bleed easily. Involution of acinar epithelium, storage of iodine- poor colloid
How does the thyroid gland appear in viral thyroiditis?
Visibly enlarged more on one side
What is the mechanism of viral thyroiditis?
Virus attacks thyroid gland causing pain and tenderness
Thyroid stops making thyroxine and makes viruses instead
No iodine uptake
Describe the course of viral thyroiditis
Neck becomes painful; All stored thyroxine released Free T4 levels rise YSH levels drop 1 month HYPERthyroidism BUT no new thyroxine being made
FT4 slowly falls
Patient gets HYPOthyroidism
After 3 months, theres slow recovery
