Endo 5 - Hyperthyroid Disorders Flashcards
State two common causes of hyperthyroidism?
- Grave’s Disease
2. Plummer’s Disease
What type of disease is Grave’’s disease?
Autoimmune
Describe the mechanism of Grave’s disease?
an autoimmune antibody which behaves like TSH and binds to the TSH receptor thus stimulating thyroid hormone production
What does the thyroid gland look like in Grave’s disease on a scan?
The thyroid gland is smoothly enlarged and the whole gland is active
What are some of the signs and symptoms in Grave’s disease?
- rapid pulse
- warm
- localised pretibial myxoedema
- exopthalmos
- excitability/nervousness
- loss of weight
- oligomenorrhoea/ amenorrhoea
What are the two defining features of Grave’s disease?
- Localised pretibial myxoedema
2. Exopthalmos
Explain how pretibial myxoedema happens in Grave’s?
antibody mediated
non-pitting
What causes the exopthalmos?
another antibody, binds to muscles behind eye
What causes Plummer’s disease?
Benign adenoma in the thyroid gland
What would an iodine scan show in a patient with Plummer’s disease?
all the iodine will be taken up by the overactive tumourous part of the thyroid, so you see a hot nodule appear
the rest of the thyroid will not be seen as TSH is 0 so is not being stimulated
How does Plummer’s differ from Grave’s?
not autoimmune
so no pretibial myxoedema and no exopthalmos
Describe the effects of thyroxine on the sympathetic nervous system?
it sensitises beta adrenoceptors to basal levels of adrenaline and noradrenaline
So excess thyroxine causes…
symptoms of having high adrenaline
What causes lid lag?
High adrenaline
What is a thyroid storm?
medical emergency, a rare complication of hyperthyroidism
What are the features of a thyroid storm?
- hyperpyrexia
- accelerated tachycardia
- cardiac failure
- delirium
- hepatic failure
What are the 4 treatments of hyperthyroidism?
- Thionamides
- Potassium iodide
- radioiodine
- beta blockers
Outline the physiology of iodine in the thyroid?
- iodine taken up by the follicular cells
- thyroperoxidase allows for iodination of tyrosine residues
- allows for coupling of t1 and t2 to form t3 and t4
Describe the synthesis of thyroxine by follicular cells
- thyroglobulin is a protein produced by follicular cells
- iodine taken up by the follicular cells
- thyroid peroxidase iodinates tyrosyl residues on the thyroglobulin to form t1 and t2 in the presence of hydrogen peroxide
What is the mechanism of action of thionamides?
- inhibit thyroperoxidase so t3/t4 cannot be made
- reduced synthesis of thyroxine hromones
Why do thionamides take around 2 weeks for their effects to be felt?
stores of thyroxine last 2 weeks + long half life
What two diseases can thionamides be used to treat?
Plummer’s and Grave’s
When do you use thionamide in a patient?
Use it before a thyroidectomy to stabilise the patient
Why do you need to stabilise the patient before surgery?
cannot give anaesthesia to a hypertensive and tachycardiac patient
Name 2 thionamides?
Carbimazole
Propylthiouracil
What would you give a hyperthyroid patient while the thionamide takes two weeks to work?
non selective beta blockers
this will reduce the sensitisation of beta adrenoceptors to thyroxine
What are some of the other added benefits of thionamides other than inhibiting thyroperoxidase?
- suppress antibody production
- reduces deiodination of t4 to t3
What are some of the unwanted effects of thionamides?
- agranulocytosis
- nausea
- headaches
- rashes
- jaundice
- joint pain
Carbimazole is a pro drug, what does it get converted to to have its affect?
Methimazole
Do thionamides cross the placenta?
Yes
What should you do when prescribing thionamides to pregnant women/women looking to conceive?
Give as low dose as possible
Which drug out of carbimazole and propylthiouracil crosses into the breast milk LESS?
PTU
What is the mechanism of action of potassium iodide treatment?
massive dose of iodine can turn off the thyroid, inhibits the iodination of thyroglobulin and inhibits the production of hydrogen peroxide
What is the Wolff-Chaikoff effect?
temporary reduction in thyroid hormones following ingestion of a huge amount of iodine
Why is potassium iodide given before surgery?
reduces the size and vascularity of the thyroid gland
Name 3 unwanted effects of potassium iodide?
rashes
fever
angioedema
What is the form of potassium iodide given?
Lugol’s iodine
What 3 things is Radioactive iodine 131 used to treat?
Grave’s disease
Plummers
Thyroid cancer
What is the mechanism of action of radioactive iodine treatment?
Radioiodine taken up by the thyroid and accumulates in the colloid
emits beta particles in the colloid which destroys the follicular cells
Why do you discontinue anti-thyroid drugs 7 days before radioactive iodine treatment?
to let the thyroid become really active so it will absorb the radioactive iodine
What are some of the cautions with this treatment>
Avoid contact with children for several weeks
contra-indicated in pregnancy and breast feeding
What other molecule can be used instead?
Technetium 99 pertechnetate
What are the symptoms of viral thyroiditis?
dysphagia
pyrexia
hyperthyroidism
raised ESR - eythrocyte sedimentation rate
What is viral thyoiditis caused by?
Virus attacking the thyroid and causing a fever
What are the symptoms caused by?
all the thyroxine gets released so presents with hyperthyroidism
meanwhile virus is replicating itself using thyroid
What would an iodine thyroid scan show in a patient with viral thyroiditis?
not visible on the scan because thyroid gland is not taking up any iodine as not producing any thyroxine
What is the treatment of viral thyroiditis?
Nothing, wait for virus to go
Why will the patient present with hyperthyroidism and then hypothyroidism?
all thyroxine released at beginning
when virus gone, no stores left so hypo
