3.6 Hyperthyroidism Flashcards
When are the two important functions of TSH?
activates iodide uptake
activates the release of T3 and T4 into the blood stream
What does thyroxine do? (1)
Increase basal metabolic rate
What is TRH?
Thyrotropin releasing hormone
Where does TRH come from?
hypothalamus
What is the action of TRH?
TRH acts on thyrotrophs in the anterior pituitary, to secrete TSH
What does T3 and T4 feedback to?
T3 and T4 feedback negatively to the anterior pituitary and the hypothalamus
What will the TSH levels of a patient with primary hypothyroidism?
high
How do we adjust the dose of levothyroxine
Increase dose until TSH falls to normal
What is Graves’ disease?
Autoimmune disease where antibodies bind to and stimulate TSH receptors in the thyroid, resulting in hyperthyroidism
What are some of the observable features of graves’ disease?
breast enlargement
facial flashing
goitre (swelling of neck –> due to swelling of thyroid gland)
shortness of breath
weight loss
muscle wasting –> causing muscle weakness
perspiration
What are some of the non - observable features of graves’ disease?
feeling hot
increased appetite
tachycardia
diarrhoea
insomnia
nervousness/excitability/emotional instability
oligomenorrhea or amenorrhea
What symptoms in graves disease are caused by other antibodies not affecting the thyroid?
other antibodies bind to muscles behind the eye (cause growth) and cause exophthalmos
other antibodies cause pretibial myxoedema
What is pretibial myxoedema?
The swelling that occurs (non-pitting) on the shins of patients with graves disease.
myxoedema–> swelling of LL
caused by hypertrophy
What is the difference between myxoedema and pretibial myxoedema?
myxoedema caused by hyperthyroidism
pretibial myxoedema caused by Grave’s disease
What would you see if do a radio-iodine uptake scan a patient with graves disease?
uniform radioiodine uptake and enlarged thyroid gland
very dark as very active
What is toxic nodular goitre?
benign adenoma that is overactive at making thyroxine
What is the difference between toxic nodular goitre and graves disease?
toxic nodular goitre: NOT autoimmune NO pretibial myxoedema NO exophthalmos swelling on neck tends to be on one side
What would you see if do a radio-iodine uptake scan a patient with toxic nodular goitre?
lots of spill over, dark spot = ‘hot spot’ not uniform thyroid gland shape (as can be due to just hyperproliferation once cell thats secreting too much thyroxine, and rest of thyroid atrophys)
Why can hyperthyroidism be a medical emergency?
If hyperthyroidism gets extremely severe (high), the can have a thyroid storm.
Thyroid storm –> 50% mortality rate
What is the effect of thyroxine on the sympathetic nervous system?
sensitises beta adrenoreceptors to ambient levels of adrenaline and noradrenaline.
–> some symptoms similar to extra adrenaline (palpitations, tachycardia, tremor in hands, lid lag)
propanaol - beta blocker
What is thyroid storm?
Hyperthyroidism
AND TWO OR MORE OF:
- hyperpyrexia >41 degrees
- accelerated tachycardia/arrythmia
- cardiac failure
- delirium/frank psychosis (brain affected)
- hepatocellular dysfunction; jaundice (liver affected)
What are the treatment options for hyperthyroidism?
surgery
radioiodine
drugs
What are the four classes of drugs used in the treatment of hyperthyroidism?
- Thionamides
- Potassium Iodide
- Radioiodine
- Beta-blockers
What are the names of two thianomides used to treat hyperthyroidism?
propylthiouracil (PTU)
carbimazole (CBZ)
What are the role of thianomides in the treatment of hyperthyroidism?
they are anti-thyroid drugs; block iodine uptake into iodide gland
How can potassium iodide and radioiodine be used in the treatment of hyperthyroidism?
big dose, decreases thyroid function synthesis as a bit overloaded, reduces thyroid function for a few days (short acting)
How are beta blockers used in the treatment of hyperthyroidism?
Used to reduce symptoms causes by extra adrenaline.
What is the mechanism of thionamides?
inhibit thyroid peroxidase and hence T3/4 synthesis and secretion
biochemical effect: hours
clinical effect: 4-6 weeks because stores thyroxine had to be used up
Why are beta blockers prescribed initially for patients with hyperthyroidism but then stopped after a few weeks?
Thionamides take a few weeks to work
BB provide symptom relief straight away then stopped when thionamides work
What are some side effects of thionamides ?
rashes (common)
agranulocytosis (rare) - usually reduction in neutrophils and reversible on withdrawal of drug
What is the follow up for treatment of hyperthyroidism?
usually aim to stop anti-thyroid drug treatment after 18 months (half then cured)
review patient periodically incl. thyroid function tests for remission/relapse
When is potassium iodide used in the treatment of hyperthyroidism?
- preparation of hyperthyroidism patients for surgery
- thyroid storm (thyrotoxic crisis)
What dose of KI used in the treatment of hyperthyroidism?
30x average daily requirement daily
What is the mechanism of KI, what is this effect known as?
–> inhibition of T3/4 synthesis and secretion
presumed auto-regulatory effect (WOLFF -CHAIKOFF effect)
How long does it take for KI to start working in treatment of hyperthyroidism?
symptoms reduce in 1-2 days
Why do surgeons like KI to be prescribed before surgery?
vascularity and size of gland reduce within 10 to 14 days
How long does the effects of KI last?
about 10 days
What are the risks of thyroid surgery? (4)
risk of voice change (ability to shout or sing)
risk of also losing parathyroid gland
scar
anaesthetic
How is radioiodine used in the treatment of hyperthyroidism?
swallow capsule containing 370 MBq of isotope I 131
What are the rules of using radioiodine in the treatment of hyperthyroidism, when should it not be used?
contraindicated in pregnancy
isolate for about 10 days (avoiding children and pregnant women)
radiation lasts about 6 weeks
Is radioiodine treatment the same as what is used in scans?
Can be.
99-Tc (pertchnetate) is cheaper option can be used for scans only (not treatment)
What is the name of the beta blocker used in hyperthyroid treatment?
propranolol
What is viral thyroiditis?
Virus attacks thyroid gland, causing thyroid to stop making thyroxine and makes viruses instead.
What are the symptoms of viral thyroiditis?
painful dysphagia hyperthyroidism pyrexia thyroid inflammation (visibly on one side) pain radiating to ear
How do we test for viral thyroiditis?
viral thyroiditis will have no iodine uptake (ZERO), because thyroid making virus
Why does viral thyroiditis cause hyperthyroidism?
When virus attacks thyroid gland, all stored thyroxine leaks out.
What does the progression of viral thyroiditis look like?
1 month hyperthyroidism (thyroxine stores released, free T4 levels rise)
1 month hypothyroidism –> when thyroxine stores run out
patient recovers from virus
normal thyroid function again
How should we treat the thyroid symptoms of viral thyroiditis?
No nothing - thyroid function will return back to normal and prescribing something could alter that
What is postpartum thyroiditis?
similar to viral thyroiditis but without neck pain and post partum (autoimmune)
What are 4 causes of hyperthyroidism
Graves disease
Nodular thyroid disease
Viral thyroiditis
Postpartum thyroiditis
What is the cause of postpartum thyroiditis?
immune system modulated during pregnancy
