Hyperthyroidism Flashcards
- State two common causes of hyperthyroidism.
Graves’ Disease
Plummer’s Disease (toxic nodular goitre)
What happens in Grave’s disease
Grave’s disease – autoimmune, antibodies bind to and stimulate TSH receptors in thyroid gland- causing hyperthyroidism- thus stimulating thyroid hormone production
another antibody will bind to TSH and cause hypertrophy of the thyroid gland
can present thyroid goitre independently of hyperthyroidism.
Describe the appearance of the thyroid gland in Grave’s disease
Smooth enlargement- not nodular
Highly vascular
Antibodies bind to THS receptors on follicular cells all over the gland- so radioactive iodine will be taken into the whole gland- whole gland is overactive.
- 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
Explain the action of antibodies in Grave’s disease that cause exophthalmos (proptosis) and pretibial myxoedema
A third antibody can bind to and stimulate growth factor receptors behind the eye, which cause muscle hypertrophy. These are responsible for the appearance of exophthalmos (the forward protrusion of the eyeballs)- sometimes called proptosis.
A fourth antibody binds to and stimulates growth factor receptors at the front of the shin, causing pretibial myxoedema- non-pitting oedema.
In which order can these four antibodies appear in
Any order
Although commonly, the first two (causing goitre and hyperthyroidism) appear first
The other 2 tend to appear about a year later- so patients tend to blame these symptoms (wrongly) on their anti-thyroid therapy
Sometimes the 3rd antibody (causing proptosis) appears first and in the absence of hyperthyorid
Distinguish between proptosis and exopthalamos
Both represent the same condition.
However exopthalmaos is usually used when associated with an endocrinopathy (i.e hyperthyroid).
Summarise the key features of Plummer’s disease
Plummer’s disease – NOT autoimmune but a benign adenoma.
§ Toxic nodular goitre.
§ NO pretibial myxoedema.
§ NO exophthalmos.
§ Also called a “Hot Nodule” on a thyroid uptake scan.
Benign adenoma (not a cancer- just a tumour) that is overactive at making thyroxine
Describe what happens in Plummer’s disease (or a hot nodule)
Not autoimmune- so antibody test will be negative- no exophthalmos or swollen knee caps
A clone of follicular cells in the thyroid gland becomes autonomous and makes thyroxine out of control ( as it’s a benign adenoma)
There may be one ‘hot nodule’ or several.
When can hot nodules occur
With only minor derangement of the thyroid function, or occasionally with frank hyperthyroidism.
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.
oral or I.V administration of radioiodine.
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 :
Tachycardia, lid lag, palpitations, tremors in hands
Describe lid lag
Occurs due to hyperthyroidism of any cause (even with an overdose of thyroxine)
The muscle that opens the eye (levator palpabrae superioris) has two nerve supplies, one from the third cranial nerves (voluntary) and the other sympathetic (autonomous).
When a patient has hyperthyroidism, the beta receptors are sensitised to systemic adrenaline levels. This causes the eye to open or close more slowly than normal.
This is the opposite of ptosis which occurs when the sympathetic nerve is severed.
How can you see lid lag in a patient
Bring your hand down and ask them to follow it
In a normal patient- the eyelid should come down with the eye
But in hyperthyroidism- the eyelid is held back momentarily by adrenaline- but it’s not tethered- so eventually it comes back down
Can see white of eye above iris as the eye moves down.
What can be given to treat some of the symptoms of hyperthyroidism
Propanolol- a beta blocker
to lower HR and BP
State some general features of hyperthyroidism
Weight loss despite increased appetite Breathlesness Palpitations Tachycardia Sweating heat intolerance Diahhroea Dyspnoea
What is a consequence of having the radioactive iodine test
Receiving a dose of radiation
Therefore you need to stay out of contact with people for a while
i.e can’t go to work etc
What is the consequence of a mismanaged thyroid storm
Death
What is a thyroid storm
This is a medical emergency – 50% of those untreated die
Blood tests will confirm hyperthyroidism
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 (high fever >41)
Accelerated tachycardia/arrhythmia (>140 bpm)
Cardiac failure (breathless at rest)
Delirium/frank psychosis
Hepatocellular dysfunction, jaundice
2 of these criteria in the presence of hyperthyroidism.
Needs urgent treatment
Summarise the treatment options for hyperthyroidism
o Surgery (thyroidectomy).
o Radioiodine.
o Drugs.
