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Endocrinology > Hyperthyroidism > Flashcards

Hyperthyroidism Flashcards

1
Q

State two common causes of hyperthyroidism.

A

Graves’ Disease

Plummer’s Disease (toxic nodular goitre)

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2
Q

What type of disease is Graves’? Describe its mechanism.

A

Autoimmune
An autoimmune antibody is produced that behaves like TSH and binds to the TSH receptor thus stimulating thyroid hormone production

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3
Q

What does a thyroid gland look like in Graves’ Disease?

A

The thyroid gland is smoothly enlarged and the whole gland is active

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4
Q

State some features of Graves’ Disease.

A 
Rapid pulse 
Warm 
Localised pretibial myxoedema 
Exophthalmos 
Excitability/nervousness 
Loss of weight  
Muscle wasting  
Oligomenorrhoea/amenorrhoea
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5
Q

What are two defining features of Graves’ and what is it caused by?

A

Localised pretibial myxoedema
Exophthalmos
Antibodies cause both of these

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6
Q

Describe the appearance of a thyroid gland of a Graves’ patient in a thyroid scan using radioactive iodine.

A

The whole gland is smoothly enlarged and the whole gland is overactive

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7
Q

What causes Plummer’s Disease?

A

It is caused by a benign adenoma in the thyroid gland

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8
Q

How does Plummer’s disease differ from Graves’?

A

NO pretibial myxoedema
NO exophthalmos
NOT autoimmune

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9
Q

What will a technetium or iodine scan of the thyroid show in a patient with Plummer’s Disease?

A

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

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10
Q

Describe the effects of thyroxine on the sympathetic nervous system.

A

Thyroxine sensitises beta adrenoceptors to ambient levels of adrenaline and noradrenaline
So you get symptoms of having high adrenaline

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11
Q

What causes lid lag?

A

High adrenaline

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12
Q

What is thyroid storm (thyrotoxic crisis) and what are the features of thyroid storm?

A 
This is a medical emergency that is a rare but important complication of hyperthyroidism  
Features: 
Hyperpyrexia 
Accelerated tachycardia/arrhythmia 
Cardiac failure  
Delirium/frank psychosis  
Hepatocellular dysfunction, jaundice
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13
Q

State four treatments for hyperthyroidism.

A

Thionamides
Potassium Iodide
Radioiodine
Beta Blockers

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14
Q

State two thionamides.

A

Propylthiouracil

Carbimazole

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15
Q

What are thionamides used to treat and when would you use it?

A

Graves’ Disease
Plummer’s Disease
You can use it before thyroidectomy to stabilise the patient (you wouldn’t want to give general anaesthetic to someone who is tachycardic with a labile heart rate)
It can be used after radioiodine treatment while you’re waiting for the clinical effects of the treatment

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16
Q

Describe the synthesis of thyroxine by follicular cells.

A

Thyroglobulin is a protein produced by the follicular cells
Iodine is taken up by the follicular cells
Thyroperoxidase, in the presence of hydrogen peroxide, iodinates the tyrosyl residues on the thyroglobulin to produce monoiodotyrosine or diiodotyrosine
Peroxidase transaminase then couples MIT and DIT to form T3 and T4, which is stored in the colloid

17
Q

What is the mechanism of action of thionamides?

A

Thionamides inhibit thyroperoxidase
This prevents the iodination of thyroglobulin and coupling of MIT and DIT
It also inhibits peroxidase transaminase

18
Q

Why do thionamides have a delayed effect on thyroid hormone levels?

A

Thionamides are quick in inhibiting synthesis of thyroid hormone but it does nothing to the thyroid hormone that has already been synthesised and is stored in the colloid ready for release
So there is a big delay between the biochemical effects and the clinical effects

19
Q

What would you give the patient temporarily whilst waiting for thethionamides to have their clinical effect?

A

Non-selective beta-blockers

This will reduce the effects of beta sensitisation by thyroxine

20
Q

Other than its main function in inhibiting thyroperoxidase, what else do thionamides do?

A

Suppress antibody production (in Graves’)

Reduces deiodination of T4 to T3

21
Q

State some unwanted effects of thionamides.

A 
Agranulocytosis/granulocytopenia (rare and reversible with withdrawal of the drug) 
Nausea 
Headaches  
Rashes 
Jaundice 
Joint pain
22
Q

Carbimazole is a pro-drug. What is it converted to become active?

A

Methimazole

23
Q

What are the implications of thionamides in pregnancy?

A

Thionamides can cross the placenta and is present in breast milk so it can cause foetal hypothyroidism
This means that you would want to give as low a dose as possible to a patient who is trying to conceive and is taking thionamides
Both drugs cross into breast milk but PTU does this less than CBZ
It is metabolised in the liver and excreted in the urine

24
Q

What is the mechanism of action of potassium iodide treatment?

A

If you give a massive dose of iodine it can turn off the thyroid gland
It inhibits the iodination of thyroglobulin and inhibits the production of hydrogen peroxide

25
Q

What is the Wolff-Chaikoff effect?

A

The temporary reduction in thyroid hormones following ingestion of a large amount of iodine

26
Q

Why is potassium iodide useful before surgery?

A

It reduces the size and vascularity of the thyroid gland

27
Q

State some unwanted actions of potassium iodide.

A

Rashes
Fever
Angioedema

28
Q

In what form is potassium iodide given?

A

Lugol’s Solution or Aqueous iodine

29
Q

What is radioiodine use to treat?

A

Iodine 131 is used to treat Graves’ Disease, Plummer’s Disease and Thyroid Cancer

30
Q

Describe the mechanism of action of radioiodine.

A

Radioiodine is taken up by the thyroid gland and it accumulates in the colloid
From the colloid it emits beta particles that destroy the follicular cells

31
Q

Describe the pharmacokinetics of radioiodine.

A

It is given orally as a single dose
Discontinue anti-thyroid drugs 7-10 days before radioiodine treatment to allow time for the thyroid to become really active again so that it takes up a lot of thyroid hormone
Radioactivity is negligible after 2 months

32
Q

What are some cautions of radioiodine?

A

Avoid close contact with small children for several weeks after receiving radioiodine
Contra-indicated in pregnancy and breast feeding

33
Q

Name another molecule that is cheaper and can be used instead of radioiodine.

A

Technetium 99 Pertechnetate

34
Q

State some symptoms of viral thyroiditis (de Quervain’s thyroiditis).

A

Painful dysphagia
Pyrexia
Hyperthyroidism
Raised ESR

35
Q

Describe how viral thyroiditis causes hyperthyroid effects.

A

The virus takes over the function of the thyroid and makes the thyroid produce more virus particles rather than producing thyroid hormone
It damages the thyroid follicles so that all the thyroxine gets released
Though the virus is stopping the production of thyroid hormone, thepatient actually presents with hyperthyroid symptoms because of the release of stored thyroid hormone

36
Q

What is the appearance of a thyroid scan in a patient with viral thyroiditis?

A

It is not visible in the scan because the thyroid gland isn’t taking up any iodine because no thyroid hormone is being synthesised

37
Q

Describe the progression of viral thyroiditis from the time of presentation with hyperthyroid symptoms.

A

As it is viral, you just wait for the virus to eventually leave
Eventually, all the stored thyroxine in the colloid will run out (afteraround a month)
Then the patient will have hypothyroid symptoms
After another month the cells would have recovered and will start to produce thyroxine again so it will return to normal (euthyroid)

Endocrinology (18 decks)

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