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Endo > Hyperthyroidism > Flashcards

Hyperthyroidism Flashcards

1
Q

Describe the synthesis of thyroxine by follicular cells.

A

Thyroglobulin is a protein produced by the follicular cells. I- is taken up by the follicular cells
Thyroid peroxidase, in the presence of H2O2, 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

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2
Q

State two common causes of hyperthyroidism.

A

Graves’ Disease

Plummer’s Disease (toxic nodular goitre)

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3
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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4
Q

What happens to the thyroid gland in Graves’ disease?

A

Smooth, symmetrical hypertrophy due to overstimulation. Entire gland overactive in radioactive iodine scan.

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5
Q

State some features of Graves’ Disease.

A 
Thyroid 
Rapid pulse 
Warm 
Excitability/nervousness 
Loss of weight 
Muscle wasting 
Oligomenorrhoea/amenorrhoea

Other antibody effects (defining features)
Localised pretibial myxoedema
Exophthalmos

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6
Q

What causes Plummer’s Disease?

A

It is caused by a benign adenoma in the thyroid gland

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7
Q

How does Plummer’s disease differ from Graves’?

A

NO pretibial myxoedema
NO exophthalmos
NOT autoimmune
Only Thyroidtoxicosis symptoms

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8
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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9
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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10
Q

What causes lid lag?

A

High adrenaline

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11
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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12
Q

State four treatments for hyperthyroidism.

A

Thionamides
Potassium Iodide Radioiodine
Beta Blockers

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13
Q

What are thionamides (with examples) used to treat and when would you use them?

A

Graves’ Disease
Plummer’s Disease

You can use thionamides (such as Propylthiouracil or Carbimazole) 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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14
Q

What is the pro-drug Carbimazole converted to become active?

A

Methimazole

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15
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

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16
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

17
Q

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

A

Non-selective beta-blockers

This will reduce the effects of beta sensitisation by thyroxine

18
Q

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

A

Suppress antibody production (in Graves’)

Reduces deiodination of T4 to T3

19
Q

State some unwanted effects of thionamides.

A 
Agranulocytosis/granulocytopenia (rare and reversible with withdrawal of the drug) 
Nausea 
Headaches 
Rashes 
Jaundice 
Joint pain
20
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

21
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 (the Wolff-Chaikoff effect)
It inhibits the iodination of thyroglobulin and inhibits the production of hydrogen peroxide

22
Q

Why is potassium iodide useful before surgery?

A

It reduces the size and vascularity of the thyroid gland

23
Q

State some unwanted actions of potassium iodide.

A

Rashes
Fever
Angioedema

24
Q

In what form is potassium iodide given?

A

Lugol’s Solution or Aqueous iodine

25
Q

What is radioiodine use to treat?

A

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

26
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

27
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

28
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

29
Q

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

A

Technetium 99m Pertechnetate

30
Q

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

A

Painful dysphagia
Pyrexia
Hyperthyroidism
Raised ESR (Erythrocyte Sedimentation Rate)

31
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, the patient actually presents with hyperthyroid symptoms because of the release of stored thyroid hormone

32
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

33
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 (after around 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)

Endo (17 decks)

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