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Y2 LCRS1 Endocrinology > Hyperthyroidism > Flashcards

Hyperthyroidism Flashcards

1
Q

State two common causes of hyperthyroidism.

A

Graves’ Disease

Plummer’s Disease (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 in the thyroid 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 hyperthyroidism.

A 
Weight loss despite increased appetite
Breathlessness, 
palpitations, tachycardia
Sweating
Heat intolerance
Diarrhoea
Lid lag and other sympathetic features

Graves also has:

  • Exophthalmos
  • Pretibial myxoedema
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5
Q

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

A

Exophthalmos - antibodies bind behind the eye

Localised pretibial myxoedema - different antibodies bind causing hypertrophy of shins and ankles (non-pitting)

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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
Should see a smooth lump (cold nodule=cancer)

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7
Q

What causes Plummer’s Disease?

A

It is caused by a benign adenoma in the thyroid gland that is overactive and making thyroxine

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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 e.g. lid lag, tachycardia, tremor, palpitations.

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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 - 50% mortality if untreated. It is a rare but important complication of hyperthyroidism

Features: 
Hyperpyrexia >41oC
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

bblockers help with symptoms; other 3 reduce thyroid hormone sythesis

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14
Q

State two thionamides.

A

Propylthiouracil PTU

Carbimazole CBZ

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15
Q

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

A

Graves’ Disease
Toxic thyroid goitre

  1. 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)
  2. 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
  1. Thyroglobulin is a protein produced by the follicular cells
  2. Uptake of iodide (AT) - Iodine is taken up by the follicular cells by active transport
  3. Iodination: THYROID PEROXIDASE, in the presence of hydrogen peroxide, iodinates the tyrosyl residues on the thyroglobulin to produce monoiodotyrosine or diiodotyrosine
  4. Coupling reaction: PEROXIDASE TRANSAMINASE then couples MIT and DIT to form T3 and T4, which is stored in the colloid
  5. This is then endocytosed and secreted
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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? Why?

A

Non-selective beta-blockers E.G PROPRANOLOL/ATENOLOL
This will reduce the effects of beta sensitisation by thyroxine

It takes several weeks for the ATDs to have clinical effects e.g. reduced tremor, slower HR, less anxiety. So bb’s can achieve these effects in the interim.

20
Q

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

A
  1. Suppress antibody production (in Graves’)

2. Reduces deiodination of T4 to T3 in peripheral tissues

21
Q

State some unwanted effects of thionamides.

A
  • agranulocytosis (usually reduction in neutrophils) - rare and reversible on withdrawal of drug.
  • rashes (relatively common)
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

  1. It inhibits the IODINATION step of thyroglobulin
  2. Inhibits the production of hydrogen peroxide + thyoperoxidase
25
Q

What is the Wolff-Chaikoff effect?

A

The temporary reduction in thyroid hormones following ingestion of a large amount of iodine - presumed AUTOREGULATORY effect

26
Q

Why is potassium iodide useful before surgery? How early must it be given?

A

It reduces the size and vascularity of the thyroid gland

This happens in 10-14days

27
Q

State some unwanted actions of potassium iodide.

A

Allergic reaction e.g. 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, toxic nodular disease (Plummer’s) 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
Half-life = 8 days
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, the patient 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 (after around 4 weeks) –> hypothyroid symptoms

After another 4 weeks the cells would have recovered and will start to produce thyroxine again so it will return to normal (euthyroid)

38
Q

How long does it take to see the biochemical and clinical effects of thionamides?

A

Biochem effect - hours

Clinical effect - weeks

39
Q

When is idodide (KI) treatment given to patients?

A
  1. In prep of hyperthyroid patients for surgery

2. Severe thyrotoxic crisis (thyroid storm)

40
Q

How quickly do hyperthyroid symptoms reduce after KI teratment?

A

Hyperthyroid symptoms reduce within 1-2days

41
Q

Why should anti-thyroid drugs be discontinued prior to radioiodine treatment?

A

to allow time for the thyroid to become really active again so that it takes up a lot of thyroid hormone

Y2 LCRS1 Endocrinology (18 decks)

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