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YR2: Endocrinology > Hyperthyroidism > Flashcards

Hyperthyroidism Flashcards

1
Q

State 2 common causes of hyperthyroidism.

A 
Graves’ Disease 
Nodular goitre (Plummer's disease)
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2
Q

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

A

Autoimmune

An autoimmune antibody is produced that 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

Smoothly enlarged (goitre) and the whole gland is active

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4
Q

State 8 features of Graves’ Disease.

A 
Weight loss despite increased appetite
Warm skin, excessive sweating 
Palpitations, tachycardia
Tremor
Pretibial myxoedema 
Exophthalmus 
Muscle wasting  
Oligomenorrhoea/ amenorrhoea
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5
Q

What are2 defining features of Graves’ and what is it caused by?

A

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 + the whole gland is overactive

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7
Q

What causes Plummer’s Disease?

A

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= hot nodule
The rest of the thyroid gland won’t be seen because the high thyroxine production will decrease TSH release, so the normal part of the thyroid gland won’t produce thyroxine + 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 A + NA
Thus causes symptoms of having excess adrenaline e.g. Tachycardia, Palpitations, Tremor in hands

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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 
A rare medical emergency.
Features: 
Hyperpyrexia >41C
Accelerated tachycardia/ arrhythmia 
Cardiac failure  
Delirium/ frank psychosis  
Hepatocellular dysfunction, jaundice
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13
Q

State 3 treatments for hyperthyroidism.

A

Thyroidectomy
Radioiodine
Drugs

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14
Q

What 4 classes of drugs are used in the treatment of hyperthyroidism?

A

Thionamides
Potassium iodide
Radioiodine
Beta-blockers (symptomatic relief)

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15
Q

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

A

Graves’ Disease + Plummer’s Disease
Could use before thyroidectomy to stabilise the patient (don’t want to give GA to tachycardic patient)
Could use to reduce symptoms while waiting for radio iodine to act

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16
Q

Describe the synthesis of thyroxine by follicular cells.

A

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

17
Q

What is the mechanism of action of thionamides?

A

Thionamides inhibit thyroperoxidase
This prevents iodination of thyroglobulin + coupling of MIT + 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 + stored in the colloid
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 the thionamides to have their clinical effect?

A

Non-selective beta-blockers e.g. Propranolol

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 in peripheral tissue

21
Q

State 2 unwanted effects of thionamides.

A

Agranulocytosis (rare + reversible with withdrawal of the drug)
Rashes

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 + are present in breast milk so can cause foetal hypothyroidism
So give as low a dose as possible to a patient who is trying to conceive
Both drugs cross into breast milk but PTU does this less than CBZ
It is metabolised in the liver + excreted in the urine

24
Q

What is the mechanism of action of potassium iodide treatment?

A

A massive dose of iodine can turn off the thyroid gland

It inhibits iodination of thyroglobulin + inhibits 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 + vascularity of the thyroid gland

27
Q

State unwanted actions of potassium iodide.

A

Allergic reaction: Rashes, Fever, Angioedema

28
Q

In what form is potassium iodide given? When are maximum effects seen?

A

Orally (Lugol’s Solution or Aqueous iodine)

Maximum effects after 10 days’ continuous administration

29
Q

What is radioiodine use to treat?

A

Graves’ Disease
Plummer’s Disease
Thyroid Cancer

30
Q

Describe the mechanism of action of radioiodine.

A

Radioiodine is taken up by the thyroid gland + accumulates in the colloid
It emits beta particles that destroy the follicular cells

31
Q

Describe the pharmacokinetics of radioiodine.

A

Given orally as a single dose
Discontinue anti-thyroid drugs 7-10 days before
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 + breast feeding

33
Q

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

A

Technetium 99 Pertechnetate

34
Q

What is pretibial myxoedema?

A

Non-pitting swelling occurring on shins of patients with Graves’ disease
Growth of soft tissue

35
Q

Name 2 thionamides

A

Propylthiouracil (PTU)

Carbimazole (CBZ)

36
Q

What happens after prescription of thionamides + propranolol?

A

Aim to stop anti-thyroid drug after 18 months
No need for propranolol after a few weeks
Review patient periodically for remission/relapse

37
Q

Why is propranolol used in treatment of hyperthyroidism?

A

It is a non-selective B blocker, so reduces tremor, slows HR + reduces anxiety

38
Q

When is potassium iodide used?

A

In preparation of hyperthyroid patient surgery

In severe thyrotoxic crisis (thyroid storm)

YR2: Endocrinology (19 decks)

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