Hyperthyroidism

Question 1

Which cells respond to TSH?

Answer 1

Follicular cells of the thyroid gland

Question 2

Which endocrine cells release TSH?

Answer 2

Thyrotrophs within the anterior pituitary gland

Question 3

How is iodine pumped into follicular cell of the thyroid gland?

Answer 3

Sodium-iodine symporter, using secondary active transport.

Question 4

How is iodide pumped from the follicle into the colloid?

Answer 4

Pendrin pumps within the apical membrane

Question 5

Which thyroglobulin residues are iodinated?

Answer 5

Tyrosine residues

Question 6

Which thyroid pro-hormone is iodinated?

Answer 6

Thyroglobulin

Question 7

How is iodine activated into iodide?

Answer 7

Under the action of thyroid peroxidase in the presence of hydrogen peroxide.

Question 8

Where does iodination occur within the thyroid gland?

Answer 8

Within the colloid

Question 9

What are the two direct products of iodination of thyroglobulin within the colloid?

Answer 9

MIT and DIT

Question 10

How is triiodothyronine formed?

Answer 10

Coupling of MIT and DIT

Question 11

How is tetraiodothyronine formed?

Answer 11

Coupling of DIT molecules

Question 12

Which thyroid hormone is active?

Answer 12

T3

Question 13

Which structures are directly inhibited by thyroxine via negative feedback mechanisms?

Answer 13

Anterior pituitary gland (thyrotrophs)
Hypothalamic neurones (secreting TRH)

Question 14

What level of TSH will you find in a patient with primary hypothyroidism where the thyroid gland has been destroyed by the immune system?

Answer 14

There is an elevated TSH, considering thyroxine secretion from the thyroid gland is reduced. Thus through negative feedback mechanisms, TSH is elevated as a compromise.

Question 15

Which drug is prescribed in patients with hypothyroidism?

Answer 15

Levothyroxine

Question 16

How should levothyroxine be administered?

Answer 16

Levothyroxine is administered as oral preparations to patients, the dose is increases until the TSH levels are normal.

Question 17

Which effect demonstrates the auto-regulatory function of iodine control?

Answer 17

Wolff-Chaikoff effect

Question 18

What is the Wolff-Chaikoff effect?

Answer 18

The Wolff-Chaikoff effect demonstrates an autoregulatory function, whereby an excess ingestion of iodine inhibits thyroid peroxidase activity and thus reducing iodothyronine production within thyroid follicular cells, independent from the serum-level of thyroid-stimulating hormone (TSH).

Question 19

What is the pathophysiology of Grave’s disease?

Answer 19

TSH Immunoglobulins binds to TSH receptors in the thyroid gland.
-Stimulation of TSH receptors subsequently result in smooth goitre formation and hyperthyroidism.

Question 20

What are the clinical features of Grave’s disease?

Answer 20

Respiration, facial flushing
Muscle wasting
Shortness of breath
Heat intolerance 
Weight loss - despite increased appetite
Localised myxoedema 
Tremor
Sweating
Palpitations
Exophthalmos (proptosis)

Question 21

What is pretibial myxoedema?

Answer 21

The swelling that occurs on the shins of patients with Grave’s disease: growth of soft tissue

Question 22

What type of goitre is shown in a patient with Plummer’s disease?

Answer 22

Toxic nodular goitre

Benign nodules of the thyroid gland (not autoimmune associated)

Question 23

What type thyroid scan is conducted to identify the type of goitre?

Answer 23

Iodine-123 scan

Question 24

Which part of the thyroid gland uptakes iodine-123 in Plummer’s disease?

Answer 24

The toxic nodular goitre. The inactive thyroid gland is suppressed due to the adenoma.

Question 25

What is the effect of thyroxine on the heart rate?

Answer 25

Sensitives beta adrenoreceptors to ambient levels of adrenaline and noradrenaline. This increases the heart rate ( tachycardia and tremor in hands) -lid lag

Question 26

What are the main clinical features of a thyroid storm?

Answer 26

``` Hyperpyrexia > 41 Accelerated tachycardia/arrhythmia Cardiac failure delirium/frank psychosis Hepatocellular dysfunction; jaundice ```

Question 27

What are the main treatment options for a thyroid storm?

Answer 27

Thyroidectomy Radioiodine Drugs

Question 28

What class of drug is the main anti-thyroid?

Answer 28

Thionamides - Propylthiouracil (PTU) - Carbimazole (CBZ)

Question 29

What are the four main classes of drugs used in the treatment of hyperthyroidism?

Answer 29

1) Thionamides 2) Potassium Iodide 3) Radioiodine 4) Beta-blockers

Question 30

What purpose do beta-blockers have in terms of hyperthyroidism treatment?

Answer 30

Alleviate the symptoms concerned with arrhythmia.

Question 31

Which enzyme is inhibited by thionamides?

Answer 31

Thyroid peroxidase

Question 32

What is the mechanism of action of thionamides?

Answer 32

Inhibition of thyroid peroxidase and peroxidase transaminase, therefore reduce iodine activation and iodination of thyroglobulin into MIT & DIT.

Question 33

Why does it take 3-4 weeks for the clinical effects of anti-thyroid hormones to become apparrent?

Answer 33

There is a months store of thyroxine

Question 34

Which co-drug is prescribed alongside thionamides?

Answer 34

Propanolol rapidly reduces tremors and tachycardia.

Question 35

What are the unwanted actions of thinamides?

Answer 35

Agranulocytosis (reduction in neutrophils) - neutropenia increases risk of sepsis. -Rashes (common)

Question 36

How long should anti-thyroid drugs typically be prescribed for?

Answer 36

18 months

Question 37

What is the role performed by beta blockers in thyrotoxicosis?

Answer 37

Reduces heart rate and beta adrenoreceptor sensitivity

Question 38

Which drug should be pre-operatively administered in hyperthyroid patients?

Answer 38

Potassium Iodide - induces Wolff-Chaikoff effect (10 days)

Question 39

What effect does KI have in hyperthyroid patients?

Answer 39

Inhibits hydrogen peroxide generation and thyroid peroxidase. Reduces vascularity and size of gland (atrophy of thyroid gland) Inhibits the iodination of thyroglobulin by inducing the Wolff-Chaikoff effect

Question 40

Which nerve is at risk of damage during a thyroidectomy?

Answer 40

The recurrent laryngeal nerve

Question 41

What are the associated risks with a thyroidectomy?

Answer 41

1) Risk of voice change 2) Risk of also losing parathyroid glands 3) Scar 4) Anaesthetic

Question 42

Which isotope is used in radioiodine?

Answer 42

Iodine 131 | Emits radiation for 10 days therefore avoid pregnant individuals

Question 43

Which radioisotope is administered for a thyroid scan?

Answer 43

Tc-99

Question 44

What are the four main features of viral thyroiditis?

Answer 44

Painful dysphagia Hyperthyroidism (The thyroid gland is tender and palpable) Pyrexia (fever) Thyroid inflammation

Question 45

Describe the pattern of iodine uptake in an individual with viral thyroiditis?

Answer 45

There is no iodine uptake as the thyroid gland stops making thyroxine.

Question 46

How is hyperthyroidism induced in individuals with viral thyroiditis?

Answer 46

Round follicle is damaged, subsequently causing stored thyroxine within the colloid to be released

Question 47

How is hypothyroid caused in individuals with viral thyroiditis?

Answer 47

Four weeks upon the onset of viral thyroiditis, stored thyroxine is depleted.