Hyperthyroidism

Question 1

Control of thyroid activity

Answer 1

Hypothalamus release TRH
Pituitary release TSH
Thyroid produces T3 and T4 - negative feedback to hypothalamus and pituitary

Question 2

Control of thyroid replacement

Answer 2

Autoimmune destroys thyroid gland
TSH rises
Replace thyroxine and adjust dose until TSH falls

Question 3

Graves’ Disease

Answer 3

Autoimmune
Antibodies bind to and stimulate the TSH receptor in the thyroid
Cause goitre (smooth) and hyperthyroidism

Other antibodies bind to muscles behind the eye and cause exophthalmos

Other antibodies cause pretibial myxoedema (hypertrophy) - The swelling (non-pitting) that occurs on the shins of patients with Graves’ disease - growth of soft tissue (not myxoedemua - hypothyroidism)

Question 4

Plummer’s disease

Answer 4

Toxic nodular goitre
NOT autoimmune
Benign adenoma that is overactive at making thyroxine.
NO pretibial myxoedema
NO exophthalmos

Question 5

Effects of thyroxine on the sympathetic nervous system

Answer 5

Sensitises beta adrenoceptors to ambient levels of adrenaline and noradrenaline.

Thus there is apparent sympathetic activation

Tachycardia, palpitations, tremor in hands, lid lag

Question 6

Hyperthyroidism

Answer 6

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

Question 7

Thyroid storm

Answer 7

Medical emergency : 50% mortality untreated
Blood results confirm hyperthyroidism

Hyperpyrexia > 41oC
accelerated tachycardia / arrhythmia
cardiac failure
delirium / frank psychosis
hepatocellular dysfunction; jaundice

Needs aggressive treatment

Question 8

Treatment options for hyperthyroidism

Answer 8

Surgery (thyroidectomy)
Radioiodine
Drugs

Question 9

Classes of drugs used in the treatment of hyperthyroidism

Answer 9

1. The thionamides (thiourylenes; anti-thyroid drugs)
   - propylthiouracil (PTU)
   - carbimazole (CBZ)
2. Potassium Iodide
3. Radioiodine
4. β-blockers - help symptoms

Question 10

Thionamide mechanism

Answer 10

inhibition of thyroid peroxidase and hence T3/4 synthesis and secretion

Aim to stop after 18 months

Question 11

Unwanted actions of thionamides

Answer 11

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

Question 12

Role of b blockers in thyrotoxicosis

Answer 12

Several weeks for ATDs to have clinical effects eg reduced tremor, slower heart rate, less anxiety

NON-selective (ie b1 & b2) b blocker
eg propranolol
achieves these effects in the interim

Question 13

IODIDE, usually KI

Answer 13

Doses at least 30 times the average daily requirement

preparation of hyperthyroid patients for surgery

severe thyrotoxic crisis (thyroid storm)

Question 14

KI mechanism

Answer 14

Inhibits iodination of thyroglobulin

Inhibits H2O2 generation + thyoperoxidase

Inhibition of thyroid hormone synthesis & secretion
WOLFF–CHAIKOFF effect - presumed autoregulatory effect

Question 15

Problem with surgery

Answer 15

Risk of voice change
Risk of also losing parathyroid glands
Scar
Anaesthetic

Question 16

Radioiodine

Answer 16

Swallow a capsule containing about 370 MBq (10 mCi) of the isotope I (131)
Contraindicated in pregnancy
Need to avoid children and pregnant mums for a few days
For scans only (not treatment), 99-Tc pertechnetate is an option.

Question 17

Viral (de Quervain’s) thyroiditis

Answer 17

Painful dysphagia
Hyperthyroidism
Pyrexia
Thyroid inflammation

Question 18

Natural history of viral thyroiditis

Answer 18

Virus attacks thyroid gland causing pain and tenderness
Thyroid stops making thyroxine and makes viruses instead
Thus no iodine uptake (ZERO)

Radioiodine uptake zero
Stored thyroxine released - free T4 level rises
Thus toxic with zero uptake
Four weeks later, stored thyroxine exhausted, so hypothyroid.

After a further month, resolution occurs (like in all viral diseases).
Patient then becomes euthyroid again.

Postpartum thyroiditis similar but no pain and only occurs after pregnancy