Hyperthyroidism Flashcards
What level of TSH will you find in a patient with primary hypothyroidism, where the thyroid gland has been destroyed by the immune system?
High TSH
How do you control thyroid replacement in primary hypothyroidism?
By monitoring TSH levels (until dose falls to normal)
Describe Graves’ Disease and its pathophysiology
Autoimmune
Antibodies bind to and stimulate the TSH receptor in the thyroid
Causes goitre (smooth) and hyperthyroidism
List symptoms of Graves’ Disease
Weight loss despite increased appetite
Tachycardia, palpitations
A/oligomenorrhoea
Heat intolerance
Sweating
Tremor
Exophthalmos
Muscle wasting
Localised myxoedema (not to be confused with hypothyroidism)
What causes exophthalmos?
Other antibodies bind to muscles behind the eye, causing them to grow - pushes eyes forward
What is pretibial myxoedema?
The swelling (non-pitting) that occurs on the shins of patients with Graves’ disease - growth of soft tissue (hypertrophy caused by antibodies)
What changes to the thyroid gland are observed in Graves’ Disease and how does this present on a thyroid scan?
Diffuse enlargement and engorgement of thyroid gland
Thyroid scan: Diffuse goitre of moderate size and uniform radioiodine uptake
What are the characteristics of Plummer’s Disease (toxic nodular goitre)?
Benign overactive adenoma that produces thyroxine
Not autoimmune
No pretibial myxoedema
No exophthalmos
Why is there atrophy of the normal functioning thyroid gland when there is a toxic nodular goitre?
The thyroxine being released from the tumour suppresses TSH so the normal gland doesn’t work as much.
How would a toxic nodular goitre present on a thyroid scan?
‘Hot nodule’ - single nodule of radio-iodine uptake
What effect does thyroxine have on the sympathetic nervous system and what is the relevance of this?
Sensitises beta adrenoceptors to ambient levels (slight changes) of adrenaline and noradrenaline
Thus there is apparent sympathetic activation
Causes tachycardia, palpitations, tremor in hands, lid lag
Patient with hyperthyroidism - slight scare, HR will rocket
What are some symptoms of hyperthyroidism?
Weight loss despite increased appetite
Breathlessness,
palpitations, tachycardia
Sweating
Heat intolerance
Diarrhoea
Lid lag and other sympathetic features
What are the symptoms of a thyroid storm?
Hyperpyrexia > 41oC
Accelerated tachycardia / arrhythmia
Cardiac failure
Delirium / frank psychosis
Hepatocellular dysfunction; jaundice
How is thyroid storm identified?
Two symptoms + hyperthyroidism (confirmed by blood test)
How is thyroid storm diagnosed?
Two symptoms + hyperthyroidism (confirmed with blood tests)
What are the treatment options for hyperthyroidism?
Thyroidectomy
Radioiodine
Drugs
What drugs are used to treat hyperthyroidism?
Thionamides (anti-thyroid drugs) e.g. carbimazole, propylthiouracil (PTU)
Potassium iodide (KI)
Radioiodine
Beta-blockers
What is the mechanism of action of thionamides?
Inhibition of thyroid peroxidase and hence inhibition of T3/4 synthesis and
secretion
How long does it take to see the clinical effect of thionamides and what medication should be taken with them as a result?
Weeks - follicular cells have a month store of thyroxine
Beta blockers, e.g. propranolol are taken to rapidly reduce symptoms - tremors, palpitations
What are the unwanted side effects of thionamides?
Agranulocytosis (usually reduction in neutrophils) - rare and reversible on withdrawal of drug - e.g. sore throat - strep in throat starts to multiply
Rashes (relatively common)
What is the follow-up for thionamides?
Aim to stop ATD treatments within 18 months
Review patient periodically including thyroid function tests for remission/relapse
What is the role of beta blockers in thyrotoxicosis?
Takes several weeks for ATDs to have clinical effects (reduced tremor, slower heart rate, less anxiety) so NON-selective (ie b1 & b2) beta blocker, e.g. propranolol achieves these effects in the interim
What is the dose of KI and what is it used for?
Dose 30x the average daily requirement
Used to prepare hyperthyroid patients for surgery and in severe thyrotoxic crisis (thyroid storm)
What is the mechanism of potassium iodide?
Inhibition of thyroid hormone synthesis & secretion:
- Inhibits iodination of thyroglobulin
- Inhibits H2O2 generation (+ thyroperoxidase)
WOLFF–CHAIKOFF effect - presumed autoregulatory effect
Why can’t KI be used for more than 10 days?
After 10 days, the iodine is used to make more thyroxine
What is the effect of potassium iodide?
Hyperthyroid symptoms reduce within 1-2 days
Vascularity and size of gland reduce within 10-14 days
What are the risks of thyroid surgery?
Risk of voice change
Risk of also losing parathyroid glands
Scar
Anaesthetic
How is Radioiodine administered?
Swallow a capsule containing about 370 MBq (10 mCi) of the isotope I (131)
What precautions must be taken when taking Radioiodine?
Contraindicated in pregnancy
Need to avoid children and pregnant mums for a few days
What can used instead of Radioiodine if you only require a scan and not treatment?
99-Tc pertechnetate
List characteristics of Viral (de Quervain’s) thyroiditis
Painful dysphagia
Hyperthyroidism
Pyrexia (fever)
Thyroid inflammation
Why is there no iodine uptake in viral thyroiditis?
Virus attacks thyroid gland causing pain and tenderness
Thyroid stops making thyroxine and makes viruses instead
Describe a thyroid scan for viral thyroiditis?
No iodine uptake - blank
Outline the progression of viral thyroiditis
Virus attacks thyroid gland causing pain and tenderness
Thyroid stops making thyroxine and makes viruses instead
Thus no iodine uptake (ZERO)
Stored thyroxine released - FT4 levels rise, TSH falls - hyperthyroid
Four weeks later, stored thyroxine exhausted, so hypothyroid
After a further month, resolution occurs (like in all viral diseases)
Slow recovery after 3 months - becomes euthyroid again
What’s the difference between viral thyroiditis and postpartum thyroiditis?
Postpartum thyroiditis - similar but no pain and only occurs after pregnancy - immune system modulated during pregnancy
