Hyperthyroidism Flashcards
What inhibits TRH and therefore TSH?
T4 and T3
What is Graves’ disease?
- Autoimmune
- TSH receptor antibodies (TRAb) bind and stimulate the TSH receptor in the thyroid
- Causing a smooth goitre and hyperthyroidism
What are distinctive symptoms of Graves’ disease?
- Exophthalmos
- Pretibial myxoedema
What causes exophthalmos in people with Graves’ disease?
Antibodies binding to the muscles behind the eye
What is pretibial myxoedema?
The swelling (non-pitting) that occurs on the shins of patients with Graves' disease (growth of soft tissue) associated with hyperthyroidism NOT hypothyroidism
Describe the goitre caused by Graves’ disease.
- Diffuse enlargement and engorgement of the thyroid gland
- with uniform radioiodine uptake
What is the difference between toxic nodular thyroid disease and Graves’ disease?
Toxic nodular thyroid disease =
- not autoimmune
- no pretibial myxoedema
- no exophthalmos
- non-symmetrical and non-diffuse goitre
- possible sore throat
What is toxic nodular thyroid disease?
Characterised by:
- toxic nodular nodule or multinodular goitre
- benign adenoma produces excess thyroxine
How does thyroxine impact the sympathetic nervous system?
- sensitises beta adrenoreceptors to the ambient levels of adrenaline and noradrenaline
- causes apparent sympathetic activation without adrenaline increasing
How does the impact of thyroxine on the sympathetic nervous system present?
- tachycardia
- palpitations
- tremor in the hands
- lid lag
What are the symptoms of hyperthyroidism?
- weight loss (despite increased appetite)
- breathlessness
- palpitations
- tachycardia
- sweating
- heat intolerance
- diarrhoea
- lid lag (+ other sympathetic features)
What is a thyroid storm?
A medical emergency resulting in a 50% mortality if untreated
(aggressive treatment is required)
What are the characteristics of a thyroid strom?
- Hyperpyrexia (>41C)
- accelerated tachycardia/arrhythmia
- cardiac failure
- delirium/frank psychosis
- hepatocellular dysfunction; jaundice
What are the possible treatments for hyperthyroidism?
- surgery (thyroidectomy)
- radioiodine
- drugs
What are the 4 classes of drugs involved in the treatment of hyperthyroidism?
Thionamides (thiourylenes; anti-thyroid drugs) - propylthiouracil (PTU) - carbimazole (CBZ) Potassium Iodide Radioiodine Beta-Blockers
What is the aim of thionamides, potassium iodide and radioiodine?
To reduce thyroid hormone synthesis
What is the aim of Beta-blockers?
To help with the symptoms associated with hyperthyroidism
What are the 2 main enzymes involves in thyroid hormone synthesis?
- Thyroid peroxidase (TPO)
- Peroxidase transaminase
What is the mechanism of action of thionamides?
The inhibition of thyroid peroxidase and therefore T3/4 synthesis and secretion
How long does it take for thionamides to come into effect?
- biochemical effect: hours
- clinical effect: weeks
What drug often accompanies thionamides in a treatment plan?
- Propanolol (beta-blocker)
- rapidly reduces tremors and tachycardia
Describe the synthesis of thyroid hormones
- Uptake of iodide via active transport
- Iodination of thyroglobulin (TG) into MIT and DIT
- Coupling reaction of MIT and DIT into T3 and T4: storage in the colloid
- Endocytosis and secretion
What are the unwanted actions of thionamides?
- rashes (common)
- Agranulocytosis (normally a reduction in neutrophils) - rare, and reversible by stopping the drug
How to follow up on the patient using drugs to treat hyperthyroidism?
- aim to stop the anti-thyroid drug treatment after 18 months
- review patient periodically, including thyroid function tests for remission/relapse.
Why are beta-blockers like propanolol involved in treatment plans with anti-thyroid drugs?
Anti-thyroid drugs take several weeks to have clinical effects, therefore non-selective beta-blockers do so in the interim.
When is potassium iodide used?
- in preparation for surgery
- during a thyroid storm (severe thyrotoxic crisis)
- usually in doses >30x daily requirement
- NOT used in patients opting for medical treatment of Graves’
What is the mechanism of action of potassium iodide?
- Actual mechanism is unknown
- Inhibits the iodination of thyroglobulin
- Inhibits hydrogen peroxide generation and thyroperoxidase
What is the impact of potassium iodide in hyperthyroidism?
- inhibition of thyroid hormone synthesis and secretion
- Wolff-Chaikoff effect
- hyperthyroid symptoms reduce in 1-2 days
- vascularity and size of the gland reduce in 10-14 days
What is the Wolff-Chaikoff effect?
presumed reduction in thyroid hormone levels caused by ingestion of a large amount of iodine
What are the risks involved in surgery/thyroidectomy?
- risk of voice change
- risk of parathyroid gland loss
- scarring
- risk involved in anaesthesia
What do people taking radioiodine need to do?
need to avoid children and pregnant women for a few days
When is radioiodine contrindicated?
Pregnancy
What are the symptoms of Viral (de Quervain’s) thyroiditis?
- painful dysphagia
- hyperthyroidism
- pyrexia
- thyroid inflammation
- one-sided visible enlargement of the thyroid gland
What causes Viral (de Quervain’s) thyroiditis?
- virus attacks the thyroid gland causing pain and tenderness
- thyroid stops making thyroxine and makes viruses instead
- therefore no iodine uptake (ZERO)
- stored thyroxine is released
- thus, thyrotoxic with 0 reuptake
- 4 weeks later, stores are exhausted > hypothyroidism
- 8 weeks later, resolution occurs
- patient becomes euthyroid
How does Viral (de Quervain’s) thyroiditis present?
- painful neck
- all stored thyroxine is released
- fT4 levels rise
- TSH levels drop
- 1 month of hyperthyroidism
- no new thyroxine synthesis
- fT4 slowly falls
- patients becomes hypothyroid (thyroid just replicates the virus)
lasts another month - after 3 months, slow recovery
What is the difference between viral (de Quervain’s) thyroiditis and postpartum thyroiditis?
postpartum thyroiditis has no pain, and only occurs post pregnancy
What are thionamides used to treat?
- Grave’s disease
- Toxic nodular thyroid disease
