Hyperthyroidism Flashcards
What inhibits TRH and therefore TSH?
T4 and T3
What is Graves’ disease?
Autoimmune
Antibodies bind and stimulate the TSH receptor in the thyroid
Causing a smooth goitre and hyperthyroidism
What are common 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 Plummer’s disease and Graves’ disease?
Plummers is:
- not autoimmune
- no pretibial myxoedema
- no exophthalmos
- non-symmetrical and non-diffuse goitre
What is Plummer’s disease?
Characterised by:
- toxic nodular goitre
- benign adenoma (overactive) produces excess thyroxine
How does thyroxine impact the sympathetic nervous system?
It sensitises beta adrenoreceptors to the ambient levels of adrenaline and noradrenaline - causing apparent sympathetic activation.
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 (>41)
- 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 hormones involves in thyroid hormone synthesis?
- Thyroperoxidase
- 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-blockers)
rapidly reduces tremors, and tachycardia
Describe the synthesis of thyroid hormones
- Uptake of iodide via active transport
- Iodination
- Coupling reaction: storage in the colloid
- Endocytosis and secretion
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 (>41)
- 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 hormones involves in thyroid hormone synthesis?
- Thyroperoxidase
- Peroxidase transaminase
What is the mechanism of action of thionamides?
The inhibition of thyroid peroxidase and therefore T3/4 synthesis and secretion
When is radioiodine contrindicated?
Pregnancy
What drug often accompanies thionamides in a treatment plan?
Propanolol
rapidly reduces tremors, and tachycardia
Describe the synthesis of thyroid hormones
- Uptake of iodide via active transport
- Iodination
- Coupling reaction: 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-thhyroid 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
What is the mechanism of action of potassium iodide?
- 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?
A presumed auto-regulatory effect
What are the risks involved in surgery/thyroidectomy?
- risk of voice change
- risk of parathyroid gland loss
- scarring
- risk involved in anaesthesia
What is the process involved in radioiodine?
- swallow a capsule containing 370MBq (10mCi) of the isotope I (131)
- need to avoid children and pregnant mums for a few days
- for scans ONLY: 99-Tc pertechnetate is an option
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, toxic 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
