Hyperthyroidism Flashcards
What are the causes of hyperthyroidism?
- Grave’s disease
- Plummer’s disease
- Viral (de Quervain’s) Thyroiditis
What is Grav’es disease?
Autoimmune, antibodies bind to and stimulate TSH receptors in thyroid gland. The stimulation of the gland causes growth and forms a smooth goitre.
What are the symptoms of Grave’s disease?
- Lid lag
- Other antibodies bind to muscles behind the eyes and causes an exophthalmos
- Other antibodies cause pretibial myxoedema (hypertrophy) – growth of soft tissue on the shins
What is Plummer’s disease?
Not autoimmune but a benign adenoma.
What are the symptoms of Plummer’s disease?
- Toxic nodular goitre
- No pretibial myxoedema
- No exophthalmos
- Also called a “Hot Nodule” on a thyroid uptake scan
What are the general signs and symptoms of hyperthyroidism?
- Weight loss despite increased appetite
- Dyspnoea
- Palpitations, tachycardia
- Sweating and heat intolerance
- Diarrhoea
- Lid lag and other SNS features
Why does hyperthyroidism cause SNS effects?
Thyroxine sensitises beta-adrenoceptors to ambient levels of adrenaline and noradrenaline (not more adrenaline, just more sensitive receptors).
Leads to SNS activation causing tachycardia, lid lag, etc.
What is Viral Thyroiditis?
Hyperthyroidism to hypothyroidism
- Virus attacks thyroid gland causing pain and tenderness
- Virus then lyses the cell and so thyroxine spills out into the blood (hyperthyroidism) and then the thyroid is not creating thyroxine so the hyperthyroidism becomes hypothyroidism after around a month
- Zero iodine uptake on uptake scan
- After a further month, patient is healthy again
What are the signs/symptoms of viral thyroiditis?
- Painful/tender dysphagia
- Hyperthyroidism
- Pyrexia – fever
- Raised ESR – Erythrocyte sedimentation rate
What is a thyroid storm?
too much thyroid hormones
What are the features of a thyroid storm?
Medical emergency - 50% of untreated die
- Hyperpyrexia – high fever (>41)
- Accelerated tachycardia/arrhythmia
- Cardiac failure
- Delirium/frank psychosis
- Hepatocellular dysfunction, jaundice
What is the treatment for a thyroid storm?
- Surgery (thyroidectomy)
- Radioiodine
- Drugs
What are the types of treatment for thyroid storm?
- Thionamides (thiourylenes; anti-thyroid drugs):
Propylthiouracil (PTU) and Carbimazole (CBZ). - Potassium iodide.
- Radioiodine.
- Beta-blockers.
All inhibit thyroxine synthesis besides last which combats symptoms.
How do thionamides work?
E.G. PTU and CBZ
- Inhibits TPO and peroxidase transaminase
- Suppress antibody production in Graves’
- Reduce T4 to T3 conversion in peripheral tissues (PTU).
How is PTU used?
- Daily treatment of hyperthyroid conditions – e.g. Graves’, Toxic thyroid nodule
- Treatment prior to surgery
- Reduction of symptoms while waiting for radioactive iodine to act
How long do thionamides take to work?
A biochemical effect in hours but no clinical effect until a week or so has passed as there is a large store of normal thyroxine in the thyroid gland that is released for a while.
What other drugs may be given alongside thionamides and why?
The treatment regimen may include propranolol (beta-blocker) to rapidly reduce tremor and tachycardia
What are some unwanted effects of thionamides?
Agranulocytosis – reduction or absence of granular leukocytes
Rashes
What are some of the pharmokinetic features of thionamides?
- Orally active
- Carbimazole is a pro-drug (first is converted to methimazole)
- Plasma half-life of 6-15 hours
- Crosses placenta (secreted in breast milk) – Carbimazole more so than PTU
- Metabolised in liver and secreted in urine
What is the follow up for thionamides?
Stop anti-thyroid treatment after 18 months.
Review patient frequently.
What is iodide treatment and how does it work?
Potassium iodide
- Inhibits iodination of TG
- Inhibits hydrogen peroxide generation
- WOLF-CHAIKOFF EFFECT (ingesting large amounts inhibits thyroid hormone synthesis)
When is iodide treatment used and how long does it take for effects to show?
- Preparation of hyperthyroid patients for surgery
- In severe thyroid storm crisis patients
- Symptoms reduce in 1-2 days
- Size of gland reduce in 10-14 days
What are unwanted side effects of iodide treatment?
Allergic reactions
Describe the pharmakokinetics of iodide treatment
Orally active – Lugol’s solution with maximum effect after 10 days’ continuous administration
When is radioiodine used and how does it work?
Treats hyperthyroidism and thyroid cancers.
Radioiodine accumulates in thyroid and emits beta particles which destroy follicular cells.
What are some cautions that should be taken following radioiodine treatment?
- Contact with small children avoided for several weeks after receiving.
- CONTRA-indicated in pregnancy and breast feeding.
Describe the pharmakokinetics of radioiodine
- Discontinued anti-thyroid drugs 7-10 days’ prior so radioiodine is taken up by thyroid as much as possible
- Administered as a single dose orally
- Radioactive half-life of 8 days
- Radioactivity negligible after 2 months
What is the dose of radioiodine given for Graves and thyroid cancer?
Graves – approx. 500 MBq.
Thyroid cancer – approx. 3000 MBq.
