5. Hyperthyroidism Flashcards
Two common causes of hyperthyroidsim
- Grave’s Disease
- Nodular goitre (Plummer’s Disease)- A benign tumour that produces thyroxine
Causes of Grave’s disease
An autoimmune disease
Antibodies bind to and stimulate the TSH receptor in the thyroid
The stimlation leads to the thryoid gland becoming smoothly enlarged (goitre) and results in hyperthyroidism
Presentation of Grave’s patient
- The patient will be overactive and anxious with a rapid pulse due to raised basal metabolic rate
- Patient is warm with localised pretibial myxoedema- growth of soft tissue in the skin
- Exophthalamos- antibodies bind to growth receptors behind the eye so that the muscles ituated there grow and push it forwards
Imaging using radioactive iodine will show that the whole thyroid is overactive
Cause of Plummer’s disease
This is a toxic nocualr goitre- a bit of the thryoid gland has become tumerous- a benign adenoma
NOT autoimmune- no pretibial myxoedema, no exophthalmos
May be a lump on one side of the neck due to a tumerous growth
Presentation of Plummer’s patients
Iodine scan will show concentrated activity around the hot tumour
Overproduction of thyroxine coming from the tumerous part of the thryoid causes the pituitary to stop producing TSH, so that the functional part of the thyroid shrinks and stops producing thyroxine
Sometimes patients may have a multinodular goitre which is relatively common
Effects of thyroxine on the sympathetic nervous system
SENSITISES beta adrenoceptors to ambient levels of adrenaline and noradrenaline
So patients with hyperthyroidism will also show signs of hyperadrenal disorder
Summary of common hyperthyroid symptoms
- Weight loss despite decreased appetite
- Breathlessness
- Palpitations, tachycardia
- Sweating
- Heat intolerance
- Diarrhoea
- Lid lag and other sympathetic features
Thyroi storm features and treatment options
A thyroid storm is a medical emergency- a rare and severe complication of hyperthyroidism
50% mortality if left untreated- heart failure or arrhythmia
Features:
- hyperpyrexia> 41 degrees
- tachycardia/ arrhythmia HR> 170
- cardiac failure
- delirium
- jaundice
Requires aggressive treatment by surgery, radiodine or drugs
Classes of drugs used in the treatment of hyperthyroidism
- Thionamides- Propylthiouracil, carbimazole
- Potassium iodide
- Radioiodine
- Beta-blockers
When are thionamides used
- To control hyperthyroidism before thyroidectomy because you dont want to give general anaesthetic to someone who is tachycardic with a labile HR
- Following radioactive iodine treatment since the reatment takes awhile to have an effect
Review of thyroid hormone synthesis
Main actors are thyroperoxidase (iodination of tyrosine) and peroxide transaminase (coupling of mono/diiodotyrosine)
Thionamides mechanism of action
thionamides inhibit thyroperoxidase and hence the iodination of of thyroglobulin- reduction in secrtion of thyroid hormones
Also reduces deiodinisation of T4 to T3 in peripheral tissues
Biochemical effects of inhibition takes hours, but clinical effects only seen after weeks- STORED T4 in lumen of follicles
Manage symptoms in short term by using beta blockers etc.
Unwanted actions of thionamides
- Agranulocytosis/ glanulocytopenia (reduction or abscence of leukocytes)- reversible
- Rashes
- Headaches
- Nausea
- Jaundice
- Joint pain
Carbimazole can cross th placenta and is scereted in milk- can cause foetal hypothyroidism- propylthiouracil does this less
Carbimazole activation
carbimazole is a pro-drug which must be converted to methianazole to be active
Role of beta blockers in hyperthyroidism treatment
NON-SELECTIVE beta blockers can be used to reduce stimulation of sympa system by T4
Mechanism of Action of iodine treatment
An autoregulatory phenomenon- the thyroid rejects the ingested iodine (30 times normal amount) and causes temporary inhibition of thyroglobulin iodination
Quicker effect than anti-thyroid drugs- useful for pre surgery
Wolf-Cahikoff effect
the temporary reduction in thyroid hormones following ingestion of large amounts of iodine
Unwanted effects of iodine treatment
ALLERGIC REACTIONS:
- rashes
- fever
- angioedema
How is iodine given in iodine treatment?
- Orally
- AS Lugol’s solution or aqueous iodine
Treatment of Grave’s, Plummer’s, Thyroid cancers (radioiodine)
When given in high doses, 131I, radioiodine can permanently switch off the thyroid.
From the colloid the absorbed iodine emits beta particles, breaking down the thyroid follicles
Contra indicated in pregnancy and breast feeding
Pharmacokinetics of radioiodine
Discontinue anti thyroid drugs 7-10 days before treatment (more likely to absorb iodine)
Single oral dose:
- Grave’s= 500MBq
- Thyroid cancer= 3000MBq
Half-Life= 8 days- negligable after 2 months
Use of technetium 99 pertechnetate in radioiodine treatment
Much cheaper
Used for thyroid uptake scans
Results of scan:
- Graves’ - the entire thyroid gland is active and smoothly enlarged
- Plummer’s/Toxic Nodule - single focus of activity and the rest is supressed
- Thyroiditis - unhappy, inflamed thyroid gland where there is NO activity at all
Viral Thyroiditis cause, symptoms, diagnosis
This disease is caused by a virus attacking the thyroid gland and causing fever- damages thyroid follicles and all stored thyroxine is released- So patient actually presents with overactive thyroid
Symptoms:
- malaise
- painful dysphagia
- tender pretracheal lymph nodes
- pyrexia (fever)
Can be diagnosed using a technetium scan: will show nothing, since the thyroid is not actually producing any new thyroxine
After 4 weeks the stored thyroxine will run out
After another month, the cells will have recovered and will start to produce thyroxine again so they will return to normal
