Hyperthyroidism Flashcards
What are the causes of hyperthyroidism?
- Graves’ disease
- Nodular goitre (Plummer’s disease) - benign thyroxine-producing tumour
- Viral thyroiditis
What are the clinical features of hyperthyroidism
- Weight loss despite increased appetite
- Breathlessness
- Palpitations, tachycardia
- Sweating
- Heat intolerance
- Diarrhoea
- Lid lag
How is hyperthyroidism diagnosed?
- Thyroid function tests: low TSH, high T3/T4
- Scintigram
How is hyperthyroidism treated?
- Thionamides (thiourylenes, anti-thyroid drugs) - propylthiouracil (PTU), carbimazole (CBZ) - daily treatment before thyroidectomy + following radioactive iodine treatment
- Potassium iodide
- Radioiodine
- Non-selective beta blocker (propranolo) - to manage symptoms short-term as thionamides don’t affect the stored thyroid hormone
- Attempt to stop anti-thyroid drug after 18 months + review periodically (TFTs) for remission/relapse
How do thionamides work?
- Inhibit thyroperoxidase
- Tf inhibit iodination of thyroglobulin + coupling of iodotyrosines
- Net result = reduction in synthesis + secretion of thyroid hormones
- Also reduces deiodination of T4 to T3 in peripheral tissues
- Anti-thyroids may also suppress antibody production in Graves’
What are the side effects of thionamides?
- Agranulocytosis/granulocytopenia
- Rash
- Headache
- Nausea
- Jaundice
- Joint pain
How does potassium iodide treatment help hyperthyroidism?
- Give dose 30x average daily requirement
- High dose to turn thyroid gland off
- Inhibits iodination of thyroglobulin + H202 generation
- Temporary reduction in thyroid hormones following ingestion of large amounts of iodine
- Thyroid rejects ingested iodinde + hence prevents gland sucking up loads of iodine + making too much thyroid hormone
- Symptoms reduce within 1-2 days
- Useful for pre- surgery - reduces size + vascularity of thyroid in couple of weeks
What is the problem with giving thionamides to pregnant women?
- Crosses placenta and secreted in milk
- Patients can conceive on drug but must get dose as low as possible
- High doses could cause foetal hypothyroidism
How do you differentiate between Graves’ disease and other causes of hyperthyroidism?
Plummer’s disease:
- Gland may be unilaterally enlarged or multinodular
- Technetium/iodine scan shows iodine going into hot nodule (where tumour is) + rest of thyroid can’t be seen
Graves’:
- Pretibial myxoedema + exapthalmos
- Goitre - large, smooth thyroid gland
- Scintigram after giving radioactive iodine will show whole thyroid gland being active
Viral thyroiditis:
- Painful dysphagia
- Raised erythrocyte sedimentation rate
- Technetium scan shows NOTHING - bc no iodine uptake
What are the clinical features of a thyroid storm?
- Hyperpyrexia >41 degrees
- Accelerated tachycardia/arrhythmia
- Cardiac failure
- Delirium/ frank psychosis
- Hepatocellular dysfunction, jaundice
What are the unwanted effects of iodide treatment?
Allergic reaction: rash, fever, angioedema
What is radioiodine 131 used for?
- To treat Graves’, Plummer’s + thyroid cancer
- Permanently switches off thyroid w/o surgery
- Relies on the fact that thyroid gland takes up iodine to make thyroid hormone –> thyroid follicular cells take up radioactive iodine and it accumulates in colloid
- From colloid, it emits beta particles of radiation that destroy follicular cells
What are the unwanted effects of radioiodine treatment?
- Discomfort in neck
- Contra-indicated in pregnancy and breast feeding
Why is propylthiouracil better than carbimazole for breast-feeding women?
Propylthiouracil doesn’t cross into breast milk as much as carbimazole
Lower risk of causing foetal hypothyroidism
