Hyperthyroidism Flashcards
What is hyperthyroidism?
A biochemical diagnosis which occurs when there is pathologically increased thyroid hormone production and secretion by the thyroid gland.
What is thyrotoxicosis?
Thyrotoxicosis is the clinical manifestation of excess circulating thyroid hormones due to any cause, including hyperthyroidism.
What is primary hyperthyroidism?
Primary hyperthyroidism occurs when thyrotoxicosis is caused by an abnormality of the thyroid gland such as Graves’ disease.
What risk factors are associated with hyperthyroidism?
- Female
- Family history
- Smoking
- Low iodine intake
- Autoimmune disease
What are the causes of thyrotoxicosis with hyperthyroidism (increased thyroid hormone synthesis)?
- Grave’s disease
- Toxic multinodular goitre
- Toxic thyroid nodule (adenoma)
- High concentrations of human chorionic gonadotrophin (hCG)
- Iodine
What are the causes of thyrotoxicosis without hyperthyroidism (increased availability of preformed thyroid hormone)?
- Thyroiditis
- Exogenous thyroid hormone
What is Grave’s disease?
This is the most common cause of hyperthyroidism in iodine-sufficient areas, accounting for about 80% of cases. It is a systemic autoimmune disorder mediated by thyroid-stimulating hormone (TSH)-receptor antibodies (TRAbs) that stimulate the TSH receptor, leading to thyroid hyperplasia and unregulated excessive production and secretion of thyroid hormone.
What are the signs of hyperthyroidism?
- Agitation, fine tremor, warm moist skin and palmar erythema
- Sinus tachycardia, atrial fibrillation, heart failure and peripheral oedema
- Thyroid enlargement (a goitre)
- Pruritus, urticaria, vitiligo and diffuse alopecia
- Muscle wasting, proximal myopathy and hyper-reflexia
- Gynaecomastia in men
What are the symptoms of hyperthyroidism?
- Rapid-onset malaise, fever and thyroid pain
- Compression symptoms of breathlessness, hoarse voice and dysphagia
- Agitation, emotional lability, insomnia, irritability, anxiety and palpitations
- Exercise intolerance, fatigue and muscle weakness
- Heat intolerance and increased sweating
- Increased appetite with unintentional weight loss and diarrhoea
- Subfertility, oligomenorrhoea and amenorrhoea
- Polyuria, thirst and generalized itch
- Reduced libido and gynaecomastia in men
What investigations should be ordered for hyperthyroidism?
- TSH
- Serum free or total T3
- Serum free or toral T4
- Calculation of T3/T4 or T3/T4 ratio
Why investigate TSH? And what may this show?
- Initial screening test
- TSH level is below the normal reference range
Why investigate serum free or total T3? And what may this show?
- If the TSH level is below the normal reference range, the free thyroxine (FT4) and free triiodothyronine (FT3) levels should be measured in the same sample
- T3 levels are raised above the normal reference ranges
Why investigate serum free or total T4? And what may this show?
- If the TSH level is below the normal reference range, the free thyroxine (FT4) and free triiodothyronine (FT3) levels should be measured in the same sample
- T4 levels are raised above the normal reference ranges
What test needs to be done if Grave’s diease is suspected?
TSH-receptor antibodies (TRAbs)
When is a thyroid ultrasound used in investigating hyperthyroidism?
Arrange an ultrasound of the neck to image palpable thyroid enlargement or focal nodularity.
Highly sensitive for detection of thyroid nodules.
What are the treatment options for hyperthyroidism?
- Antithyroid drugs
- Radioactive iodine treatment
- Thyroid surgery
Briefly describe the use of antithyroid drugs
Antithyroid drug treatments (carbimazole and propylthiouracil) are used to decrease thyroid hormone synthesis, by acting as a preferred substrate for iodination by thyroid peroxidase, the key enzyme in thyroid hormone production.
Antithyroid drugs should only be initiated on specialist advice, and are typically used:
- Short-term to restore euthyroidism in preparation for definitive treatment with radioactive iodine treatment or thyroid surgery
- Medium-term with the aim of inducing remission of Graves’ disease
- Long-term if radioactive iodine treatment or surgery is contraindicated or declined
Give examples of drugs used in antithyroid treatment
Carbimazole and propylthiouracil
Briefy describe the use of radioactive iodine treatment
Radioactive iodine treatment induces damage of DNA leading to death of thyroid cells, causing a decrease in thyroid function and/or reduction in thyroid size.
It is a first-line definitive treatment for adults with Graves’ disease and those with toxic multinodular goitre.
Briefly describe the use of thyroid surgery
Options include total thyroidectomy, or hemithyroidectomy for a single thyroid nodule, in people:
- To prevent the recurrence of hyperthyroidism
- With compression symptoms from a large toxic multinodular goitre
- With a co-existing potentially malignant thyroid nodule
- Who have not tolerated antithyroid drug treatment or it is ineffective, especially in pregnancy or active Graves’ orbitopathy, or if radioactive iodine treatment is unsuitable
What are the complications of hyperthyroidism?
- Graves orbitopathy
- Thyrotoxic crisis (thyroid storm)
- Atrial fibrillation
- Heart failure
- Osteoporosis
What can trigger a thyrotoxic crisis?
May occur after a trigger such as acute infection, trauma, pregnancy, surgery including thyroidectomy or stroke.
It may occur in people with previously undiagnosed hyperthyroidism or those who have abruptly stopped antithyroid medication.
What are the clinical features of thyrotoxic crisis?
linical features reflect systemic decompensation and include fever, tachycardia, agitation, hyperthermia, hypertension, atrial fibrillation, heart failure, jaundice, delirium and coma.
The mortality rate is estimated at about 10% due to hyperthermia, cardiac arrhythmias, multi-organ failure and sepsis.
