Hyperthyroidism refers to the condition where the thyroid gland makes too much thyroid hormone. Thyrotoxicosis refers to the condition where there is too much thyroid hormone from any cause.
The symptoms of hyperthyroidism include: preference for cold, increased appetite, weight loss, excessive sweating, anxiety, palpitations and tiredness. Wayne’s index rates the symptoms and signs of hyperthyroidism and is accurate at making a clinical diagnosis of hyperthyroidism.
Hyperthyroidism causes
There are three causes of hyperthyroidism:
- Graves’ disease
- 2. Autonomous functioning thyroid nodule AFTN (autonomous hot nodule)
- Toxic multinodular goitre (toxic MNG).
In hyperthyroidism the TSH is suppressed and the fT4 level is elevated.
Graves’ disease is an autoimmune disease. There are elevated levels of TSH receptor antibodies. It typically affects middle-aged (40–60-year-old) females but can occur at any age and also occurs in men. It is the most common
cause of hyperthyroidism. The eyes are involved in one third of patients and the skin (pretibial myxoedema) is rarely involved. Eye involvement includes
proptosis, extraocular muscle involvement leading to diplopia and optic nerve involvement leading to blindness.
Toxic MNG is usually seen in a long-standing goitre that slowly over time starts to secrete excessive thyroid hormone. It is usually proceeded by compensated hyperthyroidism (suppressed TSH and normal fT4 levels).
Traditionally a radionucleotide thyroid scan is requested to differentiate between the causes of hyperthyroidism. In Graves’ disease there is diffuse homogenous uptake of the isotope. In an autonomous hot nodule there is
localised uptake of the isotope by the nodule with no uptake in the rest of the thyroid gland. In toxic MNG there is heterogenous uptake of the isotope.
An ultrasound scan can frequently differentiate between Graves’ disease, autonomous functioning thyroid nodule and toxic MNG. In Graves’ disease we
see a homogenous mild to moderately enlarged thyroid gland with a markedly increased blood flow (thyroid inferno). In AFTN we see a thyroid nodule in the setting of a low TSH and elevated fT4. In toxic MNG we see an enlarged multinodular thyroid gland in the setting of a low TSH and elevated fT4.
Hyperthyroidism treatment options
There are three main treatment options for hyperthyroidism:
1. Anti-thyroid medication. Carbimazole is the most commonly used medication (initially up to 60mg per day, then reduced slowly down to 10mg per day). Many doctors request liver function tests and a full blood count as a baseline because carbimazole may cause liver dysfunction and agranulocytosis. Patients should be informed to report immediately any fever, mouth ulcers or sore throat so that urgent repeat FBC and liver function tests can be performed. Carbimazole is contraindicated in
the first trimester of pregnancy. Over 50% of patients develop recurrent hyperthyroidism after stopping carbimazole.
2. Radioactive iodine (RAI). RAI takes about six months to work. Following RAI, about 25% of patients develop recurrent hyperthyroidism. RAI may exacerbate eye disease in Graves’ disease. RAI is not particularly effective in large toxic multinodular goitres. Pregnancy should be avoided for 6–12 months after RAI. RAI may cause chronic sialadenitis.
3. Surgery. Surgery is very effective in Graves’ disease, autonomous hot nodules and toxic multinodular goitre. Total thyroidectomy is recommended for both Graves’ disease and toxic MNG. Hemithyroidectomy
is recommended for an autonomous functioning thyroid nodule. Surgery facilitates the treatment of Graves’ eye disease. It is important that the hyperthyroidism is controlled with antithyroid medication prior to surgery
to help prevent a thyrotoxic storm. Potential complications of surgery include injury to the recurrent laryngeal nerve and hypocalcaemia.
Finally, radiofrequency ablation (RFA) is an acceptable treatment for an autonomous hot nodule. It is a scarless procedure performed under local anaesthetic and ultrasound guidance.
If you have further questions about hyperthyroidism that have not been answered here, please email Dr Francis Hall at francis@drfrancishall.co.nz.
References:
1. Karla S, et al. Clinical scoring scales in thyroidology: A compendium.
Indian J. of Endo Metabolism. 2011: 15;S2: S89-94.
2. Campbell K, Doogue M. Evaluating and managing patients with
thyrotoxicosis. Aust. Fam. Physician. 2012; 41(8): 564-572.
3. Kim JH, et al. 2017 Thyroid Radiofrequency Ablation Guidelines: Korean
Society of Thyroid Radiology. Korean J Radiol. 2018; 19(4): 632-655.