The term thyrotoxicosis is sometimes interchanged with hyperthyroidism though their definitions are slightly different.
Thyrotoxicosis is the name given to the clinical effects experienced due to an excess of thyroid hormones in the bloodstream. Hormones produced by the thyroid gland control how fast or slow the body works (metabolic rate). Too much thyroid hormone (thyroxine and triiodothyronine) speeds up the metabolism and results in the signs and symptoms of thyrotoxicosis.
The main cause of thyrotoxicosis is hyperthyroidism, which is an overactivity of the thyroid gland resulting in it producing excess levels of thyroid hormones. If the hyperthyroidism is due to an autoimmune cause, it is called Graves' disease.
Other rarer causes of thyrotoxicosis include excessive intake of thyroid hormone in patients treated for hypothyroidism (an underactive thyroid gland) and sometimes, inflammation of the thyroid gland (thyroiditis), which causes release of large quantities of thyroid hormone into the bloodstream. Other conditions that may cause excessive thyroid hormone production include toxic multinodular goitre and toxic thyroid adenoma (the term ‘toxic’ refers to over-production of thyroid hormones). Certain medications, for example, amiodarone and lithium, can also cause excessive thyroid hormone production.
The symptoms of thyrotoxicosis are a result of the high levels of thyroid hormones in the blood, increasing the metabolic rate. These can include diarrhoea, weight loss (although around 10% develop weight gain due to increased appetite), shaking or tremor (notably in the hands), sweating, increased heart rate that can be felt by the patient (palpitations), overactivity, agitation, anxiety, changes in emotions and feeling hot even though the room may feel cold to everyone else. Patients may also experience an increased heart rate, thinning of the hair, swellings or nodules in the thyroid gland (goitre) or other signs of hyperthyroidism. Some signs are only seen in patients with Graves’ disease (an autoimmune cause) including thyroid eye disease, and rarely, skin changes on the legs and swellings of the finger tips.
Thyroid disease tends to be commoner in women than men (up to 10 times more). Thyrotoxicosis can occur at any age and there is a 1 in 100 chance of a woman developing it in her lifetime and a 1 in 1,000 risk for men. The number of new cases diagnosed each year is 3 per 1,000 women.
The main cause of thyrotoxicosis is hyperthyroidism, which can run in families. However, there is no single gene that is responsible for this condition. Individuals may inherit a greater likelihood of having Graves’ disease, the commonest cause of hyperthyroidism, but if one of the parents is affected, it does not necessarily mean that the children will develop the condition. The other causes of thyrotoxicosis are not known to be inherited.
The diagnosis is based on the combination of symptoms, as described above, together with abnormalities in blood tests used to examine thyroid hormone levels. To diagnose thyrotoxicosis, tests should show raised thyroid hormone levels in the blood (raised thyroxine and/or triiodothyronine) and low, undetectable thyroid stimulating hormone (a hormone released by the pituitary gland that stimulates the thyroid gland to release its hormones). Thyroid stimulating hormone becomes suppressed in this way due to the excessive thyroxine and triiodothyronine already circulating in the body. This is sensed by the pituitary gland, which inhibits it from producing any more thyroid stimulating hormone.
If the patient is suspected of having autoimmune hyperthyroidism (Graves’ disease), an additional blood test to check for thyroid autoantibodies is helpful.
Exact treatment depends on the cause of the condition. There are three main methods of treatment for thyrotoxicosis:
If medication is used to treat the thyrotoxicosis, it is normal for it to take a little time to find the right dose of medication to suit the individual. Therefore, the doctor will request that the patient has regular blood tests, particularly at the start of treatment, so that the levels of thyroid hormones in the blood can be measured and the medication regime altered if levels are too high or too low.
As with most treatments, there are side-effects associated with each of the treatment options:
Long-term implications of treated thyrotoxicosis depend on which of the treatment methods are used, but often result in the need for lifelong medication (thyroid hormone tablets) to be taken daily. Patients on medication should have blood tests taken by their GP at regular intervals to confirm that the dose remains correct. The majority of patients are able to find a medication regime that works well for them and live normal lives.
If untreated, besides feeling poorly and unwell, the patient is also at risk of developing a fast irregular heart beat (atrial fibrillation) which increases the risk of stroke. In extreme cases, patients may develop heart failure due to the rapid irregular heart rate and increased metabolic demand. Long-standing thyrotoxicosis can also affect the patient’s bones and increase the risk of developing osteoporosis, which is associated with an increased risk of fracture (broken bones).
Last reviewed: Mar 2018