Hyperthyroidism

What is it

Hyperthyroidism is when the thyroid is overactive, producing too much thyroid hormone. This results in an increased metabolism. Diagnosis will be made via thyroid function tests and signs of hyperthyroidism.

Signs and symptoms

There are lots of symptoms and signs (clinical markers) of hyperthyroidism and they are dependent on the degree of abnormality of thyroid hormone levels.  As the thyroid controls the rate of metabolism, the effects on the body in the case of an overactive thyroid are wide ranging and result in an "increase" in function of the body. An individual with hyperthyroidism may not have all the following symptoms and signs.

• General: Fatigue,
• Dermatological: Insomnia, increased sweating, clammy skin, hair loss
• Neuromuscular: Hand tremor, muscle weakness
• Psychiatric: Insomnia, anxiety, irritability, hyperactive behaviour, nervousness, difficulty concentrating
• Metabolic: Heat intolerance, weight loss, increased appetite
• Cardiovascular: Palpitations, increased heart rate
• Gastrointestinal: Diarrhoea, more frequent bowel movements
• Endocrine: Irregular menstrual cycle (lighter flow, increased time to next period), amenorrhea (absence of menstrual cycle)
• Exophthalmos (protruding eyes)
• Goitre (swelling of the thyroid, leading to visible swelling of the neck, at the level of the thyroid)

What are the causes?

Hyperthyroidism can be the result of different diseases. The majority of causes are due to the overproduction of thyroid hormones.

    -Graves' Disease is the most common cause of hyperthyroidism. Named after Robert Graves who discovered it, it is an autoimmune disease, where antibodies -which normally fight infection - attack the thyroid. Why antibodies attack the thyroid is unknown. These antibodies bind to thyroid cells, acting like TSH, to stimulate growth and production of thyroid hormones. This results in goitre due to the growth and overproduction of thyroid hormones.

   As it is an autoimmune disease, people with Graves' disease may develop other autoimmune disorders. A recent study showed that those with Graves’ disease had a 9.4% chance of developing another autoimmune disease. Therefore, while the chances of developing another disorder are increased, the majority of people with Graves’ disease will not.

Symptoms specific to Grave's disease include:

• Dermopathy – a skin condition often seen on the lower leg, caused by a build up of carbohydrates. This results in red, swollen skin, with a texture similar to orange peel

• Ophthalmopathy – an inflammatory disorder mainly affecting tissue of the orbit of the eyes and the peritorbital area (around the eyes). Vision is affected subsequently to this; for example people suffer from double vision

Graves' disease has been found to run in families, which suggests a genetic link, although no genes have yet to be identified. Its onset has also been associated with severe stress, such as traumatic life events. However Graves' disease can occur without an episode of severe stress.

Pregnancy and infection have also shown to have links to the development of hyperthyroidism.

Graves' disease does need treatment and left untreated it has the possibility of continual and progressive overproduction of thyroid hormone. Severe cases can lead to a thyroid storm - which is excessive levels of thyroid hormone and is life threatening.

    -Thyroid Nodules are a less common cause of hyperthyroidism.

Nodules are lumps of thyroid tissue that develop, but are benign (i.e. non-cancerous) in 9 out of 10 cases. Why they develop is unknown. Although non-cancerous, they are still abnormal in function, often growing in size. Their increased size leads to increased thyroid hormone production.

Nodules can be multiple or singular. One nodule is referred to as toxic solitary adenoma; multiple nodules are known as toxic multinodular adenoma. Toxic does not here denote poisonous; it is simply used to refer to hyperthyroidism.

Treatment

An endocrinologist – a specialist in disorders of the endocrine system – ultimately decides on the best course of medical treatment.

• Anti-thyroid Drugs

Anti-thyroid drugs tend to be the initial choice of treatment for hyperthyroidism. The main two types of drugs given are Carbimazole and Proplythiouracil. These drugs act to reduce thyroid hormone production, bringing thyroid back to the euthyroid state. Time for these drugs to take effect is normally 2-4 weeks as they act on hormone production, not circulating hormone levels.

    > Carbimazole -, tends to be the preferred ant-thyroid drug prescribed. It is produced in 5mg and 20mg tablets; starting doses   tend to be high and are then reduced. Doses depend on thyroid hormone levels. For further drug information click here

    >Propylthiouracil (PTU) - can be prescribed if patient is deemed unsuitable for Carbimazole or has suffered from side effects. For further drug information click here

It is important to note that Carbimazole and PTU can cause agranulocytosis – a life threatening condition – that reduces white blood cell count, reducing the immune system function. If you are taking either of the above drugs and develop a persistent sore throat and/or mouth ulcer and/or fever, seek an urgent appointment with your GP, who should take a blood test and potentially change the drug you are taking.

Due to potential side effects for these drugs, they are not usually a long term option. In recurrent hyperthyroidism, surgery or radioiodine are often the long term solution.

A treatment option with anti-thyroid drugs and thyroxine is known as 'block and replace'. Thyroid hormone production is almost all blocked, with thyroxine given to replace thyroid function.

Beta blockers such as Propranolol may be given to treat cardiac symptoms.

• Surgery

Surgery is preferred option in recurrent hyperthyroidism in the UK, especially with patients of fertile age. In other countries (such as the USA), radioiodine is the more common option. Surgical removal of part or of the entire thyroid is referred to as a partial or a total thyroidectomy.

Although surgery is developing and recently keyhole thyroidectomies have been performed, it is not common practice.  

The amount of thyroid removed depends on the individual and their condition, but is ultimately up to the surgeon. It is possible that the post-surgical hypothyroidism will result, as surgeons will often err on the side of caution and remove more tissue than may be necessary to prevent reoccurrence. This may result in hypothyroidism. Hypothyroidism is a well managed – although chronic – condition, treated with thyroxin. For more information click here.

The procedure is done under general anaesthetic, and the surgeon will make an incision along the base of the neck, at the level of the thyroid, normally 8cm long. This will result in a scar which will fade over time and won't be noticeable to the majority of people.

Surgery always carries risks, but the risks associated with thyroidectomies are small.

•       Radioiodine

Radioactive iodine is given in the form of tablets or a drink to the patient. After swallowing the radioactive iodine, it is concentrated in the thyroid, which normally functions to absorb all iodine from the bloodstream.

The dose given is dependent on the level of thyroid dysfunction, but will always be medically safe and does not present a danger to a patient. It is not suitable for those who are pregnant, or breast feeding.

There are specific requirements after taking the radioiodine, including isolated contact and specific instructions for 48 hours. Limited contact with certain people must continue 2-4 weeks later, dependent on the level of radioiodine taken.

References

Singer, P.A., et al. Treatment Guidelines for Patients with Hyperthyroidism and Hypothyroidism. Journal of American Medical Association. 1995;273:808–12

Boelaert K, Newby PR, Simmonds MJ, et al. Prevalence and relative risk of other autoimmune diseases in subjects with autoimmune thyroid disease. American Journal of Medicine. Feb 2010;123(2):183.e1-9.

https://www.dundee.ac.uk/medther/tayendoweb/thyroidectomy.htm