Hyperthyroidism

The thyroid is a small, butterfly-shaped gland in the front of the neck. It makes hormones that control your metabolism, which is the rate at which your body uses energy. When the thyroid makes too much of these hormones, the condition is called hyperthyroidism, or an overactive thyroid.

With too much thyroid hormone, many body systems speed up. This can affect heart rate, weight, temperature, mood and energy. Symptoms can come on gradually and are sometimes mistaken for stress or other conditions, so a blood test is often needed to confirm the diagnosis.

Common symptoms include unintentional weight loss despite a normal or increased appetite, a fast or irregular heartbeat, feeling anxious, irritable or restless, trembling hands, sweating, sensitivity to heat, difficulty sleeping and tiredness or muscle weakness. Some people have more frequent bowel movements, and women may notice changes in their periods.

The thyroid may become enlarged, causing a swelling in the neck known as a goitre. In Graves' disease, some people develop eye problems such as bulging, gritty or watery eyes. Sudden severe symptoms, including a very high heart rate, fever and confusion, are rare but need urgent medical attention.

The most common cause is Graves' disease, an autoimmune condition in which the immune system stimulates the thyroid to make too much hormone. Another cause is one or more overactive lumps, called nodules, within the thyroid gland.

Hyperthyroidism can also result from inflammation of the thyroid (thyroiditis), which may follow a viral illness or pregnancy, and occasionally from taking too much thyroid hormone medicine or from some medicines and supplements that contain iodine. Identifying the cause helps guide the most suitable treatment.

Hyperthyroidism is diagnosed mainly with blood tests that measure thyroid hormones and a pituitary hormone called TSH. A low TSH with raised thyroid hormones usually confirms an overactive thyroid. Further blood tests can look for the antibodies seen in Graves' disease.

To find the cause, a clinician may examine the neck and arrange imaging, such as an ultrasound scan or a thyroid uptake scan, to see how the gland is working and whether nodules are present. These tests help decide which treatment is likely to work best for you.

There are three main treatments. Anti-thyroid medicines reduce the amount of hormone the thyroid makes and are often used first. Radioactive iodine is a treatment taken by mouth that gradually shrinks the overactive thyroid tissue. Surgery to remove part or all of the thyroid may be advised in certain situations, such as a large goitre or when other treatments are not suitable.

Medicines called beta blockers are sometimes used in the short term to ease symptoms like a fast heartbeat and tremor while other treatment takes effect. Some treatments, particularly radioactive iodine and surgery, can leave the thyroid underactive afterwards, so thyroid hormone replacement and regular blood tests may then be needed.

Hyperthyroidism cannot usually be prevented, but it can be effectively treated. With the right treatment and follow-up, most people have their thyroid levels brought back into a healthy range and their symptoms settle. Because some causes can come back or treatment can change thyroid activity, ongoing monitoring with blood tests is important.

If left untreated, an overactive thyroid can lead to complications such as an irregular heart rhythm, heart problems and weakened bones, and in Graves' disease the eyes may be affected. Getting diagnosed and treated, and attending review appointments, greatly reduces these risks.