Thyrotoxicosis (hyperthyroidism, Graves' disease) is a condition in which the thyroid gland produces excess thyroid hormone (thyroxine) which results in effects on the whole body.

The thyroid gland, which is in the front of the neck, controls the rate of at which the body's cells work (the metabolic rate). In thyrotoxicosis, the rate of metabolism is increased, and this results in most of the symptoms:

• weight loss in spite of increased appetite
• rapid heart rate
• a fine tremor
• increased nervousness and emotional instability
• intolerance of heat, and excessive sweating
• staring, bulging eyes
• enlargement of the thyroid gland, which is at the front of the neck, at the level of the voice box

Most often the cause seems to be the body developing an immune reaction against itself, in this case the parts of the thyroid cells which normally act as the receptors for thyroid stimulating hormone (TSH), which is the hormone coming from the gland hanging beneath the brain (the pituitary gland).

This hormone normally stimulates the thyroid to produce thyroxine, so antibodies bound on to these receptors cause production of thyroid hormone, and because it attaches to these receptors better than TSH would, more thyroxine than usual is produced.

In the presence of symptoms such as some or all of those above, your doctor is likely to arrange for a blood test to check on the amount of thyroid hormone (thyroxine) and other tests, looking at other hormones which control or are produced by the thyroid gland. These tests are collectively known as thyroid function tests.

In thyrotoxicosis the level of thyroid hormone is elevated, and the hormone (thyroid stimulating hormone, TSH) that is produced by a gland hanging from the underside of the brain (pituitary gland) to drive the thyroid gland, is almost undetectable.

Especially if the thyroid gland is enlarged and has lumps in it, an ultrasound scan or a scan which involves the injection of radioactive technetium (⁹⁹Tc which tends to concentrate in the thyroid), a radio-isotope scan, may be arranged.

Your doctor is likely to prescribe medication known as a thiourea drug (carbimazole, methimazole or propylthiouracil) that will reduce the output of hormone from the thyroid.

This starts off at quite a high dose, and the dose comes down slowly once the blood test returns to normal. Usually most people are able to come off the tablets after a year or two, but sometimes the tablets need to be continued for longer, or restarted.

Sometimes your doctor may prescribe another type of medication, a beta blocker, to overcome some of the worst symptoms of an over-active thyroid gland, while waiting for the specific treatment for the thyroid to take its effect.

Sometimes, in certain cases, a surgical procedure is recommended, to remove part of the thyroid gland. This is known as a partial thyroidectomy. Removing part of the overactive gland results in a drop in the amount of hormone that it produces.

Another treatment that is sometimes used is the injection of radioactive iodine (¹³¹I, a longer lasting isotope than is used for scanning) which is concentrated in the thyroid gland and results in damage to, and destruction of, some of the cells of the thyroid.

Thyroid eye disease

The effects of thyrotoxicosis on the eyes are usually minimal, but when more severe can lead to excessive bulging of the eyes and weakness of the eye muscles. In extreme cases this can put the vision at risk, and specialist treatment is required.

For most people with thyrotoxicosis all that is required is treatment to reduce the excessive levels of thyroid hormone.

After the acute period of this condition, when you may have frequent blood tests, it is important to have a blood test done at regular intervals, as recommended by your doctor.

This is to make sure that you do not develop an over active thyroid again, and also because many people who have thyrotoxicosis later develop an underactive thyroid gland (hypothyroidism).

• American Thyroid Association

Books

Thyroid Disease: The facts, by R I S Bayliss, W M G Tunbridge (Oxford University Press)

Aimed at patients with thyroid disease and their relatives, this book offers an authoritative account of the symptoms, causes and treatments of the various ailments of the gland.

Understanding Thyroid Disorders (BMA Family Doctor Books), by Dr Anthony Toft

Reference source on thyroid disorder, providing case histories, key points, questions, answers, and practical tips for overcoming problems.