Family doctor

What is the thyroid gland?

The thyroid gland is a small organ in the neck, just below the Adam's apple. Its job is to make a chemical called a hormone. The thyroid hormone is named thyroxine. A normal amount of thyroxine is required for normal physical and mental development. For this reason all babies in New Zealand are screened at birth for the presence of possible thyroid hormone deficiency. In adults, thyroxine keeps cells and tissues working at just the right metabolic rate. Too much thyroxine put out by an overactive thyroid causes an illness with a high metabolic rate called hyperthyroidism. Too little thyroxine from an underactive gland causes an illness with a low metabolic rate called hypothyroidism.

Goitre is the name given to a visible swelling of the thyroid gland in the neck. The goitre is usually normally active. That is, the thyroxine level in the blood is normal and the metabolic rate is normal. Most goitres cause no general symptoms and can often by ignored. Some people with a goitre may be advised to have simple diagnostic tests to find out exactly what kind of goitre it is and to test for the unlikely possibility of a low-grade cancer. Fortunately cancer of the thyroid is very rare. When it does occur it is nearly always low grade, can be removed by surgery, and has a much better outlook than most other types of cancer.

Virtually all forms of thyroid disease can be easily treated resulting in good health. If left untreated, however, underactive or overactive glands can cause years of severe ill health or even death. After the initial assessment you may be asked to return to the clinic for follow-up in conjunction with your own doctor.

Hyperthyroidism (an overactive thyroid)

The exact cause of an overactive thyroid is unknown. The common form results from unusual antibodies circulating in the blood stream which stimulate the thyroid(Grave's Disease). Overactivity is not caused by stress or changes in the diet. It may wax and wane in an individual over a period of years. Women are more often affected than men and thyrotoxicosis may appear for the first time three to six months after pregnancy.

Hyperthyroidism affects different people in different ways. Many experience weight loss (despite increased appetite), tiredness, nervous symptoms and a dislike of hot weather. Shakiness of the hands and awareness of a rapid heart beat and difficulty sleeping are also common. Hyperthyroidism is a prolonged illness which, if untreated, can have severe consequences. Everyone who has it needs treatment. Careful supervision by a doctor is also required, usually for many years.

Treatment of hyperthyroidism

There are three different ways to treat an overactive thyroid:

1. Antithyroid tablets (Carbimazole, Propylthiouracil, PTU)

Once the diagnosis is made, most people are given tablets, usually 3 tablets morning and night. If you take them regularly, there is a marked improvement of symptoms in most people after three to four weeks. These tablets act as a brake on the thyroid by blocking an enzyme in the gland. In themselves the tablets don't make the unknown cause of hyperthyroidism go away. But by taking the tablets for one or more years, the disorder may then disappear by itself as mysteriously as it came, just with the passage of time. You will enjoy excellent health as long as the tablets are taken and the level of thyroxine is monitored by a blood-test. If you forget a dose you can 'double-up' with the next dose. Even after a year or more of treatment however, on stopping the tablets hyperthyroidism returns in nearly two thirds of patients, sometimes within weeks. In a minority, about one third, there may be no return of symptoms even for years.

When beginning treatment with antithyroid drugs, most people suffer no ill effects. Rarely (one in every thousand people), an important side effect may develop because of lowering of the white cell count in the blood. The symptoms of this side effect may include a sore throat, mouth ulcers or high fever and usually begin within two to six weeks of starting treatment. If you experience these effects while taking antithyroid tablets, you must contact your doctor immediately. It is stressed that this is a rare occurrence but it is important to be on the alert for it as your doctor can arrange measurement of your while blood count and the effect is rapidly reversed by stopping treatment.

A more minor but irritating side effect in about 3 percent is an itchy red skin rash which also usually develops within two to six weeks of starting the tablets. This rash sometimes goes away by itself and the tablets can be continued but if it persists, you should stop the pills and contact your doctor for further advice. Often it is possible to switch to the alternate drug. Antithyroid tablets, either carbimazole or PTU, can safely be taken under supervision during pregnancy and breast feeding. Fortunately an overactive thyroid often subsides during pregnancy, only to return 2 to 6 months after delivery.

2. Radioactive Iodine (Radioiodine)

Radioiodine treatment is often recommended once the overactive thyroid is brought under control with tablets. The great advantage of radioiodine is that it is given at an outpatient visit, as a single tasteless drink. It has little or no side effects but smoothly and painlessly cures the thyroid condition. Radioiodine is the most common form of treatment worldwide and has been in safe and effective use for 50 years.

Naturally, none of us likes the idea of taking in radioactive substances unless it is absolutely necessary. In the case of radioiodine given under a doctor's prescription, there is no cause for alarm. The radiation dose is concentrated in the thyroid - other parts of your body receive very little. In fact, most of the radioactivity is excreted in the urine. Because it is radioactive iodine, there are some precautions necessary in the first few days of treatment.

Precautions following radioiodine treatment

Radioactive iodine is not given to pregnant women. Although there is no evidence of harm to family members, we advise against intimate or prolonged body contact for 2 to 4 days after treatment. Babies and children in particular, are thought to be more sensitive to unnecessary exposure to radiation.

The nature and duration of precautions will depend on the recommended dose and your family or job circumstances. More specific precautions as they apply to you will be discussed and written down by the clinic doctor.

After radioiodine treatment

The radioiodine does most of its work over the first 4 to 6 weeks but continued benefits such as shrinkage and disappearance of the goitre continue for about 6 months. If you are taking antithyroid tablets, you will be asked to stop them 5 days before therapy and restart one week afterwards and continue until your first follow-up visit. Usually you will be asked to continue monitoring blood tests at 2-4 week intervals, until the results are stable. Sometimes a second radioiodine treatment is needed in about a quarter of individuals for a complete cure.

An expected effect of treatment is that the thyroid gland may become underactive in as many as one half in the first year. If this occurs it will be necessary for you to take thyroxine tablets. This is a small inconvenience to ensure continued normal thyroid function but you will need to take thyroxine on a lifelong basis. At the same time, you will be discharged from the clinic to the care of your GP who will provide a three monthly prescription of thyroxine tablets and arrange an occasional blood test to ensure that your dose of thyroxine tablets is suitable.

Even if thyroid gland function remains normal in the first year of treatment, a regular annual blood test of thyroid function is necessary indefinitely because an underactive thyroid can still happen many years after radioiodine treatment.

3. Surgery

Rarely, neither tablet or nor radioiodine treatment is suitable and thyroid surgery may be recommended. About three quarters of the gland is removed. There are definite risks to surgery and because of the safety and simplicity of radioiodine, operations are infrequent nowadays.