Thyroid Stimulating Hormone

How is thyroid disease discovered?

As with any disease, it is important that you watch for the early warning signs. However, only your doctor can tell for sure whether or not you have thyroid disease. He or she can measure the amount of thyroid hormones in your blood, as well as look at the structure and function of your thyroid gland. If a nodule is found, your doctor can test whether or not it is cancerous.

What are the signs and symptoms of thyroid disease?

When your doctor examines you for thyroid disease, he or she should first ask about your symptoms and then check for physical signs. Your doctor will ask questions about your memory, emotions, or menstrual flow, and then check your heart rate, muscles, skin, and thyroid gland.

Which blood tests will my doctor use?

After a physical examination, your doctor may examine certain hormone levels in your blood. The most common tests check the levels of thyroid hormones (T₄ and T₃) and thyroid stimulating hormone (TSH). Your doctor may also perform a test with an injection of thyrotropin releasing hormone (TRH). If your doctor suspects Hashimoto’s thyroiditis or Graves’ disease, he or she will probably test you for antithyroid antibodies or thyroid stimulating antibodies.

What does the radioactive iodine uptake show?

Iodine is an important building-block for thyroid hormones. Your doctor may give you a small amount of radioactive iodine and then measure the amount absorbed by the thyroid gland. If the thyroid absorbs a lot of this iodine, you may be hyperthyroid. Low iodine uptake may signal hypothyroidism or thyroiditis.

Why is the structure of my thyroid important?

Examining the structure of your thyroid gland and the surrounding area tells your doctor about a lump (nodule) which may be cancerous or enlargement of the thyroid (goiter).

Which tests look at the structure of my thyroid?

• A thyroid image (or scan) shows the size, shape, and function of the gland. It uses a radioactive chemical, usually iodine or technetium, which the thyroid absorbs from the blood. A special camera then creates a picture, showing how much chemical was absorbed by each part of the gland. The test shows the size of the thyroid and tells whether lumps are hot (usually benign) or cold (either benign or malignant). The scan is frequently done at the same time as the radioactive iodine uptake.
• In needle aspiration biopsy, a small needle is inserted into the nodule in an effort to suck out (aspirate) cells. If the nodule is a fluid-filled cyst, the needle often removes some or all of the fluid. If the nodule is solid, several small samples are removed for examination under the microscope. Over 90% of the time, this testing tells the doctor whether the nodule is cancerous or not.
• Ultrasound uses high-pitch sound waves to find out whether a nodule is solid or filled with fluid. About 10% of nodules are fluid-filled cysts, and they are usually not cancerous. Ultrasound may also detect other nodules that are not easily felt by the doctor. The presence of multiple nodules reduces the likelihood of cancer.

How does radioactive iodine work?

The thyroid gland absorbs iodine from the blood. When radioactive iodine enters your thyroid, it slowly shrinks the gland over a period of weeks or months.

The treatment is safe, simple, convenient, and inexpensive. It is usually given only once, rarely causes any pain or swelling, and does not increase the risk of cancer. However, it must be avoided during pregnancy or nursing, and patients should not become pregnant for at least six months after treatment.

When is radioactive iodine used?

Radioactive iodine is the most common treatment for hyperthyroidism. It does not require hospitalization. About 90% of patients need only one treatment. They usually start getting better in three to six weeks, and most are cured within six months.

This treatment may also be used after surgery for certain thyroid cancers. Radioactive iodine dissolves any cancerous tissue that could not be removed by surgery. The dose of radioactive iodine is larger in this case, and patients usually stay in the hospital for a day or two.

What can be expected with radioactive iodine treatment for hyperthyroidism?

• It is usually given in liquid form or as a capsule. The dose can range from 4 to 29 millicuries.
• It is tasteless.
• There are almost never any side effects. In some rare cases, there can be an inflammation of the thyroid gland causing a sore throat and discomfort.
• Radioactive iodine not taken up by the thyroid gland is excreted in urine and saliva. There is no evidence that the small amount of I¹³¹ excreted in the urine and saliva is harmful. Nonetheless, prudent nuclear medicine experts have recommended a wide variety of precautions. While these recommendations are sometimes confusing and inconsistent, it may be appropriate to take a few simple measures to avoid unnecessary exposure of infants and children to I¹³¹. Treated patients should rinse out their glasses or cups and eating utensils immediately after drinking and eating. The toilet should be flushed immediately after use, and the rim of the bowl should be wiped dry, if necessary.
• It is advisable to drink two to three extra glasses of water a day during the four- to seven- day period following radioactive treatment so that radioactive material will not collect in the bladder for a long period of time.
• Because radioactive iodine passes into breast milk, breast feeding mothers are asked to wean their babies before treatment.
• It typically takes six weeks before thyroid hormone production is noticeably reduced. The average length of time for the thyroid hormone levels to become normal is about three to four months. If thyroid levels are not considerably reduced six months after treatment, the doctor might suggest repeating the treatment. Ninety percent of the time only one treatment is required; however, it might take as many as three attempts. The patient could be advised to take beta-blocking drugs and other medications the doctor believes are necessary until normal thyroid hormone production is restored.
• Many patients treated with radioactive iodine become hypothyroid. This may happen within weeks, months, or years of treatment. Therefore, patients should be aware of the signs and symptoms of hypothyroidism, and their physicians should monitor their thyroid hormone levels regularly. When the patient becomes hypothyroid, thyroid hormone replacement begins and continues for life-one pill a day.

What do antithyroid drugs do?

Antithyroid drugs block pathways leading to thyroid hormone production.

Antithyroid drugs used in this country are Propylthiouracil (PTU) and Tapazole®. Some physicians will recommend antithyroid medication as a first line of treatment to see if the patient is one of the lucky 30% of patients who go into a remission after taking antithyroid medication for one to two years. (Patients are said to be in remission if their hyperthyroidism does not recur after discontinuing the antithyroid drugs.) If antithyroid drugs do not work for the patient, then physicians usually recommend radioactive iodine.

Antithyroid drugs are also used to treat very young children, older patients with heart conditions, and pregnant women. For severe or complicated cases of hyperthyroidism, especially in older patients, PTU or Tapazole® can be given for four to six weeks to bring the hyperthyroidism under better control prior to administering radioactive iodine treatment.

In cases when women are diagnosed with Graves’ disease while they are pregnant, PTU is prescribed. The smallest dose possible is given because the medication does cross over to the fetus. The mother should be checked every three to four weeks during the pregnancy so that the lowest possible dose can be given. Too much PTU can cause fetal goiter, hypothyroidism, and mental retardation.

® Tapozole is a registered trademark of Jones Medical Industries.

Are there any side effects?

Antithyroid drugs cause side effects in about 10% of patients. Reactions can include:

• skin rash
• swollen, stiff, painful joints
• sore throat and fever
• low white blood count, which can lead to serious infections
• jaundice (yellow coloring of the skin) and, rarely, liver failure.

Most side effects clear up once the drugs are stopped. If you think you are having a reaction to anti-thyroid drugs, call your doctor immediately.

What can be expected with antithyroid drug treatment?

• Several pills are taken from one to four times a day, every day for six to 24 months.
• Some patients complain that the pills have an unpleasant smell and taste.
• There is usually some symptom relief within one to two weeks. In some cases, it can take several months to relieve symptoms.
• Antithyroid drugs have a relatively low success rate. While PTU or Tapazole® may correct the problem temporarily or for a few years, the chances of a permanent remission are about 30% once the drugs are stopped.
• The likelihood of achieving a permanent remission is increased if the patient takes the medication for one to two years.
• There are side effects in 10% of the people treated with Tapazole® or PTU. These are:
  • skin rash over most of the body swollen, stiff, painful joints
  • sore throat and fever — if this happens, the antithyroid drugs should be stopped immediately and the physician contacted
  • jaundice
  • liver damage, which is fatal in rare cases
• Because antithyroid drugs pass into breast milk, only PTU in a dosage less than 200 mg a day is advised if the baby is not weaned.
• Within 15 years, the thyroid gland may burn out, resulting in hypothyroidism, and the patient will need thyroid hormone replacement.