Goiter (GOI-tur) is an abnormal enlargement of your thyroid gland. Your thyroid is a butterfly-shaped gland located at the base of your neck just below your Adam’s apple. Although goiters are usually painless, a large goiter can cause a cough and make it difficult for you to swallow or breathe.
The most common cause of goiter worldwide is a lack of iodine in the diet. In the United States, where the use of iodized salt is common, a goiter is more often due to the over- or underproduction of thyroid hormones or to nodules that develop in the gland itself.
Treatment depends on the size of the goiter, your symptoms and the underlying cause. Small goiters that aren’t noticeable and don’t cause problems usually don’t need treatment.
In some parts of the world, the prevalence of the condition can be as high as 80 per cent – such populations tend to be in remotely mountainous areas of southeast Asia, Latin America and central Africa, where daily intake of iodine can fall below 25 micrograms a day and children are often born with hypothyroidism.
The thyroid gland needs iodine in order to manufacture thyroid hormones, which regulate the body’s rate of metabolism.
The main cause of goiter in developed countries is autoimmune disease.4 Women over the age of 40 are at greater risk of goiter, as are people with a family history of the condition.
Hypothyroidism is the result of an underactive thyroid gland, and this causes goiter. Because the gland produces too little thyroid hormone, it is stimulated to produce more, leading to the swelling. This usually results from Hashimoto’s thyroiditis/disease, a condition in which the body’s immune system turns on itself and causes inflammation within the thyroid gland.
Hyperthyroidism is also a cause of goiter – from an overactive thyroid gland, which produces too much thyroid hormone. This usually happens as a result of Graves’ disease, also an autoimmune disorder in which the body’s immunity turns on itself and attacks the thyroid gland, causing it to swell.
Less common causes of goiter include the following:
- Nodules – benign lumps, single or multiple
- Smoking – thiocyanate in tobacco smoke interferes with iodine absorption
- Hormonal changes – pregnancy, puberty and the menopause can affect thyroid function
- Thyroiditis – inflammation caused by infection, for example
- Lithium – the psychiatric drug can interfere with thyroid function
- Overconsumption of iodine – too much iodine can cause goiter, just as too little does
- Radiation therapy – particularly if to the neck.
The thyroid gland is controlled by thyroid-stimulating hormone (TSH; also known as thyrotropin), secreted from the pituitary gland, which in turn is influenced by the thyrotropin-releasing hormone (TRH) from the hypothalamus. TSH permits growth, cellular differentiation, and thyroid hormone production and secretion by the thyroid gland. Thyrotropin acts on TSH receptors located on the thyroid gland. Thyroid hormones are synthesized from iodination of tyrosine. The iodine is transported from plasma into the thyroid cell via a sodium-iodide symporter. This is an active process resulting in an intracellular iodine level exceeding 20 times the plasma iodine level. This iodine transport activity is controlled by TSH. Serum thyroid hormones levothyroxine and triiodothyronine feed back to the pituitary, regulating TSH production. Interference with this TRH-TSH thyroid hormone axis causes changes in the function and structure of the thyroid gland. Stimulation of the TSH receptors of the thyroid by TSH,TSH-receptor antibodies, or TSH receptor agonists, such as chorionic gonadotropin, may result in a diffuse goiter. When a small group of thyroid cells, inflammatory cells, or malignant cells metastatic to the thyroid is involved, a thyroid nodule may develop.
A deficiency in thyroid hormone synthesis or intake leads to increased TSH production. Increased TSH causes increased cellularity and hyperplasia of the thyroid gland in an attempt to normalize thyroid hormone levels. If this process is sustained, a goiter is established. Causes of thyroid hormone deficiency include inborn errors of thyroid hormone synthesis, iodine deficiency, and goitrogens.
A goiter may result from a number of TSH receptor agonists. TSH receptor stimulators include TSH receptor antibodies, pituitary resistance to thyroid hormone, adenomas of the hypothalamus or pituitary gland, and tumors producing human chorionic gonadotropin.
Not all goiters cause signs and symptoms. When signs and symptoms do occur they may include:
- A visible swelling at the base of your neck that may be particularly obvious when you shave or put on makeup
- A tight feeling in your throat
- Difficulty swallowing
- Difficulty breathing
Your doctor may discover an enlarged thyroid gland simply by feeling your neck and having you swallow during a routine physical exam. In some cases, your doctor may also be able to feel the presence of nodules.
Diagnosing goiter may also involve:
- A hormone test. Blood tests can determine the amount of hormones produced by your thyroid and pituitary glands. If your thyroid is underactive, the level of thyroid hormone will be low. At the same time, the level of thyroid-stimulating hormone (TSH) will be elevated because your pituitary gland tries to stimulate your thyroid gland to produce more thyroid hormone.
Goiter associated with an overactive thyroid usually involves a high level of thyroid hormone in the blood and a lower than normal TSH level.
- An antibody test. Some causes of goiter involve production of abnormal antibodies. A blood test may confirm the presence of these antibodies.
- Ultrasonography. A wand-like device (transducer) is held over your neck. Sound waves bounce through your neck and back, forming images on a computer screen. The images reveal the size of your thyroid gland and whether the gland contains nodules that your doctor may not have been able to feel.
- A thyroid scan. During a thyroid scan, you’ll have a radioactive isotope injected into the vein on the inside of your elbow. You then lie on a table with your head stretched backward while a special camera produces an image of your thyroid on a computer screen. The time needed for the procedure may vary, depending on how long it takes the isotope to reach your thyroid gland. Thyroid scans provide information about the nature and size of your thyroid, but they’re more invasive, time-consuming and expensive than are ultrasound tests.
- A biopsy. During a fine-needle aspiration biopsy, ultrasound is used to guide a needle into your thyroid to obtain a tissue or fluid sample for testing.
Goiter treatment depends on the size of the goiter, your signs and symptoms, and the underlying cause. Your doctor may recommend:
- Observation. If your goiter is small and doesn’t cause problems, and your thyroid is functioning normally, your doctor may suggest a wait-and-see approach.
- Medications. If you have hypothyroidism, thyroid hormone replacement with levothyroxine (Levothroid, Synthroid) will resolve the symptoms of hypothyroidism as well as slow the release of thyroid-stimulating hormone from your pituitary gland, often decreasing the size of the goiter. For inflammation of your thyroid gland, your doctor may suggest aspirin or a corticosteroid medication to treat the inflammation. For goiters associated with hyperthyroidism, you may need medications to normalize hormone levels.
- Surgery. Removing all or part of your thyroid gland (total or partial thyroidectomy) is an option if you have a large goiter that is uncomfortable or causes difficulty breathing or swallowing, or in some cases, if you have nodular goiter causing hyperthyroidism. Surgery is also the treatment for thyroid cancer. You may need to take levothyroxine after surgery, depending on the amount of thyroid removed.
- Radioactive iodine. In some cases, radioactive iodine is used to treat an overactive thyroid gland. The radioactive iodine is taken orally and reaches your thyroid gland through your bloodstream, destroying thyroid cells. The treatment results in diminished size of the goiter, but eventually may also cause an underactive thyroid gland.
Hormone replacement with the synthetic thyroid hormone levothyroxine then often becomes necessary, usually for life