The thyroid gland is a small, butterfly-shaped gland located in the base of the neck just below the Adam’s apple.
The thyroid produces hormones – chemical messengers that travel via the bloodstream to cells throughout the body, regulating bodily functions. This process is controlled by the hypothalamus and pituitary gland in the brain.
The hormones produced by the thyroid are thyroxine (T4) and triiodothyronine (T3), which affect the body's metabolism and energy level. These hormones regulate carbohydrate and fat metabolism, body temperature and heart rate.
Thyroid-stimulating hormone (TSH, also called thyrotropin) is produced by the pituitary gland; this stimulates the thyroid gland to produce T4 and T3.
Thyroid disorders are very common but, because their symptoms often appear gradually, they are commonly misdiagnosed. There are several types:
- Hypothyroidism: not enough thyroid hormone (underactive thyroid)
- Hyperthyroidism: too much thyroid hormone (overactive thyroid)
- Thyroid nodules: abnormal growths in the thyroid gland. More than 95% are benign (non-cancerous).
- Thyroid cancer: Various types of tumour can develop in the thyroid gland. Most are benign but some are malignant (cancerous).
Causes of hypothyroidism
Globally, iodine deficiency is a major cause of hypothyroidism. However, where there is sufficient dietary iodine, as in most developed countries, a more common cause is a condition called Hashimoto's thyroiditis. (Thyroiditis is inflammation of the thyroid gland, not due to infection). This is an autoimmune disease, in which the individual's own immune system attacks the thyroid gland. Hashimoto’s thyroiditis is most common in middle-aged women, and seems to have a hereditary element.
Other causes may include:
- Surgical removal of thyroid tissue (thyroidectomy)
- Treatment with radioactive iodine or anti-thyroid medications
- Radiation therapy for cancers of the head and neck
- Certain medications, including lithium-based psychiatric drugs
- Less common forms of thyroiditis, such as Quervain's thyroiditis and silent thyroiditis
- Congenital hypothyroidism – a rare genetic disorder
- Pituitary tumours
- Pregnancy. Some women develop hypothyroidism during or after pregnancy (postpartum hypothyroidism).
Although anyone can develop hypothyroidism, you're at greatest risk if you are a woman older than 60. Women are more prone than men to develop hypothyroidism, and generally the incidence of hypothyroidism increases with age.
Causes of hyperthyroidism
The most common cause of hyperthyroidism is Grave's disease. In this condition, the body's immune system releases abnormal antibodies that mimic TSH, stimulating excess production of thyroid hormone. Other causes of hyperthyroidism include:
- Hyperfunctioning thyroid nodules (also called toxic adenoma, toxic multinodular goitre or Plummer's disease). There is excess production of thyroid hormones from the nodules.
- Thyroiditis, which may cause thyroid hormone to leak into the bloodstream from a swollen gland
- Excessive dietary intake of iodine
- Non-cancerous tumours (abnormal growths) on the thyroid gland
- Pituitary tumours
Anyone can develop hyperthyroidism. However, there are certain factors that increase your risk:
- Sex: Women are more likely than men to develop hyperthyroidism.
- Age: hyperthyroidism is more common in people aged 60 and older.
- A family history of hyperthyroidism
- Having certain viral infections
- Pregnancy. Postpartum thyroiditis (hyperthyroidism followed by hypothyroidism) is an uncommon disorder.
- Having had other autoimmune diseases
- Japanese ancestry
The most obvious sign of advanced hypothyroidism is a goitre: a severe enlargement of the thyroid gland. Though usually not uncomfortable, these can obstruct swallowing or breathing and affect appearance. They are more common in women and older people, and are usually caused by a shortage of dietary iodine. Often, goitres disappear with hormone replacement therapy. Some may need to be surgically removed.
Other symptoms of hypothyroidism include:
- Sensitivity to cold; cold hands and feet
- Fatigue, lack of energy
- Weight gain
- Muscle cramps
- Heavy or irregular menstruation
- Confusion, forgetfulness, difficulty thinking or concentrating
- Facial swelling, joint stiffness
- Increased blood cholesterol levels
- Depression and mood swings
- Dry, coarse hair or hair loss; dry skin
- Hoarse voice
Common symptoms of hyperthyroidism include:
- Exophthalmia – bulging eyes, characteristic of Grave's disease.
- Eye discomfort: redness, tearing, swelling, light sensitivity, blurry or double vision, reduced movement, inability to close eyelid.
- Sudden weight loss
- Rapid or irregular heartbeat
- Nervousness, irritability
- Tremors (especially in hands)
- Sleep disturbance
- Heat intolerance
- Changes in appetite
- Frequent bowel motions
- Fatigue and muscle weakness
- Menstrual disturbances, infertility
See your doctor if you have any of the symptoms of thyroid disorder. Your doctor may recommend certain tests to confirm the diagnosis:
- A blood test that measures for levels of thyroid hormone in the blood is the standard test for thyroid dysfunction. Hyperthyroidism would be expected to cause high levels of T4 and T3 and low levels of TSH. Hypothyroidism would cause low T4/T3 and high TSH.
- The fluorescent antinuclear antibody (FANA) blood test detects abnormal antibodies which cause the immune system to attack the body. People with Hashimoto's thyroiditis have positive FANA results with low thyroid hormone levels.
- If ultrasound imaging shows a mass in the thyroid that might be cancer, then the doctor may perform a biopsy with a needle.
- In a nuclear scan, the patient first swallows capsules that contain a radioactive tracer bound to iodine. The scan will then detect which parts of the thyroid gland do not take up the radioactive iodine.
- Thyroid nodules are usually harmless. However, about 4% are cancerous, so your doctor may take a small tissue sample (biopsy).
Complications of thyroid disorders develop if the condition is left untreated or if patients do not follow the prescribed treatment.
- If pregnant women with Hashimoto's thyroiditis do not receive treatment, their babies are more likely to have birth defects and developmental problems.
- If hypothyroidism is not properly treated, individuals have an increased risk of heart disease. The heart may enlarge, and this may lead to heart failure.
- Individuals may suffer from depression or a decrease in sexual desire (libido).
- Rarely, untreated Hashimoto's thyroiditis leads to a life-threatening condition called myxedema. This condition causes swelling of the skin and other tissues, especially near the eyes and cheeks. Symptoms may include extreme drowsiness followed by unconsciousness. Patients with myxedema symptoms should seek immediate emergency treatment.
- Cretinism is caused by insufficient T4. Symptoms include mental retardation, stunted growth, coarse features, a swayback and potbelly, drooling and poorly formed teeth. If a baby is diagnosed and treated within the first few months of life, it has a good chance of normal development.
- Serious complications may include tachycardia (rapid heart rate), congestive heart failure or other heart problems.
- Untreated hyperthyroidism can lead to weak, brittle bones (osteoporosis).
- Graves' disease may affect the skin, causing redness and swelling, often on the shins and feet.
- There is a risk of thyrotoxic crisis: a sudden release of thyroid hormone into the bloodstream, leading to a fever, a rapid pulse and delirium. If this occurs, immediately seek medical care.
- High levels of thyroid hormone may lead to impaired glucose tolerance.
- Artificial hormones, taken orally, make up for decreased thyroid hormone levels. Treatment is life-long, but patients can live normal, healthy lives.
- Individuals should visit their doctor every six to 12 months to monitor hormone levels. Over time, the dosage may be changed. If the dose is too high, individuals may develop osteoporosis (brittle bones) or irregular heartbeats (arrhythmias). Individuals with a history of heart disease, osteoporosis, or severe hypothyroidism may receive smaller doses that are gradually increased.
- Some individuals may develop a goitre that does not respond to hormone therapy, and will need to have their thyroid gland surgically removed (thyroidectomy). You can live healthily without the thyroid gland, although you must must take hormone pills for the rest of your life.
- Taken orally, radioactive iodine is absorbed by the thyroid gland, which it causes to shrink. Symptoms subside, usually in three to six months. Because this treatment causes thyroid activity to slow, patients may eventually need to take daily thyroid hormone medication.
- Anti-thyroid medications gradually reduce symptoms by preventing the thyroid gland from producing excess hormones. Symptoms usually begin to improve in six to 12 weeks, but treatment continues for at least a year. Some patients may later have a relapse.
- Beta blockers will not reduce thyroid levels, but can reduce rapid heart rate and prevent palpitations.
- Thyroidectomy is used in rare cases when the individual cannot tolerate other therapies. A surgeon will remove most of the thyroid gland. Risks include damage to the vocal cords and parathyroid glands, which help control blood calcium levels. Patients need to take thyroid hormone medication for the rest of their lives.
- If the parathyroid glands also are removed, medication will be needed to keep blood-calcium levels normal.
If the biopsy does not show cancer, the nodule is usually monitored over time for changes. Some specialists recommend treatment with thyroid hormone to decrease the size of the nodule. If a nodule is cancerous or suspicious for cancer, or if it interferes with swallowing or breathing, it should be removed surgically.
Adults should be screened for thyroid dysfunction, beginning at age 35 and then every five years. People with symptoms of thyroid dysfunction and those at risk may require more frequent testing.
Iodine in the diet is important to thyroid hormone production. Any type of seafood is a rich source of this element. In Australia, table salt contains high levels of iodine, and Australian bakers are required to use iodised salt in bread. Therefore, further iodine supplements are not recommended: indeed, excess iodine can cause complications.
Pregnant and breast feeding women may require iodine supplementation, but should consult with a doctor.
Regular exercise is important for maintaining healthy hormone levels.