What should I know about the thyroid?
The thyroid is a butterfly-shaped endocrine gland located in the middle of the neck, in front of the trachea, or windpipe. It has two lobes, one on either side of the trachea, below the larynx. The role of the thyroid gland is to produce hormones that are released into the bloodstream to regulate the function of several organs.
Four small and very fragile glands located behind the thyroid – the parathyroid glands – regulate calcium levels in the body.
Two small nerves that control vocal cord movement are attached to either side of the back of the thyroid gland. In some cases, damage to these nerves can result in a modification of the voice.
Regulation of hormone production
Thyroid hormones influence the stimulation of cellular activity, regulating, for instance, heart rate, weight, body temperature, sleep patterns and energy levels. They are essential for the healthy functioning of many vital organs, at all stages of life.
T3, T4, TSH
The two main hormones produced by the thyroid are T3 (triiodothyronine ) and T4 (thyroxine). Two structures in the brain regulate synthesis of these two hormones: the hypothalamus and the pituitary gland. The hypothalamus influences the pituitary gland, which in turn influences the thyroid by secreting TSH, a crucial hormone in the regulation of T3 and T4 hormone secretion. This mechanism ensures a very fine-tuned regulation of thyroid hormones in the blood, thereby enabling the body to function properly.
WHAT ARE THE DIFFERENT THYROID DISORDERS?
Hyperthyroidism is an abnormal increase in thyroid hormone production, resulting in high T3 and T4 levels and a low TSH level. When the thyroid is overactive, it produces too many hormones which in turn cause the organs to become overactive, leading to certain functional disorders. Hyperthyroidism occurs more frequently in women than in men, and the intensity of its many symptoms varies from one individual to the next.
- An autoimmune disease with antibodies that attack the thyroid, causing inflammation (thyroiditis) and hyperactivity of the thyroid (Graves’ disease, and sometimes Hashimoto’s thyroiditis in its early stages)
- Toxic hyperfunctioning thyroid nodule
- Thyroid goiter
- Graves’ disease
This autoimmune disease usually develops in young women between the ages of 20 and 30. The body produces antibodies that stimulate the thyroid gland, causing an overproduction of hormones. The diagnosis is based on a clinical analysis and the presence of hyperthyroidism symptoms such as weight loss, anxiety and an increased heart rate. An ultrasound reveals a diffuse enlargement of the thyroid gland (goiter), while blood tests reveal specific thyrotropin receptor autoantibodies (TRAb) in the blood.
The disorder usually requires medical treatment. Antithyroid drugs are used to block hormone production. These drugs are contraindicated for women hoping to conceive; surgical ablation is proposed as an alternative. In some cases, radioactive iodine therapy (in tablet form) is prescribed.
In 50 percent of cases, the disorder disappears on its own after several months, but the recurrence rate remains high. When treatment is no longer effective, the patient must undergo a thyroidectomy and begin synthetic thyroid hormone therapy.
- Early stages of Hashimoto’s thyroiditis
This illness manifests after antithyroid antibodies are detected. In its early stages, the illness is characterized by hyperthyroidism, after which the gland gradually becomes smaller (hypothyroidism). It is diagnosed using the same method as for hyperthyroidism, and treatment is usually medical.
- Toxic hyperfunctioning thyroid nodule
This is when a thyroid gland nodule increases thyroid hormone production without regulation by the pituitary gland. Often discovered accidentally during a neck palpation, it is diagnosed using a thyroid scan, also known as scintigraphy. The proposed treatment is oral radioactive iodine therapy. The iodine binds to the thyroid gland, or to the adenoma only, and destroys it. Normal thyroid function, known as euthyroidism, gradually returns. Because iodine-131 is a radioactive isotope, it emits radiation and decays spontaneously. Iodine-131 is the firstline treatment in the United States and Canada. In France, it is most frequenly used to treat hyperfunctioning nodules. In the event of recurrence and/or if the patient is trying to conceive, surgical ablation is proposed first.
Hypothyroidism is when secretion of the T3 / T4 thyroid hormones decreases while a negative feedback loop causes TSH production to increase.
When the thyroid is underactive, it produces fewer hormones, meaning the organs are less stimulated and in turn become underactive as well. This disorder usually develops in women after the age of 50.
- Hashimoto’s thyroiditis is the most frequent cause of secondary hypothyroidism
- Certain drugs designed to treat heart disease
Hypothyroidism is diagnosed with an ultrasound and blood tests confirming the presence of antithyroid antibodies.
Treatment consists in taking thyroid hormones. Regular monitoring is necessary to adjust the levels.
97 percent of the time, hypothyroidism (insufficient secretion by the thyroid gland) is treated with a synthetic version of the thyroid hormone thyroxine. Only 3 to 5 percent of patients are treated with a different synthetic hormone of which T4 accounts for 80 percent T3 accounts for 20 percent.
Thyroid nodules are a very common disorder. An estimated 50 percent of the population has a thyroid nodule larger than one centimeter. Several types of nodules exist, and in 90 to 95 percent of cases they are benign.
Micro-nodules: less than one centimeter. They only require monitoring, as they have little chance of being cancerous.
- Hyperfunctioning “toxic” nodules (see above): generally benign.
- Non-functioning nodules: benign tumors that do not produce hormones and are therefore harmless.
- Cancerous nodules: rarer but require surgical removal. Nearly 25 percent of the time, a nodule larger than four centimeters is malignant and needs to be removed without delay. When there is a high number of nodules, the challenge is to detect and eliminate any cancerous cells.
A goiter is a diffuse enlargement of the thyroid gland which may appear as unattractive swelling at the base of the neck.
There are different types of goiter:
- Single goiter: affects four to five percent of the population, is often hereditary and relatively common during adolescence.
- Nodular goiter: increased thyroid volume due to multiple nodules. The risk of cancer rises with the number of nodules. Monitoring becomes increasingly difficult as nodule number and size increase.
What are the risk factors of hyperthyroidism and hypothyroidism?
- The risk factors of hyperthyroidism are a family history of this disorder, iodine deficiency and overexposure to pesticides and chemical pollutants.
- The risk factors of hypothyroidism are a family history of this disorder, iodine deficiency and certain medications.
- Thyroid disease affects more than 15 percent of the French population.
- More than half of all women over 50 have thyroid nodules, which are two to three times more frequent in women than in men.
- Close to five percent of nodules are cancerous.
- Around 4,000 thyroid cancers are detected annually in France. This figure increases continuously, by approximately six percent per year. 40,000 patients undergo thyroid surgery annually.