Hyperthyroidism
THEhyperthyroidism denotes abnormally high production ofhormones by the gland thyroid, this butterfly-shaped organ located at the base of the neck, under the Adam’s apple (see diagram). It is not a swelling thyroid, as is sometimes believed.
The disease usually starts in adults between the ages of 20 and 40. However, it can occur at any age, and it is also seen in children and the elderly. It is less common than hypothyroidism.
The influence of the gland thyroid on the body is major: its main role is to regulate the metabolism of the cells of our body. It therefore determines the speed of the “engine” of our cells and organs and the rate at which “fuels” will be used: lipids (fat), proteins and carbohydrates (sugars). In people in hyperthyroidism, the engine runs in accelerated mode. They may feel nervous, have frequent bowel movements, shake and lose weight, for example.
Basic metabolism At rest, the body consumes energy to keep its vital functions active: blood circulation, brain function, breathing, digestion, maintaining body temperature, etc. This is called the basal metabolism, which is partly controlled by thyroid hormones. The amount of energy expended varies from one individual to another, depending on the size, weight, age, sex and activity of the person. thyroid gland. |
Causes
The main causes
- Graves’ disease (or by Graves). It is by far the most common cause of hyperthyroidism (around 90% of cases7). This is an autoimmune disease: antibodies over-stimulate the thyroid to produce more hormones. The disease also sometimes attacks other tissues, such as the eyes. This disease affects approximately 1% of the population in Canada7.
- Thyroid nodules. Nodules are small masses that form in the thyroid gland, alone or in groups (see our Thyroid Nodule sheet). Not all nodules produce hormones, but the ones that do (called “toxic”) can lead to hyperthyroidism.
- thyroiditis. If inflammation affects the thyroid, it can also cause excess thyroid hormones in the blood. Often, the cause of the inflammation is not known. It can be infectious in nature or occur after pregnancy. Usually, thyroiditis causes short-lived hyperthyroidism, with the thyroid returning to normal function after a few months, without intervention. Medication can help relieve symptoms while you wait for the disease to pass. Thyroiditis progresses to hypothyroidism permanent in about 1 in 10 cases.
Note. Some pharmaceuticals, like those who are rich in iodine, can lead to temporary hyperthyroidism. This is the case, for example, with amiodarone, prescribed in certain cases of cardiac arrhythmia, and iodinated contrast agents sometimes injected during a radiology examination.
Possible complications
L’hyperthyroidism causes a accelerated metabolism, therefore an increased expenditure of energy. In the long term, untreated hyperthyroidism increases the risk of developing osteoporosis because the absorption of calcium from the bones is affected. The risk of developing a type of heart arrhythmia called atrial fibrillation also increases.
Untreated major hyperthyroidism can lead to thyreotoxic crisis. During such an attack, all the signs of hyperthyroidism come together and are expressed at their peak, which can lead to serious complications, such as heart failure or coma. The person is confused and agitated. This situation requires urgent medical attention.
Diagnostic
The symptoms hyperthyroidism can be subtle, especially in older people. Only one blood analyse (see box below) showing both a drop in TSH hormone levels and an increase in thyroid hormone levels (T4 and T3) will confirm the diagnosis. The onset of the symptoms listed below should prompt you to seek medical attention in order to obtain a sure diagnosis.
TSH, thyroid hormones T3 and T4 and Co The 2 main ones hormones secreted by the thyroid are T3 (triiodothyronine) and T4 (tetra-iodothyronine or thyroxine). Both include the term “iodo” because theiodine is essential for their production. The amount of hormones produced depends on other glands. It is the hypothalamus that controls the pituitary gland to produce the hormone TSH (for thyroid stimulating hormone). In turn, the hormone TSH stimulates the thyroid to produce its hormones. You can detect an underactive or overactive thyroid gland by measuring the level of TSH in the blood. In case of’hypothyroidism, the TSH level is high because the pituitary gland responds to the lack of thyroid hormones (T4 and T3) by secreting more TSH. In this way, the pituitary gland tries to stimulate the thyroid to produce more hormones. In situation ofhyperthyroidism (when there is too much thyroid hormone) the reverse happens: the TSH level is low because the pituitary gland perceives the excess thyroid hormones in the blood and stops stimulating the thyroid gland. Even at the very beginning of a thyroid problem, TSH levels are often abnormal.
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