The hyperthyroidism refers to an abnormally high production of hormones by the gland thyroid , the butterfly-shaped member located at the base of the neck under the Adam’s apple (see diagram). It is not a swelling of the thyroid, as is sometimes believed.
The disease usually starts in adults between 20 and 40 years old. That said, it can happen at any age, and it can also be seen in children and the elderly. It is less common than hypothyroidism.
The influence of the thyroid gland 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 “motor” of our cells and organs and the rate at which “fuels” will be used: lipids (fats), proteins and carbohydrates (sugars). In people with hyperthyroidism , the motor works in fast motion. They may feel nervous, have frequent bowel movements, shake and lose weight, for example.
At rest, the body consumes energy to maintain its vital functions: blood circulation, brain function, respiration, digestion, body temperature maintenance, etc. This is called basal metabolism, which is partly controlled by thyroid hormones. The amount of energy spent varies from one individual to another, depending on the size, weight, age, sex and activity of the thyroid gland .
The main causes
- Basedow’s disease (or Graves ). This is by far the most common cause of hyperthyroidism (about 90% of cases). This is an autoimmune disease : antibodies excessively stimulate the thyroid to produce more hormones. The disease also sometimes attacks other tissues, such as those of the eyes. This disease affects approximately 1% of the population in Canada.
- Nodules thyroid . Nodules are small masses that form in the thyroid gland, alone or in a group (see our Thyroid Nodule). Not all nodules produce hormones, but those that do (called “toxic”) can cause hyperthyroidism.
- Thyroiditis . If inflammation affects the thyroid, it can also cause an excess of thyroid hormones in the blood. Often, the cause of inflammation is not known. It can be infectious in nature or occur after pregnancy. Usually, thyroiditis causes short-term hyperthyroidism, the thyroid returning to normal functioning after a few months without intervention. Medications can help relieve symptoms until the disease passes. Thyroiditis progresses to permanent hypothyroidism in about 1 in 10 cases.
Note. Some medications , such as those that are high in iodine , can lead to temporary hyperthyroidism. This is the case, for example, amiodarone, prescribed in some cases of cardiac arrhythmia, and iodinated contrast media sometimes injected during a radiology examination.
The hyperthyroidism causes an increased metabolism , thus increasing energy expenditure. In the long term, untreated hyperthyroidism increases the risk of developing osteoporosis because bone absorption is impaired. The risk of developing a type of cardiac arrhythmia called atrial fibrillation also increases.
Untreated major hyperthyroidism can lead to a thyrotoxic crisis . During such a crisis, all signs of hyperthyroidism are combined and 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 emergency medical care.
Diagnostic of hyperthyroidism
The symptoms of hyperthyroidism can be subtle, especially in older people. Only a blood test (see box below) showing both a decrease in TSH levels and a rise in thyroid hormone levels (T4 and T3) will confirm the diagnosis. The onset of symptoms listed below should prompt consultation with a doctor for a safe diagnosis.
|TSH, thyroid hormones T3 and T4 and Co.
The 2 main hormones secreted by the thyroid are T3 (triiodothyronine) and T4 (tetraiodothyronine or thyroxine). Both include the term “iodo” because iodine is essential for their production. The amount of hormones produced depends on other glands. It is the hypothalamus that causes the pituitary gland to produce the thyroid stimulating hormone ( TSH ). In turn, the hormone TSH stimulates the thyroid to produce its hormones.
Hypoactivity or hyperactivity of the thyroid gland can be detected by measuring the level of TSH in the blood. In case of hypothyroidism , the TSH level is high because the pituitary gland reacts to the lack of thyroid hormones (T4 and T3) by secreting more TSH. By this means, the pituitary gland tries to stimulate the thyroid to produce more hormones. In a situation of hyperthyroidism(when there are too many thyroid hormones), the opposite occurs: the TSH level is low because the pituitary gland perceives the excess of thyroid hormones in the blood and stops stimulating the thyroid gland. Even at the very beginning of a thyroid problem, the rate of TSH is often abnormal.
Symptoms of hyperthyroidism
Here are the main symptoms of hyperthyroidism . If the hyperthyroidism is mild, it may go unnoticed. In addition, in the elderly, the symptoms are often less pronounced.
- Fast heart rate (often more than 100 beats per minute at rest) and heart palpitations ;
- Excessive sweating, and sometimes hot flashes
- Fine hand tremors;
- Difficulty finding sleep
- Mood swings;
- Frequent stools
- Muscle weakness;
- A short breath;
- Weight loss despite normal or even increased appetite
- A change in the menstrual cycle;
- The appearance of a goitre at the base of the neck;
- An abnormal protrusion of the eyes out of their orbits (exophthalmos) and irritated or dry eyes, in case of Basedow’s disease;
- Exceptionally, redness and swelling of the skin of the legs, in case of Graves’ disease.
People at risk for hyperthyroidism
- The women are more at risk: Hyperthyroidism affects 8 women to 1 man;
- The frequency of Graves’ disease is higher in families diagnosed with a case of thyroid disorder.
Medicine does not recognize a specific risk factor for hyperthyroidism. In most cases, it is an autoimmune disease (Graves’ disease) whose exact cause is unknown.
Some experts believe that the systematic addition of iodine to table salt would significantly increase the incidence of hyperthyroidism, but only for a minority of people already at risk. The addition of iodine to table salt is to prevent iodine deficiency, which was the main cause of hypothyroidism in the early XX th century.
Prevention of hyperthyroidism
|Can we prevent?|
|There is currently no way to prevent hyperthyroidism.|
|Measures to prevent complications|
Note. Some foods render iodine unusable by the thyroid: this is the case of all cabbage-like plants (cauliflower, broccoli, turnip, rutabaga, mustard and rapeseed), soybean (soybean) , millet, peanut and pine nuts. This effect is attributable to the isothiocyanates they contain. This property may seem interesting for people with hyperthyroidism. However, the isothiocyanate content of these foods is too low to contribute to the treatment of hyperthyroidism. It would be necessary to eat excessive amounts to obtain a therapeutic effect. In addition, cooking inactivates isothiocyanates.
Prevention and relief of eye problems
Medical treatments for hyperthyroidism
As a matter of priority, it is important to recover euthyroidism , ie the normal functioning of the thyroid as soon as possible in order to relieve the patient and avoid complications . Treatment with antithyroid drugs or radioactive iodine generally achieves this goal in a few months, depending on the severity of the hyperthyroidism.
In case of failure of these treatments, surgical removal of the thyroid is sometimes considered.
Each of these solutions has advantages and disadvantages and the person will have to ask his doctor to make the best decision for his case.
These drugs (propylthiouracil or methimazole) prevent the production of new thyroid hormones without causing permanent damage. They restore a normal level of hormones after 2 to 4 months of treatment. Often, the medication should be continued for 1 ½ years. Hyperthyroidism sometimes occurs again.
Radioactive iodine treatment
The radioactive iodine (at low levels) is used to permanently destroy a part of thyroid cells, so that the thyroid gland produces less hormones. Radioactive iodine not absorbed by the thyroid gland will be eliminated by the body in a few days. The treatment allows a return to normal after about 3 to 6 months. In more than 90% of cases, a single dose of radioactive iodine is sufficient (otherwise, a second dose is sometimes offered).
This treatment often causes a permanent state of hypothyroidism. Hypothyroidism is much easier to treat than hyperthyroidism. Synthetic thyroid hormones in the form of tablets taken daily and for life can correct hypothyroidism (Eltroxin, Levothyroid or Synthroid), without causing any adverse effects.
The pregnant women or nursing mothers can not receive such treatment because radioactive iodine can impair the function of the thyroid gland of the fetus or newborn.
|Pregnancy after treatment with radioactive iodine
It is recommended that a woman who wishes to become pregnant wait for 6 to 12 months after radioactive iodine treatment before conceiving a child. Indeed, radioactive iodine can affect the development of the fetus.
In addition, it is preferable that the thyroid hormone levels of the future mother be well controlled before pregnancy. Thyroid hormone requirements generally increase in the first trimester of pregnancy (weeks 1 to 13). For pregnant women taking synthetic hormones, monitoring of the level of TSH hormone in the blood each quarter with a family doctor or endocrinologist is necessary. After delivery, the dosage is often lowered.
For its part, a man who receives radioactive iodine treatment should wait 3 months before conception.
Ablation of the thyroid
Total or partial removal of the thyroid gland by surgery (thyroidectomy) may be considered, but is rarely used.
To relieve specific symptoms , other medications are sometimes used as needed. To relieve heart palpitations and reduce heart rate and tremors, beta-blocking medications are sometimes prescribed (for example, propranolol).
The eye disorders that accompany Graves’ disease, when severe, may require treatment with corticosteroids (to reduce inflammation behind the eye) or surgery (to reduce pressure in the eye). It could be that smokers respond less well to these treatments . Moreover, it is strongly recommended not to smoke in case of ocular symptoms caused by Graves’ disease.