Hypothyroidism
L’hypothyroidism is the consequence of a production ofhormones insufficient by the gland thyroid, this butterfly-shaped organ located at the base of the neck, under the Adam’s apple. The people most affected by this condition are women after 50 years.
The influence of the gland thyroid on the body is major: its role is to regulate the basic metabolism of the cells of our body. It controls energy expenditure, weight, heart rate, muscle energy, mood, concentration, body temperature, digestion, etc. It thus determines the intensity of the energy that makes our cells and organs work. In people with hypothyroidism, this energy works in slow motion.
At rest, the body consumes energy to keep its vital functions active: blood circulation, brain function, breathing, digestion, maintaining body temperature. This is called the basic metabolism, which is partly controlled by thyroid hormones. The amount of energy expended varies from individual to individual depending on the size, weight, age, gender, and activity of the thyroid gland. |
In Canada, about 1% of adults havehypothyroidism, the women being 2 to 8 times more affected than men. The prevalence of the disease increases with age, reaching more than 10% after age 6014. In France, 3,3% of women and 1,9% of men are affected by hypothyroidism (source: HAS: summary of professional recommendations 2007).
Congenital or neonatal hypothyroidism
In about 1 in 4 babies, hypothyroidism is present from birth due to a malformation or dysfunction of the thyroid gland. If left untreated, thehypothyroidism congenital has serious consequences on the physical and mental development of the child. Fortunately, in France, Canada and other developed countries, this disease is systematically detected in all newborns, thanks to a blood test developed in the mid-1970s by Canadian researchers. This screening allows treatment to be initiated from the first days of life to prevent the consequences of the disease.1.
Thyroid hormones under control The 2 main ones hormones secreted by the thyroid are T3 (triiodothyronine) and T4 (tetra-iodothyronine or thyroxine). Both understand the term “iodine” because iodine is one of their component, essential for their production. The amount of hormones produced is under the control of other glands, located in the brain: the hypothalamus and the pituitary gland. The hypothalamus commands the pituitary gland to produce the hormone TSH (for thyroid stimulating hormone). In turn, the hormone TSH stimulates the thyroid to produce thyroid hormones, including T3 and T4. An underactive or overactive thyroid gland can be detected by a blood test to measure the level of TSH in the blood. In hypothyroidism, the TSH level is high because the pituitary gland responds to the lack of thyroid hormones (T3 and T4) by secreting more TSH. In this way, the pituitary gland tries to stimulate the thyroid to produce more hormones. In a situation of hyperthyroidism (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. |
Causes
Before the 1920s, the iodine deficiency was the main cause ofhypothyroidism. Iodine is a trace mineral necessary for life and for the production of the thyroid hormones T3 and T4. Since adding iodine to table salt – practice born in Michigan in 1924 because of the many cases of hypothyroidism – this deficiency is rare in industrialized countries. However, according to estimates from the World Health Organization, nearly? 2 billion people are still at risk of iodine deficiency12. It remains the number 1 cause of hypothyroidism in the world. In industrialized countries where people are asked to limit salt intake, there may be a risk of recurrence of iodine deficiencies.
Nowadays, main causes hypothyroidism in industrialized countries are:
- A Hashimoto’s thyroiditis. This autoimmune disease causes the destruction of the thyroid gland by the immune system. Scientists cannot explain what triggers this disease. It would sometimes appear as a result of stress or a viral infection, in people who are predisposed to it.
- Un treatment that alters the thyroid gland. Radioactive iodine treatment to treat a hyperthyroidism or surgery to remove the thyroid gland (due to a nodule, tumor or thyroid cancer) causes permanent hypothyroidism in about 80% of cases. Also, a treatment of radiotherapy neck causes transient hypothyroidism in about 50% of cases, and permanent hypothyroidism in about 25% of cases.
- A postpartum thyroiditis. In 8-10% of women, an autoimmune reaction against the thyroid can occur a few weeks to a few months after thedelivery15. This is called “postpartum” thyroiditis. In 40% of cases, this thyroiditis leads to hypothyroidism, the symptoms of which are more or less marked. They are most often transient.
Other rarer causes
– Some pharmaceuticals. Lithium, for example, used for certain psychiatric disorders, or amiodarone (a medicine containing iodine), prescribed for heart rhythm disturbances, can lead to hypothyroidism.
– An abnormality congenital of the thyroid gland, that is to say present from birth. Sometimes the gland does not develop normally, or it functions poorly. In this case, hypothyroidism is detected a few days after birth thanks to the systematic blood test.
– A malfunction of thepituitary gland, the gland which regulates the thyroid by the hormone TSH (represents less than 1% of cases).
– A infection bacterial or viral to the thyroid gland.
– See the People at risk and Risk factors sections.
Possible complications
Left untreated, the disease can have serious long-term consequences. In adults, a myxoedème, a severe form of hypothyroidism, can occur. Symptoms of myxedema are a puffy face, yellowing, and dry skin, which appears thickened. In severe cases, certain conditions (infection, cold, trauma, surgery, etc.) can cause loss of consciousness or coma “Myxedematous”. In addition, studies suggest that people withhypothyroidism for several years are at greater risk of cardiovascular disease.
In untreated children, there are significant delays in growth and irreversible intellectual development, commonly called cretinism. Adequate treatment, initiated quickly, usually avoids complications and sequelae.