Disorders of the thyroid function

The butterfly-shaped thyroid gland absorbs iodine from the blood and uses it to produce vital hormones for the body’s metabolism. An overactive or underactive thyroid throws this interaction out of balance. Read more about the causes, symptoms and treatment of an underactive or overactive thyroid here.

Functions of the thyroid hormones

The thyroid hormones triiodothyronine and thyroxine have essential functions in the body. They increase the basal metabolic rate, which increases cardiac work, body temperature and tissue oxygen consumption. They increase sensitivity to the stress hormone adrenaline and support muscle protein build-up. In addition, growth and maturation of the central nervous system are promoted, which is particularly important during pregnancy and childhood.

Like other hormones, their production is subject to a control loop. Suppose their concentration in the blood is too low. In that case, the upper regulatory authority in the brain’s hypothalamus sends the messenger substance TRH to the pituitary gland, which releases another hormone, thyrotropin (TSH). After about 10 seconds, this reaches the thyroid with the message to produce hormones or to release existing hormones stored in the depots of the 3 million thyroid follicles into the blood.

The organization of this process in the thyroid takes about 20 minutes, and the thyroid hormones in the blood are on their way to their destinations. Another hormone produced in the thyroid gland is calcitonin, which, along with a few others, regulates blood calcium levels.

 

Thyroid function: enough, too much, too little hormones

There are a variety of diseases or changes that affect thyroid function. For example, acute or chronic inflammation, thyroid gland enlargement (goitre or goitre), autoimmune diseases such as Graves’ disease or Hashimoto’s thyroiditis, or cancerous diseases of the thyroid gland itself can affect its function. However, disturbances in the control centres, for example, caused by a brain tumour, can also affect the thyroid gland.

• Overactive thyroid (hyperthyroidism):  The cause of increased production and release of thyroid hormones is almost always in the thyroid. Sometimes, areas that produce hormones independently of the regulatory circuit (thyroid autonomy) develop in one place or diffusely. If these areas are too large or too active, the down-regulation of the healthy areas is no longer sufficient to compensate for the increased levels of hormones.
• Another fairly common cause is Graves’ disease, an autoimmune disease in which substances are produced in the body that act like TSH and thus stimulate the thyroid gland to make it independently of need. An overproduction of thyroid hormones can also occur at the beginning of an inflammation of the thyroid gland as a result of a thyroid tumour or an overdose of thyroid hormone tablets (which are sometimes dangerously taken as a laxative ).
• Thyroid hypofunction (hypothyroidism):  A lack of thyroid hormones can be congenital (cretinism), caused by maternal iodine deficiency during pregnancy or a faulty thyroid system. Inflammation, operations and radioiodine therapies of the thyroid gland, as well as medication, can also lead to hypofunction. With certain brain tumours, the release of thyrotropin and, thus, of the thyroid hormones can be reduced. Such disorders, where the cause does not lie directly in the thyroid gland itself, are also referred to as secondary hypothyroidism.

How are functional disorders manifested?

The increased or absent hormone effects cause complaints and symptoms. In overactivity, the expected effects of T3 and T4 increase to unhealthy levels; in underactivity, the opposite effects occur. The effects are diverse but unspecific and often less pronounced with age.

• Hyperthyroidism:  Many sufferers have an enlarged thyroid. Typical symptoms are a rapid and irregular pulse, trembling hands, sensitivity to heat, and a tendency to sweat. The skin tends to be warm and moist, and bowel movements are frequent and loose as signs of increased metabolic activity and weight loss despite increased appetite and hair loss. The muscles can hurt, and menstrual disorders often occur in women. Those affected are nervous and irritable and suffer from insomnia. If Graves’ disease is the cause, visual disturbances and eye changes (“glaring” with protruding eyes) can also occur.
• Hypothyroidism: A lack of thyroid hormones leads to a slow heart rate, enlarged heart, sensitivity to cold, decreased appetite, and weight gain. The skin is cool and dry; the hair becomes thin and fuzzy, the voice hoarse and rough. Blood cholesterol levels are often elevated. Menstrual disorders can also occur here. Those affected often appear slowed down and sluggish or depressed, which can lead to a misdiagnosis, especially in older people. 
• Congenital hypothyroidism causes intellectual disabilities and developmental delays, gait and posture disorders, short stature and facial deformities. The babies are lazy about drinking and moving about and suffer from constipation. Fortunately, this clinical picture has become quite rare in industrialized countries due to the monitoring and administration of iodine during pregnancy and the screening TSH test in the early diagnosis examination after birth.

 

How is the diagnosis made?

First, the doctor will take the medical history and feel the thyroid to see if it is enlarged or nodular. Ultrasound provides further information on the size and condition, and a tissue sample may also be taken.

It is essential to check for hormone changes in the blood. Depending on the suspected cause, other hormones and possibly their release after stimulation and antibodies against the thyroid tissue can also be determined in the blood. Metabolic activity and function of the thyroid gland can be assessed using scintigraphy, in which radioactively marked substances are injected, and their storage in the thyroid tissue is recorded with unique cameras and displayed in colour.

What therapy is there?

• Treatment for hyperthyroidism depends on the underlying cause. Possibilities are drugs that inhibit the function (hydrostatic) and operations, for example, the removal of affected areas, or radioiodine therapy, in which radioactively treated iodine is given, which leads to the death of thyroid tissue.
• In the case of hypofunction, artificial thyroid hormones in tablet form must be taken for life. It starts with a low dose and slowly increases. Once the hormone levels in the blood have normalized, the patient must see their doctor once a year.

Adequate therapy and reasonable hormone control are vital for both diseases. Otherwise, in certain situations, such as serious illnesses or operations, a life-threatening condition can occur (“thyrotoxic crisis” or “myxedema coma”), which can lead to death even under intensive medical care. Therefore, those affected should take their medication reliably and visit their doctor regularly.

How to prevent it?

An adequate supply of iodine through the diet is essential to prevent an enlargement of the thyroid gland due to iodine deficiency. Iodized salt and sea fish are good sources. Possibly, iodide can also be taken in the form of tablets, especially during pregnancy and breastfeeding. However, it would help if you clarified this with your doctor.