Excessive hormone production by the thyroid gland is called hyperthyroidism.
Hyperthyroidism, the main cause of which is Graves’ disease, is the condition where there is an inappropriate functioning of the thyroid gland (also called the thyroid), leading to an excessive production of hormones.
To understand hyperthyroidism you have to understand what the thyroid gland is and what it is for. For this, I suggest reading the text first: DISEASES AND SYMPTOMS OF TIREOID.
If you are looking for information about hypothyroidism (low thyroid function) the text indicated is this: HYPOTHYDROID (HYPOTHYDROID HASHIMOTO)
WHAT IS HYPERTREOIDISM?
The thyroid produces two hormones called triiodothyronine and thyroxine, better known as T3 and T4. These hormones control our metabolism and are responsible, among others, for our caloric expenditure, for body temperature, for our weight gain, etc.
Read the next two paragraphs calmly, following the figure below.
The pituitary or pituitary gland is an organ that is located at the base of the brain and controls the degree of thyroid function through a hormone called TSH (Thyroid Stimulating Hormone). The presence of TSH in the blood stimulates thyroid function; The absence of TSH inhibits it.
When there is little circulating thyroid hormone, the pituitary gland detects this fall and immediately increases the secretion of TSH, stimulating a greater production of T3 and T4 by the thyroid. When there is too much circulating hormone, it decreases TSH secretion, discouraging the thyroid to produce T3 and T4. Thus, the body is able to keep its metabolism always at an ideal level.
Hyperthyroidism occurs, therefore, when there is an excess of T3 and T4 in the circulation that can not be corrected by the normal mechanisms. This can occur in 2 ways:
1- A problem in the pituitary causing it to become uncontrollable and produces a lot of TSH, which in turn stimulates the thyroid to produce T3 and T4 indefinitely.
When the cause of hyperthyroidism is central, ie a malfunctioning pituitary, we will have a very high TSH associated with a very high T4.
2- The thyroid becomes an independent organ, producing T3 and T4 at its pleasure, ignoring the levels of blood TSH.
When the problem is in the thyroid itself, the first thing the pituitary does when it detects high levels of hormones is to stop production of TSH. Therefore, we will have a very low TSH, but still a very high T4.
Note: in clinical practice we measured the free T4 (T4L), which is the fraction of the chemically active hormone.
→ To learn more about TSH, T3 and T4, read: TSH AND T4 FREE – Thyroid exams.
SYMPTOMS OF HYPERTIREOIDISM
Regardless of the cause, the symptoms of hyperthyroidism are always caused by the excess of circulating T4L, which is a common consequence, either by central problem or in the thyroid itself.
Excessive thyroid hormone may cause:
- Anxiety and irritability.
- Weight loss without loss of appetite (sometimes there is increased appetite).
- Tachycardia = increase in heart rate above 100 beats per minute.
- Cardiac arrhythmias.
- Tremors in the hands.
- Retraction of the eyelids.
- Sweating and excessive heat.
- Loss of muscle strength.
- Diarrhea or increased number of bowel movements.
- Decrease or cessation of menstruation.
Goiter, the last sign described above, occurs when there is enlargement of the thyroid gland. This growth is common when there is a permanent stimulus for production of T3 and T4, and can be clinically noted as a bulging in the neck.
The most common cause of hyperthyroidism is Graves’ disease. This disease is an autoimmune process (read: AUTO-IMUNE DISEASE) where the body improperly produces antibodies against the thyroid itself. These antibodies actually attack the TSH receptors, causing the thyroid to think that there is too much TSH in the bloodstream. The end result is an excessive release of thyroid hormones.
Severe disease is 8 times more common in women and usually occurs between 20 and 40 years of age.
In addition to all the signs and symptoms described above, Graves ‘hyperthyroidism may present the so-called Graves’ ophthalmopathy.
The antibodies attack not only the thyroid, but also the muscles and fatty tissue around the eyes. This aggression causes injury and edema of the extraocular muscles, leading to a protrusion of the eye, in addition to swelling and inflammation around it (periorbital edema).
Patients with Graves’ ophthalmopathy may also have double vision, constant eye irritation, eye pain, blurred vision and, in more severe cases, blindness.
Some people have naturally more protruding eyes. In addition, too much thyroid hormone excess can lead to a retraction of the eyelid. However, in Graves’ ophthalmopathy the protrusion is so important that it is possible to see the whites of the eyes (sclera), above and below the iris, as exemplified below.
A rarer manifestation of Graves’ disease is dermopathy, called myxedema, which occurs by infiltration of the skin by autoantibodies. The skin is swollen, hard, with nodules on its surface and darker.
OTHER CAUSES OF HYPERTREOIDISM
In addition to Graves’ disease, there are other causes for hyperthyroidism:
– Plummer’s disease or toxic multinodular goiter: occurs by the formation of adenomas, benign tumors, in the thyroid. These adenomas are chemically active and produce T4 and T3 independently of the thyroid or circulating TSH levels.
– Toxic Adenoma: Same as above except for the fact that there is only one solitary adenoma producing excess hormones.
To know more about thyroid nodules: TIREOID NODE | Diagnosis and how to differentiate it from cancer
– Thyroiditis: occurs by inflammation of the thyroid. It may be due to viral infections, autoimmune causes other than Graves’ disease, postpartum, etc.
– Excessive thyroid hormone: Patients with hypothyroidism who have excessive hormone replacement may present with hyperthyroidism. In this case, correction of the dose is enough for the symptoms to disappear.
– TSH secreting adenomas: less than 1% of cases of hyperthyroidism occur due to inappropriate secretion of TSH. The main cause is adenomas in the pituitary gland. Although they are benign tumors, their growth can compress brain structures and cause neurological changes such as loss of vision.
TREATMENT OF HYPERTIREOIDISM
There are 3 different treatment modalities for hyperthyroidism: drugs, radiation or surgery. The choice of the most appropriate should take into account individual data of patients such as age, severity of the condition and cause of hyperthyroidism.
The two main drugs used in the treatment of hyperthyroidism are methimazole and propylthiouracil. Both act to prevent the production of hormones by the thyroid. Its effect takes an average of 3 weeks, since these drugs only prevent the synthesis of new hormones, having no effect on those already produced and circulating.
For rapid symptom control, one can use beta-blocking drugs such as the famous propranolol or atenolol.
Approximately 30% of patients are able to permanently suspend the drug after 2 years without returning hyperthyroidism. However, most remain dependent on these drugs.
As side effects are common and sometimes severe, other therapeutic modalities are necessary.
The destruction of the thyroid by radiation is a definitive treatment option for hyperthyroidism. Treatment consists of the ingestion of capsules with radiative iodine. As the thyroid uses the iodine from the feed to produce T3 and T4, it starts to concentrate all the radiation ingested and is destroyed by it over 6 to 18 weeks. The radiation from this treatment is very small and virtually restricted to the thyroid, not being able to cause cancer in other parts of the body. However, it is recommended to distance pregnant women in the first 7 days of treatment, since there is always some chance of exposure to radiation.
Surgery for thyroid removal is the 3rd treatment option. It is the least used because of the risks of operative complications. Its great indication is in the cases in which the thyroid is very increased, with great goiter and risk of obstruction of the airways.
Both surgery and radioactive iodine cure hyperthyroidism, but by destroying the thyroid, they lead to hypothyroidism. Therefore, T4 (levothyroxine) replacement is indicated (read: LEVOTIROXIN (Puran T4) – Indications and side effects).