Hyperthyroidism vs hypothyroidism: everything there is to know!

The thyroid is a small, butterfly-shaped endocrine gland at the base of the neck that regulates our hormonal system, notably through the secretion of thyroxine (T4) and triiodothyronine (T3).

The first hormone (T4) accelerates all chemical reactions in our body. The second (T3) is involved in the regulation of calcium in our blood.

The thyroid enables our metabolism to function by supplying energy to our body and regulating the functioning of the organs. It acts on the nervous system, body temperature, digestive tract, genital tract, hair, skin, etc. and therefore has an impact on the general well-being of a person.

When your thyroid secretes too many or not enough hormones, you may suffer from hyperthyroidism or hypothyroidism.

What is hyperthyroidism?

Hyperthyroidism refers to an abnormally high production of hormones by the thyroid gland. Less common than hypothyroidism, it can affect everyone from small children to the elderly. But it usually affects adults aged between 20 and 40, and particularly women between 30 and 40 years old.

Hyperthyroidism, if mild, can go unnoticed. However, the main symptom of the condition is an increase in heart palpitations and a heart rate of up to 100 beats per minute at rest.

Hyperthyroidism can lead to a real heart condition, that is why it is essential to make sure that the condition is not overlooked.

Other symptoms of hyperthyroidism include:

• Difficulty breathing, shortness of breath,
  
• Increased sweating,
  
• Hot flushes,
  
• Sleep disturbances,
  
• Frequent mood swings and nervousness,
  
• Muscle weakness,
  
• An enlarged thyroid gland (goitre) at the base of the neck,
  
• Slight trembling in the hands,
  
• A change in menstrual pattern,
  
• Weight loss despite a normal appetite.
  

What is hypothyroidism?

Conversely, hypothyroidism happens when the thyroid gland stops working properly and does not produce enough hormones. Hypothyroidism is more common than hyperthyroidism and mainly affects women.

The main symptom of hypothyroidism is a general slowing down of body functions, which usually causes significant physical and psychological fatigue, as well as concentration and memory problems.

Other symptoms include:

• Weight gain despite poor appetite,
  
• Slower heart rate and shortness of breath,
  
• Irritability or even depression,
  
• Joint pain and muscle stiffness,
  
• Enlarged thyroid gland (goitre) at the base of the neck,
  
• Increased level of cholesterol in the blood,
  
• Risk of infertility,
  
• Irregular or sometimes absent menstrual cycles,
  
• Swelling of the face and eyes.

What are the similarities between hypothyroidism and hyperthyroidism? 

With hyperthyroidism, a lot of body processes and functions are accelerated. On the contrary, with hypothyroidism, everything is slowed down. These two disorders cause very different symptoms, and are therefore easily distinguishable. The only common symptom between the two is fatigue.

In most cases, hypothyroidism and hyperthyroidism are autoimmune diseases:

• Hashimoto's disease (also known as Hashimoto's thyroiditis) is most commonly involved in hypothyroidism.
  
• Graves' disease is the most common cause of hyperthyroidism.

How are hypothyroidism and hyperthyroidism diagnosed? 

The diagnosis is first established by performing clinical examination and then a TSH test.

TSH is a hormone produced by the pituitary gland, which is located in the brain and controls almost all the glands in the body, including the thyroid gland. Thus, by secreting TSH, the pituitary gland regulates the levels of T3 and T4 hormones in the blood.

When there is a lack of thyroid hormone, as in hypothyroidism, a signal is sent to the brain to increase TSH production. The TSH level is therefore high in hypothyroidism, above 4 mIU/L.

In contrast, in hyperthyroidism, the opposite signal reaches the brain - to decrease TSH production. The TSH level is therefore low in hyperthyroidism, below 0.1 mIU/L.

What are the treatment options for hypothyroidism and hyperthyroidism? 

Hypothyroidism 

The aim of the treatment for hypothyroidism is to bring the levels of thyroid hormone in the blood back to normal. This involves taking a synthetic thyroid hormone (levothyroxine) for the rest of the patient's life.

Once the hormone levels are back to normal, follow-up care is necessary in order to adjust the dose of the prescribed hormones. The frequency of follow-up visits is decided by your doctor. Regular blood tests to check the TSH level are also very important.

In addition, a TSH check is recommended 6 to 8 weeks after the start of the treatment or after any change in the dosage.

Hyperthyroidism 

There are a number of treatment options available to manage hyperthyroidism. The choice will depend on the cause of the disease.

Treatment of hyperthyroidism with synthetic antithyroid drugs

Synthetic antithyroid drugs reduce the production of thyroid hormones. Within 3 to 8 weeks after the start of the treatment, normal values can be achieved. Maintenance treatment must then be continued for several months.

Regular blood tests are carried out during treatment to monitor T3, T4 and TSH levels and to check blood counts and liver function because of possible side effects of the treatments.

Other drugs may sometimes be useful in treating the consequences of hyperthyroidism:

• Beta-blockers, to reduce heart rhythm disturbances,
• Steroids, for eye problems associated with Graves' disease.
  

Treatment of hyperthyroidism with radioactive iodine

The thyroid gland needs a small amount of iodine to function properly. Therefore, treatment with radioactive iodine permanently destroys part of the thyroid cells so that the thyroid gland could produce less hormone.

It is not uncommon for the treatment to have a greater effect than desired, resulting in a permanent state of hypothyroidism. This can be treated with thyroid hormone replacement therapy.

Surgical treatment of hyperthyroidism

The surgical procedure consists of removing the thyroid gland. It is done under general anesthesia and the gland is removed either:

• entirely: this is called total thyroidectomy; or
  
• partially: this is called partial thyroidectomy.
  

Total removal requires daily and lifelong replacement medication with thyroid hormone tablets. These drugs can also be prescribed for partial removal if there is insufficient residual secretion.