Overactive thyroid (hyperthyroidism)

Overactive thyroid at a glance

An overactive thyroid (hyperthyroidism) is a condition in which too many thyroid hormones are produced and released into the blood in large quantities, which has far-reaching effects on several bodily functions. This results in an increased metabolism with possible symptoms such as diarrhoea, nervousness, irritability, palpitations or high blood pressure. Hyperthyroidism affects about 1 in 100 people and usually occurs between the ages of 20 and 50.

In patients, a distinction is generally made between overt and subclinical hyperthyroidism.

• Overt hyperthyroidism: the disease is already fully developed and is accompanied by certain symptoms.
• Subclinical hyperthyroidism: the disease is not (yet) showing any symptoms, although abnormalities are already present in the hormone levels of patients.

Causes of an overactive thyroid

The most common causes of an overactive thyroid are thyroid autonomy and the autoimmune disorder known as Graves’ disease. What’s noticeable is that Graves’ disease occurs significantly more frequently in women than in men, with women 5 to 10 times more likely to be affected by it.

Graves’ disease

In Graves’ disease, the immune system produces TSH receptor antibodies (also known as TRAb). These antibodies target the thyroid tissue. In the thyroid gland, they bind to the receptors (binding sites), where the thyroid-stimulating hormone TSH also binds.

The function of TSH is to regulate hormone production. The thyroid-stimulating hormone is secreted by the pituitary gland (hypophysis) so that it can do its job. However, when TRAb bind to TSH receptors, they mimic the effect of TSH. As a result, the thyroid’s hormone production is stimulated, independently of control by the brain. As with many other immune disorders, it is not yet known what causes this malfunction of the immune system, i.e., why Graves’ disease develops.

Thyroid autonomy

If thyroid autonomy is present, thyroid tissue is no longer regulated by higher-level brain cells and produces thyroid hormones independently. In cases of thyroid autonomy, hyperthyroidism can be more or less pronounced.

Based on the amount of autonomous tissue in the thyroid gland and the associated excess of hormones, three forms of thyroid autonomy are distinguished between:

• Disseminated thyroid autonomy: autonomous tissue that produces hormones independently develops throughout the thyroid gland.
• Unifocal thyroid autonomy: the autonomous tissue is limited to a benign ‘lump’ in the thyroid gland (autonomous thyroid adenoma).
• Multifocal thyroid autonomy: several benign ‘lumps’ in the thyroid gland produce hormones independently.

Less frequent causes

Während sich meist der Morbus Basedow oder die Schilddrüsenautonomie als Ursache für eine Hyperthyreose erweisen, kommen in gewissen Fällen auch andere Ursachen infrage:

• Thyroid cancer
• Benign tumour of the pituitary gland (pituitary adenoma) that produces too much TSH, which stimulates hormone production in the thyroid gland
• Inflammation of thyroid gland (thyroiditis)
• Overdose of thyroid hormones used to treat an underactive thyroid (hypothyroidism)
• Excessive intake of iodine (for example via contrast agents that contain iodine or sometimes via medication therapy with the iodine-containing drug amiodarone for cardiac arrhythmia)

Symptoms

Hyperthyroidism speeds up the body’s metabolism. As a result, patients may experience a wide range of symptoms.

Symptoms that may indicate an overactive thyroid include:

• Weakness
• Tiredness
• Decline in performance
• Nervousness
• Irritability
• Trembling
• Shortness of breath
• Sleep disorders
• Mood swings
• Weight loss despite a healthy appetite
• Excessive sweating
• Sensitivity to heat/cold
• Diarrhoea
• High blood pressure
• Irregular and/or unusually fast heart rate (palpitations), cardiac arrhythmia
• Hair loss
• Visible enlargement of the thyroid gland

If the thyroid gland is visibly enlarged, swelling will appear at the front of the neck, which is colloquially referred to as goitre and in medical terms as struma.

A typical characteristic of patients with Graves’ disease is protruding eyeballs (exophthalmos). In addition, other eye problems such as increased tearing, sensitivity to light and very dry or red eyes are also commonly associated with Graves’ disease.

Diagnosis

When investigating a possible overactive thyroid, the first step is to look at your medical history. Your attending doctor will ask you about any underlying conditions or previous illnesses you may have, as well as your symptoms. They will also ask you about any medication you are taking.

The aim of these questions is to find out about your medical history. The discussion will be followed by a physical examination, which involves palpating the thyroid gland to check for lumps and any enlargement, and examining whether the patient has protruding eyeballs or other eye problems.

An overactive thyroid can ultimately be diagnosed based on the symptoms and by measuring the thyroid hormones in the blood. Further examinations such as ultrasound, contrast x-ray (scintigraphy) or biopsy (tissue sample) can also be carried out to determine the cause.

Treatment of an overactive thyroid

Depending on the symptoms and cause of hyperthyroidism, different treatment options are available. Initially, hyperthyroidism is usually treated with a type of medication known as antithyroid medication, which block the production or release of thyroid hormones.

If medication therapy is not sufficient, an overactive thyroid can be treated with radiotherapy (radioactive iodine therapy). For thyroid tumours, when the thyroid gland is enlarged or when there are numerous lumps with increased hormone production, surgical removal of the thyroid gland is recommended in some cases. You can find out more about surgery on the thyroid gland in the chapter Thyroid surgery.

Prevention

There are currently no ways to prevent Graves’ disease and thyroid autonomy, the most common causes of hyperthyroidism. However, there are certain rarer causes of hyperthyroidism that can be prevented by taking simple measures.

Thyroid health can be promoted through adequate iodine intake. The recommended daily intake for adults is between 180 and 200 micrograms of iodine. Important: the amount is crucial, since excessive iodine intake can trigger hyperthyroidism. For this reason, you should never consume more than the recommended daily amount of iodine.

If you are taking medication that contains iodine, do not take an overdose of thyroid hormones under any circumstances. Otherwise, you run the risk of triggering symptoms of an overactive thyroid.