Hyperthyroidism, also known as overactive thyroid, is a medical condition caused by an abnormally high level of thyroid hormones in the bloodstream. In other words, the thyroid gland produces an excessive amount of thyroid hormones.
The thyroid gland is located in the neck. It produces hormones that are released into the bloodstream to control the body's growth and metabolism.
There are several causes of hyperthyroidism and a wide range of possible symptoms; it is more common in women than men.
Hyperthyroidism can be effectively controlled with drugs that reduce the production of hormones from the thyroid gland. In some cases, radiotherapy and surgery are recommended.
In this article, we will cover the causes, diagnosis, treatment, and possible complications of an overactive thyroid gland.
Fast facts on hyperthyroidism
Here are some key points about hyperthyroidism. More detail and supporting information is in the main article.
Symptoms of hyperthyroidism
The thyroid is a relatively large gland, situated in the neck.
The incidence and severity of symptoms vary from person to person. Patients with mild hyperthyroidism are often not aware that they have it because there are no symptoms.
Usually, the symptoms are related to the increase in metabolic rate.
Signs and symptoms linked to hyperthyroidism may include:
- Swelling in the neck caused by an enlarged thyroid gland (goiter)
- Decreased concentration
- Difficulty breathing
- Difficulty sleeping
- Excessive sweating
- Extreme tiredness
- Oversensitivity to heat
- Increased appetite
- Increased bowel movements
- More frequent urination
- Moodiness, irritability
- Itchy skin with raised itchy swellings (urticaria)
- Nails become loose
- Loss of interest in sex
- Menstrual problems in women, especially lighter periods or absence of periods
- Muscle weakness
- Alopecia - usually, hair is lost in patches
- Accelerated heartbeat, sometimes with palpitations
- Redness on the palms of hands
- Shakiness and muscle weakness
- Sudden weight loss or gain
- Trembling hands
- Warm, damp skin
(Patients rarely have all symptoms listed).
Patients with diabetes and hyperthyroidism may experience heightened diabetes symptoms, such as fatigue and increased thirst. In the majority of cases, the signs and symptoms of hyperthyroidism are not of concern.
Patients with heart disease, however, have a higher risk of arrhythmia, heart failure, and other cardiovascular risks, which are of concern.
Causes of hyperthyroidism
Graves' disease - this is the most common cause. Graves' disease is an autoimmune condition in which the body's immune system mistakenly targets the thyroid gland and causes it to produce too much thyroid hormone.
It is unclear what triggers this condition. However, there is a genetic basis for Graves' disease, meaning that it often runs in families.
It is most common in women aged 20-40 and has a higher incidence amongst smokers.
Graves' disease may also affect the eyes, causing discomfort and double vision. Patients commonly have eyes that bulge out.
Nodular thyroid disease - lumps can develop in the thyroid gland. They are known as nodules. It is unclear why they develop. They are usually benign (non-cancerous).
The thyroid is usually enlarged, but there is no pain. Nodules may be felt with the fingertips. The nodules can contain abnormal thyroid tissue, affecting the regular function of the thyroid, causing overactive thyroid.
Nodules that contain abnormal thyroid tissue are described as toxic.
Excessive iodine intake - the thyroid gland removes iodine from the blood which comes from foods such as seafood, bread, and salt. It then uses the iodine to produce thyroid hormones.
The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3). Taking additional iodine in supplements can cause the thyroid gland to produce too much of the hormones.
Intake of thyroid hormones - lack of patient follow-up can result in patients taking too many doses of their thyroid medications.
Medications - certain medications used in the treatment of heart problems contain a large amount of iodine. They may be associated with changes in thyroid function.
An example is amiodarone, which is sometimes prescribed for patients with atrial fibrillation; it can cause amiodarone-induced hyperthyroidism.
Thyroiditis - this is an inflammation of the thyroid; it is often the result of a viral infection. The signs and symptoms may include fever, sore throat, painful swallowing, generalized aches, and pains in the neck.
Follicular thyroid cancer - in rare cases, overactive thyroid can be caused by thyroid cancer. The malignant cells may themselves start producing thyroxine or triiodothyronine.
The doctor will ask the patient questions about symptoms, carry out a physical examination, and order a blood test.
Cases of advanced hyperthyroidism are fairly straightforward to diagnose - however, early on in the condition, symptoms are not so obvious, and a significant number of patients are overlooked.
The blood test is known as a thyroid function test. It helps evaluate how well the thyroid gland is working. The thyroid function test checks for levels of thyroid-stimulating hormone (TSH), thyroxine, and triiodothyronine.
In some cases of hyperthyroidism, a special diagnostic scan of the thyroid gland is made using radioactive iodine called radioactive iodine uptake (RAIU).
Treatment options for hyperthyroidism
Some medications treat the consequences of hyperthyroidism, such as heart beat problems, while others target thyroid hormone productions.
Antithyroid drugs - stop the thyroid gland from producing excess amounts of thyroxine or triiodothyronine.
Radioactive iodine - this is picked up by the active cells in the thyroid and destroys them. The destruction is local, and there are no widespread side effects with this therapy. The dose of radioactivity contained in the radioiodine is very low and is not harmful.
Radioiodine treatment is not suitable for women who are pregnant or breastfeeding. Following radioiodine treatment, women should avoid getting pregnant for at least 6 months and men should not father a child for at least 4 months.
Surgery - if other treatments are not possible (for instance, during pregnancy), cannot tolerate other therapies, or has cancer, part of the thyroid gland is removed.
Complications related to hyperthyroidism
Graves' ophthalmopathy - patients may experience pain or discomfort in the eye, photophobia (light oversensitivity), and have some vision problems. Their eyes may also bulge out.
For most people, the symptoms can be relieved using eye drops and wearing sunglasses. In severe cases, treatment with certain drugs such as steroids or immunosuppressive drugs can decrease the swelling behind the eyes.
Complications in pregnancy - hyperthyroidism may affect a woman's ability to become pregnant. Pregnant women with the condition are more at risk of developing complications during pregnancy and birth, such as miscarriage and eclampsia (seizures during pregnancy), premature labor, and low birth weight.
In most cases, the pregnancy can be expected to progress normally if properly treated.
Thyroid storm - this is an uncommon reaction that can be set off by an infection, injury, or trauma. It can also occur in pregnant women with undiagnosed or poorly controlled hyperthyroidism, and can be triggered by childbirth or surgery.
The signs and symptoms include rapid heartbeat, high fever, agitation, jaundice, vomiting, diarrhea, dehydration, and hallucinations. This reaction is life-threatening and requires immediate emergency medical treatment.
The seriousness of hyperthyroidism depends on the body's capability to react to the changes resulting from excess thyroid hormones. Thyroid disease is common - with proper care, it can be easily diagnosed and treated.
Patient adherence to treatment guidelines (instructions by the doctor) is crucial for effective results.