最後更新日期 九月 9, 2021.
Hyperthyroidism is an endocrine disorder in which a thyroid gland is overactive, producing too much thyroid hormone and leading to metabolic acceleration. Early symptoms of hyperthyroidism often go unnoticed by patients, making it a commonly underdiagnosed illness. Although hyperthyroidism is curable, a neglected overactive thyroid can result in fatal complications. Here is your ultimate guide to stay away from hyperthyroidism.
What is Hyperthyroidism?
Hyperthyroidism is the overaction of the thyroid, resulting in excessive thyroid hormone production and secretion. The thyroid is a butterfly-shaped endocrine gland located at the lower front neck. It produces 2 main hormones that regulate cellular metabolism called thyroxine (T4) and triiodothyronine (T3). These 2 kinds of hormones regulate normal metabolism. However, when an overactive thyroid produces excess T3 and T4 hormones, cellular metabolism would be accelerated, giving rise to a series of signs and symptoms such as unexplained weight loss, palpitation, nervousness, etc.
Causes of Hyperthyroidism
A healthy thyroid keeps normal levels of thyroid hormones to maintain regular body temperature, regular heart rate, respiration rate, usual breathing pattern, as well as many other cellular metabolisms to allow a normal body function.
However, in patients with hyperthyroidism, their thyroid gland can become overactive owing to the following causes:
- Graves’ disease: Graves’ disease is the most common cause of hyperthyroidism. It is an autoimmune disease in which antibodies stimulate the growth of the thyroid to produce too much thyroid hormone.
- Toxic adenoma / Toxic multinodular goiter: These are conditions in which parts of the thyroid are isolated from the rest of the gland, forming nodules or lumps that gradually grow independently and contribute too much thyroid hormones into the circulation.
- Thyroiditis: This form of hyperthyroidism happens because of inflammation of the thyroid gland. The thyroid can be inflamed under viral infections, autoimmunity, or post-pregnancy reactions. Inflammation of the thyroid causes a leak of stored thyroid hormones into blood circulation, resulting in hyperthyroidism.
- Excessive consumption of thyroid hormone medication or Iodine: Consuming too much iodine would over-stimulate the thyroid, thus causing hyperthyroidism. Besides, excessive intake of thyroid hormone medication boosts bloodstream thyroid hormone levels directly.
Risk Factors of Hyperthyroidism
Apart from the above-mentioned causes of hyperthyroidism, there are several other risk factors contributing to a higher risk of hyperthyroidism, namely:
- Sex: Females are more susceptible to Grave’s disease than males.
- Medical history: Patients with type-1 diabetes, pernicious anemia (a vitamin B12 deficiency), Addison’s disease (a primary adrenal insufficiency) or any other past thyroid disorders may develop hyperthyroidism more easily.
- Family history: Heredity increases the risk of hyperthyroidism. People with a family history of thyroid diseases have a higher chance of hyperthyroidism development.
Signs and Symptoms of Hyperthyroidism
Thyroid hormones, thyroxine and triiodothyronine, regulate most of our body’s metabolisms. By upsetting one’s metabolic status, hyperthyroidism may cause the following signs and symptoms:
- Goiter: Enlarged thyroid gland appears as a swelling in the neck.
- Palpitation: Feeling of a fluttering or pounding fast-beating heart.
- Arrhythmia: Irregular heart rate and rhythm. Tachycardia (rapid heartbeat) often occurs in hyperthyroidism.
- Tremor: Unintentional shaking movements of the upper limbs, usually hands and fingers.
- Fatigue: Hyperthyroidism speeds up metabolism. Although a large amount of energy is released initially, fatigability increases rapidly afterward.
- Weight loss
- Increased appetite
- Heat intolerance
- Excessive sweating
- Increased bowel movement and/or Diarrhea
- Skin thinning
- Brittle hair
- Nervousness, Anxiety or Irritability
Complications of Hyperthyroidism
If hyperthyroidism is unrecognized and untreated, severe and fatal complications may occur, for instance:
- Atrial fibrillation: Such rapid and irregular heart rhythm contributes to a higher risk of congestive heart failure and stroke.
- Thyroid storm (Thyrotoxic crisis): It is an acute life-threatening hypermetabolic syndrome that causes acute high fever, rapid heartbeat, nausea, shock and delirium.
- Thyrotoxic Eye Signs: Examples of thyrotoxic eyes include dry eyes, red and swollen eyes, bulging eyes, etc. Some cases also show excessive tear secretion, double vision or even loss of vision.
- Osteoporosis: Hyperthyroidism can weaken bones eventually. Brittle bones may occur when calcium absorption of bones is interfered by excessive thyroid hormones.
Diagnosis of Hyperthyroidism
In addition to the clinical signs and symptoms, hyperthyroidism is diagnosed mainly by physical examination, blood test, imaging and iodine test.
- Physical examination: Physicians usually examine a patient’s neck for an enlarged thyroid and irregular pulse to diagnose hyperthyroidism. Besides, doctors may also look for signs of finger tremor, moist skin and eyes reflex, etc.
- Laboratory test: Confirmation of hyperthyroidism is made by laboratory tests of blood thyroid hormones. A high level of blood thyroid hormone with a low level of thyroid-stimulating hormone (TSH) confirms hyperthyroidism.
- Thyroid scan / Ultrasound: Imagings are applied to differentiate which parts of the thyroid are overactive.
- Radioiodine uptake test: Oral radioactive iodine can be taken to assess the iodine collection ability of the thyroid. A high iodine uptake indicates excessive thyroxine production, whereas a low uptake level of radioiodine implies a leakage of stored thyroxine.
Treatments of Hyperthyroidism
Treatments of hyperthyroidism depend on various factors like the exact cause, severity, sex, age, medical history and other physical conditions, etc. In general, hyperthyroidism can be treated by the following approaches:
- Anti-thyroid drugs: Anti-thyroid medications, including methimazole (Tapazole) and propylthiouracil (PTU), are usually induced to inhibit thyroid hormone production. Even though such agents can improve symptoms and signs readily, they bring alongside effects like allergy, skin rashes, fever, joint pain, decreased white cell count and even severe liver damage. As Methimazole causes relatively fewer side effects, it is often preferred.
- Radioactive iodine: Radioactive iodine treats hyperthyroidism by destroying thyroid cells to reduce thyroid hormone production. Thyroid cells that absorb radioactive iodine will be damaged by radiation, thus shrinking the gland and lowering thyroid hormone levels. Radioactive iodine is usually taken as an oral capsule in a single course, while a second dose can be given with a physician’s prescription.
- Beta-blockers: Beta-blocker is a class of drugs that does not lower thyroid hormone levels, but can be taken to relieve specific symptoms of hyperthyroidism, such as tremor, nervousness and palpitation.
- Thyroidectomy: Surgical removal of the whole or part of the thyroid is a long-lasting cure of hyperthyroidism. As the source of thyroid hormones is removed, hyperthyroidism is gone. However, a lifelong indication of thyroid hormone supplements will be needed following the removal of the thyroid. By carrying out thyroidectomy, there are risks of vocal cords and parathyroid glands damages.
*This article is medically reviewed by Dr. Gordon Chak Man Cheung from the London Medical Clinic, Central, Hong Kong. Dr. Cheung is a General Practitioner in HK who received his medical degree from King’s College London, University of London. Before completing his General Practice specialist training in UK, Dr. Cheung had worked in various hospitals in London and South East England in Cardiology, Endocrinology, Oncology, Paediatrics, Obstetrics and Gynaecology. He holds numerous postgraduate medical qualifications including Memberships to the Royal Colleges of Physicians in UK and to the Royal College of General Practitioners, Diploma of the Royal College of Obstetricians and Gynaecologists, Child Health as well as Clinical Dermatology.