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Thyroid Guide


Hyperthyroidism

Hyperthyroidism

General Overview
The thyroid is a small butterfly-shaped gland, which rests in the lower neck. Its main function is to control your body's growth and metabolism. To control metabolism, your thyroid gland produces hormones (thyroxine [T4] and triiodothyronine [T3]). A properly functioning thyroid will produce the right amount of hormones required to keep your body functioning normally. The level of thyroid hormones in the blood is controlled by your pituitary gland.
Hyperthyroidism occurs due to the effects of excess thyroid hormone. It is also known as thyrotoxicosis or overactive thyroid and can be caused by various disorders. The treatment and outcome depends upon the type of disorder triggering hyperthyroidism. The prevalence of thyroid disorders in India is estimated to be 42 millions according to countrywide studies conducted in 2000. Studies have also shown that the prevalence of hyperthyroidism is 1.9% among those who have goiter (swelling of the thyroid gland). According to an Indian study, prevalence of hyperthyroidism is 2% in children and adolescents.
Introduction
What is hyperthyroidism?
Hyperthyroidism is a condition in which the thyroid gland produces an increased amount of thyroid hormones (T4 and T3). It is more common in persons above 60 years of age. Too much of thyroid hormones in your blood speeds your metabolism. You may develop symptoms like nervousness, weight loss, and insomnia, and sometimes even a very fast heartbeat, which can be life-threatening. In case, your condition is untreated or under treated, you can develop symptoms of thyroid storm, such as delirium, severe tachycardia, fever, vomiting, diarrhea, and dehydration. If hyperthyroidism is chronic and is not treated, it can lead to heart problems and osteoporosis (thinning of the bones) due to the increased metabolic demands on the bone.
Signs and Symptoms
How do I know that I have hyperthyroidism?
Symptoms of hyperthyroidism depend on your age, duration of the disease, presence of any comorbid conditions, and the level of thyroid hormones. You may not develop the classic signs and symptoms of hyperthyroidism, if you are in the older age group.
The symptoms associated with hyperthyroidism include:
  • nervousness and irritability.
  • increased resting heart rate.
  • palpitations.
  • hypertension (high blood pressure).
  • heat intolerance.
  • increased sweating.
  • tremor (shaking of the hand).
  • weight loss.
  • frequent bowel movements.
  • sudden paralysis.
  • thyroid enlargement (lump in the neck).
  • pretibial myxedema (painless lumpy skin thickening in front of the shin).
  • thin, delicate skin.
  • irregular fingernail and hair growth.
  • decreased menstrual flow.
  • impaired fertility.
  • mental disturbances.
  • sleep disturbances (including insomnia).
Causes
What causes hyperthyroidism?
When the thyroid gland releases an excess amount of its hormones over a period of time, it leads to hyperthyroidism. Many disorders or conditions can lead to hyperthyroidism, and they are mentioned below.
Graves' disease:
This is the commonest type of hyperthyroidism and is also known as diffuse toxic goiter. Graves' disease is caused due to an abnormal reaction of the body's immune system (body's defense system), which produces antibodies that stimulate thyroid gland to grow and produce too much of the thyroid hormone. Around 60% to 80% of cases of hyperthyroidism are due to Graves' disease. It is an autoimmune disease (condition in which antibodies are formed against your own tissues). Graves' disease can occur in families and occur in association with other autoimmune diseases. Graves' eye disease or infiltrative ophthalmopathy can occur in half of these cases causing swelling and inflammation of the muscles surrounding your eyes.
Toxic multinodular goiter:
This is another type of hyperthyroidism, where excess thyroid hormone is produced by thyroid nodule(s). It usually occurs in persons older than 40 years of age who usually have a goiter for a longtime.
Thyroid adenoma:
In this type of hyperthyroidism, a nodule within the thyroid gland overproduces thyroid hormone. Autonomously functioning nodules usually develop in younger persons living in iodine-deficient areas.
Thyroiditis:
In this condition, there is an inflammation of the thyroid gland, possibly due to a viral infection. It is a self-limiting disease. Thyroiditis can also develop after pregnancy usually due to problems with the immune system. This is called postpartum thyroiditis.
Excess iodine consumption:
Iodine-induced hyperthyroidism can occur after intake of excess iodine in the diet, certain medications, or exposure to radiographic contrast media.
Overactive metastatic thyroid cancer or rare diseases of the ovary/testicles:
Very rarely, these conditions can cause over-stimulation of the thyroid gland leading to hyperthyroidism.
Tumors of the pituitary gland:
Pituitary gland is a small gland located at the base of the brain. It produces thyroid-stimulating hormone (TSH), which stimulates the secretion of thyroid hormones. Tumors of this gland can stimulate the thyroid gland to produce too much of hormones causing hyperthyroidism.
Overdoses of thyroid hormone pills:
Accidentally or intentionally (to lose weight), some people take an overdose of thyroid pills, and this can lead to hyperthyroidism.
Risk Factors
What are the risk factors for hyperthyroidism?
The risk factors for hyperthyroidism include:
  • Sex. If you are a female, you are at eight times higher risk of developing hyperthyroidism.
  • Foodstuffs. High concentrations of iodine in certain foods and medications that you are taking can trigger hyperthyroidism.
  • Family history. Your risk is higher, if anybody else in your family has thyroid problem.
  • Stress and emotions. Highly stressful situations can trigger the onset of hyperthyroidism.
  • Past history. You are at greater risk, if you have had a thyroid condition during previous pregnancy, or were diagnosed with a thyroid nodule or thyroid enlargement previously.
  • Autoimmune disease. You are at higher risk, if you have any other autoimmune diseases.
  • Smoking. Women who smoke are at double the risk of developing hyperthyroidism due to Graves' disease. The risk is three times higher in women who smoke more than 25 cigarettes a day.
Diagnosis and Screening
How is hyperthyroidism diagnosed?
To evaluate whether you have hyperthyroidism, your doctor will ask a detailed medical and family history, and perform a physical examination.
Medical and family history:
Your doctor will question you about:
  • Any family history of thyroid disease.
  • The presence of any symptoms that you might be having or experienced.
  • Whether you had undergone any thyroid surgery or any radiation treatment on your neck.
  • Medicines that you are currently taking or have taken earlier, which could trigger the condition.
Physical examination:
Your doctor will conduct a thorough physical examination, during which he will check:
  • your weight.
  • your blood pressure.
  • your thyroid gland to determine size, nodularity, and vascularity.
  • your skin and hair for any changes.
  • your pulse to calculate the rate at which your heart is beating.
  • your reflexes for any signs of change.
  • your eyes to detect evidence of exophthalmos or ophthalmopathy.
Should I undergo any tests for diagnosing hyperthyroidism?
If your doctor suspects hyperthyroidism, he will recommend certain diagnostic tests. Thyroid disorders can be confidently diagnosed with the availability of ultra-sensitive, third-generation TSH assays.
Blood tests:
For diagnosing hyperthyroidism, your doctor will advise certain blood tests to measure the hormone level.
Free thyroxine (T4) test: This test is done to determine, if your thyroid gland is functioning properly. Thyroxine is a hormone produced by the thyroid gland, which is markedly increased in hyperthyroidism. During this test, your blood is collected from a vein, usually from the inside of your elbow or the back of your hand. As some drugs can alter the results, your doctor may advise you to stop them before the test. Your normal T4 level will range between 4.5 mcg/dL to 11.2 mcg/dL.
Triiodothyronine (T3) test: Triiodothyronine is another hormone produced by the thyroid gland, and its level is usually high in hyperthyroidism. During this test, your blood is collected from a vein, usually from the inside of your elbow or the back of your hand. As some drugs can alter the results, your doctor may advise you to stop them before the test. Your normal T3 level will range between 100 ng/dL to 200 ng/dL.
Thyroid-stimulating hormone test: Thyroid-stimulating hormone is a hormone produced by the pituitary gland. This hormone regulates the production and release of T4 and T3 from the thyroid gland. This is the most important and sensitive test for diagnosing hyperthyroidism. During this test, your blood is collected from a vein, usually from the inside of your elbow or the back of your hand. As some drugs can alter the results, your doctor may advise you to stop them before the test. Your normal TSH level will range between 0.4 mIU/L to 4.0 mIU/L. If you are undergoing treatment for any thyroid disorder, then your TSH level should lie in the range of 0.5 mIU/L to 3.0 mIU/L. This is the only initial test necessary in a patient with hyperthyroidism without the evidence of pituitary disease. Low TSH level is usually diagnostic of hyperthyroidism.
Antithyroid antibodies: Your doctor may recommend this test to follow-up the other thyroid test results (T4, T3, and/or TSH) that show the signs of thyroid dysfunction and/or for investigating the cause of goiter (enlarged thyroid gland). During this test, your blood is collected from a vein, usually from the inside of your elbow or the back of your hand. There is no standard reference range for this test. Presence of thyroid antibodies indicates that you have an autoimmune thyroid disease. The higher the level of antibodies, the greater is your chance of having autoimmune thyroid disease. Increasing antibody level rather than stable level is more significant.
Other blood tests: You may also have to undergo tests for calculating your complete blood count to check for the presence of anemia, granulocytosis, and lymphocytosis that are often associated with hyperthyroidism. Your doctor may advise other blood tests for calculating the levels of liver enzymes and calcium that could be altered, if you have hyperthyroidism.
Imaging studies:
Radioactive iodine uptake and thyroid scan: For this test, a radioactive dye is injected into your vein or you will be asked to drink a solution containing the dye. After 2 to 48 hours, pictures of your thyroid are taken using special machines. These pictures will show areas of your thyroid that have absorbed the dye. Thyroid imaging can be done after injecting a small amount of radioactive substance (iodine-123 and/or technetium-99m) into your vein. Radionuclide uptake is high in Graves' disease and low in the case of thyroiditis.
Treatment
How is hyperthyroidism treated?
The aim of the treatment is to correct the hypermetabolic state with the least side effects and the minimal incidence of hypothyroidism. The cause and severity of the disease, as well as your age, goiter size, presence of comorbid conditions, determine the nature of therapy your doctor chooses. Antithyroid drugs, radioactive iodine, and surgery are the main options available for treating persistent hyperthyroidism. Satisfactory outcomes are produced with any of the therapies when properly used. Your doctor may also use beta-blockers and iodides to treat some of the symptoms like rapid heart rate, sweating, and anxiety until the hyperthyroidism can be controlled.
Antithyroid drugs:
Your doctor may prescribe antithyroid drugs like methimazole and propylthiouracil that can suppress the production and release of thyroid hormones or block the effect of thyroid hormone activity throughout the body. These drugs are also capable of suppressing the immune response, which is associated with thyroiditis. Side effects of antithyroid drugs may include minor skin rashes, joint pain, fever, liver injury, and allergic reaction.
Radioactive iodine:
Your doctor may recommend radioactive iodine therapy, if you have Graves' disease. You will be asked to ingest a radioactive iodine tablet and the thyroid tissue will take up radioactive iodine, which destroys the tissue. This will make your thyroid to shrink in size and produces hormone at normal level, as the overactive cells are destroyed. Your doctor will not choose to treat you with radioactive iodine, if you are pregnant or breastfeeding.
Surgery:
Surgery is recommended for pregnant women and children who cannot tolerate antithyroid drugs, and for those who have very large or multinodular goiters. You may be advised with the supplementation of thyroid hormone lifelong thereafter.
Self Care and Lifestyle Change
  • Quitting smoking could greatly reduce the risk of developing Graves' disease.
  • Due to weight loss issues, it is advisable to avoid foods, such as broccoli, cabbage, sprouts, cauliflower, spinach, soy, beans, mustard greens, refined foods, dairy products, wheat, caffeine, alcohol, caffeinated green tea products, and Chinese or Korean ginseng. They could also interfere with your thyroid function.
Tips for Grave's ophthalmology
  • Take calcium supplements everyday to prevent osteoporosis as hyperthyroidism may contribute to thinning bones. Adults younger than 50 years of age should aim for a total of 1,000 mg daily, either from food or from supplements or from both. Adults older than 50 years of age should get 1,200 mg of calcium everyday.
  • Wear sunglasses to protect your eyes from ultraviolet rays and bright light.
  • Use lubricating eye drops. Eye drops may relieve the dry, scratchy sensation on the surface of your eyes.
  • Elevate the head of your bed. Keeping your head higher than the rest of your body lessens fluid accumulation in the head, and may relieve the pressure on your eyes.
  • Use over-the-counter creams or ointments containing hydrocortisone to relieve swelling and reddening of the skin.
References