Spotlight on... thyroid disease: hyperthyroidism
There are two main types of thyroid disease – in this article, Lyn Mynott explains all about hyperthyroidism, which is the overproduction of the thyroid hormone. She also gives some information on what causes this disease, how it can be diagnosed and the treatments currently available, as Thyroid Awareness Week (19th – 25th October) draws nearer.
(Continued from "Spotlight on thyroid disease: hypothyroidism")
What is hyperthyroidism?
Hyperthyroidism is the term given when the thyroid produces more thyroid hormone than it should. Other names for this are an overactive thyroid and thyrotoxicosis.
Thyroid physiology is complex. The thyroid is part of the endocrine system. The pituitary produces a hormone called thyroid stimulating hormone (TSH) which stimulates the thyroid to produce thyroxine (T4). Thyroxine is inactive and needs to be converted by the tissues and organs of the body into the active hormone, tri-iodothyronine (T3).
Subclinical hyperthyroidism is the term used when patients have symptoms of hyperthyroidism and have an abnormally low serum TSH but normal FT4 levels and FT3 levels.
What causes hyperthyroidism?
Primary Hyperthyroidism is caused by problems with the thyroid gland:
• Graves' disease: an autoimmune disease where antibodies stimulate the thyroid cells to secrete excess thyroid hormone. This is the most common cause of an overactive thyroid (80%).
• Toxic multinodular goitre (Plummer's disease): this is an enlarged thyroid gland that has lumps on it that have become overactive.
• Toxic adenoma: single, benign, non-cancerous lump.
• Thyroiditis: this is an infection or inflammation of the thyroid gland, which may temporarily cause excessive amounts of thyroid hormone. The thyroid gland will be painful and tender. It may be painful to swallow.
"Hyperthyroidism is the term given when the thyroid produces more thyroid hormone than it should."
Secondary Hyperthyroidism is caused by problems outside of the thyroid gland:
• Pituitary problems: the pituitary can produce too much TSH, which over-stimulates the thyroid. This can be due to pituitary adenoma.
• Over medication of thyroxine.
Who is at risk?
The prevalence of hyperthyroidism in women is between 0.5% and 2%, and is 10 times more common in women than in men in iodine-replete communities.
The reported prevalence of subclinical hyperthyroidism is 3%, with men and women over 65 having the highest prevalence - 50% caused by excess levothyroxine.
Risk factors are: genetic susceptibility, high iodine intake, smoking, trauma to the thyroid gland such as surgery, toxic multinodular goitre, childbirth, and highly active antiretroviral therapy (HAART).
Possible triggers for Graves' disease are smoking, stress, pollutants, allergy, iatrogenic causes (percutaneous injection of ethanol, interferon therapy such as interferon beta-1b or interleukin-4 therapy) and selenium intake.
What are the symptoms to look out for?
Signs and symptoms of hyperthyroidism are often noticed fairly quickly. These include:
• Weight loss
• Increased appetite
• Weakness and fatigue
• Anxiety / psychosis
• Heat intolerance
• Lid lag
Some patients have Graves' ophthalmopathy (thyroid eye disease - TED) giving symptoms such as protruding eyeballs, red or swollen eyes, excessive tearing or discomfort in one or both eyes, light sensitivity, blurry or double vision, inflammation or reduced eye movement. This is a separate condition and can occur after the Graves' disease has been treated.
"Signs and symptoms of hyperthyroidism are often noticed fairly quickly."
Some patients may have a thyrotoxic storm if they are either undiagnosed or ineffectively treated.
Symptoms include fever, tachycardia, delirium, seizures, vomiting, diarrhoea and jaundice. Early recognition and aggressive treatment is necessary.
How is hyperthyroidism diagnosed?
The tests usually done to diagnose Graves' disease are:
• TSH - Thyroid Stimulating Hormone
• FT4 - Thyroxine
• FT3 - Tri-iodothyronine
• TPO Ab - Anti-thyroid Peroxidase Antibody
• TgAb - Anti-thyroglobulin Antibody
• TSI - Thyroid Stimulating Immunoglobulin
• TSH-receptor antibodies – TRAb - commonly present in Graves' disease but not routinely measured.
Genetic tests, a thyroid ultrasound scan and a thyroid uptake scan, to locate hot (overactivity) and cold (no activity) spots can also be done.
A level of FT4 above the reference range together with a TSH level below the reference range and positive antibody tests will usually give a diagnosis of hyperthyroidism.
Subclinical hyperthyroidism is diagnosed when the patient has suppressed TSH levels with normal FT4 and FT3 levels. However, there is controversy as to whether this should be treated.
Hyperthyroid patients are often diagnosed with bipolar or anxiety neurosis and this can lead to dangerous delays in treatment.
What treatment is available?
Beta blockers are usually given to immediately control the symptoms (calcium-channel blockers are an alternative if patients cannot tolerate beta-blockers) along with anti-thyroid medication – carbimazole (methimazole) or propylthiouracil if patients cannot tolerate carbimazole or if the patient is pregnant.
Liver damage has been reported with these drugs so the patient should be carefully monitored.
"Safer medications need to be found for hyperthyroid patients, especially those that are pregnant."
Treatment will be titrated depending on response and thyroid test results until the FT4 level falls within the normal range. TSH levels can take some time to increase to the normal range. Once levels have normalised, the carbimazole is reduced to the amount needed to keep the thyroid levels within the normal range. Hypothyroidism occurs in 40-60% of patients.
Another method of treatment is "block and replace", where antithyroid drugs are given with levothyroxine.
Medication is usually continued for 18-24 months when the antithyroid drugs are slowly stopped. Patients are then monitored to see if the problem recurs.
Side effects of these drugs can be nausea and a bitter taste after taking the medication. If a patient develops a sore throat, checks for bone marrow suppression should be done.
If thyroid levels do not stay within range, other methods of treatments are used:
Radio-iodine is given to the patient in the form of a drink. This destroys the thyroid gland. Some patients may need a second treatment. It can take 3-4 months to take effect.
This cannot, however, be given to pregnant or breast-feeding women and women should not get pregnant for at least four months. Contact with children and pregnant women must be avoided after treatment and patients should sleep alone for a week.
Radioactive iodine may worsen eye problems in Graves' disease, especially in smokers, and 50% – 80% of patients can develop hypothyroidism after treatment.
Surgery to remove either one or both lobes (thyroidectomy) achieves a 98% cure rate. Surgery is usually done if the response to anti-thyroid medication or radio-iodine was poor, especially in patients who are pregnant or who have TED.
Complications include haemorrhage, hypoparathyroidism and vocal cord paralysis. Thyroidectomy often causes the patient to become hypothyroid either immediately or over time so the patient needs to be monitored.
The patient must be euthyroid before radio-iodine treatment or surgery.
What does the future look like for hyperthyroid patients?
Safer medications need to be found for hyperthyroid patients, especially those that are pregnant.
Research to address the autoimmune aspect of both hypothyroidism and hyperthyroidism may find the causes of autoimmune thyroid disorders which could then lead to prevention.
About the author:
Lyn Mynott is Chair / Chief Executive of Thyroid UK and has been campaigning for change in the diagnosis and treatment of thyroid disease since 1998.
Thyroid UK is an independent charity providing information and resources to promote effective diagnosis and appropriate treatment for people with thyroid disorders in the UK.
Thyroid UK promotes public awareness of thyroid disorders and encourages scientific research for the education, alleviation, care, treatment and cure of thyroid disease. The number of beneficiaries has increased significantly from its beginnings and this has resulted in a corresponding and substantial growth in the range of services provided.
Tel: 01255 820407
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