Hyperthyroidism
Hyperthyroidism is a endocrine disease in which the thyroid gland produces excessive amounts of thyroid hormones. Thyrotoxicosis is a condition that occurs due to elevated levels of thyroid hormones of any cause and therefore includes hyperthyroidism. Some, however, use the terms interchangeably. Signs and symptoms vary between people and may include irritability, muscle weakness, sleeping problems, a fast heartbeat, heat intolerance, diarrhea, enlargement of the thyroid, hand tremor, and weight loss. Symptoms are typically less severe in the elderly and during pregnancy. An uncommon but life-threatening complication is thyroid storm in which an event such as an infection results in worsening symptoms such as confusion and a high temperature; this often results in death. The opposite is hypothyroidism, when the thyroid gland does not make enough thyroid hormone.
Graves' disease is the cause of about 50% to 80% of the cases of hyperthyroidism in the United States. Other causes include multinodular goiter, toxic adenoma, inflammation of the thyroid, eating too much iodine, and too much synthetic thyroid hormone. A less common cause is a pituitary adenoma. The diagnosis may be suspected based on signs and symptoms and then confirmed with blood tests. Typically blood tests show a low thyroid stimulating hormone and raised T3 or T4. Radioiodine uptake by the thyroid, thyroid scan, and measurement of antithyroid autoantibodies may help determine the cause.
Treatment depends partly on the cause and severity of the disease. There are three main treatment options: radioiodine therapy, medications, and thyroid surgery. Radioiodine therapy involves taking iodine-131 by mouth, which is then concentrated in and destroys the thyroid over weeks to months. The resulting hypothyroidism is treated with synthetic thyroid hormone. Medications such as beta blockers may control the symptoms, and anti-thyroid medications such as methimazole may temporarily help people while other treatments are having an effect. Surgery to remove the thyroid is another option. This may be used in those with very large thyroids or when cancer is a concern. In the United States, hyperthyroidism affects about 1.2% of the population. Worldwide, hyperthyroidism affects 2.5% of adults. It occurs between two and ten times more often in women. Onset is commonly between 20 and 50 years of age. Overall, the disease is more common in those over the age of 60 years.
Signs and symptoms
Hyperthyroidism may be asymptomatic or present with significant symptoms. Some of the symptoms of hyperthyroidism include nervousness, irritability, increased perspiration, heart racing, hand tremors, anxiety, trouble sleeping, thinning of the skin, fine brittle hair, and muscular weakness—especially in the upper arms and thighs. More frequent bowel movements may occur, and diarrhea is common. Weight loss, sometimes significant, may occur despite a good appetite, vomiting may occur, and, for women, menstrual flow may lighten and menstrual periods may occur less often, or with longer cycles than usual.File:Proptosis and lid retraction from Graves' Disease.jpg|left|thumb|Exophthalmos seen in Graves' ophthalmopathy
The thyroid hormone is critical to the normal function of cells. In excess, it both overstimulates metabolism and disrupts the normal functioning of sympathetic nervous system, causing speeding up of various body systems and symptoms resembling an overdose of epinephrine. These include fast heartbeat and symptoms of palpitations, nervous system tremor such as of the hands and anxiety symptoms, digestive system hypermotility, unintended weight loss, and, in lipid panel blood tests, a lower and sometimes unusually low serum cholesterol.
Major clinical signs of hyperthyroidism include weight loss, anxiety, heat intolerance, hair loss, muscle aches, weakness, fatigue, hyperactivity, irritability, high blood sugar, excessive urination, excessive thirst, delirium, tremor, pretibial myxedema, emotional lability, and sweating. Panic attacks, inability to concentrate, and memory problems may also occur. Psychosis and paranoia, common during thyroid storm, are rare with milder hyperthyroidism. Many persons will experience complete remission of symptoms 1 to 2 months after a euthyroid state is obtained, with a marked reduction in anxiety, sense of exhaustion, irritability, and depression. Some individuals may have an increased rate of anxiety or persistence of affective and cognitive symptoms for several months to up to 10 years after a euthyroid state is established. In addition, those with hyperthyroidism may present with a variety of physical symptoms such as palpitations and abnormal heart rhythms, shortness of breath, loss of libido, amenorrhea, nausea, vomiting, diarrhea, gynecomastia and feminization. Long term untreated hyperthyroidism can lead to osteoporosis. These classical symptoms may not be present often in the elderly.
Bone loss, which is associated with overt but not subclinical hyperthyroidism, may occur in 10 to 20% of patients. This may be due to an increase in bone remodelling and a decrease in bone density, which increases fracture risk. It is more common in postmenopausal women; less so in younger women and men. Bone disease related to hyperthyroidism was first described by Frederick von Recklinghausen, in 1891; he described the bones of a woman who died of hyperthyroidism as appearing "worm-eaten".
Neurological manifestations can include tremors, chorea, myopathy, and in some susceptible individuals periodic paralysis. An association between thyroid disease and myasthenia gravis has been recognized. Thyroid disease, in this condition, is autoimmune in nature, and approximately 5% of people with myasthenia gravis also have hyperthyroidism. Myasthenia gravis rarely improves after thyroid treatment and the relationship between the two entities is becoming better understood over the past 15 years.In Graves' disease, ophthalmopathy may cause the eyes to look enlarged because the eye muscles swell and push the eye forward. Sometimes, one or both eyes may bulge. Some have swelling of the front of the neck from an enlarged thyroid gland.
Minor ocular signs, which may be present in any type of hyperthyroidism, are eyelid retraction, extraocular muscle weakness, and lid-lag. In hyperthyroid stare the eyelids are retracted upward more than normal. Extraocular muscle weakness may present with double vision. In lid-lag, when the person tracks an object downward with their eyes, the eyelid fails to follow the downward-moving iris, and the same type of upper globe exposure which is seen with lid retraction occurs, temporarily. These signs disappear with treatment of the hyperthyroidism.
Neither of these ocular signs should be confused with exophthalmos, which occurs specifically and uniquely in hyperthyroidism caused by Graves' disease. This forward protrusion of the eyes is due to immune-mediated inflammation in the retro-orbital fat. Exophthalmos, when present, may exacerbate hyperthyroid lid-lag and stare.
Thyroid storm
Thyroid storm is a severe form of thyrotoxicosis characterized by rapid and often irregular heartbeat, high temperature, vomiting, diarrhea, and mental agitation. Symptoms may not be typical in the young, old, or pregnant. It usually occurs due to untreated hyperthyroidism and can be provoked by infections. It is a medical emergency and requires hospital care to control the symptoms rapidly. The mortality rate in thyroid storm is 3.6-17%, usually due to multi-organ system failure.Hypothyroidism
Hyperthyroidism due to certain types of thyroiditis can eventually lead to hypothyroidism, as the thyroid gland is damaged. Also, radioiodine treatment of Graves' disease often eventually leads to hypothyroidism. Such hypothyroidism may be diagnosed with thyroid hormone testing and treated by oral thyroid hormone supplementation.Causes
There are several causes of hyperthyroidism. Most often, the entire gland is overproducing thyroid hormone. Less commonly, a single nodule is responsible for the excess hormone secretion, called a "hot" nodule. Thyroiditis can also cause hyperthyroidism. Functional thyroid tissue producing an excess of thyroid hormone occurs in a number of clinical conditions.The major causes in humans are:
- Graves' disease. An autoimmune disease to 90% in the USA ). Thought to be due to varying levels of iodine in the diet. It is eight times more common in females than males and often occurs in young females, around 20 to 40 years of age.
- Toxic thyroid adenoma
- Toxic multinodular goiter
- Inflammation of the thyroid is called thyroiditis. There are several different kinds of thyroiditis, including Hashimoto's thyroiditis, and subacute thyroiditis. These may be initially associated with secretion of excess thyroid hormone but usually progress to gland dysfunction and, thus, to hormone deficiency and hypothyroidism.
- Oral consumption of excess thyroid hormone tablets is possible, as is the rare event of eating ground beef or pork contaminated with thyroid tissue, and thus thyroid hormones. Pharmacy compounding errors may also be a cause.
- Amiodarone, an antiarrhythmic drug, is structurally similar to thyroxine and may cause either under-or overactivity of the thyroid.
- Postpartum thyroiditis occurs in about 7% of women during the year after they give birth. PPT typically has several phases, the first of which is hyperthyroidism. This form of hyperthyroidism usually corrects itself within weeks or months without the need for treatment.
- A struma ovarii is a rare form of monodermal teratoma that contains mostly thyroid tissue, which leads to hyperthyroidism.
- Excess iodine consumption, notably from algae such as kelp.
Hypersecretion of thyroid stimulating hormone, which in turn is almost always caused by a pituitary adenoma, accounts for much less than 1 percent of hyperthyroidism cases.