Diseases of thyroid function: Hyperthyroidism
HyperthyroidismHyperthyroidism - overactive thyroid is a disease in which the thyroid is hyperactive and makes too much thyroid hormone. Like most conditions of the thyroid gland, it is more common in women. Hyperthyroidism can be caused by either overproduction of thyroid hormone or excessive release of thyroid hormone from the thyroid gland due to inflammation and/or destruction. It is important to distinguish between these two causes, in order to choose the appropriate treatment. A thyroid uptake scanThyroid uptake scan - radioactive iodine scan to detect hyperfunctioning thyroid nodules (also known as a radioactive iodine scan) can help tell the difference between these two causes. Problems causing thyroid hormone overproduction have increased uptake on thyroid scanning (i.e. a "hot" scan), while thyroid gland inflammation and/or destruction have low uptake on thyroid scanning. Overproduction of thyroid hormone is the most common cause of hyperthyroidism and can be caused by Graves' diseaseGraves' disease - autoimmune overproduction of thyroid hormone resulting in hyperthyroidism, toxic multinodular goiterGoiter - enlarged thyroid, and toxic adenomaToxic adenoma - single nodule in an otherwise normal thyroid gland that makes too much thyroid hormone and leads to hyperthyroidism.
Symptoms that may be associated with hyperthyroidismHyperthyroidism - overactive thyroid include anxiety, insomnia (inability to sleep through the night), tremors, palpitations, weight loss, muscle weakness, heat intolerance, excessive sweating, and menstrual changes. The number, degree, and severity of these symptoms can provide some clue as to the severity of hyperthyroidism.
Diagnosing hyperthyroidismHyperthyroidism - overactive thyroid is based on history and physical exam findings along with appropriate laboratory testing. On physical exam, the physician may find that the patient has a rapid heart rate (tachycardia), irregular heart beats (arrhythmias, including atrial fibrillation), eye symptoms (such as dryness, burning, bulging, double vision), or hand tremors. In addition, the thyroid gland may be larger than normal.
Laboratory testing to confirm the diagnosis of hyperthyroidism will include thyroid function tests. Usually, the TSHTSH - Thyroid stimulating hormone; also known as thyrotropin. The hormone that causes the thyroid to make and release thyroid hormone level will be lower than normal and the T3 and/or T4T4 - thyroxine thyroid hormone levels will be higher than normal. Subclinical hyperthyroidism is defined as cases where there are no clear symptoms or physical signs of hyperthyroidism on history and physical examination, but the blood level of TSH is low, and T3/T4 levels are normal.
Thyroid uptake scanning is used to determine if the thyroid is making too much thyroid hormone, leading to a high, or "hot" uptake scan versus if the thyroid is being destroyed (as in thyroiditis), in which case the scan will be a low, or "cold" uptake scan.
4. Common causes
Graves' diseaseGraves' disease - autoimmune overproduction of thyroid hormone resulting in hyperthyroidism is an autoimmune problem where the body's immune system overstimulates the thyroid. It is the most common cause of hyperthyroidismHyperthyroidism - overactive thyroid. TSH-R AbTSH-R Ab - antibodies to the TSH receptor; present in Graves' disease, an antibody to the TSHTSH - Thyroid stimulating hormone; also known as thyrotropin. The hormone that causes the thyroid to make and release thyroid hormone receptor, causes the overproduction of thyroid hormone. Laboratory findings show a low TSH and high T4T4 - thyroxine thyroid hormone and T3. The thyroid uptake scanThyroid uptake scan - radioactive iodine scan to detect hyperfunctioning thyroid nodules will be high, or "hot". On physical exam, patients with Graves' disease may have bulging eyes and violet plaque-like lesions, on the front of their lower legs, which are possibly associated with itchiness.
Toxic multinodular goiter
Hyperthyroidism due to toxic multinodular goiterGoiter - enlarged thyroid occurs when one or more nodules (growths) in the thyroid begin to make too much thyroid hormone. In general, the hyperthyroidism tends to be less severe than that seen in Graves' disease. Laboratory diagnosis is the same as in other cases of hyperthyroidism with low TSH and high T4 and T3 levels. Thyroid uptake scans may note several separate "hot" spots corresponding to the hyperactive nodules, while the rest of the gland has decreased activity.
If a single nodule, or a solitary toxic adenomaToxic adenoma - single nodule in an otherwise normal thyroid gland that makes too much thyroid hormone and leads to hyperthyroidism, in an otherwise normal thyroid gland makes too much thyroid hormone, it can lead to hyperthyroidism. This is a less common cause of hyperthyroidism than either Graves' disease or toxic multinodular goiterToxic multinodular goiter - multinodular goiter that produced excess thyroid hormone and causes hyperthyroidism. The diagnosis can be made in the same fashion as above.
The three main treatments for hyperthyroidismHyperthyroidism - overactive thyroid are: 1) medical therapy, 2) surgery, and 3) RAI ablationRAI ablation - the use of radioactive iodine to destroy thyroid cells (either benign or cancer). The best treatment depends on a number of factors and the treatment plan should be made with the help of experts in thyroid disease including endocrinologists and surgeons. In general, the first treatment that is usually tried once a diagnosis is made is usually antithyroid medications. If medical therapy does not work, then a more definitive therapy such as surgery or RAI ablation is considered. The choice between surgery and RAI ablation will depend on the expertise and experience of the patient's doctors. Both have equal success rates and low risks of complications.
The two goals for medical therapy are to control symptoms and to prevent excess thyroid hormone production. Beta blockers are medications that are used to control symptoms such as palpitations, anxiety, and tremors. These medications are usually given until thyroid function has returned to normal. Antithyroid medications are used to block excess thyroid hormone production. The two drugs used most commonly are Methimazole and propylthiouracil (PTU). Methimazole is the preferred medication because it acts faster and has fewer side effects. Usually, patients are put on antithyroid medications for one to two years. At that point the medication is stopped. If hyperthyroidism returns, as happens in over 50% of patients, a more definitive treatment to cure the disease is considered. The options for definitive treatment of hyperthyroidism are RAI ablation or surgical removal of all or part of the thyroid. Both are effective in the long-term control of hyperthyroidism.
Surgery for hyperthyroidism usually means removing the entire thyroid gland (total thyroidectomyTotal thyroidectomy - removal of the whole thyroid) with the goal of making the patient hypothyroid and then starting thyroid hormone replacement pills. Trying to leave remove enough thyroid to cure the hyperthyroidism while leaving enough thyroid to have normal thyroid function (subtotal thyroidectomySubtotal thyroidectomy - removal of almost the entire thyroid) without medication is very difficult. Even if everything is ok at first, over time, the thyroid can grow back and cause recurrent hyperthyroidism (i.e. return of hyperthyroidism). For this reason, most experienced surgeons now perform a total thyroidectomy for the surgical treatment of hyperthyroidism, in order to lower the risk of recurrence that can otherwise occur with leaving part of the thyroid behind. Surgery does have the small risk of postoperative complications, but it has the advantages of rapidly fixing the hyperthyroidism with only a 3% recurrence rate. When performed by an experienced surgeon, thyroid surgery is safe. (See Thyroid Surgery) After a total thyroidectomy, patients absolutely must take thyroid hormone replacement pills because removing the whole thyroid makes them hypothyroid. Patients with a large goiterGoiter - enlarged thyroid, with significant compressive symptoms, suspicion for thyroid cancer, moderate or severe eye disease in Graves' diseaseGraves' disease - autoimmune overproduction of thyroid hormone resulting in hyperthyroidism, and pregnant patients who cannot tolerate antithyroid medications should have an operation.
In RAI ablation, the patient is given a pill that contains radioactive iodine that is absorbed by thyroid cells and destroys them. RAI ablation has the advantage of avoiding thyroid surgery. Currently, most patients are given doses of RAIRAI - radioactive iodine that are high enough to destroy the entire thyroid and then are started on thyroid hormone replacement pills. This controls the hyperthyroidism sooner and more definitively. With proper treatment, hypothyroidismHypothyroidism - underactive thyroid following RAI ablation should occur within three to six months. In general, the chance of the hyperthyroidism returning (i.e. recurrence) is less than 3%. A disadvantage of RAI ablation is the potential to worsen thyroid eye disease (ophthalmopathyOphthalmopathy - thyroid eye disease) associated with severe cases of Graves' disease. Patients who are pregnant, have large thyroids, suspicious thyroid nodules, risk factors for thyroid cancer, or who have symptoms from a large goiter should not have RAI ablation. There is debate as to whether young children should have RAI ablation because they may then be at increased risk for other cancers and heart damage later on in life. In general, most practitioners do not recommend RAI ablation for patients younger than 15 years old. (See RAI Ablation)