WHAT IS HYPERTHYROIDISM?

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Hyperthyroidism refers to a condition that occurs when there is too much thyroid hormone present in the blood stream. This is also called Thyrotoxicosis. Thyrotoxicosis may be caused by thyroid disorders, or by taking too much thyroid hormone medication.


Certain symptoms and signs are characteristic of hyperthyroidism. Hyperthyroidism patients tend to notice fatigue and generalized weakness (may be very severe), varying degrees of heat intolerance, increased perspiration, palpitations and/or heart awareness. Nervousness may occur in association with tremors. Patients also notice emotional liability and mood swings. Irritability is also a common symptom. Some patients lose weight despite eating large amounts of food.


Older patients may be less severely affected by these symptoms; however, they are more predisposed to various heart problems that are caused by hyperthyroidism. Depending on the cause of the hyperthyroidism state, thyroid enlargement (goiter) may or may not be present.






CAUSES OF HYPERTHYROIDISM




The most common cause of Hyperthyroidism is termed "diffuse toxic goiter." This occurs in patients with a medical problem called 
Graves' disease. Graves' disease is a condition that may include (in varying combinations) a diffuse toxic goiter, Thyroid eye disease 
(ophthalmopathy) and, rarely, Pretibial Myxedema.


The diffuse toxic goiter that occurs in Graves' disease is characterized by generalized enlargement of the thyroid gland and overproduction of thyroid hormone. The actual cause of this condition is unknown. However, it is associated with the production of antibodies (which normally fight infection) that stimulate the thyroid gland to make excessive amounts if thyroid hormone.


Graves' ophthalmopathy is rarely severe. This condition is caused by the inflammatory reaction involving the tissue surrounding the eyes, as well as the muscles that control eye movement.


Pretibial myxedema is an inflammatory condition of the skin that usually involves the front of the lower legs, and is usually not a severe problem. Hyperthyroidism may also be caused by thyroiditis and thyroid nodular disease. Thyroiditis-induced thyroidtoxicosis is thought to be caused by an inflammatory process that injures the thyroid gland and allows the "leakage" of the thyroid hormone into the blood stream.


Hyperthyroidism associated with thyroid nodules occurs when the nodules develop autonomous function (not under normal pituitary control) and manufacture excess amounts of thyroid hormone.






DIAGNOSING HYPERTHYROIDISM




The laboratory diagnosis of hyperthyroidism is usually straightforward. This is done by performing a blood test which measures the level of thyroid hormone.


In hyperthyroid states, the result is usually clearly elevated. Once the physician has established the diagnosis of hyperthyroidism, the next task is to determine which type of abnormality is causing the hyperthyroid state. This is important because proper treatment depends on the underlying cause.


The primary diagnostic question is usually the differentiation of the toxic goiter from thyroiditis. This can usually be answered by obtaining a 24-hour iodine uptake. In this study, the patient is given (by mouth) a very small dose of radioactive iodine which is accumulated by the thyroid gland and the rate of accumulation can be measured. Toxic goiters usually demonstrate a high 24-hour uptake.


In addition to the 24-hour uptake, one may also take a picture of the thyroid gland. This is called a thyroid scan, and also supplies useful information in many patients.






TREATMENT OF HYPERTHYROIDISM




Patients have three choices of treatment of a diffuse toxic goiter. A popular treatment in years past has been surgery which involves a subtotal thyroidectomy. The surgeon simply removes all but a small portion of the thyroid gland. This is an effective form of therapy, but obviously carries a disadvantage of requiring hospitalization and surgical procedure, which carries with it certain risks.


A second form of therapy consists of taking medications that slow the thyroid gland function. These are called antithyroid drugs. Although this form of therapy is effective (often takes weeks to months), frequent follow-up visits are needed, allergic reactions may occur and, very often, the disease recurs once the medication has been stopped (patients usually remain on therapy for one to two years). This form of therapy is often used in children and adolescents in the hope they will remain disease-free after stopping the medication. For unclear reasons, this seems to happen a little more frequently in children than in adults.


The most common for of therapy now used in nonpregnant adults is radioactive iodine treatment. This form of therapy is simple (usually done as an outpatient) and very effective. Radioactive iodine works by damaging the thyroid tissue gradually and painlessly. This usually results in a decrease in gland size, as well as slowing down of the rate of thyroid hormone production. The main side effect is that most patients eventually develop hypothyroidism (low thyroid function). This may occur within several months after treatment, or it may happen years into the future. On the other hand, hypothyroidism is very simple to treat, and often occurs after the other two-forms of therapy, anyway.


Perhaps the most important thing to remember is that, once a patient has been treated for hyperthyroidism (regardless of the method) conscientious medical follow-up with the physician is critical in order to monitor the response to therapy, as well as to watch for the possible development of hypothyroidism.


Lastly, if the cause of the thyroidtoxicosis is excessive thyroid hormone administration, the dose of thyroid hormone can be adjusted. Hyperthyroidism caused by thyroiditis is usually a transient problem and patients are treated symptomatically until the inflammatory process resolves spontaneously.






Brought to you by:
Integris Southwest Medical Center Department of Endocrinology 
Jonathan L. Davis, M.D.