The thyroid is a gland located in your neck that secretes thyroid hormone. Thyroid hormone affects many organ systems throughout the body. Thyroiditis (inflammation of the thyroid) can cause an overproduction or underproduction of the thyroid hormone. Too much (hyperthyroidism) or too little thyroid (hypothyroidism) hormone can both create problems. Sub-clinical hypothyroidism is also on the spectrum of thyroid disorders and occurs when the level of thyroid hormone is on the lower side of normal (but still within the range of normal).
As with RA, the exact cause of thyroiditis is unknown and seems to be affected by a combination of genetic and environmental factors. For instance, smoking increases the risk of developing some forms of thyroiditis. Autoimmune conditions that affect the thyroid include: Hashimoto's thyroiditis, post-partum thyroiditis, sporadic thyroiditis, and Grave's disease.
Hashimoto's thyroiditis usually involves a painless enlargement of the thyroid gland, which causes hypothyroidism. Both post-partum (after pregnancy) thyroiditis and sporadic thyroiditis often have an initial period of hyperthyroidism, followed by a period of too little thyroid hormone, with many women returning to a normal thyroid range within approximately one year.
Grave's disease, which is a hyperthyroid condition, is the most common autoimmune thyroid disorder, and the most common autoimmune condition overall in the U.S. This disease occurs at a rate of approximately 0.5 per 1000 people. Grave's disease occurs more commonly in women than men and typically starts when someone is between 40 and 60 years old.
The symptoms of thyroid disease depend on whether the person is hyperthyroid or hypothyroid. Hyperthyroidism causes fatigue, increased heart rate, palpitations (racing heart beat), nervousness, weight loss, heat intolerance, and loose stools. In contrast, hypothyroidism causes fatigue, weight gain, dry skin, constipation, irregular periods, slowed thinking, depressed mood, and sometimes forgetfulness.
The first test used to screen a person for possible thyroid disease is called a thyroid-stimulating hormone (TSH) test. TSH controls the body's secretion of thyroid hormones. If a person has an increased amount of thyroid hormone, then the level of TSH decreases. In contrast, if the level of thyroid hormone is low and a person is hypothyroid, then TSH rises. TSH levels change slowly relative to changes in thyroid hormone levels, often taking months to adjust. Usually, if a woman's TSH test results are low, then the specific levels of individual thyroid hormones are also measured.
If a woman has low TSH and high levels of thyroid hormone, then additional tests are performed to determine the cause of hyperthyroidism. Often, the next test is a 24-hour radioactive iodine-123 uptake scan. For this test, a woman takes a radioactive iodine pill and returns in twenty-four hours for a scan to pinpoint where in the gland the thyroid hormone is being produced. Iodine is necessary for the body to make thyroid hormone. The pattern of iodine usage in the thyroid indicated by the I123 uptake scan allows doctors to determine which disease is causing a problem. For example, in Grave's disease the thyroid uses high amounts of iodine throughout the entire gland, whereas in postpartum thyroiditis the thyroid gland only uses a small amount of the iodine. Other conditions may have iodine uptake in a small, localized area of the thyroid.