Thyroid Disorders

Thyroid: Overview

Thyroid

The thyroid is an endocrine gland that produces the thyroid hormones triiodothyronine (T3) and tetraiodothyronine (thyroxine or T4). These are chemical substances that act as messengers in distant parts of the body.

Thyroid hormones are essential for life and have multiple effects on the body’s metabolism, growth, and development. They help regulate body temperature, heart rate, blood pressure, bowel function, weight control, and mood, among other functions. They are transported via the bloodstream to every cell in our body; simply put, they regulate the rate at which cells function.

The activity of the thyroid gland is controlled by two hormones produced in other organs:

• pituitary gland—a gland located at the base of the brain that produces TSH
• the hypothalamus—a region of the brain immediately above the pituitary gland, which produces TRH

The pituitary gland and the hypothalamus act as sensors, responding to the levels of circulating thyroid hormones. If circulating levels of T3 and T4 are low, the hypothalamus releases TRH, which stimulates the pituitary gland to release TSH. Elevated TSH levels, in turn, stimulate the thyroid to produce more thyroid hormone in order to restore normal levels.

Conversely, if circulating thyroid hormone levels exceed normal values, the hypothalamus and the pituitary gland reduce the release of TRH and TSH, respectively, so that the thyroid produces less T3 and T4. These three glands and the hormones they produce constitute what is known as the hypothalamic-pituitary-thyroid axis.

All women of childbearing age undergoing preconception evaluation and all pregnant women should be screened for thyroid hormone abnormalities.

Diagnostic Criteria for Diseases

Suspicion of thyroid dysfunction arises from observing the patient’s signs and symptoms. However, it is necessary to measure thyroid hormone levels through laboratory testing.

In other cases, in the absence of specific signs and symptoms, abnormalities in thyroid hormone levels may be detected during routine testing.

*N = within reference ranges ◊ TSH - Thyrotropin; FT4 - Free thyroxine; FT3 - Free triiodothyronine;AATPO - Antiperoxidase antibodies; AATG - Anti-thyroglobulin antibodies; TRAb - Anti-thyrotropin receptor (TSH) antibodies – Adapted from New England J Medicine 2006; 354,2785

Signs and symptoms that should raise suspicion of thyroid dysfunction, even when present in isolation

Conclusion

Thyroid disorders are very common and occur more frequently in women than in men. There are many different thyroid disorders, the most common of which are:

Hyperthyroidism—when there is excessive production of thyroid hormones

Hypothyroidism—when there is insufficient production of thyroid hormones

Autoimmune diseases—these are caused by antibodies directed against the thyroid gland, which can either stimulate or destroy the gland. Examples include Graves’ disease (a cause of hyperthyroidism) and Hashimoto’s thyroiditis (a cause of hypothyroidism).

Goiter—when the thyroid gland is enlarged overall

Nodules—which may be single or multiple.

To optimize clinical and laboratory diagnosis, the Dr. Germano de Sousa Center for Laboratory Medicine offers a panel of immunological and biochemical parameters that enable accurate and appropriate characterization of the condition in question. These include:

• T3
• FT3
• T4
• FT4
• TSH
• Urinary iodine
• Anti-thyroglobulin antibody
• Anti-peroxidase antibodies
• Anti-TSH receptor antibodies

See the brochure