Thyroid Diseases

Your thyroid is a butterfly-shaped gland in your neck, just above your collarbone. It is one of your endocrine glands, which make hormones. Thyroid hormones control the rate of many activities in your body. These include how fast you burn calories and how fast your heart beats. All of these activities are your body’s metabolism.

Thyroid problems include:

• Goiter – enlargement of the thyroid gland
• Hyperthyroidism – when your thyroid gland makes more thyroid hormones than your body needs
• Hypothyroidism – when your thyroid gland does not make enough thyroid hormones
• Thyroid cancer
• Thyroid nodules – lumps in the thyroid gland
• Thyroiditis – swelling of the thyroid
To diagnose thyroid diseases, doctors use a medical history, physical exam, and thyroid tests. They sometimes also use a biopsy. Treatment depends on the problem, but may include medicines, radioiodine therapy, or thyroid surgery.

Diagnosis and Tests

• Needle Biopsy (Mayo Foundation for Medical Education and Research)
• Thyroid Antibodies (National Library of Medicine)
• Thyroid Scan and Uptake (American College of Radiology; Radiological Society of North America)
• Thyroid Tests (National Institute of Diabetes and Digestive and Kidney Diseases)
• Thyroxine (T4) Test (National Library of Medicine)
• Triiodothyronine (T3) Tests (National Library of Medicine)
• TSH (Thyroid-stimulating hormone) test (National Library of Medicine)
• Ultrasound – Thyroid (American College of Radiology; Radiological Society of North America)
• Ultrasound-Guided Fine Needle Aspiration Biopsy of the Thyroid (American College of Radiology; Radiological Society of North America)


Thyroid hormone is used in two situations:

1. to replace the function of a thyroid gland that is underactive or has been surgically removed (“replacement therapy“) and
2. to prevent further growth of thyroid tissue (“suppression therapy“). Suppression therapy is used primarily in patients with thyroid cancer to prevent recurrence or progression of their cancer.



Many people have a thyroid gland that cannot make enough thyroid hormone for the body’s needs. This is called Hypothyroidism and is most commonly caused by an under functioning thyroid gland due to Hashimoto’s disease. Other causes of hypothyroidism are: surgical removal, destruction of thyroid gland from radiation treatment, or a nonfunctioning pituitary gland (see Hypothyroidism Brochure). Hypothyroidism is the most common reason for needing thyroid hormone replacement.
Thyroid hormone is necessary for the health of all the cells in your body. Taking thyroid hormone is different from most medications, because its job is to replace a hormone that is missing. The goal of thyroid hormone treatment is to closely replicate normal thyroid functioning. Thyroid hormone is available as levothyroxine, which is biologically equivalent to your own thyroid hormone, thyroxine (T4). It is most commonly prescribed in tablet form but is now also available in gel capsule or liquid forms. The only safety concerns about taking thyroid hormone are taking too much or too little. Your thyroid function will be monitored by your physician to keep your levels at the goal range.


The thyroid gland makes T4 predominantly, along with a small amount of T3. T3 is the active form of thyroid hormone, and is mainly formed when T4 is converted to T3 on an as-needed basis in the cells of the body. This conversion of T4 to T3 occurs normally even if your thyroid gland is sick or absent. T3 has a very short life span in the body, while the life span of T4 is much longer, ensuring a steady supply. A preparation of synthetic T3 (Cytomel®) is available. After taking a tablet of Cytomel® there are very high levels of T3 for a short time, and then the levels decrease very rapidly in the bloodstream. This means that T3 has to be taken several times each day, but even this does not smooth out the T3 levels entirely. In addition, it is impossible to avoid having too much thyroid hormone in the system soon after each dose of T3 is taken. High T3 levels can lead to unpleasant symptoms such as rapid heartbeat, insomnia and anxiety. High T3 levels also can possibly harm the heart and the bones. Another concern with using T3 treatment is that the body is deprived of the ability to adjust the conversion of T4 to T3 to regulate the supply of T3 according to the body’s own needs. Thus, there is no indication for the use of T3 alone for the treatment of hypothyroidism.


Some hormone preparations containing both T4 and T3 are available in the United States (Thyrolar ®). Combination T4/T3 preparations contain much more T3 than is usually produced naturally within the body. Because of this, they can have the same side effects as T3 given by itself. It is also given once a day, despite the short life span of T3 in the body. There has been interest in whether a combination of T4 and T3 given separately might result in better symptom control in treatment of hypothyroidism, especially in those patients that do not feel completely normal on T4 alone. In these cases, Cytomel® (T3) is taken in addition to levothyroxine (T4), in doses that are closer to the normal human thyroid balance of T4 and T3. One challenge of adding T3 is that it is currently available only as a short acting formulation, requiring multiple doses in a day. Studies are underway to provide more information on the benefits and best dosing of combination therapy. A trial period of 3 – 6 months may be reasonable to determine if combination T4 and T3 therapy will help.