The Thyroid Gland

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The thyroid gland is located in the anterior mid-neck. The thyroid is the control center for the entire endocrine system. The gland releases mostly thyroxine, known as T4, and small amounts of triiodothyronine, or T3. Iodine is necessary for production of thyroid hormone. In the western world, the most common source of dietary iodine is iodized salt. Low levels of dietary iodine can cause the thyroid to become enlarged, a condition called goiter. Lack of iodine in infants causes severe mental retardation, a condition formerly known as cretinism. The release of thyroid hormone is controlled by the hypothalamus, which is located in the midbrain. Using a feedback loop, the hypothalamus releases thyroid stimulating hormone, or TSH, when it detects low levels of T4 and shuts down TSH release when it detects high levels of T4.

In 1835, an American physician, Robert Graves, described a syndrome with a high metabolic rate, enlarged thyroid gland, and exophthalmos (bulging, protruding eyes). This syndrome, called Graves’ disease, is an autoimmune disease in which, for reasons still mostly unknown, the body make antibodies that attack the thyroid gland. In Europe, Graves’ disease is known as Basedow disease after the physician who described it in 1840. Graves’ disease and Hashimoto’s thyroiditis, another autoimmune thyroid disease, like most autoimmune diseases are much more common in women. There are also genetic factors for both diseases. Graves’ disease is often treated with radioactive iodine, which often causes the thyroid to become underactive, a condition known as hypothyroidism. Likewise, Hashimoto’s causes hypothyroidism because the thyroid inflammation, or thyroiditis, it causes makes the gland eventually “burn out.”

Symptoms of an overactive thyroid gland, or hyperthyroidism, include weight loss, nervousness, palpitations, excessive perspiration, muscle weakness, atrial fibrillation and other tachycardias, tremor, enlarged thyroid gland, smooth, warm skin, and frequent bowel movements. Hypothyroidism, also known as myxedema, can cause weight gain, weakness, fatigue, coarse, cool, dry skin, husky voice, swelling of the hands, face, and legs, memory loss, constipation, muscle cramps, and aches and pains. Besides the clinical picture, hyper and hypothyroidism can be easily diagnosed with a blood test. Basic thyroid function tests, or TFTs, include levels of T3, T4, and TSH. In addition, other thyroid tests including anti-thyroid antibodies can be performed depending on the situation. When performing TFT testing, it is important to check to see what medications, if any, the patient is taking, as many medications may cause elevation or depression of thyroid hormone levels. Medications that can alter thyroid function and TFT testing include dopamine (L-dopa), lithium, sulfonylureas (Bactrim), dilantin, aspirin and other salicylate compounds, furosemide, propranolol, and amiodarone. As unfortunately many medical specialists do not provide feedback to the patient’s primary care provider, if you are seeing your primary care provider for thyroid testing, be sure that he or she is aware of all medications you are taking.

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