The importance of the thyroid hormone for the adequate functioning of multiple organ systems within the body cannot be overstated. The production of adequate quantities of thyroid hormones (thyroxine [T4] and triiodothyronine [T3]) is necessary for normal fetal and neonatal growth and development, as well as, proper functioning of adult organ systems, including the skeletal system, the cardiovascular system, lipid and carbohydrate metabolism, and the neuromuscular system.
The major effects of abnormal thyroid levels relates largely to changes in ovulation and menstruation. Ovulation may be impaired by changes in the production of: sex hormone binding globulin (SHBG), follicle stimulating hormone (FSH), estrogen, and androgens to name a few. The body compensates by altering the production of thyroid releasing hormone (TRH) from the hypothalamus. The changes in TRH will affect the feedback loop between the hypothalamus, pituitary, and the ovary, leading to changes in ovulation and menstruation. These changes can be subtle, especially when symptoms of thyroid dysfunction are not obvious and do not lead to changes in menses or ovulation. Early stages of thyroid dysfunction (before symptoms are manifest) can lead to subtle changes in ovulation and endometrial receptivity, which then may have profound effects on fertility.
Symptoms that a patient may complain about differ for hypothyroidism and hyperthyroidism. The hypothyroid patient may complain of: lethargy, mild weight gain, cold intolerance, constipation, dry skin, mental impairment, depression, irregular menses, and hoarseness. Physical findings noted by the physician on exam may include: an enlarged/tender thyroid gland, a low heart rate, changes in the texture of skin/hair, and changes in neurological reflexes. The hyperthyroid patient will complain of: nervousness, fast heart rate, heat intolerance, weight loss, emotional changes, and neck tenderness. Physical findings may include: an enlarged or nodular thyroid gland, bulging of the eyes (exophthalmos), tachycardia (rapid heart rate), tremors, changes in the skin and hair, and in severe cases loss of muscle tissue and cardiac changes noted on EKG.
A blood test to measure thyroid stimulating hormone (TSH) is the most efficient and sensitive test for hypo or hyperthyroidism available. TSH is produced by the pituitary gland in response to TRH secretion. An elevated TSH value indicates thyroid failure and a lack of adequate amounts of thyroid hormone to maintain normal body functioning. Conversely, a low TSH value indicates excess production of thyroid hormone. The normal range of serum TSH is 0.5 – 5.0 mU/ml. If the TSH value is abnormal, then evaluation of the serum free- T4 becomes necessary to further evaluate the exact location of the dysfunction (i.e.: at the level of the thyroid, the pituitary, or hypothalamus).
Treatment differs based on the type of thyroid dysfunction. Patients with hypothyroidism require thyroid replacement therapy to supply the thyroid hormone that the body is not able to produce.
The treatment of hyperthyroidism is based on decreasing production of thyroid hormones. In most instances, medications are administered to inhibit both thyroid gland production and secretion of T3 and T4. Some patients may temporarily require other medications to counteract the effects of excess thyroid hormone throughout the body until such time as the quantities of thyroid hormone have been reduced. Once the source of increased thyroid hormone production is found, treatment with radioactive iodine will be used to destroy the site of overproduction.