Thyroid Disorders

Hyperthyroidism exists when there are excessive levels of the thyroid hormone. The most common form of hyperthyroidism is Graves’ disease. This disorder causes a hypermetabolic state characterized by a variety of symptoms, including heat intolerance and tachycardia. If left untreated, this disorder can be life threatening

Is directed toward correcting the hypermetabolic state. Antithyroid drugs can be used to block the synthesis of thyroxine and triiodothyronin, but they do not inactivate an existing or stored hormone. Although these medications can affect the symptoms of hyperthyroidism, they do not treat the underlying causes. These medications (propylthiouracil and methimazole) can be used to stimulate a remission. Iodides block peripheral conversion of T4 to T3 and inhibit hormone release. Generally, iodide is used in preparation for surgery. Until they are effective, beta blockers can be used to control the symptoms. Treatment for six to twelve months is usually required. Resumption of hormone synthesis occurs quickly after the drugs are withdrawn since iodine is no longer blocked from use.

Medications to Review:

• Propylthiouracil
• Methimazole (Tapazole)
• Iodide (Lugol’s Solution)
• Radioactive Iodine

Includes congenital hypothyroidism, Hashimoto’s thyroiditis (an immune-mediated disorder where TSH receptors are damaged), and subacute thyroiditis (inflammation of thyroid). Primary hypothyroidism is based on the hypothalamic pituitary thyroid gland feedback system and occurs when the hypothalamus responds to a decreased thyroid hormone level with an increase in TRH, resulting in increased TSH, which in turn stimulates thyroid gland enlargement, goiter formation, and preferential synthesis of T3 over T4.Secondary hypothyroidism is much less common and can occur due to pituitary or hypothalamic failure, Cushing’s syndrome, or overtreatment with antithyroid drugs. In secondary disorders, the TSH response is inadequate, so the gland is normal or possibly reduced in size and both T3 and T4 synthesis is equally reduced. The treatment for either type of hypothyroidism is to correct the hypometabolic state and return to a normal state.

Medications used for the treatment of hypothyroidism include levothyroxine (T4), liothyronine (T3), and liotrix (a mixture of T3 and T4). These compounds produce the same effects in the body as the endogenous thyroid hormones. They also produce negative feedback loops to reduce further secretion of TSH and thyroid hormones. Of the choices, levothyroxine has the longest half-life. Patients who have hypothyroidism are very sensitive to these medications, so treatment should begin slowly.Medications to Review:

• Levothryroxine (Synthroid)
• Liothyronine (Cytomel)
• Liotrix (Thyrolar