Thyroid Hormones. Thyroid Hormone Action Thyroid gland is the largest endocrine gland in the body Thyroid hormones facilitate normal growth and maturation.

Thyroid Hormones Thyroid Hormone Action Thyroid gland is the largest endocrine gland in the body Thyroid hormones facilitate normal growth and maturation of tissue by promoting an optimal level of metabolism Thyroid hormones affect virtually every organ system in the body Thyroid hormones are essential for fetal growth Cretinism(child w/lack of thyroid, a form of mental retardation) Happens when mother lacks thyroid hormone during preggers/birthgiving Thyroid Hormones Thyroid gland produces two hormones Tetraiodothyronine or thyroxine (T 4 ) Triiodothyronine (T 3 ) Proper levels of iodine are needed for synthesis of thyroid hormones Thyroid gland secretes mostly T 4 Peripheral tissues convert T 4 to T 3 T 3 is more active than T 4 Terminology Hypothyroid Hyperthyroid Euthyroid Regulation of Synthesis Thyroid function is controlled by thyroid stimulating hormone (TSH) Secretion of TSH is stimulated by TRH Feedback inhibition of TRH is occurs with high levels of circulating thyroid hormone Regulation Spectrum of Thyroid Disease Two general modes of presentation Changes in size or shape of gland Changes in hormone secretion Changes in Shape In hypothyroidism Enlarged thyroid glands are often referred to as goiters(mass in the neck) Goiters are common in developing countries and are caused by an iodine deficiency Iodine Deficiency Relatively common in developing countries Iodized salt is usually used as primary treatment Iodine deficiency in children can cause mental retardation and dwarfism or cretinism Laboratory Assessment TSH T 4 T 3 Measurement of TSH is adequate for diagnosis of most cases of hypo and hyperthyroidism hyperthyroidism(TSH levels go down) hypo(TSH elevated) Hypothyroidism Most common clinical thyroid disorder Majority have primary gland failure Common causes Autoimmune thyroiditis Silent thyroiditis Drugs Severe hypothyroidism is know as myxedema Symptoms Fatigue Sleepiness Mental impairment Depression Cold intolerance Dry skin and other skin changes Weight gain Slow movement Slow speech Slow to respond Hyporeflexia Laboratory Diagnosis Goals of Treatment Replace missing hormones Relieve symptoms Achieve euthyroid state Drug Treatment Number of products available None are more effective than synthetic T 4 Bioequivalence of synthetic T 4 products are of concern Dont change manufacturers once optimal dose has been determined Consultation (levothyroxine) Follow administration instruction DO NOT take more than recommended Do not switch brands once stabilized on a particular product Take on an empty stomach with a full glass of water at least 30 minutes before breakfast Take at the same time each day Administer apart from medications known to decrease absorption Antacids Calcium Iron Vitamin and mineral supplements Consultation It may be several weeks before you notice an improvement in your condition It may be necessary for you to take this medicine for the rest of your life, not a cure Do not stop using this medicine unless your doctor advises you to. Hyperthyrodism Caused by excessive amounts of circulating thyroid hormone Most common type is Graves disease Hyperthyroidism Diffuse thyroid enlargement Exopthalmos Abnormal skin finding Hyperthyroidism Graves disease is most common cause Graves disease is an autoimmune syndrome that includes Hyperthyroidism Diffuse thyroid enlargement Exopthalmos Dermatological abnormalities Other Causes Thyroid cancer Iodine excess TSH secreting pituitary tumors Exopthalmos Skin Changes Clubbing Signs and Symptoms Nervousness Weakness Fatigue Heat intolerance Tremor Irritability Tachycardia and/or palpitations Weight loss Hyperactivity Hyperreflexia Warm, moist skin Laboratory Diagnosis Goals of Treatment Relieve symptoms Reduce thyroid hormone production Achieve euthyroid state Prevent long-term sequelae Drug Treatment Beta blockers help relieve symptoms Palpitations Tremors Anxiety Heat intolerance Used until more specific anti-thyroid therapy begins to work Given in addition to propranolol Propranolol is treatment of choice The one drug out of top 200 used for tx of hyperthyroidism Other Therapy Drugs that reduce production of thyroid hormone Iodine Antithyroid drugs Radioactive thyroid Surgery Iodine Large doses inhibit synthesis and release of T 4 and T 3 T 4 levels are reduced within 24 hours Used prior to surgery for Graves disease Drugs SSKI (30mg I/drop) Lugols solution(6.3mg I/drop) Dose is mg/day for 7-14 days before surgery Antithyroid Drugs Inhibit thyroid hormone synthesis by interfering with iodination of tyrosine Used before surgery or as primary treatment Drugs Propylthiouracil Methimazole Consultation Take this medicine with or without food. Always take it the same way to make sure the effects are the same Do not stop taking this medicine except on the advice of your doctor If you are going to have surgery or dental surgery, tell your doctor, dentist, or health care professional that you are taking this medicine. Side Effects Low rate of adverse reactions Hepatotoxicity % PTU Cholestatic jaundice % Methimazole Agranulocytosis 0.3% Depression of bone marrow so you dont synthesize/release granulocytes (help you developing bacterial infections) Indosyncratic hypersensitivity reaction Can get infections and DIE, **must go back to physician once in a while to get blood cell counts Duration of Treatment Antithyroid drugs are given for 1-2 years and then stopped Relapse occurs in 40% of patients within 3-6 months after stopping If replase occurs most patients will opt for treatment with radioactive iodine rather that go back to taking antithyroid medications If pts relapse, usually pts wont want to go back on antithyroid, theyd rather get radiodine tx