1. Thyroid Hormones

2. 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

3. 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

6. Terminology Hypothyroid Hyperthyroid Euthyroid

7. 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

8. Regulation

9. Spectrum of Thyroid Disease Two general modes of presentation  Changes in size or shape of gland  Changes in hormone secretion

10. 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

11. 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

14. 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)

15. Hypothyroidism Most common clinical thyroid disorder Majority have primary gland failure Common causes  Autoimmune thyroiditis  Silent thyroiditis  Drugs Severe hypothyroidism is know as myxedema

16. Symptoms Fatigue Sleepiness Mental impairment Depression Cold intolerance Dry skin and other skin changes Weight gain Slow movement Slow speech Slow to respond Hyporeflexia

17. Laboratory Diagnosis

18. Goals of Treatment Replace missing hormones Relieve symptoms Achieve euthyroid state

19. Drug Treatment Number of products available None are more effective than synthetic T 4 Bioequivalence of synthetic T 4 products are of concern Don’t change manufacturers once optimal dose has been determined

21. 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

22. 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.

23. Hyperthyrodism Caused by excessive amounts of circulating thyroid hormone Most common type is “Graves” disease  Hyperthyroidism  Diffuse thyroid enlargement  Exopthalmos  Abnormal skin finding

24. Hyperthyroidism Graves’ disease is most common cause Graves’ disease is an autoimmune syndrome that includes  Hyperthyroidism  Diffuse thyroid enlargement  Exopthalmos  Dermatological abnormalities

25. Other Causes Thyroid cancer Iodine excess TSH secreting pituitary tumors

26. Exopthalmos

27. Skin Changes

28. Clubbing

29. Signs and Symptoms Nervousness Weakness Fatigue Heat intolerance Tremor Irritability Tachycardia and/or palpitations Weight loss Hyperactivity Hyperreflexia Warm, moist skin

30. Laboratory Diagnosis

31. Goals of Treatment Relieve symptoms Reduce thyroid hormone production Achieve euthyroid state Prevent long-term sequelae

32. 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

33. Other Therapy Drugs that reduce production of thyroid hormone  Iodine  Antithyroid drugs  Radioactive thyroid Surgery

34. 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)  Lugol’s solution(6.3mg I/drop)  Dose is 200-400mg/day for 7-14 days before surgery

35. Antithyroid Drugs Inhibit thyroid hormone synthesis by interfering with iodination of tyrosine Used before surgery or as primary treatment Drugs  Propylthiouracil  Methimazole

36. 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.

37. Side Effects Low rate of adverse reactions Hepatotoxicity 0.1-0.2%  PTU Cholestatic jaundice 0.1-0.2%  Methimazole Agranulocytosis 0.3%  Depression of bone marrow  so you don’t 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

38. 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 won’t want to go back on antithyroid, they’d rather get radiodine tx