NM 4203 Section 3

1. NM 4203 Section 3 Endocrine System

2. Endocrine System • Elaboration of hormones • Pituitary Gland • Thyroid Gland • Parathyroid Gland • Islet cells of the pancreas • Adrenal Glands • Gonads (ovaries & testes)

3. Anterior Pituitary Consists of 2 cell types: acidophils and basophils Basophil cells elaborate polypeptide hormones: TSH, ACTH, FSH, LH,ICSH Posterior Pituitary Vasopressin (ADH) Oxytocin Pituitary GlandPea sized gland at the base of the midbrain

5. Octreoscan • In 111 – DTPA Pentetreotide • Became available in U.S. in 1994 • Adult Dose 6.0 mCi • Usually SPECT scan at 24hrs. • Able to image the pituitary gland tumors arising from the pituitary gland. • Based on increased amounts of somatostatin receptors in the anterior pituitary.

6. Understanding the Lab Results • Why does a LOW TSH level indicate Hyperthyroidism? • Elevated levels of target gland hormone (Thyroid T4) , causes pituitary secretion of stimulating hormone (TSH) to be suppressed

7. Thyroid Gland • Butterfly shaped • Embryonic decent into the neck – sometimes leaves midline tissue arising from the isthmus, called pyramidal lobe. • Secretes thyroid hormones thyroxine (T4) and triiodothyronine (T3) • Thyroid hormone synthesis depends on trapping and organification of iodine.

9. Hyperthyroidism • TSH is low • Thyroid hormone thyroxine (T4) is high • The elevation of thyroxine can be due to Grave’s Disease, autonomous nodule function, or ingestion of replacement T4

10. Hypothyroidism • T4 is low (usually due to primary failure of thyroid gland) • TSH level is elevated (pituitary gland is trying to compensate for the low T4 and tell the thyroid to produce more) • Low T4 and Low TSH: hypothyroid secondary to hypothalamic or pituitary disease. • May feel cold, tired and even depressed. May gain weight, even though eating less.

11. Proper evaluation of the thyroid should look at :Clinical examLab resultsNuclear Medicine uptake/scan

12. Symptoms of Hyperthyroidism (thyrotoxicosis) • Increased appetite • Weight loss • Poor sleep / fatigue • Muscle weakness • Gastrointestinal problems • Warm feeling/ sweating • Tremors • Nervous feeling • Tachycardia

13. Graves’ Disease • Thought to be autoimmune disease • Enlarged thyroid • Some patients will have swelling in muscles around the eye, causing eye prominence, discomfort or double vision. • Uniform distribution of increased activity throughout the thyroid gland.

14. Multinodular Goiter • Enlarged gland, usually causing hyperthyroidism, with multiple cold and hot nodules. Patchy appearance. • Most frequent in middle-aged women • Much less likely to be cancer than a single cold nodule

15. Plummer’s Disease • Toxic Nodule • Can give uptake values that are high, normal or only mildly elevated. • Resistant to radioactive iodine therapy and frequently requires doses 2-3 times higher than diffuse toxic goiter • Normal or borderline elevated uptake cannot be used to exclude hyperthyroidism

16. Subacute Thyroiditis • Rapid onset of symptoms of hyperthyroidism • Elevated T3 and T4 • Low TSH • Very low uptake • Painful, swollen gland • Little or no activity on the 99mTc scan or I 123 scan • Usually heals itself over a few months. • NOT appropriate to treat these patients with radioactive iodine

17. Hashimoto’s Thyroiditis • Chronic thyroiditis – most common thyroid disease in the U.S. • Thought to be autoimmune disease • Inherited, and much more common in women • Immune cells damage thyroid cells & compromise their ability to make thyroid hormone. • Will eventually cause hypothyroidism and a goiter. • Fatigue, drowsiness, forgetfulness, brittle hair, itchy skin, constipation, and weight gain.

18. Primary Hypothyroidism • Thyroid gland fails to synthesize and release thyroid hormone • Unless TSH stimulation is controlled (by hormone replacement therapy) , the thyroid gland will continue to grow.

19. Thyroid Cancer • Papillary, follicular, medullary and anaplastic. Majority are papillary and follicular – these are the only two that are treatable with radioiodine. • Tumors are seen as cold nodules. • 80-90% are papillary – twice as often in females • Almost always seen as a cold, solitary nodule • Thyroglobulin levels are a good method to monitor patients for recurrence after thyroidectomy and ablation.

20. Facts • About 14,000 new thyroid cancer cases in the U.S. each year • Women account for 77% of new cases • Five-year survival rate is over 90%

21. Hormone Synthesis • Iodides are actively transported into the thyroid gland, called “trapping” • Iodide then goes through “organification” • 99mTc is “trapped” , but not “organified”. It slowly washes from the thyroid gland.

22. RadionuclidesI 131 • Half – life 8.1 days • 364 keV gamma emission • Beta Decay (useful for therapy) • Uptake : • 5 – 10 uCi oral dose • Most accurate at 24 hrs.

23. RadionuclidesI 123 • Half – life 13.3 hours • 159 keV gamma emission (good for imaging) • Limited by expense and availability • No beta emission (less dose to thyroid) • Scanning: • 300 – 400 uCi oral dose • Imaging is best at 3-4 hrs. *one source *

24. Radionuclides99mTC • Great for imaging • Ionic charge and size allow 99mTc to be trapped and concentrated in the thyroid. • NOT organified (can’t be used for uptake) • Scan: • No prior patient prep • 4 - 15 mCi I.V. dose • Images done 15 – 20 minutes after injection

25. Thyroid Uptake • Value is effected by total iodine intake. • Uptake will be higher in a patient with low – iodine diet. • Uptake will be lower in a patient with high iodine diet. (supplements, medications, seafood)

26. Thyroid Uptake • Some additional considerations: • Each facility must determine their own range of “normal” • Good renal function is essential for a normal uptake. • Renal failure will result in low uptake • Large meals before or after oral dose can decrease absorption and lower uptake.

27. Thyroid Uptake • TSH level is used to diagnose hyper or hypothyroid. • Uptake is used to differentiate Graves’ disease from subacute thyroiditis or factitious hyperthyroidism. • Uptake determines whether or not the thyroid will take up iodine and how much (VERY useful for determining therapy)

28. Thyroid Uptake % Thyroid uptake = Neck counts – Thigh counts / Counts in standard X 100%

29. Thyroid Scan • Pinhole collimator • Should be used at the same distance on each patient • Anterior, LAO, RAO is standard and sternal notch should be identified.

30. Cold Nodules (nonfunctioning) • Most commonly a colloid cyst • Most are benign: 20 – 30 % are malignant • Even in multinodular goiter, 10% of dominant cold nodules are malignant. • Warrant further investigation (biopsy)

31. Hot Nodule • Most represent hyperfunctioning adenoma • Most are benign • Can sometimes produce enough thyroid hormone to inhibit pituitary secretion of TSH

32. Total Thyroidectomy from Thyroid Cancer • Whole Body I 131 imaging determines if there is residual tissue or metastases. • TSH should be elevated (over 50 uU/Ml is optimal) • Not taking thyroid replacement hormones or injection of Thyrogen • Failure of the TSH to rise could mean there is a significant amount of functioning thyroid tissue left after surgery.

33. I 131 Whole Body Imaging • Ranges from 1 to 10 mCi • A recent study showed that whole body I131 imaging is not as sensitive as TSH thyroglobulin level for recurrent metastatic thyroid cancer. ?? • I 123 has also been used for whole body imaging to determine mets.

34. I 131 Therapy for hyperthyroidism • “simple, safe, effective, inexpensive” • Alternatives are antithyroid medication and surgery. • Toxic multinodular goiter and a solitary toxic nodule is more resistant to I 131

35. Metastatic thyroid cancer

36. I 131 Ablation for Thyroid Cancer • Normal and malignant tissue is ablated • 75 – 100 mCi is generally given following thyroidectomy to ablate any residual tissue. • In the past, any patient receiving more than 30 mCi had to be hospitalized. That has changed with the NRC and is no longer required.

37. Thyroid Storm • Sudden release of thyroid hormone after radiation • Concern for severely hyperthyroid patients with severe symptoms. • Can be avoided with pretreatment using antithyroid drugs • Not normally a concern

38. Radioiodine Therapy • Female patient’s must have pregnancy test and must cease breastfeeding. • Following Therapy: • No evidence of increased incidence of cancer (including leukemia) • No change in fertility rates or genetic damage in children has been found.

39. Following Radioiodine treatment • Patient may experience: • Sore throat • Dysphagia • Increase in hyperthyroid symptoms • Patient should stay well hydrated and void frequently

40. 18F – FDG imaging • Shown to identify thyroid cancer even when the I 131 imaging is negative. • Gives improved anatomic localization

41. Parathyroid • Usually 4 parathyroid glands. • Location can vary: • Alongside the thyroid • Within the thyroid gland • In the neck • In the mediastinum • Within the thymus • Among great vessels

42. Parathyroid function • Synthesize, store and secrete parathyroid hormone • Regulates Calcium and phosphorus metabolism in bone, kidneys and G.I. Tract • Excessive secretion of parathyroid hormone is hyperparathyroidism • Increased urinary secretion of calcium • Kidney stones • Bone mineral loss • Usually due to a parathyroid adenoma

43. Parathyroid Imaging • Helps to localize the parathyroid adenoma • Meaning less time in surgery • 99mTc MIBI is most commonly used. • Images are usually done at 30 minutes and again at 90 to 150 minutes. • Parathyroid adenomas are metabolically active and are mitochondrial dense – where the MIBI will localize. • SPECT is helpful • Image fusion with CT is gaining popularity. Allows precise anatomical localization.

44. Parathyroid Imaging • No patient prep • Large field of view should include salivary glands to mediastinum.

45. Parathyroid adenoma Mediastinum

46. Salivary Gland • Warthin’s tumor • Benign parotid gland lesions • More frequent in elderly men • Usually bilateral • 5 – 15 mCi 99mTc pertechnetate • Image 1 minute images for 20 mintues.