THYROID GLAND DISORDERS AND ITS MANAGEMENT

Various disorders related to thyroid gland, evaluation and management

1. Dr Vijay Kumar, Asso. Prof.

2. RLN has more distance in which to reach TE groove and therefore runs in a medial plane There is less distance and the nerve runs more obliquely to reach the TE groove 2% →non-recurrent R L

3. R L

4. Course of the recurrent laryngeal nerve RLN runs post. to thyroid, enters the larynx at the cricothyroid joint This entry point is at the level of Berry’s ligament, a condensation of pretracheal fascia that binds thyroid to trachea. Most risk of injury Located in the TE groove where it forms one side of Beahrs’ (other 2 sides - carotid artery and inferior thyroid artery)

5. Berry’s ligament

6. Beahr’s TRIANGLE

7. The pathway T3 & T4 - bound to thyroglobulin within the colloid Synthesis within the thyroglobulin complex- ● Trapping of iodide from blood; ● Oxidation of iodide to iodine; ● Binding of iodine with tyrosine to form iodotyrosine; ● Coupling of monoiodotyrosines and di-iodotyrosines to form T3 and T4 When hormones are required, the complex → cell & thyroglobulin is broken T3 and T4 are liberated and enter the blood The small amount of hormone that remains free in the serum is biologically active.

8. T3 / T4 Effects of the thyroid hormones - d/t free T4 and T3 (0.03% and 0.3%) T3 is the more important physiological hormone Periphery : T4 →T3 T3 is quick acting (within a few hours), T4 acts more slowly (4–14 days)

9. Calcitonin Parafollicular C cells of the thyroid - neuroendocrine origin Arrive in the thyroid ultimobranchial body Produce calcitonin.

10. Calcitonin Vs Parathromone

11. TFT - Normal vs Pathological states

12. Thyroid-stimulating antibodies Bind with TSH receptor sites (TRAbs) and activate TSH receptors on the follicular cell membrane Long action than TSH (16–24 versus 1.5–3 hours) Responsible for thyrotoxicosis in all cases of thyrotoxicosis not due to autonomous toxic nodules

13. Thyroid autoantibodies Antibodies against thyroid peroxidase (TPO) and thyroglobulin Autoimmune thyroiditis may be associated with thyroid toxicity, failure or euthyroid goitre. >25 units/mL for TPO antibody >1:100 for antithyroglobulin →considered significant The presence of antithyroglobulin antibody interferes with assays of serum thyroglobulin. TSH receptor antibodies (TSH-Rab or TRAB) are often present in Graves’ disease

14. Thyroid imaging Ultrasound Assessment of the gland + regional lymphatics Number, size, shape, margins, vascularity and microcalcifications →predict malignancy Advantage Regional lymphatics can be assessed for metastatic deposits USG guided FNA- more accurate No ionising radiation Non-invasive Cheap

15. CT / MRI Retrosternal extension, requires CT Scan CECT can determine the extent of airway invasion MRI is superior at determining the presence of prevertebral fascia invasion

16. Isotope scanning Radiolabelled iodine (123I) / technetium (99mTc) will demonstrate activity in the gland. Routine isotope scanning is unnecessary ,majority (80%) of ‘cold’ swellings are benign and some (5%) functioning or ‘warm’ swellings will be malignant. Thyrotoxicosis + nodule or nodularity ? Localisation of overactivity in the gland will differentiate between a toxic nodule with and toxic MNG Whole-body scanning →metastases(must have all normal thyroid ablated ) Metastatic thyroid cancer tissue cannot compete with normal thyroid tissue in the uptake !

17. Fine-needle aspiration cytology FNAC-investigation of choice Excellent patient compliance Simple and quick OPD procedure Readily repeated Classification of FNAC reports Thy1 Non-diagnostic Thy1c Non-diagnostic cystic Thy2 Non-neoplastic Thy3 Follicular Thy4 Suspicious of malignancy Thy5 Malignant

18. THYROID ENLARGEMENT GOITRE - generalised enlargement of the thyroid gland. SOLITARY swelling→Discrete swelling (nodule) in one lobe with no palpable abnormality elsewhere isolated (or solitary) DOMINANT swelling→Discrete swellings with evidence of abnormality elsewhere in the gland

19. Simple goitre Aetiology Stimulation of the thyroid gland by TSH d/t T3 /T4 The most important factor in endemic goitre - deficiency of iodine Defective hormone synthesis →sporadic goitres Other growth factors, including immunoglobulins, exert influence

20. IODINE DEFICIENCY Daily requirement - 0.1–0.15mg Endemic areas Mountain ranges → Rocky Mountains, Alps, Andes , Himalayas UK- Derbyshire and Yorkshire. Ca is also goitrogenic (goitre common in low-iodine areas on chalk or limestone) Failure of intestinal absorption

21. GOITROGENS Vegetables of the brassica family e. Cabbage(contain thiocyanate) Drugs -para-aminosalicylic acid (PAS) and the antithyroid drugs Thiocyanates and perchlorates Carbimazole and thiouracil compounds

22. Natural history - simple goitre Growth stimulation → diffuse hyperplasia;(diffuse hyperplastic goitre) reversible F luctuating stimulation, a mixed pattern develops Active lobules become more vascular → haemorrhage occurs, causing central necrosis and leaving only a surrounding ring of active follicles Necrotic lobules coalesce to form nodules Continual repetition → nodular goitre Nodules are inactive, and active follicles are present only in internodular tissue.

23. DIFFUSE HYPERPLASTIC GOITRE 1st stages The goitre appears in childhood in endemic areas Can occurs at puberty(metabolic demands) Goitre may regress Reappear at pregnancy Soft, diffuse

24. NODULAR GOITRE Nodules are multiple Occasionally, only one macroscopic nodule is found, but microscopic changes will be present throughout the gland(solitary) Appear early in endemic goitre and later in sporadic goitre, F>M (presence of oestrogen receptors in thyroid)

25. Colloid goitre. Large multinodular goitre

26. Diagnosis Straightforward Nodules are palpable They are smooth,firm painless and moves freely Hardness and irregularity, due to calcification,may simulate carcinoma

27. Investigations TFT Thyroid antibodies (autoimmune thyroiditis) Ultrasound - gold standard FNAC → nodule of concern USG guided Biopsy CT scan

28. Complications Tracheal obstruction Secondary thyrotoxicosis - up to 30% of patients. Carcinoma usually in endemic areas Rapidly growing nodule is of concern and go for FNAC

29. Prevention and treatment of simple goitre Iodised salt Early stages,- thyroxine (diffuse hyperplastic) Nodular stage of simple goitre is irreversible, Most patients of MNG -asymptomatic (no surgery) Indication of Surgery→ Doubt of malignancy,pressure effects, cosmetic

30. Choice of surgical treatment in MNG Total thyroidectomy +lifelong replacement of thyroxine Subtotal thyroidectomy - involves partial resection leaving up to 8 g of relatively normal tissue B/L Hemithyroidectomy- total lobectomy on the more affected side Adv. of total thyroidectomy Reoperation for recurrent nodular goitre -hazardous - total thyroidectomy in younger patients too Additional advantage - therapeutic for incidental carcinoma

31. Clinically discrete swellings F>M 70% of discrete thyroid swellings isolated, 30% are dominant Clinically impalpable nodules - often detected on operation/ imaging Importance of discrete swelling= risk of neoplasia ( 15% → malignant)

32. Investigation TFT -toxicity +nodularity = Isotope scanning AUTOANTIBODY TITRES - Chronic lymphocytic thyroiditis ISOTOPE SCAN- Toxicity associated with nodularity ULTRASONOGRAPHY- Gold standard.Microcalcification and increased vascularity- malignancy Should be used as the primary investigation of any thyroid nodule

33. FNAC - papillary thyroid cancer (reliable), follicular (unreliable) Can’t distinguish between a follicular adenoma and carcinoma( capsular +vascular invasion) RADIOLOGY - CT scanning - metastatic disease LARYNGOSCOPY - vocal cords CORE BIOPSY - rarely indicated d/t vascularity.

34. Indication for operation Selection for operation according to the risk of neoplasia and malignancy Removal of all follicular neoplasms - Not possible to distinguish between a follicular adenoma and carcinoma Evidence of RLN paralysis, suggested by hoarseness, cough and confirmed by laryngoscopy, is almost pathognomonic of Ca Thyroid carcinoma in women is about three times that in men

35. Indication for operation

36. Selection of thyroid procedure Diagnosis Risk of thyroid failure- Total / Near total / Subtotal Risk of RLN injury :Subtotal resections - later growth - second operation → risk to the RLN and parathyroid Risk of parathyroid injury Risk of recurrence Graves’ disease: larger remnants have a better chance of normal function but a higher risk of recurrence Multinodular goitre Differentiated thyroid cancer

37. HYPERTHYROIDISM Thyrotoxicosis Types Diffuse toxic goitre (Graves’ disease) Toxic nodular goitre Toxic nodule Hyperthyroidism due to rarer causes

38. Diffuse toxic goitre(Graves’ disease) Diffuse vascular goitre appearing at the same time as hyperthyroidism Eye signs Primary thyrotoxicosis F/H autoimmune endocrine diseases Whole thyroid involved Cause→abnormal TSH-RAb that bind to TSH receptor

39. Toxic nodular goitre Starts with simple nodular goitre → hyperthyroidism No eye signs. Secondary thyrotoxicosis Nodules are inactive - internodular tissue - overactive

40. Toxic nodule / toxic adenoma Solitary overactive nodule It is autonomous (Not d/t TSH-RAb) TSH secretion is suppressed by the high level of circulating thyroid hormones and the normal thyroid tissue surrounding the nodule is itself suppressed

41. Graves disease Toxic adenoma Toxic MNG Normal

42. Principles of treatment of thyrotoxicosis Options :1.antithyroid drugs, 2. Surgery, 3. radioiodine ANTITHYROID DRUGS Carbimazole, Propylthiouracil Cannot cure a toxic nodule (overactive thyroid tissue autonomous) Advantages: No surgery and no use of radioactive materials. Disadvantages: Tt prolonged, failure 50%

43. SURGERY In diffuse toxic goitre and toxic MNG -surgery cures by reducing the mass of overactive tissue After subtotal thyroidectomy → euthyroid state Long-term risks of recurrence Total/ near total thyroidectomy - immediate thyroid failure and lifelong thyroxine replacement Allows the suppressed normal tissue to function again

44. SURGERY Advantages Goitre removed, cure rapid and high Disadvantages. Recurrence (5%) when subtotal Risk of permanent hypoparathyroidism and nerve injury

45. RADIOIODINE Destroys thyroid cells and reduces the mass of functioning thyroid tissue to below a critical level. Advantages. No surgery and no prolonged drug therapy. Disadvantages. Isotope facilities must be available. Must be quarantined while radiation levels are high and avoid pregnancy and close physical contact

46. Choice of therapy DIFFUSE TOXIC GOITRE - antithyroid drugs with radioiodine for relapse TOXIC NODULAR GOITRE - should be treated surgically because it does not respond as well or as rapidly to radioiodine or antithyroid drugs as does a diffuse toxic goitre. TOXIC NODULE- Surgery or radioiodine treatment FAILURE OF ANTITHYROID DRUGS - surgery or radioiodine