Lecture 16


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Lecture 16

  1. 1. Thyroid Disorders
  2. 2. Thyroid Anatomy <ul><li>Macroscopically </li></ul><ul><li>The thyroid has two lobes joined by an isthmus </li></ul><ul><li>Embedded into the upper and lower poles of both lobes are the parathyroid glands. </li></ul>
  3. 5. Thyroid Structure <ul><li>Microscopically </li></ul><ul><li>The gland is formed of follicles, which are rings of thyroid cells enclosing a colloid which contains the stored hormones and thyroglobulin the precursor </li></ul>
  4. 7. Thyroid Hormone Formation <ul><li>Essential requirements are the protein Thyroglobulin, Iodine and enzymes which join the two together </li></ul><ul><li>The hormones are composed of tyrosine ( a subcomponent of thyroglobulin) and 1, 2, 3 or 4 Iodine molecules, </li></ul><ul><li>The active hormones are the tri form = tri-iodo thyronine and thyroxine, which has 4 Iodine molecules </li></ul>
  5. 8. Control of Thyroid hormone production <ul><li>Thyroid releasing hormone (TRH) from the Hypothalamus causes the pituitary to release Thyroid Stimulating Hormone (TSH) </li></ul><ul><li>There is a negative feedback loop between the Thyroid hormones and these control hormones </li></ul><ul><li>Iodine is also required </li></ul>
  6. 10. Action of Thyroid Hormones <ul><li>Increase sweating </li></ul><ul><li>Increase cardiac output </li></ul><ul><li>Increase pulse pressure ( higher syst. and lower dias.)due to an increase in the stroke volume and a reduction in peripheral vascular resistance </li></ul><ul><li>Increased utilization of CHO, Protein and Fat </li></ul><ul><li>Increased excitation of Nervous system </li></ul><ul><li>Plus Thyroid hormones are essential for the growth and development of the Skeleton, Teeth, Epidermis and CNS </li></ul>
  7. 11. Thyroid Disorders <ul><li>Common disorders are </li></ul><ul><li>Goitre = an enlarged thyroid </li></ul><ul><li>Hypothyroidism = symptoms of reduced levels of thyroid hormones </li></ul><ul><li>Hyperthyroidism = symptoms of increased levels of thyroid hormones </li></ul><ul><li>Less common are thyroid tumours </li></ul>
  8. 12. Terms and their definitions <ul><li>Goitre = enlarged thyroid (does not refer to the function of the thyroid) </li></ul><ul><li>Toxic = increased thyroid hormone output </li></ul><ul><li>Nodule = palpable lump in thyroid </li></ul>
  9. 13. Goitres <ul><li>Can be either simple or toxic </li></ul><ul><li>Diffuse or Multinodular </li></ul>
  10. 14. <ul><li>Simple (non-toxic)Goitre </li></ul><ul><li>= thyroid is enlarged ( either diffusely or in a multinodular form) but there is no excess thyroid hormone production </li></ul><ul><li>Aetiology </li></ul><ul><li>Inadequate iodine, </li></ul><ul><li>Excessive amounts of goitrogens </li></ul><ul><li>Pregnancy ( higher need for Iodine) </li></ul><ul><li>Drugs </li></ul>
  11. 15. Clinical Features of Simple Goitre <ul><li>Enlarged thyroid which is soft and symmetrical </li></ul><ul><li>No changes in any of the hormones = euthyroid </li></ul><ul><li>Usually no treatment is required and the goitre resolves </li></ul>
  12. 18. Simple Multinodular Goitre <ul><li>A gradually enlarging thyroid which develops localised areas of hyperplasia resulting in palpable nodules </li></ul><ul><li>The gland can become large enough to compress nearby structures but it does not usually produce excessive levels of hormones </li></ul><ul><li>Unless causing pressure problems or early hyperthyroidism the thyroid is merely reviewed annually </li></ul>
  13. 19. Multinodular goitre
  14. 20. Hypothyroidism <ul><li>Most common thyroid disorder </li></ul><ul><li>Is the clinical syndrome that results form a deficiency of thyroid hormones </li></ul><ul><li>It can develop in utero (cretinism) or as an adult </li></ul><ul><li>If It occurs in the latter situation it can result in deposition of glycosaminoglycans (GAGS) and thus produce myxedema </li></ul>
  15. 21. Pre tibial Myxedema
  16. 22. Causes of Hypothyroidism <ul><li>Primary = failure of thyroid gland to produce thyroid hormone. Can be caused by, </li></ul><ul><li>Hashimoto’s thryoiditis (+/- goitre) </li></ul><ul><li>End stage Graves disease </li></ul><ul><li>Surgical removal of thyroid or radioactive ablation of thyroid as treatment of Graves </li></ul><ul><li>Secondary = failure of pituitary to produce TSH </li></ul><ul><li>Can also be tertiary </li></ul>
  17. 23. Hashimoto’s Thyroiditis <ul><li>Most common cause of hypothyroidism and also causes a goitre </li></ul><ul><li>Aetiology </li></ul><ul><li>Cause by an auto-immune reaction to thyroid but mechanism is still unclear </li></ul><ul><li>There are auto-antibodies to thyroglobulin, etc but their levels do not correlate well with the severity of the disease </li></ul>
  18. 24. Hashimoto’s cont’d <ul><li>Pathology </li></ul><ul><li>The thyroid undergoes infiltration by lymphocytes and fibrosis follows resulting in an initially enlarged gland shrinking </li></ul>
  19. 25. Lymphoid follicles at right and centre Hashimoto’s thyroiditis
  20. 26. Clinical Features of Hypothyroidism <ul><li>There is usually a goitre and variable levels of thyroid hormones </li></ul><ul><li>Some are due to reduced levels of thyroid hormones eg slowness, cold intolerance </li></ul><ul><li>Others are due to a build up of GAGS eg non-pitting oedema of hands, eyes </li></ul>
  21. 28. Complications <ul><li>5% develop thyroid cancer </li></ul><ul><li>As it is usually a disease of the elderly it can co-exist with CAD so treatment can unmask and stress the previously protected coronary vessels </li></ul>
  22. 29. Thyrotoxicosis <ul><li>Definition </li></ul><ul><li>Clinical features of excess thyroid hormone </li></ul>
  23. 30. Aetiology of Thyrotoxicosis <ul><li>Graves Disease, which is associated with autoantibodies which act to stimulate TSH receptors and thus cause the production of greater amounts of thyroid hormone </li></ul><ul><li>A nodule in a multinodular goitre which produces excess thyroid hormone ( ie becomes toxic) </li></ul><ul><li>Toxic adenoma </li></ul>
  24. 32. Clinical Features of Thyrotoxicosis <ul><li>General = heat intolerance, warm moist skin, LOW in spite of increased appetite </li></ul><ul><li>GIT = malabsorption and diarrhoea </li></ul><ul><li>CVS = palpitations, tachycardia </li></ul><ul><li>Neuromuscular = tremor, irritability, proximal myopathy </li></ul><ul><li>Ocular = wide, staring gaze, lid lag </li></ul>
  25. 33. Graves Disease <ul><li>Is the most common form of thyrotoxicosis (90%) </li></ul><ul><li>F:M = 4-5:1, 30-50 yoa </li></ul><ul><li>Aetiology </li></ul><ul><li>autoantibodies which stimulate the thyroid ( in contrast with Hashimoto’s) </li></ul>
  26. 34. Graves Disease <ul><li>Thyrotoxicosis and goitre due to increased stimulation </li></ul><ul><li>Infiltrative opthalmopathy = exopthalmos </li></ul><ul><li>Dermopathy ( pretibial myxedema) due to accumulation of GAGS </li></ul>
  27. 36. Toxic Adenoma <ul><li>A benign tumour which secretes excess thyroid hormones </li></ul><ul><li>Note there can also be malignant thyroid tumours but these are uncommon </li></ul>