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Thyroid Lecture
Thyroid Disorders
| Question | Answer |
|---|---|
| Anatomic size of Thryoid | About 4 cm high vertically and each lobe is about 2.5cm across |
| Thyroid examination | Visual inspection, landmark identification, palpation, auscultation (for bruits), lymph node examination (cervical and supraclavicular). One side at a time, then the isthmus |
| How much Thyroxine per day does the thyroid produce? | 100mcg; thyroid has a 50 day reserve supply of thyroxine |
| Thyroid hormone synthesis requires a minimum of ___ mcg of elemental iodine/day | 60 |
| Which is more pharmacologically active Thyroid hormone? | T3 |
| Endocytosis and degradation of _______ is required to create biologically active thyroid hormones | Thyroglobulin |
| Thyroid hormones are bound to | thyroid binding globulin (TBG), transthyretin, or albumin in plasma |
| TBG is _____ by estrogen and ______ by androgen | increased; decreased |
| TRH is released by the | hypothalamus |
| TSH is released by the | anterior pituitary |
| What provides negative feedback to the hypothalamus? | Free T3 and Free T4. |
| Most common blood tests to determine thyroid function | Ultra-sensitive TSH (thyrotropin) and Free T4 |
| Direct test of thyroid function | 131-Iodine Uptake; measured at 24 hours; nl is 15-30% of iodine load goes into thyroid |
| Imaging | Thyroid scan, US, CT, MRI, PET |
| Biopsy | Fine Needle Aspiration, open biopsy |
| What can a thyroid do? | Overact, under-perform, enlarge (like a toddler) |
| Main hyperthyroid symptoms | Unintentional weight loss, heat intolerance, palpitations/tachycardia |
| Brisk DTR relaxation phase is seen in what condition? | Hyperthyroidism. Slow with hypo |
| Common Causes of hyperthyroidism | Graves dz, toxic multinodular goiter, toxic nodule, thyroiditis |
| Graves Disease | Autoantibody reacting with the TSH receptor. Symmetric non-tender goiter. Bruit is pathognomonic. Ocular findings, pretibial myxedema |
| Evaluation of Graves Disease | TSH, Free T4 and T3, Thyroid uptake and scan |
| Eye protuberance in Graves Disease | Autoantibody binds to extraocular eye muscles, eyes pushed out, optic nerve can be squished. Difficult to manage. Radiation may be used |
| Pharmacologic Treatment for Graves Disease | Two agents to suppress the thyroid:PTU - 3x/day dosing, pregnant patients must use this oneMethimazole (tapazole)- 1x/day dosingBeta-blockers acn also be used:propanolol or atenolol |
| Other Treatment for Graves Disease | Surgery: subtotal thyroidectomyRadioactive Iodine Ablation: Drink a substance, radioactive iodine goes to thyroid and destroys part of thyroid. Problem is that some pts become hypothyroid. |
| Favorable Prognosticators for remission of Graves Dz | Small goiter, Free T3 predominance, Negative TSI titer, Decrease in goiter size with thionomide therapy |
| Etiology of Toxic Multinodular Goiter | Multicellular autonomous function. Usually in patients >50. Arises from non-toxic multinodular goiter. Exam: enlarged, irregular, nodular thyroid. |
| Treatment for Toxic Multinodular Goiter | Only treatment is Radioactive iodine to knock out nodule. Thyroid stays in tact |
| Etiology of Toxic nodule | Constitutive activation of the TSH receptor through a somatic mutation of the receptor gene. Age: 30-40. Exam: Enlarged, irregular, nodular thyroid, Oncholysis (ring finer). Hot Nodule |
| Thyroiditis | Two types: Subacute (deQuervain's), Silent or painless (Hashitoxicosis). Course: hyper, hypo, euthyroidism |
| Etiology of subacute thyroiditis | Thyroid hormone leakage from destruction the thyroid gland secondary to a viral infection (mumps) |
| Pain in the thyroid gland and fever is associated with what diagnosis | Subacute thyroiditis |
| Treatment for Subactute thyroiditis | Aspirin, NSAIDs, prednisone |
| Sudden onset of hyperthyroidism that is self-limited and can also be seen post-partum suggests what diagnosis? | Silent Thyroiditis. Not a thyroid problem, just leakage. Rx: BB. This is a transient autoimmune dysfunction |
| Thyrotoxic Crisis (thyroid Storm) | Come back to thiss |
| Hypothyroidism can cause | high cholesterol. First address the hypothyroidism |
| Etiology of Hypothyroidism | Primary, Goiterous, Cenral (lack of TSH; pituitary or hypothalamic failure; unusual) |
| Primary cause for hypothyroidism | Hashimoto Thyroiditis; marked by cytotoxic anti-thyroid antibodies. Anti-thyroglobulin in 80-90% |
| How to treat hypothyroidism | Thyroxine replacement |
| Levothyroxine facts | T1/2 is 7 days, 6 weeks to get to equilibrium, dosage is based on ideal body weight. Okay to make up a dose if you miss one. Virtually no AEs |
| Adjust Levothyroxine in which patients? | Elderly (>65), or angina patients; start slower and lower. In pregnant patients, increase dose by 50% |
| When should patients treated with levothyroxine be assessed? | Assess response with TSH after 6weeks; re-assess at 6 months because of euthyroid state increases clearance of t4, then annually |
| What are the side effects of thyroxine overtreatment? | osteoporosis, increased cardiac contractility, increased risk of atrial fibrillation, allergic reaction to dye in tablets |
| Describe the half life of T3 (Liothyronine) | it is short, so patient feels the ups and downs of the drug |
| Desiccated thyroid is made from | pigs and cows. Amount of T3 and T4 is variable |
| Goiter | General term for enlargemet of the thyroid |
| Nontoxic goiter | not caused by neoplastic process or inflammation. Two types: endemic - in more than 10% of pop. , Sporadic - genetic or environmental factors that do not affect the general population |
| Endemic Goiter | Impaired thyroid hormone. Prevalence determined by iodine deficiency |
| Multinodular Goiter | Sporadic, unknown etiology, multifactorial, some genetic connection |
| Multiple nodules as opposed to a single nodule suggests | benign course |
| ______% of the population have thyroid nodules on US | 40-60%. Only 5% become palpable, of those 5% are malignant |
| Benign characteristics of thyroid nodules | symptoms of hypo or hyperthyroidism, pain or tenderness over thyroid nodule, Family hx |
| Suspicious historical features of thyroid nodules | recent changes in size, age <20, >70, Male, History of neck irradiation, Previous h/o thyroid cancer, recent changes in voice, breathing or swallowing (recurrent laryngeal nerve), family hx of thyroid malignancy. |
| Suspicious exam of thryoid nodules | firm nodules with irregular shape, fixation to underlying tissues, regional adenopathy |
| Evaluation of Thyroid nodule | TSH, US, FNA (no thyroid scan!) |
| Size cutoff for watching nodules | 1.5 cm |
| Predictors of histological malignancy of thyroid nodule | microcalcifications, blurred margins, size >10mm, hypoechoic, Vascularity (intranodular blood flow on multiple vascular images) |
| Benign Follicular Cell Tumors | Follicular and Hurthle cell adenomas |
| Papillary Thyroid Carcinoma | F:M 4;1, high survival rate, age: 30-50 |
| Follicular Thyroid Carcinoma | F:M 2:1, Age>50, more common to have distant metastases (lung and bone) |
| Medullary Thyroid Carcinoma | F:M 1:1, Age>40, Associated with MEN type2, Rx: aggressive surgery |
| Thyroid cancer staging factors: | Tumor size, Tumor characteristics, Metastases, Patient age |
| Treatment for Thyroid Carcinoma | Thyroidectomy by experience surgeon. Papillary <1cm w/o invasion: rx - thyroxine. suppression and follow thyroglobulin (should be low and non) and exam annually. |
| Hyperthyroid with normal thyroid exam | Graves dz or iatrogenic. Possilbe low lying thyroid, consider thyroid uptake scan, consider referral |
| Graves Dz | Symmetric +/- bruit, Rx: anti-thyroid meds, endo referral |
| Toxic Multi-nodular goiter | irregular contour, Rx: TMG - uptake, scan, ablation |
| Subacute thyroiditis | tender, hard, Rx: aspirin |
| Silent thyroiditis | non-tender, firm, Rx: follow |
| Most common malignant thyroid tumor | Papillary Carcinoma; greatest incidence is in adults 40years old or younger, F>M. Least malignant of the thyroid cancers |
Created by:
ltm12
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