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Thyroid – Episode 251 – Step 1, Step 2CK, Step 3Embryology – develops in base of tongue at the foramen cecum. The thyroglossal duct (endoderm derived) burrows down and forms thyroid gland. If the thyroglossal duct doesn’t go away, then problem. Vignette 1: neck mass derived from endoderm in the midline that moves with swallowing, then it is a thyroglossal duct cyst. Buzz word: field obliteration of a thyroglossal duct or endodermal derivative.If the cyst is derived from pharyngeal grooves/clefts and ectoderm and is lateral and does not move with swallowing, think branchial cleft cyst. Buzz word: field obliteration of second to fourth pharyngeal groove or cleft or ectoderm.Vignette 2: if person comes in for something else and finds out that s/he does not have a thyroid gland, but thyroid level is normal, then they have a functioning lingual thyroid.Vignette 3: newborn with hypothyroidism (thyroid dysgenesis). Newborn will present with umbilical hernia, big tongue macroglossia.Vignette 4: Mom taking PTU or methimazole. Newborn will be born hypothyroid but will become normal in a few days.GENERAL PRINCIPLE: if there is a cyst, do U/S and aspiration (FNA) and send for cytology.Thyroid nodule question (most common thyroid question):First: get TSH levelIf low TSH, then hyperthyroid state (hot nodule).Get radioactive iodine optic scan (RAIU scan)If entire thyroid gland is hot: global or diffuse thyroid gland stimulation – TSH receptor agonist – (possible Graves’ disease (HY) - hyperthyroidism)Give PTU or methimazole (causes agranulocytosis)Give I131 as radioactive iodine (1st line)NOT thyroidectomy (!!)If one hot spot, think toxic adenoma. One spot is not responding to normal function and is secreting T3 and T4. This increases T3, T4 in serum, resulting in decreased TSH.If multiple hot spots, think toxic multinodular goiter. If TSH is normal or high, then it is a cold nodule.U/S to visualize nodule and FNATypical: colloid cyst (70%)Atypical: thyroid cancer (20%)Thyroid nodule has no increased uptake but recent URI in person. Exquisitely tender thyroid gland. Think De Quervain's thyroiditis, subacute thyroiditis, granulomatous thyroiditis or giant cell thyroiditis (different names; same thing). Lots of inflammation and macrophages. Causes preformed thyroid hormone to be released. This kills TSH. And thyroid gland will be cold on radioactive scan. Differentiate between De Quervain’s and factitious thyroiditis: vignette will have healthcare person or weightlifter or anorexia or bulimia person who wants to increase metabolism. Excess Synthroid will cause preformed thyroid hormone to be released. This kills TSH. And thyroid gland will be cold on radioactive scan. Look for: C-peptide. (Same answer to differentiate between illegal or excess exogenous Synthroid use and insulinoma).Thyroglobulin: do not confuse with thyroxin binding globulin. This is like the C-peptide. If this is elevated, then think insulinoma or De Quervain’s. If this is not elevated, then exogenous Synthroid use. (Otherwise, T3 and T4 will be elevated in all scenarios). Hyperthyroidism with decreased uptake in RAIU scan: adnexal mass. Think teratoma or stromal ovarian mass that is making ton of thyroid hormone that will reduce TSH.Thyroid storm: History of Graves and person is decompensating. Tachycardic, hypertensive, altered mental status. First: Give beta blocker or propranolol (almost always the answer).Why? Thyroid hormone puts extra beta1 receptors on myocytes. Causes super adrenergic state. Permissive effect on SNS. Why propranolol: it will inhibit adrenergic symptoms AND also inhibit conversion of T4 → T3.Second: give PTU → inhibits thyroperoxidase (inhibit making of thyroid hormone) and inhibits conversion of T4 → T3. Aside: PTU can be given in 1st trimester. Methamazole in 2nd and 3rd trimester. Third: SSKI (Super saturated potassium iodide). Takes advantage of Wolff-Chaikoff effect and shuts down thyroid production transiently. Fourth: steroidsThyroid cancerNeck mass and biopsy shows papillary thyroid cancer. Question asks what is the biggest risk factor for this condition? Prior radiation of head and neck. Hodgkin’s as a child. Papillary thyroid cancer is associated with Psammoma bodies or laminated calcifications and Orphan Annie eye nuclei. (Aside: Meningiomas, mesothelioma, papillary serous cystadenocarcinoma of ovary also have psammoma bodies).Differentiate between spread of papillary thyroid cancer and follicular thyroid cancer.Follicular: hematogenous spread – CRAP recoveryPapillary: lymphatic spread – AMAZING recoveryTested on NBME: cancer spreads from thyroid to brain. What is it? Follicular thyroid cancer.Aside: choriocarcinoma of the ovary spreads hematogenous to brain or lung. How to differentiate between follicular adenoma and follicular carcinoma?FNA will NOT workLobectomy of gland neededNeck mass with seizures, calcium = 6 or EKG QT prolongation (or family members have died from neck mass)Think medullary cancer – MEN2A or MEN2B mutation – AWFUL prognosisWhat surgical procedure is indicated? Prophylactic thyroidectomy because matter of when and not if.Tumor marker: calcitonin – tones down blood calcium levels. Therefore, vignette will have hypocalcemia. Calcitonin will form amyloid (think Congo red stain and apple green birefringence). (HY)Medullary cancer is cancer of C cells found in thyroid gland. (HY)Old person (60s – 80s) with widespread, very firm thyroid mass – anaplastic thyroid cancer – terrible prognosis.Young person, IV drug user, pancreatitis leads to sepsis and tons of labs. This person is very sick, in ICU, anorexia nervosa, big time fasting, loss of ton of weight. Think euthyroid sick syndrome. Look for increased reverse T3 (HY), decreased T3, normal TSH, normal T4. Why? Person not eating will decrease metabolic rate. This will decrease T3 (metabolically active thyroid hormone). HypothyroidismThink Hashimoto’s on the exam. Most common cause of hypothyroidism except in newborn (thyroid dysgenesis). Bradycardia, low T3, T4 and high TSH. Give triiodide or levothyroid.Vignette: Person with Hashimoto’s or hypothyroidism will almost always be infertile. Why?TRH is also called prolactin releasing factor. Increased prolactin decreases GnRH and reduced stimulation of ovaries. Vignette: Person with myxedema will have non-pitting edema and bradycardia.Give them IV thyroid.Psych question: lithium will cause hypothyroidism. Vignette: Person with history of Hashimoto’s develops large neck mass. Biopsy shows germinal follicles and tons of lymphocytes, think thyroid lymphoma. ................
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