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Presentation on theme: "ENDOCRINOLOGY BOARD REVIEW"— Presentation transcript:


2 General - Thyroid produces two related hormones thyroxine(T4) and triidothyronine (T3) - Function is through nuclear receptors playing a role in cell differentiation - Maintains thermogensis, and metabolic homeostasis - Disorders result from autoimmune processes that either stimulate overproduction of hormones (thyrotoxicosis) or glandular destruction and hormone deficiency (hypothyroidism) - Benign nodules and various forms of thyroid cancers

3 Anatomy - Located anterior to trachea consist two lobes
-  Weighs 12-20gm soft and highly vascular a posterior region gland contain four parathyroid gland that produce parathyroid hormone - Lateral borders of the gland is transversed by the recurrent laryngeal nerves - Develops from the floor of the primitive pharynx third week of gestation migrates from the foramen cecum, at the base of tongue along the thyroglossal duct to neck - Hormonal synthesis usually begin at about 11 weeks’ gestation

4 Thyroid Physiology - Thyroid releases (2) forms of hormones
- Thyroxine (T4) and triiodothyroxine (T3) ratio 14:1 - T3 is 80% derived from peripheral tissue - T4 all within the thyroid gland - T3 is produced from T4 in liver, kidneys, pituitary gland and CNS - T3 is the physiologically active in almost all tissue binding to specific nuclear receptors regulating the transcription of thyroid hormone dependent genes



7 Drugs decreasing Peripheral conversion of T4 to T3
       Propranolol        Corticosteroids        Propylthiouracil (PTU)        Amiodarone


9 - TSH controls release under the influence TRH from the hypothalamus
- TSH stimulate thyrocyte function resulting in iodide uptake actively on the basal surface of the thyroid follicle cell - Iodide undergoes oxidation to iodine which iodinates tyrosine residues catalyzed by peroxidase - Thyroglobulin coupling occurs to form mono- and diiodotyrosine (MIT and DIT - Two DITs coupling = T4 - One DIT and one MIT combine =T3 - If iodine scarce, the production of T3 is increase - Activity is dictated by # iodines attached to tyrosine molecules and location



12 Secretion Degradation process with endocytosis of the follicular colloid containing MIT, T3, T4, DIT attached to thyroglobulin undergoes fusion with lyosome resulting in proteolysis release Deiodination occurs with the recycling iodide and secretion of T3 and T4 Circulating thyroid hormones are more than 99% protein bound, are thyroxine-binding globulin, albumin, and transthyretin. 80% of circulating T3 is derived from the conversion of T4 outside the thyroid Serum half-life of T3 is much shorter than that T4 (1day vs 8days)


14 Storage - Iodine as iodinated tyrosine of
thyroglobins 8000 micrograms total - T4 and T3 represent 600 micrograms each - Enough hormone is stored in the follicular colloid to last 2-3 months 


16 Overveiw of Thyroid Fx Workup
1st Test 2nd Test 3rd Test TSH FT4-I, FT4 Clinical Status HIGH Low Prim hypothyr’ism N/A Normal Subclinical hypothy’ism TRH to confirm High Pituitary hyperthyr’ism LOW Thyrotoxicosis RAIU Subclinical hypothyr’ism

17 Measurement RAIU Levels Specific disorders High
Hyperfunction (Graves’, multinodule goiter, toxic solitary nodule, hCG secreting tumor) Normal Euthyroid Low Thyroiditis, severe iodine excess, amiodarone induced thyrotoxicosis

18 Drugs and condition that affect thyroid Function Tests

19 Increase TBG Decrease TBG Block peripheral conversion of T4 to T3 Blocks thyroidal release T4 and T3 Estrogen OCT, pregnancy Tamoxifen Clofibarate Narcotics Hepatitis Bililary cirrhosis Androgens Gluccorticoid Nephrotic syn Propranolol Glucorticoid PTU Amiodarone Lithium Iodine

20 Thyroid Pathology A. Thyroid Gland
1. Multinodular goiter (nontoxic goiter) Presentation i. Females > males ii. Frequently asymptornatic iii. Typically euthyroid iv. Goiter v. Plummer's syndrome:development of hyperthyroidism (toxic multinodular Goiter) late in course

21 B. GROSS enlarged thyroid gland with multiple colloid nodules C. MICROSCOPIC i. Nodules of varying sizes composed of colloid follicles ii. Calcification, hemorrhage, cystic degeneration, and fibrosis D. LAB: normal T4, T3, and TSH

22 i. Elevated free T4 ii. Primary hyperthyroidism: decreased TSH
B Hyperthyroidism 1. General features of hyperthyroidism I a. Clinical features i. Tachycardia and palpitations ii. Nervousness and diaphoresis iii. Heat intolerance iv. Weakness and tremors v. Diarrhea vi. Weight loss despite a good appetite b. Labs i. Elevated free T ii. Primary hyperthyroidism: decreased TSH

23 Graves'disease a. Definition: autoimmune diseases characterized by production of IgG autoantibodies to the TSH receptor b. Clinical features i. Females > males; age 20‑40 ii. Hyperthyroidism iii. Diffuse goiter iv. Ophthalmopathy: exophthalmus v. Dermopathy: pretibial myxcdema c. Micro: hyperplastic follicles with scalloped colloid

24 Other causes of hyperthyroidism
a. Toxic multinodular goiter b. Toxic adenoma: functioning adenoma producing thyroid hormone c. Hashimoto’s and subacute thyroiditis (transient hyperthyroidism)

25 Juvenile Graves Disease
Diffuse hyperplasia Most common cause of thyrotoxicosis in children and adolescents Clinical manifestation - muscle weakness behavior problems - anxiety cardiomegaly - palpitations tachycardia - appetite widen pulse pressure - Tremor Emotional liability - rapid DTR time Excessive perspiration Opthalmopathy, dermopathy, pretibial myxedema rare in children

26 Test: TSH suppressed and serum T4 high Treatment:
a. Blunting toxic effects circulating T3/T4 b. Stop further increase in production B-blockers prior to Sx intervention RAI rarely used in children and adolescences potential risk leukemia, thyroid Ca, and genetic disorder. Medical management: PTU and methimazole mechanism: Both inhibit the coupling of iodotyrosines, oxidation and binding of iodide

27 PTU 5-10mg/kg PO div q8hr Methimazole 0.2 mg/kg PO daily Once gland cools off and decrease in size tapper drugs Give synthetic T4 once euthyroid adjust to maintain a euthyroid status

28 Neonatal Thyrotoxicosis
Due to TSH-receptor stimulating antibodies(TSH) Transmitted transplacentally in mother with inactive or active Graves or Hashimoto thyroiditis Presentation: newborn irritability, flushing, tachycardia, HTN, thyromegaly High total T4, FT4, T3 postnatal blood, low TSH Treatment: a. sedative and digitalis if needed b. Iodide c. Lugol (5% iodine and 10% K iodine) d. Methimazole

29 Hypothyroidism a. Clinical features i. Fatigue
ii. Sensitivity to cold temperatures iii. Decreased cardiac output iv. Myxedema: - Facial and periorbital edema - Peripheral edema of the hands and feet - Deep voice - Macroglossia v. Constipation vi. Anovulatory cycles

30 Iatrogenic hypothyroidism Most common cause of hypothyroids in US
b. Lab i. Decrease Free T4 ii. Primary hypothyroidism: elevated TSH Iatrogenic hypothyroidism Most common cause of hypothyroids in US Secondary to thyroidectomy or RAI rx Rx: Levothyroxine mcg PO qd adjusting dose by mcg/d q4-8wks

31 Congential Hypothyroidism(cretinism)
a. Etiology i. Endemic region: iodine deficiency during intrauterine and neonatal life ( worldwide) ii. Non endemic regions: thyroid dysgenesis b. Presentation i. Failure to thrive ii. Stunted bone growth and dwarfism -Commonly absent distal femoral epiphysis iii. Spasticity and motor incoordination iv. Mental retardation v. Goiter (endemic cretinism) ‑ Endemic goiter a. Uncommon in the US b. Etiology: dietary deficiency of iodine

32 Clinical Manifestation congenital Hypothyroidism
Occurs in 1/4000 Worldwide Most infant are asymptomatic at birth because of transplacental passage of T4 (usu 3rd day of life) Most common cause is thyroid dysgenesis Presentation: hypoglycemia, jaundice micropenis, midline facial anomalies, enlarge posterior fontanelle, macroglossia Rx: Initial dose: Sodium L-tyroxine 10-15 microgrms/kg/day( should not be mixed soy protien or iron) Then, 4 micrgms/kg/day

33 Thyroiditis Hashimoto's thyroiditis
a. Definition: chronic autoimmune disease characterized by immune destruction of the thyroid gland and hypothyroidism b. Most common noniatrogenic cause of hypothyroidism and Goiter in children > 6yo and adults in US c. Clinical presentation i. Females > males; age 40‑65 ii. Painless goiter iii. Hypothyroid iv. Initial inflammation may cause transient hyperthyroidism. d. Gross: pale enlarge gland e. Micro: i. Lymphocytic inflammation with germinal centers ii. Epithelial "Harthle cell" changes f. May be associated with other autoimmune diseases (SLE, RA, SS [Sjogren's syndrome], etc.) g. Complication: increased risk of non‑Hodgkin‘ lymphoma (NHL) B‑cell lymphoma

34 2. Subacute thyroiditis a. Synonyms: De Quervain's thyroiditis, granulomatous thyroiditis b. Clinical features i. Second most common form of thyroiditis ii. Females > males; age 30‑50 iii. Preceded by a viral illness iv. Tender, firm, enlarged thyroid gland v. May have transient hyperthyroidism c. Micro: granulomatous thyroiditis d. Prognosis: typically the disease follows a self‑limited course e. Symptoms: control with analgesics, prednisone very severe dx

35 Riedel's thyroiditis a. Definition: rare disease of unknown etiology characterized by destruction of the thyroid gland by dense fibrosis and fibrosis of surrounding structures (trachea and esophagus) b. Clinical features i. Females > males; middle age ii. Irregular, hard thyroid that is adherent to adjacent structures iii. May mimic carcinoma and present with stridor, dyspnea, or dysphagia c. Micro i. Dense fibrous replacement of the thyroid gland ii. Chronic inflammation d. Associated with retroperitoneal and mediastinal fibrosis

36 Thyroid Neoplasia a. Follicular adenomas are the most common Adenomas
b. Clinical features i. Usually painless, solitary nodules In first 20 yrs life likely malignant than older person ii. "Cold nodule" on thyroid scans iii. May be functional and cause hyperthyroidism (toxic adenoma) 2. Papillary carcinoma a. Epidemiology i. Account for 80% of malignant thyroid tumors ii. Females > males; age 20‑50 iii. Risk factor: radiation exposure b. Micro i. The tumor typically exhibits a papillary pattern. ii. Occasional psammoma bodies iii. Characteristic nuclear features Clear "Orphan Annie eye" nuclei Nuclear grooves

37 Intranuclear cytoplasmic inclusions
c. Lymphatic spread to cervical nodes is common. d. Treatment i. Resection is curative in most cases. ii. Radiotherapy with iodine 131 is effective for metastases. e. Prognosis: excellent; 20‑year survival = 90% Follicular carcinoma a. Accounts for 15% of malignant thyroid tumors b. Females > males; age 40‑60 c. Hematogenous metastasis to the bones or lungs is common. d. High mortality rate because most present with distant mets

38 Treatment: primarily surgical
Medullary carcinoma a. Accounts for 5% of malignant thyroid tumors b. Arises from C cells (parafollicular cells) and secretes calcitonin c. Micro: nests of polygonal cells in an amyloid stroma d. Minority (25%) are associated with MEN 2 and MEN 3 syndromes Treatment: primarily surgical - Advance disease external RT and chemo

39 i. Females > males; age > 60 ii. Firm, enlarging, bulky mass
Anaplastic carcinoma a. Presentation i. Females > males; age > 60 ii. Firm, enlarging, bulky mass iii. Dyspnea and dysphagia iv. Tendency for early widespread metastasis and invasion of the trachea and esophagus b. Micro: undifferentiated, anaplastic, and pleornorphic cells c. Prognosis: very aggressive and rapidly fatal

40 Diagnosis Fine needle aspirate vs. excision - Hx RT to neck or head
- rapidly growing nodule - satellite LN and/or distant mets - Hoarseness or dysphagia Rx: Well differentiated neoplasm should be excised - TSH suppression - RAI ablation


42 Q1 An 18yo old boy presents with a 1 month history of slowly enlarging neck mass. You palpate a 2-cm mass in the superior lobe of the rt. thyroid with no lymphadenopathy. Of the following, the BEST next step is to: Begin therapy with RAI Obtain anteroposterior and lateral CXR Perform needle bx of the neck Perform total thyroidectomy Prescribe oral cephalexin

43 Q2. 15yo female presents with an asymptomatic goiter
Q2. 15yo female presents with an asymptomatic goiter. She has type 1 diabetes that was diagnosed at age 7 years Of the following, study that is MOST likely to establish the diagnosis is Measurement of antiperoxidase antibodies Needle bx of thyroid Technetium thyroid scan Thyroid-binding globulin levels US of the thyroid

44 Q3. 44yo male involved in a MVA unresponsive intubated in ICU with multiple orthropedic injuries. He is stabilized medically on day 2 undergoes open reduction and internal fixation of right femur and right humerus. After returning to the ICU, his TSH is 0.3mU/L and total T4 is normal. T3 is 0.6 micrograms/dl. What is the next appropriate step in the management of this patient? Start levothyroxine RAIU scan Thyroid US Observe patient Initiate prednisone

45 Q4. Which of the following statements regarding hypothyroidism is true?
Hashimoto’s thyroiditis is the most common cause of hypothyroidism worldwide The annual risk of developing overt clinical hypothyroidism from subclinical hypothyroidism in patients with positive thyroid peroxidase antibodies is 20%. Hashimoto’s is characterized by marked infiltration of thyroid with activated T and B cells Low TSH excludes the diagnosis of hypothyroidism Thyroid peroxidase antibodies are present in 50% of patients with autoimmune hypothyroidism

46 References American College of Physicians MKSAP 13
MedStudy Pediatric Board Review Harrison’s Principle of Internal Medicine


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