week 9- endo 2 Flashcards
• TSH testing:
o measures pit stim of thyroid
o ↑: thyroid doesn’t make enough T4 (1st hypo)
o ↓: 1) hyperthyroid, 2) abn pit doesn’t make TSH (2nd hypo)
• Thyroid hormone state:
o free=available for uptake
o bound=circulating storage pool
• T4 tests:
o Total T4: bound + free. ~99% on TBG (doesn’t enter tissues)
o fT4/fTI (index): Free; measured direct or calc as fTI= free/bound. helps tell if abn T4 is dt abn TBG (pg, viral hepatitis, cirrhosis, breast CA)
• Triiodothyronine (T3)
o ↑: hyperthyroid (st ↓TSH, ↑T3 & T4 mb normal)
o Hypothyroid: T3 mb normal (w ↑TSH, ↓T4)
o PG and OCPs: ↑ both total T4 & T3
• N TSH, N fT4, NT3:
o Euthyroid
• N TSH, N/↑ fT4, N/↑T3:
o Euthyroid hyperthyroxinemia
• N TSH, N/↓ fT4, N/↓ T3:
o Euthyroid hypothyroxinemia
• ↑ TSH, N fT4, N T3:
o Subclinical hypothyroid
• ↑TSH, ↓fT4, N/↓T3:
o Primary hypothyroid
• ↓TSH, N fT4, N T3:
o Sunbclinical hyperthyroid
• ↓TSH, ↑/N fT4, ↑T3:
o Hyperthyroid
• T3-Resin uptake:
o serum inc w radiolabeled T3 tracer
o insoluble resin added to trap remaining unbound radio-T3
o Result: % tracer bound to resin (inverse of # free binding sites for T3)
o Distinguish TBG excess and def from hyper/hypo-thyroid
• ↑ tT4, ↑T3RU, ↑FTI:
o Hyperthyroid
• ↑ tT4, ↓T3RU, N FTI:
o TBG excess
• ↓ tT4, ↓T3RU, ↓ FTI:
o Hypothyroid
• ↓ tT4, ↑T3RU, N FTI:
o TBG def
• Serum Reverse T3:
o rT3 = biologically inactive, dt deiodination of T4 (diff enzyme), mainly in liver
o ↓ T3 & ↑ rT3: mb ssx hypothyroid → ↑ protein synthesis and O2 consumption by all cells
o ↑ rT3: mb chronic dz, Wilson’s syndrome
• Anti-thyroid antibodies (ATA):
o a-TG: (+) in Hashimoto’s
o a-thyroperoxidase (a-TPO): catalyzes iodination of tyrosine; ↑ in Hashimoto’s
o TSH receptor (TRAb)
• TRH test:
o serum TSH measured after inj w TRH to determine if thyroid problems dt ↓ TRH (3rd hypothyroid, rare)
• Thyroglobin (Tg):
o Monitor w thyroid CA w thyroid glands removed
o =protein produced by normal thyroid cells and thyroid CA cells
• Radioactive Iodine Uptake (RAIU):
o swallow sm amt radioactive iodine
o ↑: thyroid gland is overactive
o ↓: underactive
• Thyroid Scan:
o may show diffusely high or low intake or discrete (nodular) areas of high (Hot nodule) or low (cold nodule) intake
o gets a “picture” of the gland
• Ultrasound:
o used to determine if a nodule is solid or cystic
• Goiters
o = enlarged thyroid gland; diffuse or nodular
o Mb seen in normal, hypo/hyperthyroid
o Geographical differences in incidence dt I def
o Etio: I def (endemic goiter), ↑TSH, Grave’s, Pg
o Many of no clinical significance but full assessment needed
o Ssx: often asx. Early: pressure/lump in throat, choking sensation, dyspnea, dysphagia
• Goiter staging:
o Normal: ~20g in size o 0: not visible; non-palpable o 1: possibly visible; mb palpable, ↓40 g o 2: visible; easily palpable, ~40 g o 3: visible, palpable, > 40g
• Goiter work-up:
o Labs: TFTs, ATAs
o neck x-rays, thyroid scan, US w needle bx = gold standard for dx
• Euthyroid (Simple) Goiter:
o dt ↓thyroid fxn w/o clinical dz.
o Etio: Endemic, pg, menopause, hormone effects, I
o goitrogens interfere w I uptake (Brassicas, soy, peanuts, millet, strawberries, peaches, sweet potato, etc)
o drugs (amino-salicylic acid, sulfonylureas, lithium)
o Labs: ↑TSH, ↓T4 in hypothyroid
• Thyroid nodules:
o Usu benign, scan to r/o malig
o Labs: TSH, FT4, ATA titers, serum Ca
o Thyroid US, fine-needle aspiration bx
o Thyroid scan: “hot” nodules in hyperfxn, “cold” in non-fxn, “warm” = nodule w normal fxn
• Hypothyroidism, causes:
o F > M, tends to be familial; gland mb small and fibrotic, or goiter
o Causes: inherited enzymatic defects, AI, RAI exposure, anti-thyroid drugs, dietary goitrogens, thyroidectomy, inflam, granuloma, neoplasms, congenital aplasia, pituitary failure
• Hypothyroid ssx:
o weak, fatigue, lethargy, cold intolerance, wt gain
o anorexia, constipation, hair loss, dry hair, dry coarse cold skin
o dyspnea, myalgias/arthralgia, paresthesias
o irregular menses, infertility, periorbital edema, thick tongue, ascites
o pallor, ↓reflexes, anemia, bradycardia, effusions, vitiligo, goiter
o CTS, eyelid dropp, psychosis, ↓facial expression, carotenemia
o ↑heart, hoarseness, poor memory, hypothermia, myxedema coma
• Age of onset/course of hypothyroid:
o Congenital →Cretinism: resp distress, cyanosis, poor feeding, hoarse cry, umbilical hernias, slow velocity bone growth
o Juvenile: slow growth, slow dentition, eczema, mental deficiencies, other general hypoT ssx
o older: main sign mb confusion, dementia, paranoia, depression.
• Hypothyroid work-up:
o Labs: ↓ tT4 and FTI (index). ↑TSH if 1st, otherwise ↓/N. a-TPO if suspect Hashimoto’s. Serum TG when suspect subacute thyroiditis. CBC: anemia common, ↑ lipids
o Image: MRI of pituitary if suspect 2nd
o ddx: 1st vs 2nd (other hormone systems involved). 1st: ↑TSH, ↓T4 & T3. 2nd: ↓BP, ↓lipids, SSX of other def. Causes of ↓TBG: chronic LV or renal dz, starvation, ↓CHO diet
