Thyroid Talk-FMD Rds - Diagnosis of Thyroid Disorders...

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Diagnosis of Thyroid Disorders Diagnosis of Thyroid Disorders William Harper, MD, FRCPC Endocrinology & Metabolism Assistant Professor of Medicine, McMaster University www.drharper.ca
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Case 1 Case 1 31 year old female Somalia Canada 3 years ago G2P1A0, 11 weeks pregnant Well except fatigue Hb 108 , ferritin 7 TSH 0.2 mU/L, FT4 7 pM Started on LT4 0.05 TSH < 0.01 mU/L FT4 12 pM, FT3 2.1 pM
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Case 1 Case 1 1. How would you characterize her hypothyroidism? 2. What are the ramifications of pregnancy to thyroid function/dysfunction?
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TSH Low High FT4 FT4 & FT3 Low 1° Hypothyroid Low Central Hypothyroid TRH Stim. If equivocal MRI, etc. High 1° Thyrotoxicosis High 2° thyrotoxicosis Endo consult FT3, rT3 MRI, α-SU RAIU
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TRH Stimulation test TRH Stimulation test A) 1° Hypothyroidism B) Central Hypothyroidism C) Euthyroid D) 1° Thyrotoxicosis
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Case 1 Case 1 GH, IGF-1 normal LH, FSH, E2, progesterone, PRL normal for pregnancy 8 AM cortisol 345, short ACTH test normal MRI: normal pituitary TGAB, TPOAB negative LT4 increased until FT4 in hi-normal range Normal pregnancy, delivery, baby, lactation Considering TRH stim once done breast-feeding
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Thyroid Tests Thyroid Tests 1. Thyroid Function 2. Iodine Kinetics 3. Thyroid Structure 4. FNA 5. Thyroid Antibodies 6. Thyroglobulin
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T4 T3 85% (peripheral conversion) 15% Protein* binding + 0.03% free T4 Protein* binding + 0.3% free T3 (10-20x less than T4) Normal Daily Thyroid Secretion Rate: T4 = 100 ug/day T3 = 6 ug/day ( ratio T4:T3 = 14:1 ) Total T4 60-155 nM Total T3 0.7-2.1 nM T 3 RU/THBI 0.77-1.23 TBG 75% TBPA 15% Albumin 10% *
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Thyroid Function Tests Thyroid Function Tests TSH 0.4 –5.0 mU/L Free T4 (thyroxine) 9.1 – 23.8 pM Free T3 (triiodothyronine) 2.23-5.3 pM
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TSH Assay TSH Assay (0.4-5 mU/L) (0.4-5 mU/L) Early RIA < 1.0 mU/L Thyrotoxicosis / 2º hypothyroidism Unable to detect lower range of normal Monoclonal SEN < 0.1 mU/L Super SEN < 0.01 mU/L
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Case 1 Case 1 1. How would you characterize her hypothyroidism? 2. What are the ramifications of pregnancy to thyroid function/dysfunction?
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Thyroid & Pregnancy: Normal Thyroid & Pregnancy: Normal Physiology Physiology Increased estrogen increased TBG Higher total T4, T3 (normal FT4, FT3 if thyroid gland working properly) hCG peak end of 1 st trimester, weak TSH agonist so may cause slight goitre Fetal thyroid starts working at 11 wks T4 & T3 do NOT cross placenta (or do so minimally) Do cross placenta: PTU, MTZ, TSH-R Ab (stim or block) MTZ aplasia cutis scalp defects
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Thyroid & Pregnancy: Hypothyroidism Thyroid & Pregnancy: Hypothyroidism Will need ~ 25% increase in LT4 during pregnancy due to increased TBG levels Risks: increased spont abort, HTN, preterm pregnancy, 7 IQ points for fetus (NEJM, 341(8):549-555, Aug 31, 2001)
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LT4 dose adjustment in LT4 dose adjustment in Pregnancy: Pregnancy: Need TSH at baseline & q2mos while pregnant Need TSH at baseline & q2mos while pregnant Starting LT4: 2 ug/kg/d and check TSH q4wk until euthythyroid TSH Dose Adjustment TSH increased but < 10 Increase dose by 50 ug/d TSH 10-20 Increase dose by 50-75 ug/d TSH > 20 Increase dose by 100 ug/d
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