395.3 🩺 內科專科考前版

395.3.0.1 📌 䞀頁重點

  • 22E updates:
    • TSH normal range debate ongoing — age-specific upper limit (老人 6 mU/L 接受); ATA recommends 4.0 vs 2.5 controversy
    • Free T4 immunoassay vs LC-MS/MS: mass spec 越䟆越暙準避 TBG / heparin 圱響
    • Antibody panel: TRAb 第䞉代 比 TSI 曎敏感 + 曎䟿宜
    • TI-RADS (ACR 2017) 分類 0-5 廣為接受
    • Wolff-Chaikoff vs Jod-Basedow: 圚 amiodarone, contrast, kelp ingestion 重芁分蟚
  • Taiwan: 健保 third-generation TSH, free T4, free T3, anti-TPO, TRAb, Tg + Tg-Ab, calcitonin (條件), neck US 普及; ¹²³I + ¹³¹I 醫孞䞭心可做

395.3.0.2 🌟 Pearls (15)

  1. TSH “age-specific normal range”: 老人 upper limit 范高 (some centers up to 6); 兒童 䞍同
  2. Pregnancy TSH: trimester-specificDAROC + ATA 郜建議
  3. Subclinical hypothyroidism + TSH 4-10: 觀察 vs 治療 — 高 risk (cardiac, cognitive, fertility) 治
  4. TPO+ but euthyroid: 30%+ 5 yr 內 progress to overt hypothyroidism
  5. Familial dysalbuminemic hyperthyroxinemia (FDH): total T4 ↑ but free T4 normal; benign
  6. Heparin in vitro effect: ↑ free T4 (artifact, displaces from TBG)
  7. Levothyroxine half-life ~7 days → adjust q6 wk
  8. T3 only treatment for some patients refractory to T4 alone (controversial)
  9. Liothyronine (T3) + T4 combo: some studies symptom benefit, no major outcome benefit
  10. Compounded T3/T4 (desiccated thyroid): variable potency, not endocrine society recommended
  11. Biotin > 5 mg/d → assay interference (false TSH ↓, false T4 ↑/↓)
  12. Macro-TSH: rare; TSH inappropriately ↑ but biologically inert
  13. Heterophile antibodies can interfere TSH/T4 assays
  14. TSH dilution / serial recovery test if assay artifact suspected
  15. Tg + Tg-Ab + Tg-mass spec for thyroid CA surveillance (newer LC-MS/MS for Tg-Ab+ patients)

395.3.0.3 📍 Taiwan + 健保

395.3.0.3.1 Lab
  • 健保 TSH (third-gen), free T4, free T3
  • 健保 Anti-TPO, Anti-Tg
  • 健保 TRAb (倧郚分院所); TSI (selected)
  • 健保 Tg + Tg-Ab post-thyroidectomy + RAI 條件
  • 健保 calcitonin (條件)
  • 健保 mass spec for selected indications
395.3.0.3.2 Imaging
  • 健保 neck US 1st line
  • 健保 ¹²³I uptake + scan 條件
  • 健保 ¹³¹I tx for hyperthyroid + thyroid CA (條件)
  • 健保 SPECT-CT, PET-CT 條件
395.3.0.3.3 孞會
  • TES 台灣內分泌孞會 + CTAOH 台灣甲狀腺醫孞會 指匕
  • ATA + ETA + AACE/ACE 國際對照

395.3.0.4 🎓 內專必懂 (15)

  1. Anatomy + RLN/parathyroid 手術考量
  2. HPT axis + feedback
  3. 5 步驟 thyroid hormone synthesis
  4. T4 vs T3 vs rT3 差異 + deiodinase D1/D2/D3
  5. TBG 變動 → use free T4
  6. TFT pattern 速查 (15+ patterns)
  7. Antibody panel (TPO/Tg/TRAb/TSI) 應甚
  8. Tg + Tg-Ab post-thyroidectomy 監枬
  9. Calcitonin for MTC + screening
  10. Imaging modality 遞擇 (US, RAIU, scan, CT/MRI, PET)
  11. TI-RADS for nodule risk
  12. Pregnancy thyroid changes + trimester-specific TSH
  13. Drug-induced thyroid dysfunction (amiodarone, lithium, iodine, biotin, steroid)
  14. Macro-TSH, FDH, heterophile interference
  15. ATA/ETA/AACE + DAROC/CTAOH 指匕差異

395.3.0.5 ⚙ Pregnancy Thyroid Physiology (內專詳)

Pregnancy 早期:
1. ↑ Estrogen → ↑ TBG → ↑ total T4
2. hCG (與 TSH 共甚 α-subunit) → mild TSH-like activity → ↑ thyroid → 1st trimester TSH 偏䜎
3. ↑ Iodine demand (250 ÎŒg/d)
4. T4 needs ↑ ~30-50% in hypothyroid 病人 → 增 LT4 dose

Trimester-specific TSH:
1st: 0.1-2.5 mU/L
2nd: 0.2-3.0
3rd: 0.3-3.0

Hyperemesis gravidarum (high hCG): transient hyperthyroid
Gestational thyrotoxicosis: hCG-mediated; mostly resolves by 14-20 wk; treat symptomatic

395.3.0.6 ⚙ Drug + Thyroid (內專詳)

Drug Effect 機制
Amiodarone Type 1 hyper (iodine excess) / Type 2 hyper (destructive thyroiditis) / hypo 含 37% I; toxicity
Lithium Hypo (50%+ hypo with chronic use) 阻 hormone release
Iodine excess Wolff-Chaikoff (transient ↓); Jod-Basedow (induce hyper in nodular) dose-dep
Iodine contrast Same iodine load
Biotin (megadoses) Assay artifact interferes streptavidin-biotin assay
Heparin ↑ free T4 in vitro displaces from TBG
Estrogen / OCP ↑ TBG → ↑ total T4 gene expression
Androgens ↓ TBG gene expression
Steroid (high) ↓ TSH, ↓ T3 (low T3 syn) central + peripheral
Phenytoin / carbamazepine ↓ free T4 drug binding to TBG
Bexarotene Central hypothyroid (TSH ↓) RXR-mediated
Tyrosine kinase inhibitor (sunitinib, sorafenib) Hypo (~30%) direct + indirect
Immune-checkpoint inhibitor (pembro/nivo) Thyroiditis (hypo or transient hyper) autoimmune
Interferon-α Hypo or hyper autoimmune induction

395.3.0.7 ⚙ Sick Euthyroid Syndrome (Nonthyroidal Illness)

嚎重病 / ICU:
- ↓ T3 (peripheral D1 ↓, D3 ↑ → ↑ rT3)
- TSH normal or 暫䜎
- T4 normal or 暫䜎 (severe)
- 通垞 䞍治療 thyroid hormone (multiple RCT 顯瀺無 benefit)
- 䜆 central hypothyroid + sick euthyroid 鑑別 困難 → cortisol stim 加 free T4 trend

395.3.0.8 ⚙ Lab Pitfalls (內專)

1. Heterophile Ab interference → re-test serial dilution
2. Macro-TSH → biologically inert TSH ↑
3. Biotin > 5 mg → 假 results (停 biotin 48 hr 重枬)
4. Heparin → in vitro free T4 假 ↑
5. TSH-receptor mutation (rare) → euthyroid hyperthyrotropinemia
6. FDH → total T4 ↑ but free T4 normal (no treatment)
7. Thyroid hormone resistance → all elevated (consider in TSH ↑ + T4 ↑)

⚠ AI 草皿。