396.3 🩺 內科專科考前版

396.3.0.1 📌 䞀頁重點

  • 22E updates:
    • L-T4/T3 combination therapy: 仍 controversial; meta-analysis æ•Žé«” no benefit, 䜆 selected patients (DIO2 polymorphism, persistent symptoms despite normal TSH on T4 alone) 可胜 benefit
    • TSH target debate: ATA 2014 “0.5-2.5”; some advocates 侊限 4.0; age-specific important
    • Subclinical hypothyroidism: TRUST trial (2017, NEJM) — ≥ 65 yo, no benefit from LT4 → 老人 conservative
    • Pregnancy: trimester-specific TSH (DAROC + ATA)
    • ICI thyroiditis: 60% hyper → hypo; lifelong replacement most
    • Myxedema coma: still high mortality despite modern care
  • Taiwan: 健保 LT4 充分; 健保 T3 (liothyronine) 條件; desiccated thyroid 䞍普遍; CTAOH/TES 指匕

396.3.0.2 🌟 Pearls (15)

  1. DIO2 polymorphism (Thr92Ala) ~12-36% population: ↓ T4-to-T3 conversion; some benefit from T4+T3 combo
  2. TRUST trial: 老人 subclinical hypothyroid → no QoL benefit from LT4 → conservative approach
  3. Hashimoto + lymphoma: rare but ↑ risk; sudden goiter rapid growth → biopsy
  4. APS-2 (autoimmune polyendocrine syndrome 2): Hashimoto + Addison + T1DM (Schmidt) ± vitiligo
  5. Postpartum thyroiditis biphasic: hyper 1-3 mo → hypo 4-8 mo → recover by 1 yr (most); 20% permanent
  6. Riedel thyroiditis: woody fibrosis; IgG4-related; mimics anaplastic CA → biopsy
  7. Thyroid hormone resistance (RTH, THRβ mutation): TSH normal/↑, T4 ↑ — 䞍需治療
  8. Familial dysalbuminemic hyperthyroxinemia (FDH): total T4 ↑ but free T4 normal; benign
  9. Consumptive hypothyroidism: D3 over-expression in 倧 hemangioma (兒童 IH) → very high LT4 needed
  10. Bariatric surgery: malabsorption → may need ↑ LT4 dose; consider liquid form
  11. Liquid LT4 (Tirosint): better absorption than tablet (gastric pH-independent)
  12. Slow-release T3 (long-acting LT3): in trials; avoid pulses
  13. LT4 brand consistency: TSH variability if generic switching (FDA bioequivalence ±20%)
  14. Heparin or biotin assay artifact: ↑ free T4 spuriously
  15. Mass spec free T4: more accurate when TBG variant or interference suspected

396.3.0.3 📍 Taiwan + 健保

396.3.0.3.1 Drugs
  • 健保 LT4 充分絊付Eltroxin, Synthroid 圚他國; Taiwan 倚 Levothyroxine 通甚
    • 泚意: 台灣沒有 Synthroid brand; 衛教請改皱「巊旋甲狀腺玠 (LT4)」
  • 健保 T3 (liothyronine, Cytomel) 條件絊付; 䞍 routine
  • Desiccated thyroid (Armour): 䞍普遍; 䞍健保
  • 健保 LT4 IV for myxedema coma
396.3.0.3.2 Lab + Monitoring
  • 健保 TSH, free T4, free T3 q6 wk-12 mo
  • 健保 anti-TPO, anti-Tg
396.3.0.3.3 孞會 + 指匕
  • CTAOH 台灣甲狀腺醫孞會 + TES 內分泌孞會 指匕
  • DAROC for pregnancy thyroid
  • ATA / ETA / AACE/ACE 國際對照
396.3.0.3.4 病人衛教資源
  • 衛教單匵: LT4 服藥時間 + 食物亀互䜜甚 + 月經/孕期泚意
  • (盧醫垫之前做過甲狀腺結節衛教單; 同步可做 hypothyroid 服藥衛教)

396.3.0.4 🎓 內專必懂 (15)

  1. Causes 5 倧類 + 各特埵
  2. TFT pattern primary / secondary / subclinical / RTH / FDH
  3. Anti-TPO + anti-Tg + TRAb 應甚
  4. Symptoms by system + key signs (myxedema, hung-up reflex, lateral eyebrow)
  5. LT4 dose 起始 by age + cardiac
  6. 空腹 + drug interactions
  7. Pregnancy adjustment + trimester-specific TSH
  8. Subclinical 治療 indications (TSH > 10 / pregnancy / TPO+ / kids / symptomatic)
  9. Myxedema coma management (HC first, LT4, ICU)
  10. Postpartum thyroiditis biphasic
  11. APS-2 association
  12. DIO2 polymorphism + T3+T4 combo
  13. 22E new: TRUST 老人 conservative; ICI thyroiditis; bariatric LT4 absorption
  14. Riedel thyroiditis (IgG4-RD)
  15. Drug-induced (amiodarone, ICI, TKI, lithium) management

396.3.0.5 ⚙ Pregnancy Hypothyroidism Detailed

Pre-conception:
- TSH < 2.5 ideal (treat subclinical)
- Anti-TPO+ → low threshold for treatment

Pregnancy:
- T4 demand ↑ 30-50% by 16-20 wk
- Pre-existing hypothyroid: increase LT4 immediately upon positive test (~30%)
- Trimester-specific TSH:
  - 1st: 0.1-2.5 (some 0.4-2.5)
  - 2nd: 0.2-3.0
  - 3rd: 0.3-3.0
- TSH q4 wk in 1st half, q6-8 wk in 2nd half
- Iodine 250 ÎŒg/d (KI in supplement)

Postpartum:
- Reduce LT4 to pre-pregnancy dose immediately after delivery
- Recheck TSH 6-8 wk

Postpartum thyroiditis (5-10%):
- Hyper 1-3 mo (transient)
- Hypo 4-8 mo
- Most recover by 1 yr; 20% permanent
- Anti-TPO+ ↑ risk
- Future pregnancy + Hashimoto risk

396.3.0.6 ⚙ Drug-Induced Hypothyroidism Detailed

Drug Mechanism Onset Reversible? 處理
Lithium Block hormone release; autoimmunity Months 倚可逆 if stop LT4 + 䞍停 lithium 通垞
Amiodarone Iodine excess (Wolff-Chaikoff) Months 郚分可逆 LT4 + 評䌰 amiodarone necessity
ICI (pembro, nivo) Autoimmune thyroiditis Weeks Often permanent LT4 lifelong
TKI (sunitinib, sorafenib, lenvatinib) Direct + indirect Months 郚分可逆 LT4
IFN-α Autoimmune induction Variable 郚分可逆 LT4
Bexarotene Central hypo (RXR) Weeks Reversible if stop LT4
396.3.0.6.1 Iodine Excess + Wolff-Chaikoff
  • Normal: 24-48 h escape (transient suppression)
  • Failure to escape → persistent hypo (in 易感者: Hashimoto 背景, post-RAI, post-thyroidectomy)
  • 重芁 sources: amiodarone (37% I), iodine contrast, Lugol, kelp/seaweed, betadine douche

396.3.0.7 ⚙ Myxedema Coma 詳现處理 (內專)

1. ICU + ABCs
2. **Hydrocortisone 100 mg IV q8h** ALWAYS (concurrent AI suspected; do not give T4 alone)
3. LT4 IV:
   - Loading 200-400 ÎŒg
   - Daily 50-100 ÎŒg until oral
   - Some add T3 IV 10 ÎŒg q8-12h × 24-48h (controversial; avoid in cardiac compromise)
4. Passive rewarming (warm blanket, no active to avoid CV collapse)
5. Cautious IV fluid (NS); avoid hypotonic (hyponatremia)
6. Hypoventilation → mechanical ventilation if needed
7. Treat trigger:
   - Infection (most common): broad-spectrum antibiotic
   - MI / PE / drug
8. Monitor: cardiac, electrolytes, glucose, mental status
9. Avoid: BZD, opioid (worsens hypoventilation)
10. Mortality 30-40% even with optimal care

396.3.0.8 ⚙ LT4 Absorption Optimization (內專)

- 空腹 ≥ 30-60 min before breakfast
- Or bedtime, ≥ 4 hr after last meal
- Avoid within 4 hr:
  - Calcium, iron, magnesium
  - PPI, sucralfate, cholestyramine, colestipol
  - Coffee (some studies)
  - Soy protein
  - Calcium-fortified juice
- Bariatric surgery / atrophic gastritis / celiac → consider liquid LT4 (Tirosint) or higher dose
- Brand consistency important (FDA bioequivalence ±20%)
- Generic switch → re-check TSH in 6-8 wk

⚠ AI 草皿。