甲狀腺功能低下

病因:

Primary: (占 >90%) (FT4低, TSH高)
   Goitrous: 
      Hashimoto's thyroiditis; 甲狀腺炎恢復期;
      缺乏碘,
      鋰鹽, amiodarone

   非goitrous:
      頸部手術後/ 放射治療/ 放射碘治療
      amiodarone

Central (中樞性) (Free T4 低, TSH 低/正常/or 輕微高)
    下視丘or腦下垂體衰竭


Major causes of hypothyroidism:

  Primary hypothyroidism
     Chronic autoimmune thyroiditis
     Iatrogenic
  Thyroidectomy
  Radioiodine therapy or external irradiation
  Iodine deficiency or excess
  Drugs - thionamides, lithium, amiodarone, interferon-alfa, interleukin-2, perchlorate, tyrosine kinase inhibitors
  Infiltrative diseases - fibrous thyroiditis, hemochromatosis, sarcoidosis
Transient hypothyroidism
  Painless (silent, lymphocytic) thyroiditis
  Subacute granulomatous thyroiditis
  Postpartum thyroiditis
  Subtotal thyroidectomy
  Following radioiodine therapy for Graves' hyperthyroidism
  Following withdrawal of suppressive doses of thyroid hormone in euthyroid patients
Congenital thyroid agenesis, dysgenesis, or defects in hormone synthesis
Central hypothyroidism
  TSH deficiency
  TRH deficiency
Generalized thyroid hormone resistance


臨床表現:

早期: 無力, 關節痛, 肌肉痛, 頭痛, 憂鬱,
          怕冷, 變胖, 便秘, menorrhagia (經血過多or來經過長)
          皮膚乾燥, 頭髮脆弱粗糙, 指甲脆弱
          腕隧道症候群
          delayed DTRs, 舒張性高血壓
          高血脂症 (LDL高, HDL低)

晚期: 說話遲緩, 聲音沙啞, 眉毛外1/3消失,
          Myxedma (非下陷性皮膚變厚(因glycosaminoglycans堆積)), 眼周浮腫 (periorbital puffiness),
          心搏過慢,
          肋膜/心包膜/腹膜積水
          粥狀動脈硬化

黏液水腫昏迷(myxedema coma): 低體溫, 低血壓, 低換氣, 意識改變

Tx:
  -eltroxin (100ug/#)  (1/4-1.5# qd)
    CAD: 1/4#
    老人: 0.5#
    一般人: 1#qd


Subclinical hypothyroidism 亞臨床性甲狀腺功能低下   (NEJM 2001; 345:260)

表現: 
    -輕微TSH上升, free T4正常, 合併輕微或沒症狀
    -少數人(每年約~4%)可能進展成明顯的hypothyroidism (假如抗甲狀腺抗體titer上升)

治療:
   -controversial:
   -追蹤
   -症狀輕微: 症狀治療
   -治療dyslipidemia
   -治療indication:
        1) TSH > 10 mL/L
        2) goiter
        3) 懷孕, 不孕