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    甲狀腺低下(hypothyroidism)的鑑別診斷

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    新陳代謝科 甲狀腺疾患 鑑別診斷
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    • T
      TinyNotes last edited by TinyNotes

      alt text
      (圖片來源:wikimedia)

      Primary hypothyroidism

      • 因為thyroid本身的疾病,導致甲狀腺功能低下
        典型Lab表現:free T4降低,TSH升高

      • Chronic autoimmune thyroiditis (Hashimoto’s thyroiditis)

        • 在碘供應充足的區域,為甲狀腺功能低下最常見的原因
        • 病理機轉:甲狀腺被淋巴球(尤其是Cytotoxic T cell)浸潤、破壞
        • 盛行率:女性較多、常會有goiter
        • Lab:甲狀腺功能逐漸減少、TSH升高、thyroid antibody (+)
      • 術後造成的甲狀腺功能低下→切甲狀腺、放射性碘療法等

      • 碘:過多或過少都可能造成hypothyroidism

        • 缺碘:全世界造成hypothyroidism最常見原因

        • 碘過多:

      Wolff-Chaikoff effect (抑制T4和T3的合成)
      當人體內的碘離子大量升高後,人體會自我調節,抑制甲狀腺素的合成,避免過多的甲狀腺素生成。通常會持續數天,之後會恢復正常(Escape phenomenon)。然而,當患者本身有甲狀腺異常(ex. Hashimoto’s thyroditis、部分甲狀腺切除、放射碘治療等),Wolff-Chaikoff effect的時間會過長,造成甲狀腺功能低下。
      碘的來源:藥物(ex. amiodarone)、食物補充、含碘的顯影劑
      • 藥物:
        抗甲狀腺藥物(ex. PTU類、Methimazole);鋰鹽;Amiodarone;IFN-alpha、Interleukin-2、某些化療藥物

      • Infiltrative disease
        纖維化甲狀腺炎(Reidel’s thyroiditis)、血鐵質沉著症、硬皮症、白血病等

      • Transient hypothyroidism:某些甲狀腺發炎,只會短暫出現

        • subacute thyroiditis:
          因為甲狀腺組織發炎,造成暫時性甲狀腺亢進、然後進入暫時性的低下,後來功能就會恢復(數周到數個月)。若症狀輕微,通常不需要特別處理

        • post-partum thyroiditis
          →20-30%患者出現甲狀腺亢進,伴隨著暫時的甲狀腺低下
          →40-50%患者只會有暫時性的甲狀腺低下
          →症狀持續數周到數個月

      Secondary and tertiary hypothyroidism

      • Secondary:因為TSH不足,導致甲狀腺低下
        →常見原因:hypopituitarism:adenoma;Sheehan’s syndrome等

      • Tertiary:因為TRH不足,導致下游的TSH和甲狀腺低下
        →下視丘疾病,或是下視丘-腦垂腺的portal blood flow受影響

      • 懷疑有central因素的甲狀腺低下→應該要接受影像學的檢查

      Resistance to thyroid hormone

      • 因為thyroid hormone receptor的突變,導致甲狀腺素無法作用

      • 會注意到T3、T4升高,TSH正常或高

      Resistance to TRH或TSH

      →因為受器的突變,導致無法接受上游的訊號

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      • S
        sniperHK last edited by

        If plasma free T 4 is low and plasma TSH is not elevated, the patient may have secondary hypothyroidism, but in a critically ill patient, this pattern of test results is more likely to be due to functional suppression of TSH and T 4 secretion by the nonthyroidal illness (the “euthyroid sick syndrome”).

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