腸胃科門診遇見慢性腹瀉的病患，由於其原因很多，病患如果沒有明顯的甲狀腺腫大，甲狀腺髓質癌是不容易被列為起初的鑑別診斷中。我們所報告的這位66歲女性，起初因水瀉四個月到腸胃科門診求診。當時安排的大便以及大腸鏡檢查並沒異狀。病患被診斷為大腸狂躁症。再經過一年多，水瀉並沒有改善。腹部超音波檢查意外發現一顆6.9 公分大小的肝腫瘤。B型及C型肝炎檢查都呈陰性，胎兒蛋白數值正常。肝腫瘤穿刺病理報告為轉移性甲狀腺髓質瘤。此時理學檢查發現病人有一顆看不明顯但摸得到的左側甲狀腺腫瘤。甲狀腺超音波發現左葉有一顆有鈣化的節結。細胞刺針結果確診為甲狀腺髓質癌。甲狀腺髓質癌併肝轉移以慢性腹瀉為最初表現，在臨床上病患卻沒有明顯的甲狀腺腫大是較少見的，這也增加了診斷的難度。若慢性腹瀉不是由腸胃道問題造成的，甲狀腺髓質癌要被列為鑑別診斷中，仔細的頸部理學檢查是必須的。

Medullary thyroid carcinoma (MTC) is a rare cause of chronic diarrhea. When systemic symptoms such as diarrhea occur, distal metastasis often exists. The most common clinical presentation of MTC is solitary thyroid nodule. It was uncommon that chronic diarrhea as initial presentation of MTC without visible thyroid nodule. A 66-year-old woman suffered from watery diarrhea for 4 months. Irritable bowel syndrome was impressed initially. Water diarrhea persisted for another one year under medical treatment. Abdominal echography showed a 6.9cm non-cirrhotic hepatic tumor unexpectedly.Finally, core-needle biopsy for the hepatic tumor revealed metastatic medullary thyroid carcinoma. Physical examination revealed a palpable nodule in
left thyroid lobe. Further thyroid ultrasonography disclosed multiple nodular goiter and the largest left thyroid nodule had punctate microcalcification. Fine needle aspiration cytology confirmed the diagnosis of MTC. Palliative surgery with total thyroidectomy, and liver bi segmentectomy were done. After palliative surgery,watery diarrhea was partially improved.