一位26歲男性患有甲狀腺機能亢進的症狀，甲狀腺功能試驗顯示甲狀腺機能亢進。身體理學檢查發現沒有甲狀腺腫大，沒有甲狀腺結節及沒有頸部疼痛的現象。甲狀腺核醫造影檢查則發現兩側甲狀腺的碘－131放射活性減少，以及放射碘吸收呈現低下的狀況。由於紅血球沉降速率、甲狀腺球蛋白抗體、及微小體抗體均呈現正常；經由再次問診，此患者才承認爲了減肥而服用甲狀腺素。因此，排除亞急性甲狀腺炎的可能性；進而確認人爲性甲狀腺高能症的診斷。鑑於亞急性甲狀腺炎與人爲性甲狀腺高能症在甲狀腺功能試驗與較甲狀腺的碘－131放射活性低下之相似，藉此案例經驗建議臨床醫師注意其鑑別診斷。

We performed an 131I thyroid imaging on a 26-year-old man who had the clinical features of thyrotoxicosis. Physical examination revealed no goiter, no palpable nodules, and no tenderness. The imaging showed decreased activity of bilateral thyroid lobes with depressed radioactive iodine uptake. The thyroid function test showed thyrotoxicosis. Thyroglobulin antibody and microsomal antibody were undetectable. ESR was 2 mm/h (normal 0-15 mm/h). While being confronted with this information, the patient admitted he was secretly taking L-thyroxine to cut down his weight. Reviewing the clinical history and data, the possibility of subacute thyroiditis was ruled out, and the results of tests confirmed the diagnosis of thyrotoxicosis factitia. As the similarities in thyroid function tests, 131I uptake and scan, differential diagnosis between subacute thyroiditis and thyrotoxicosis factiti is important. We report here such a case.